高能暂现源 · 每日文献综述

We investigate gravitational-wave birefringence from pulsar glitches in dynamical Chern-Simons gravity, a parity-violating extension of general relativity motivated by string theory and quantum gravity. Using the Hartle-Thorne slow-rotation formalism to model the neutron star background and a perturbative treatment of the Chern-Simons coupling $α$, we derive the modified Regge-Wheeler equation governing axial gravitational perturbations and compute the resulting polarization-dependent phase shift. The parity-violating interaction produces a fractional asymmetry between the right- and left-handed circular polarizations that scales as $α^2$, grows linearly with frequency and rotation rate, and falls as the fourth power of the stellar radius. For a constant-density interior model we obtain an analytic matching solution for the background scalar field, and show that the interior curvature factor vanishes identically--the interior solution being conformally flat--so that the scalar dipole is sourced entirely in the vacuum exterior; a centrally condensed equation of state can only increase the predicted signal. We further extend the analysis to a two-fluid model incorporating differential rotation between the neutron superfluid and the charged component; the resulting correction is bounded by the fractional glitch amplitude itself, independently of the equation of state, and is negligible for typical pulsar parameters. Expressed through the dimensionless quantity $ζ\propto αM/R_\star^{3}$, the fractional polarization asymmetry for millisecond pulsars reaches $\sim 10^{-3}$ at kilohertz frequencies at the boundary of perturbative validity--four orders of magnitude above the sensitivity of current ground-based detectors to strain asymmetries. However, realistic bounds are limited by the signal-to-noise ratio required to resolve a ratio of gravitational wave strains.

We present a study of the interstellar molecular and atomic gas associated with the gamma-ray supernova remnant (SNR) RCW 103 using the Mopra $^{12}$CO($J$ = 1-0), Atacama Large Millimeter/submillimeter Array $^{13}$CO($J$ = 1-0), and the Australia Telescope Compact Array & Parkes HI data. We find that CO clouds in the velocity range from $-58.7$ to $-43.5$ km s$^{-1}$ show a clear spatial correspondence with the X-ray shell of RCW 103, particularly extending from the northwestern to the southeastern regions. The position-velocity diagram of the CO emission reveals an expanding gas motion with an expansion velocity of $ΔV \sim$$7.5$ km s$^{-1}$, which may have been produced by shock waves and/or stellar winds from the progenitor system. We estimate the total cosmic-ray proton energy to be $\sim$$3.0^{+1.1}_{-0.6} \times 10^{47}$ erg, adopting a total interstellar proton density of $\sim$$810$ cm$^{-3}$. This value is more than an order of magnitude lower than those inferred for other gamma-ray emitting SNRs of comparable age. Given that a substantial amount of dense gas remains within the interior of RCW 103, where thermal X-ray emission is dominant, our results possibly suggest that a significant fraction of the shock energy may have been converted into thermal energy via gas heating, thereby reducing the efficiency of cosmic-ray acceleration.

Stellar flares have long served as stellar magnetic activity tracers. The flare waiting time, defined as the interval between two consecutive flares, provides a valuable diagnostic for probing underlying mechanisms of energy storage and release in stellar atmospheres. In this work, utilizing flaring M dwarfs observed by the Kepler satellite, we establish a simple yet effective activity proxy, i.e., median flare waiting time ($t_{\rm{w, med}}$). Our results show that the $t_{\rm{w, med}}$ can trace long-term activity levels similar to the flare rate. However, $t_{\rm{w, med}}$ corresponding to different waiting time percentiles may encode richer physical insights than flare rate. In addition, for the first time we construct a clear relation between $t_{\rm{w, med}}$ and stellar rotation period, which is quite similar to the canonical activity--rotation relation. More intriguingly, this relation exhibits a more notable supersaturation effect (i.e., below a critical rotation period, $t_{\rm{w, med}}$ begins to increase instead of keeping constant) compared to other activity proxies. The filling factor--rotation period relation favors poleward migration of active regions as the explanation for supersaturation, rather than coronal stripping. With the dramatic increase in stellar flares detected by missions like TESS and the upcoming Earth 2.0 satellite, $t_{\rm{w, med}}$ will become a powerful diagnostic for probing stellar magnetic activity and underlying physics.

Cluster emission is an exotic decay mode between alpha-decay and fission, in which a parent nucleus emits a cluster of nucleons heavier than an alpha-particle, but lighter than what is usually considered a fission fragment. The properties of cluster emission were investigated by analyzing five high-energy events detected in a spectrum of a mass A = 230 beam produced at ISOLDE (CERN). Under the assumption that these events were caused by cluster emission, the most likely parent-cluster pair responsible for the five high-energy events, was found to be $^{230}Ra$ emitting $^{22}O$, with a branching ratio of $(4.3$ +\- $1.9) \times 10^{-9}$. Four analytical formulas were used to estimate the partial half-lives of cluster emission for a group of neutron-rich nuclei. The decay rate was calculated for a selection of cluster nuclei for each parent isotope. The rates of all decay channels of cluster emission per parent nucleus were then included in calculations of the r-process nucleosynthesis in a neutron star merger in order to study the possible impact of cluster emission on the r-process nuclear production. The resulting isotopic abundance distributions were compared to those calculated for a case in which cluster emission was not considered. It was found that the inclusion of cluster emission decay rates from the simple analytical formulas available nowadays does not influence the results of the r-process nucleosynthesis.

Geomagnetic indices quantify the disturbances of the Earth's magnetic field. They form an important space weather and space climate record that tracks solar-terrestrial effects on the Earth. Although geomagnetic activity has its origins in the photospheric magnetic fields, the two have so far not been directly related. We develop a photospheric index of geomagnetic activity (PIGA) that measures the geoeffectiveness of the Sun based on photospheric magnetic field as presented in synoptic magnetograms. We construct the PIGA from synoptic magnetograms of Wilcox Solar Observatory by relating the equatorial and axial dipole components of the photospheric magnetic field to the geomagnetic Kp index by means of linear regression. PIGA captures well the evolution of the geomagnetic activity over the past 50 years at the resolution of solar rotation, having linear correlation of 0.71 with the geomagnetic Kp index. PIGA makes it straightforward to measure the geoeffectiveness of the Sun using the dominant structure of the global solar magnetic field. PIGA can for example be used to study the geoeffectiveness of the Sun using historical simulations or the predicted solar magnetic field. PIGA also allows to use observed geomagnetic activity as an additional constraint for the early magnetic field reconstructions of the solar magnetic field.

General relativity predicts the presence of a thin, bright ring of light superimposed on the image of a black hole (the ``photon ring''), whose geometry is sensitive to the spin of the black hole. Detecting this photon ring in observations of nuclear supermassive black holes would yield insight into gravity in the strong-field regime as well as their growth histories. The Black Hole Explorer (BHEX) is a mission being developed to detect the photon ring for the first time, raising the question of how precisely we can constrain spin from its observations. We use the method of Fisher information matrices (FIMs) along with a simple dual-cone semi-analytic emission model to forecast BHEX spin posterior widths for the primary science targets (M87* and Sgr~A*) in a variety of configurations. We find that BHEX can constrain the dimensionless spin of its targets to a precision of $σ_{a_*} \ll 0.1$ after 30 orbits, even in the presence of significant systematic errors. We validate our results via numerical checks for stability and robustness, as well as synthetic data cross-validation to assess handling of covariances and prior information in the FIM against a full posterior exploration.

Closure phase is robust to station based phase errors, yet its connection to image structure is often interpreted only qualitatively and a nonzero closure phase is still interpreted mainly through qualitative symmetry arguments or source specific models. We develop, to our knowledge, the first unified response theory for an arbitrary brightness distribution and an arbitrary zero free observing triangle. Away from visibility zeros, closure phase is naturally a log-visibility observable. This structure yields an exact first order master kernel for image perturbations and a Cartesian moment hierarchy that separates the spatial content of the source change from the sensitivity of the sampled triangle. For a fixed image, the same framework gives a local expansion in Fourier plane displacement, providing a direct description of closure phase evolution along observing tracks. We then identify the boundary of this regular regime: at a true visibility null, the log-visibility expansion fails and the phase behavior is controlled by the local properties of the null, including its order and winding charge, distinguishing removable phase wraps, non-null visibility minima, and nulls for which the visibility phase is multivalued. We validate these expansions using structured ring models. We then apply both branches of the theory to EHT data of M87*, and demonstrate the ability to measure asymmetric image structure associated with higher image moments directly from the evolution of the closure phase. Finally, we show that the same formalism extends naturally to Phase Closure Nulling in optical and infrared interferometry. The resulting framework turns closure phase structure into a quantitative probe of faint and asymmetric source features across interferometric regimes.

In asymptotically flat spacetimes far from an isolated source, gravitational waves (GWs) undergo nonlinear interactions with themselves and with the parts of the spacetime curvature related to the time-dependent four-momentum and angular momentum of the spacetime. These spacetime nonlinearities produce distinctive offsets in the GW strain and its time integrals, which have been referred to as the displacement memory effect for the strain and ``higher'' GW memory effects for the integrals of the strain. There are existing data analysis pipelines that search for evidence for the displacement memory effect in the population of binary-black-hole mergers observed by current GW detectors (though conclusive evidence for the effect has not yet been found). The first set of higher memory effects include the spin and center-of-mass effects (collectively, ``drift'' memory), and the second is the ``ballistic'' memory effect. Prior work has shown that next-generation, ground-based GW detectors could find evidence for the spin memory effect in the large population of binary black holes that these detectors will be capable of observing. In this paper, we investigate how well a detector network of two Cosmic Explorer detectors can measure the displacement through ballistic memory signals. We first formulate what are appropriate notions of time-dependent GW signals associated with these memory effects. With these definitions of displacement and higher memory signals, we find that the Cosmic Explorer network is capable of detecting the displacement memory from tens of individual mergers per year and capable of finding evidence for the spin and center-of-mass memory effects in a population of mergers after a roughly one-year observation run at design sensitivity. [Abstract abridged]

Under normal circumstances, an observer falling into a black hole feels nothing special upon crossing the horizon. In this paper we find an intriguing exception: For most of the parameter range of the extremal Kerr-Newman (KN) spacetime, horizon co-rotating perturbations are enhanced near the horizon, such that an infalling observer experiences an anomalously large tidal deformation as they enter the black hole. Such perturbations arise when there is a persistent source outside the black hole that is either co-rotating itself or has discrete Fourier support at the associated frequencies $ω=mΩ_H$ (where $m$ is the azimuthal number and $Ω_H$ is the horizon frequency). The enhancement is formally infinite at precise co-rotation, and we work with a nearly co-rotating mode to keep perturbation theory under control. The underlying physics is the emergence of discrete self-similarity in the extremal limit, with complex scaling weights of the form $-1/2\pm iα$ for real $α$. It is analogous to the black hole Meissner effect, except that the near-horizon field is enhanced rather than screened. We numerically calculate the scaling exponents for coupled gravitoelectromagnetic (GEM) perturbations of extremal KN black holes and show that the complex exponents arise in the parameter range $Q < Q_*$ with $Q_*\approx.93M$. These exponents also predict the decay and growth rates (Aretakis effect) of generic GEM perturbations of the KN spacetime, both on and off the horizon. The enhancement of co-rotating perturbations can be viewed as a driven Aretakis instability.

The supermassive black hole at the center of the nearby radio galaxy M87 (M87*) is a prime target for studying black hole physics. Spatially resolved spectral measurements on event-horizon scales can reveal the origin of the emission and probe the plasma and gravitational environment in the immediate vicinity of the black hole. Here, we present an analysis of spectral properties based on nearly simultaneous high-resolution images at 3.5 mm (86 GHz) and 1.3 mm (230 GHz), obtained in 2018 with the Global Millimeter VLBI Array (GMVA) including ALMA and the Greenland Telescope, and the Event Horizon Telescope (EHT). We obtain the first spatially resolved spectral-index map ($S_ν\propto ν^α$) within the compact region ($\leq 100\,μ$as). We further detect a robust radial gradient with a modest rise in the inner $\lesssim 20~μ$as (slightly inside the 1.3 mm ring), followed by a systematic decline at larger radii. The spectral index transitions from positive to negative values near $\sim 30~μ$as, close to the 3.5 mm ring radius, consistent with frequency-dependent synchrotron opacity in the innermost accretion flow. These results provide new observational constraints that can help discriminate between models of the horizon-scale emission and the launching of relativistic jets in M87*.

Axion-like particles (ALPs) bound in the solar gravitational field form the so-called ALP solar-basin. Since the two-photon decay of non-relativistic particles is approximately isotropic, this population can be searched for using observations in the anti-solar direction. In this work, we propose a search strategy for narrow decay-line signals from the ALP solar basin using \textit{XMM-Newton} blank-sky observations (XMM-BSOs) stacked spectra data taken in directions opposite to the Sun. By jointly fitting the signal and background model, we obtain limits on $g_{aγγ}^{95}$ in the mass range $m_a=1.4\text{--}16~{\rm keV}$, with typical sensitivities of $g_{aγγ}\sim10^{-10}\text{--}10^{-11}~{\rm GeV}^{-1}$. We have implemented the first anti-solar search for the solar basin, demonstrating that this strategy can exploit the stacked exposure of a large number of X-ray observations and provide a scalable analysis framework for future searches.

We reconstruct the late-time expansion history and dark energy dynamics using available cosmological data. We consider dark energy as an effective minimally coupled canonical scalar field without assuming a specific form for its potential. For reconstruction, we use Gaussian Process (GP) regression with a joint dataset consisting of 32 cosmic chronometer measurements (CC32), DESI DR2 baryon acoustic oscillation data, three Type Ia supernova compilations (Pantheon+, Union3, and DES Y5), and compressed CMB distance priors. From the reconstructed Hubble parameter and its derivatives, we obtain the scalar field kinetic and potential energy densities, the equation of state $w(z)$, and the dimensionless slope parameter $|λ(z)|$ of the scalar field potential. The reconstructed potential is nearly constant at late times, with $\tilde{V}(0) \simeq 0.68$--$0.70ρ_{c,0}$, close to the dark-energy density in flat $Λ$CDM. The kinetic term remains small over $0 \lesssim z \lesssim 2.5$, while $w(z)$ remains close to $-1$ within the uncertainties. Using only CC32 and DESI DR2, we find a mild ($1σ$) hint of a phantom-divide crossing near $z\sim0.5$. However, this feature depends on the supernova compilation and cannot be regarded as a firm conclusion with current data. The slope parameter $|λ(z)|$ shows mild evolution, with present-day central values around $0.8$--$1.0$, but large uncertainties due to its dependence on higher-order derivatives of the expansion history. The curvature parameter $Γ(z)$ requires even higher-order derivatives and is not constrained by current data; therefore, we do not report its reconstruction. Allowing small spatial curvature, $Ω_k=0$--$0.02$, changes the results only slightly and remains within the existing uncertainty bands.

We analyze quasi-periodic oscillation (QPO) candidates in the 0.1-100 GeV Fermi-LAT light curves of 41 TeV blazars with a conservative, multi-stage timing analysis combining FFT power spectra, red-noise Monte Carlo simulations, false-discovery-rate control, bootstrap period uncertainties, split-sample cross-validation, Lomb-Scargle and WWZ diagnostics, a detection-only sensitivity test, observingwindow checks, and injection-recovery experiments. A first-pass FFT search flags 16 sources above a raw 95% level and six strong candidates after data-quality and split-sample filtering, none satisfying a fully automated multi-method tier. Source-level significance is quantified with forward simulations that preserve the observed sampling and non-Gaussian flux distribution, treating the red-noise slope as a nuisance parameter and never assuming independence of periodogram powers. At simulation-selected reference slopes, only two of the 41 sources reach a raw source-level p < 0.05,only J1555.7+1111 reaches Benjamini-Hochberg significance, and none survives Benjamini-Yekutieli correction. No source survives the conservative slope envelope. Even J1555.7+1111, which the first-pass search flagged as significant but did not rank among its strong candidates, has a global p-value that rises to 7.5*10^-3 under the least favorable slope (~ 0.31 after the full-sample search), so it is not a robust detection. With substantial period uncertainties, a weak observing window, and limited injection-recovery sensitivity, we establish no robust gamma-ray QPO detection: a sampling-faithful red-noise treatment substantially contracts the candidate set, providing an explicit assessment of QPO credibility.

As a new probe, the weak lensing (WL) peak steepness statistics is sensitive to the density profile of halos that encodes important information of baryonic feedback and dark matter properties, leading to a promising means to statistically constrain these effects using WL data. In this article, we present its first application to HSC Y1 data to demonstrate the great potential of this new statistics. Within the phenomenological framework of HMcode2016 that attributes the baryonic feedback solely to the reduction of the halo concentration parameter and focusing on high peaks originated dominantly from massive clusters, our analyses by combining WL peak height and steepness statistics resulted in $S_8=0.76^{+0.08}_{-0.07}$ with the maximum-a-posteriori (MAP) of $0.79$ and low concentrations. Taking the form of the concentration-mass relation as $c(M,z)=A(1+z_{\rm f})/(1+z)$ with $z_{\rm f}$ being the formation redshift of halos with mass $M$ at redshift $z$, we obtain $A=1.93^{+1.33}_{-1.16}$ (MAP=$1.70$) in comparison with $A=3.34^{+1.52}_{-1.74}$ (MAP=3.31) from dark matter only simulated mocks. The result tends to support phenomenologically strong baryonic feedback effects at cluster scales.

High-resolution observations are expected to probe the photon-ring structure of black hole images. The critical curve is the geometrically defined limiting locus on the observer's screen toward which successive higher-order photon subrings accumulate. For a Kerr black hole, the shape of this limiting curve depends on the dimensionless spin parameter $a$ and the inclination angle $i$. We investigate whether these parameters can be determined uniquely from a connected positive-length segment of the critical curve when the segment's position and orientation on the screen are unknown. For rotating non-extremal Kerr black holes with $0<a<1$ and $0<i\leqπ/2$, we prove global uniqueness: if two such segments coincide as point sets after orientation-preserving rigid motions of the screen, then their Kerr parameter pairs coincide and the two rigid motions are identical. The proof uses an irreducible implicit polynomial to show that a segment determines the full algebraic curve containing it and then recovers the parameter pair $(a,i)$ from rigid-motion invariants of that polynomial.

Einstein-Boltzmann codes compute theoretical predictions of cosmological models and rely heavily on interpolation in their independent variables: time $τ$, wavenumber $k$ and multipole $\ell$. We give a practical summary of interpolation with Chebyshev polynomials, which converges rapidly for smooth functions and thus pairs naturally with approximation-free Einstein-Boltzmann codes. By solving the perturbations and line-of-sight integrals at Chebyshev nodes in $k$ and $\ell$, we show that Chebyshev polynomials interpolate to higher precision than traditional cubic splines from fewer explicit solutions. On a set of example spectra for matter and the cosmic microwave background (CMB), we find up to four orders of magnitude lower interpolation error using the same number of points. For a typical CMB temperature spectrum computed with interpolation in both $k$ and $\ell$, Chebyshev polynomials converge to $10^{-4}$-$10^{-5}$ relative error with only 50-80 points per variable, while cubic splines approach $10^{-4}$ error with 200 points, translating to a $2.5\times$-$4\times$ speedup. The exact improvement depends on the target function and is generally more dramatic at high precision levels. Standard Chebyshev $\ell$-interpolation needs line-of-sight integrals generalized to non-integer $\ell$, but we show a way to avoid this by rounding the nodes to integers. Chebyshev interpolation is implemented in SymBoltz, which is available at https://github.com/hersle/SymBoltz.jl.

Gaussian Processes (GPs) are widely used to model stellar variability in photometric surveys, but a statistically successful fit does not guarantee that the inferred hyperparameters correspond to physically meaningful stellar properties. This is especially important for young, active stars, whose TESS light curves contain evolving spots, harmonics, and non-sinusoidal variability. We use stellar rotation as a case study to examine when the period hyperparameter of a quasi-periodic GP can be interpreted as a physical rotation period. We introduce a regularized GP likelihood that reweights the covariance-complexity term in the marginal likelihood, reducing the tendency of unconstrained models to converge toward preferred but misleading solutions. We test this framework on 539 stars in IC2602, the Tucana-Horologium Association, Pisces-Eridanus, and GroupX, with independently reported and manually vetted rotation periods. This benchmark evaluates GP hyperparameter interpretability and automated period recovery with minimal human intervention. We compare regularized and unregularized models across several regularization strengths, λ, using literature agreement, sector-level diagnostics, and consistency across TESS sectors. Relative to the standard GP likelihood, regularization improves successful rotation-period recovery by an average of 7%. It also generally reduces the median absolute fractional deviation of periods across sectors, showing that the improvement is not limited to catastrophic failures but also mitigates smaller systematic errors. Regularization is particularly beneficial for non-sinusoidal or evolving modulation, where unconstrained GPs may recover harmonics or spurious timescales. These results show that likelihood regularization and cross-sector consistency are practical diagnostics for assessing when GP-based rotation periods are robust.

The density profiles of Dark matter (DM) halos carry imprints of the DM nature and may be constrained through the lensing effects on gravitational waves (GWs) arising from the halo gravitational potential. In this paper, we investigate GW lensing by two representative types of halo density profiles, i.e., the generalized Navarro-Frenk-White (gNFW) density profile and the Einasto density profile. Using the gravitational lensing equation, we first examine the parameter-space distribution and the imaging characteristics of both profiles under strong lensing, partitioning the parameter space into distinct regions according to the Morse index. We then conduct a detailed analysis of the modulus $\big|F\big|$ and phase $\mathrm{Arg}(F)$ of the amplification factor $F\big(w,y\big)$ at low frequency regime. Our results show that, for a fixed lens mass , increasing the gNFW slope $γ$ leads to a larger amplitude, more rapid oscillation, and more distinct wave-packet morphology in the multiple-image regime. Compared with the gNFW case, the Einasto case (with $α=0.16$, $y<0.6$, and the same $M_{200}$) produces a stronger lensing effect. Notably, the evolution of $F\big(w,y\big)$ with frequency for the Einasto profile differs from that of the gNFW case, making its behavior particularly distinctive.

Claims that neutron stars constrain quantum gravity often compare models whose new physics enters at different stages of the stellar calculation. This article provides a critical map of three representative routes: generalized-uncertainty-principle deformations of microscopic thermodynamics, noncommutative-inspired modifications of the effective matter source, and higher-curvature or scale-dependent modifications of gravitational dynamics. For each route we identify the quantity that is changed, the dimensionless parameter controlling the correction, and the consistency conditions required before masses, radii, or tidal deformabilities can be compared with observations. A deformed phase-space measure must be implemented in a thermodynamically consistent interacting equation of state; a smeared density must be completed by a conserved stress-energy tensor, generally with anisotropic pressure; and a gravitational effective field theory must remain within its derivative expansion and be applied consistently to both the equilibrium background and tidal perturbations. Simple scale estimates show that coefficients of natural size suppressed by the Planck scale are negligible in neutron stars. Observable effects consequently constrain model-dependent effective scales or enhanced couplings, not microscopic quantum gravity directly. The resulting framework is intended to separate robust phenomenological bounds from effects produced by inconsistent implementations or by degeneracies with the high-density equation of state.

Dynamical friction (DF) and gravitational-wave radiation reaction are conventionally treated as distinct dissipative mechanisms acting on a compact object inspiraling through a matter environment. We show that DF is not an additional force but a term at order $q^2ε$ in a covariant multiparameter expansion of the MiSaTaQuWa force equation that vanishes identically in the absence of a particle-induced perturbation of the environment's matter fields, where $q$ and $ε$ are respectively the mass ratio and environmental parameter. As a test of this identification, we evaluate it in weak and adiabatic field limit, solving the polar density-perturbation equation sourced by the particle's own order-$q$ vacuum metric perturbation. The reduction reproduces the Chandrasekhar-Ostriker drag force and predicts two features in strong gravity. An $\ell$-dependent splitting of the wake that only recombines into the Ostriker source in the weak-field limit, and a purely relativistic axial contribution with no Newtonian counterpart. This establishes dynamical friction as an intrinsic piece of self-force theory, extending to strong field, generic orbits, and generic environments, with direct consequences for extreme-mass-ratio inspiral waveform modeling for LISA.

The degree of spin-orbit alignment in merging binary black holes is a powerful probe of their formation history. However, assessing spin-orbit misalignment in individual events remains challenging, as most parameters commonly used to characterize precession tend to be poorly constrained. In this work, we introduce the angle between the total spin and orbital angular momentum, $θ_{LS}$, as an alternative measure of spin-orbit misalignment. Using synthetic observations, we show that $θ_{LS}$ retains more information to discriminate between the aligned- and isotropic-spins hypotheses than commonly used alternatives, including $χ_{\rm p}$. We then study this parameter on binary black hole mergers observed in the GWTC-5.0 catalog, and identify multiple events that are inconsistent with having aligned spins. In several of the examples, this is not apparent from the posteriors of the effective spin parameters ($χ_{\rm p}$ or $χ_\mathrm{eff}$) nor the individual spin-orbit tilts ($θ_1$ or $θ_2$) alone, and thus had not been previously identified. We highlight GW241127_061008 as a compelling case for a second-generation merger, with a large, tilted primary spin, unequal masses, and a large primary mass near the pair-instability-supernova mass gap. Finally, we perform population inference using $\cosθ_{LS}$ and confirm that the binary black hole population is inconsistent with either a purely isotropic or a purely aligned-spin distribution, and requires substantial spin-orbit misalignment.

Scalar-induced gravitational waves (SIGWs) probe primordial curvature perturbations beyond cosmic microwave background scales, while primordial black holes (PBHs) probe the rare tail of the same statistics. We ask whether SIGW morphology can reveal scale-dependent primordial non-Gaussianity. We adopt the internal-leg separable kernel, $\mathcal F_{\rm NL}(\mathbf{k};\mathbf q,\mathbf{k}-\mathbf q)=\bar f_{\rm NL}f(q)f(\lVert\mathbf{k}-\mathbf q\rVert)$, and compute Gaussian, reducible, and connected contributions through $\mathcal O(\bar f_{\rm NL}^{4})$ in the second-order tensor-source approximation. We compare persistent power-law running with a UV-matched tanh weight that saturates at high scalar momentum. Across narrow, finite-width, asymmetric, and multi-slope scalar spectra, running produces more than amplitude renormalization. Power-law running shifts the scalar support sampled by non-Gaussian convolutions, generating peak displacement, asymmetric shoulders, and persistent ultraviolet deformations. The tanh template instead produces a transition-localized modification and approaches a momentum-independent ultraviolet plateau. Analytical estimates of the perturbative hierarchy, weighted slopes, log-normal saddle displacement, peak shifts, and infrared scaling explain the trends and the enhanced sensitivity of the $\mathcal O(\bar f_{\rm NL}^{4})$ sector. For localized sources with finite weighted moments, smooth running preserves the leading $k^3$ infrared behavior up to logarithmic corrections. Since the PBH mass scales as $M\propto k^{-2}$, preferential high-wavenumber weighting conditionally favors lower PBH masses in a narrow-support interpretation. Peak position, spectral curvature, shoulders, and ultraviolet slopes are diagnostics for PTAs, LISA, and third-generation observations, providing finite-order templates for primordial interactions on otherwise inaccessible scales.

We obtain an exact dyonic black-hole solution in quadratic nonlinear electrodynamics defined by $-F+aF^{2}+bG^{2}$ on the special locus $b=a/2$. At this locus, the radial dependence in the electric constitutive relation cancels and the magnetic charge decouples, allowing the field equations to be integrated exactly. Using the field strength as the independent variable, we construct the solution in parametric closed form, with the radial quadrature expressed through Gauss hypergeometric functions and the cosmological constant retained. The solution recovers dyonic Reissner--Nordström--(anti-)de Sitter in the Maxwell limit, the known magnetic solution for vanishing electric charge, and the Euler--Heisenberg electric branch for vanishing magnetic charge. Its perturbative expansion agrees with the known dyonic result at first order and extends it to all orders. We find a three-horizon window requiring both electric and magnetic charges, while the corresponding Smarr integral is also expressed in closed hypergeometric form. The energy density and pressures are obtained analytically, showing that the electric charge enlarges the region satisfying the dominant energy condition relative to the purely magnetic case. Three distinct central curvature behaviors are identified, including a tuned self-energy singularity. We further develop the extended thermodynamics, treating the nonlinear coupling and pressure as thermodynamic variables, and find that the critical ratio decreases below the Maxwell value $3/8$ and disappears above a threshold coupling. Finally, birefringent photon propagation produces a split shadow doublet with a splitting of about $0.5\%$, whereas the geometric light ring and scalar ringdown are nearly insensitive to the nonlinear coupling, indicating that the main observable imprint of the nonlinearity lies in polarization-dependent photon propagation.

As alternative gravity theories with respect to the general relativity, the Brans-Dicke (BD) scalar tensor model is well known for which the BD parameter is controller the best fit observational data and so its cosmological model is studied in the literature well. On the other side, the Coleman Weinberg (CW) self-interaction scalar field potential coming from radiation corrections of Feynman diagrams is used to describe the best fit cosmic inflation phase and reheating phase. This has a logarithmic term with respect to the Higgs potential and it is applicable even for massless bosons. From particle physics point of view, this is used usually to describe the Higgs mechanism and creation of massive Goldstone bosons. As a basic model to describe the cosmic inflation the cosmological constant is used to describe the de Sitter space where the cosmological constant play as dark energy density. Since, the cosmological constant is a hierarchy problem and it is added in the Einstein equation without to describe that where that is come originally? at a first time the Albert Einstein himself proposed a uni-modular frame for which the cosmological constant generate from a integral constant. This idea is very well because it resolve `fine tuning` problem of the cosmological constant parameter. Hence we use this idea for the BD theory in presence of the CW potential and obtained suitable solutions of the field equations for a flat Robertson-Walker space time by regarding the slow roll parameters of cosmic inflation and then we find the best fit correspondence between the theoretical predictions of the parameters of the solutions and the Planck2018, DESI2024, and ACT2025 observational data.

Coronal holes (CHs) are regions of predominantly open magnetic field and important sources of high-speed solar wind streams. We present a manually compiled catalogue of newly emerging CHs during Solar Cycle 24 (2010-2019), identified from daily CHIMERA maps provided by SolarMonitor. Unlike existing area-based catalogues, our dataset tracks the daily emergence of new CHs in northern, southern, and equatorial latitude zones. The emergence rate of equatorial CHs is anti-correlated with the International Sunspot Number (Pearson r = -0.523, p = 6.2 x 10^-9), indicating reduced formation of low-latitude CHs near solar maximum. The hemispheric asymmetry of CH emergence is also anti-correlated with the hemispheric asymmetry of sunspot activity (r = -0.461, p = 5.2 x 10^-7), suggesting that new CHs preferentially emerge in the hemisphere with lower sunspot activity. The total CH emergence rate is lowest near solar maximum and highest during the declining phase. These results provide new observational constraints on the evolution of open magnetic flux over the solar cycle.

The Little Red Dots (LRDs) are a population of compact, red sources, detected abundantly at $4 \lesssim z \lesssim 9$. While their nature is still debated, many models suggest they are powered by accreting massive black holes. Multiple studies have detected blue companions in their vicinity, motivating our analysis: we compare $253$ LRDs uniformly selected across several JWST deep fields against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile host a blue ($β<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of redshift-matched controls: a $\times 2.39$ excess, significant at $3.3σ$. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. The companions of the brightest LRDs are overwhelmingly ($92\%$) blue, and significantly bluer, with a median $β\approx-2.32$, versus $β\approx-1.92$ for those of controls, rejecting a common parent distribution at $3.4σ$. The signal is thus directional in three independent ways: luminosity, separation, and companion color, all expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation for why the most luminous LRDs have nearby, young, star-forming neighbors is that the radiation from these neighbors enabled the direct collapse of the massive black holes powering the LRDs themselves.

Extensions of the Standard Model scalar sector can render the electroweak phase transition first-order and thereby provide the departure from thermal equilibrium required for electroweak baryogenesis, while at the same time sourcing a stochastic gravitational wave (GW) background in the milli-Hertz range. In this work, we investigate electroweak phase transitions in the CP-conserving type-I two-Higgs-doublet model (2HDM), focusing on the interplay between collider constraints at the HL-LHC and the projected sensitivity of LISA. We compute the expected GW background due to strong first-order electroweak phase transitions and perform extensive Monte Carlo scans over the collider-viable model parameter space. We find that GW signals within reach of LISA arise almost exclusively in regions of parameter space that necessarily predict observable deviations at the HL-LHC, in particular through the $H \to ZZ$ decay channel of the heavy CP-even and neutral Higgs state with $m_H \simeq 180\text{--}250 \, \text{GeV}$. Our results highlight the decisive complementarity between collider and GW probes and show that the largest parts of the 2HDM parameter space relevant for phase transition signals at LISA can already be tested by HL-LHC. A possible future discovery of 2HDM states at the HL-LHC, however, would not allow conclusive statements about LISA being able to find a GW background due to the amount of parameter tuning required for an observable GW signal. In order to evaluate possible caveats of this statement we study the theoretical uncertainties related to the GW predictions in a two-fold approach using both state-of-the-art tools, BSMPT and TransitionListener, and also allow for model realizations in which the electroweak symmetry is not restored in the high-temperature limit, which are the ones combining the loudest GW signals with the weakest collider coverage.

The pulsar timing arrays (PTA) collect the times of arrival of radio signals from the millisecond pulsars, and gravitational waves can modulate their arrival times. Although the PTA observable involves successive radio pulses propagating along different light paths, its standard theoretical description at linear order in perturbations is equivalent to the Sachs-Wolfe formula for the observed redshift, which describes the fractional change in photon frequency along a single geodesic. While this equivalence is well known at linear order, its validity beyond first order has not been systematically addressed in the PTA literature. Here we show that, in the limit of vanishing proper-time separation between successive emission events, the timing modulation is exactly equal to the observed redshift, without expanding the spacetime geometry. For a finite emission interval, we derive the exact relation between the timing modulation and the observed redshift, and show that their difference is controlled by the ratio between the emission interval and the characteristic timescale over which the observed redshift varies.

Mass loss during the advanced evolutionary stages of low- and intermediate-mass stars is traditionally attributed to dust-driven winds, whereas the influence of magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB) star Mira~A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO $v=1$, $J=5\rightarrow4$ maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that magnetic eruptions can dominate mass loss from evolved stars and imply that magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.

Evolved stars on the asymptotic giant branch (AGB) lose mass through stellar winds launched from their dynamic extended atmospheres. Recent high-angular-resolution observations of the archetypal AGB star Mira A (o Ceti) have revealed compact hotspots on its submillimetre (submm) surface, whose origin remains unclear. We aim to characterise the submm photosphere of Mira A and investigate the properties and temporal behaviour of the compact hotspots detected on its surface. We analysed 19 epochs of high-angular-resolution observations obtained with the Atacama Large Millimetre/submillimetre Array in Bands 4, 6, 7, and 9, ranging from 134.34 to 669.25 GHz. The complex visibilities were fitted with parametric models to derive the flux density, size, morphology, and brightness temperature of the stellar disc and an additional more compact component across multiple pulsation phases and observing frequencies.Our results show that the flux density of the stellar disc increases with frequency while its apparent size decreases, in agreement with the expected stratified radio photosphere. In Band 6, both the flux density and the size of the stellar disc vary with pulsation phase, reaching maximum values close to optical maximum light and decreasing toward minimum light. Compact hotspots are detected in Bands~6 and 7 near maximum light, with their brightness temperatures exceeding those of the stellar disc by several thousand kelvins, reaching T>8600 K in Band 6. They are highly energetic and persist on timescales of weeks but evolve over longer timescales, showing changes in both position and intensity. Hotspot activity appears to occur repeatedly across multiple pulsation cycles and may be linked to strong shocks, magnetic activity, and/or episodic mass ejections, and could therefore play an important role in the mass-loss process in AGB stars.

Originally proposed as a solution to the strong CP problem and later understood to be a good dark matter candidates, axions have appeared in a variety of beyond-the-standard-model theories and are imbued with rich phenomelogical consequences. In this dissertation, we will examine two of these consequences: the emission of axions from cosmic strings and the superradiant mechanism in black hole physics. The spontaneous symmetry breaking of a global symmetry in the early universe can give rise to a network of cosmic strings, which emit ultra light, axion-like particles that can contribute to the dark matter density. We will discuss how the associated density fluctuations of these particles can be computed from first principles by treating them as a collection of plane waves. We will then calculate the density power spectrum and compare it to well-established cosmological observables, as well as to observables from future surveys, to derive constraints on the mass of the particles and the symmetry breaking scale. These light axion-like particles can also form a gravitational atom around a spinning black hole through the superradiance process. Considering the black hole to be part of a binary system, the tidal potential of the companion periodically perturbs the gravitational atom such that an atomic transition occurs between two of its energy states. Gravitational waves are emitted by the cloud during this transition. We will derive the analytical formulae of both the strain waveform and frequency spectrum of the signal and identify the systems that would be the most promising for detecting it in future, space-based gravitational wave observatories.

We examine particle creation, evaporation, scalar wave absorption and scattering, and geodesic motion in the asymptotically flat regular black hole supported by a phantom Dirac-Born-Infeld field. For massless bosonic and fermionic fields, the Bogoliubov transformations yield thermal spectra whose Hawking temperature decreases as the regular core becomes more prominent. Energy-conserving tunneling recovers the same temperature in the low-energy limit, whereas recoil and the DBI contribution introduce nonthermal corrections and suppress particle emission. In the high-frequency regime, the enlargement of the cross section does not compensate for the reduction in temperature, resulting in a lower luminosity and a longer evaporation time. A numerical partial wave analysis shows that the total scalar absorption increases with the regular core scale, approaches the horizon area at low frequencies, and oscillates around an enlarged geometric capture limit at high frequencies. The scattering phase shifts modify the multipolar amplitudes nonuniformly and displace the interference fringes toward larger angles. Furthermore, both null and timelike trajectories experience stronger deflection as the regular core contribution increases.

Scalar-induced gravitational waves (SIGWs) provide a direct probe of the enhanced primordial curvature perturbations that may also produce primordial black holes (PBHs). We forecast the capability of the space-based gravitational-wave observatory Taiji to search for an SIGW background generated by a broken-power-law curvature spectrum. A signal-injection study is used to validate the analysis pipeline, after which a pure-noise realization is employed to derive projected upper limits on the curvature-spectrum parameters. We translate these limits into constraints on the PBH abundance using the nonlinear compaction function, critical collapse, and the joint Gaussian distribution of the compaction amplitude and curvature at its peak. The resulting projected $95\%$ upper limits on the PBH dark-matter fraction satisfy $f_{\mathrm{PBH}}^{95\%}<1$ over PBH masses from approximately $6.2\times10^{-18}\,M_\odot$ to $1.7\times10^{-8}\,M_\odot$. We compare the forecast with representative Hawking-evaporation and microlensing bounds. In part of the asteroid-mass interval, the projected Taiji limit is more restrictive than the current Subaru Hyper Suprime-Cam (HSC) microlensing constraint.

The study of black hole perturbations typically follows two main approaches: the direct perturbation of the metric, or the perturbation within the Newman-Penrose (NP) or Geroch-Held-Penrose (GHP) formalism. In the latter case, a reconstruction procedure, such as the Chrzanowski-Cohen-Kegeles (CCK) method based on the Debye (Hertz) potential, is required to obtain the corresponding metric perturbation. However, the reconstructed metric is then expressed in the radiation gauge, which is not always optimal. In this paper, we analyze stationary and axially symmetric perturbations of the Kerr black hole within both frameworks. Focusing on the vacuum part of the spacetime (outside the sources), we derive an explicit gauge transformation between the averaged radiation gauge and the gauge in which the metric takes its standard Weyl-Lewis-Papapetrou (WLP) form, and we express the linearized WLP metric functions directly in terms of the Debye potential. We further discuss perturbations of the Kerr black hole towards general type D spacetimes, and analyze the mass and angular momentum perturbations in more detail. Finally, we illustrate the procedure on two examples beyond the type D class: a perturbation of the Schwarzschild black hole by a thin disk, and a perturbation of the Kerr black hole by a rotating particle.

We investigate the thermodynamic properties, Joule-Thomson expansion, and microscopic structure of a dyonic Reissner-Nordström-AdS black hole in nonlinear electrodynamics surrounded by quintessence. Within the extended phase-space formalism, analytical expressions for the mass, Hawking temperature, equation of state, heat capacity, Gibbs free energy, Joule-Thomson coefficient, and Ruppeiner curvature are derived. The effects of the nonlinear-electrodynamics parameter $ω$, the quintessence parameters $(c,ε)$, the dyonic charge $Q$, and the pressure $P$ are systematically investigated. The temperature profiles and equation of state exhibit a Van der Waals--like phase structure, with critical points strongly modified by the quintessence and nonlinear electrodynamivs contributions. The heat capacity and Gibbs free energy further reveal the corresponding thermodynamic stability and phase-transition behaviour. The Joule-Thomson analysis shows distinct cooling and heating regions separated by inversion points. In particular, quintessence generally lowers the critical and inversion temperatures, while increasing the charge and varying the nonlinear parameter significantly deform the inversion structure. The Ruppeiner curvature exhibits pronounced peaks and sign changes near critical regions, indicating strong thermodynamic correlations and alternating attractive and repulsive effective microscopic interactions. The limiting cases $ω\sim 1$, $c\sim 0$, and $Q\sim 0$ consistently recover the corresponding Maxwell, no-quintessence, and neutral black hole behaviours. These results demonstrate that the combined effects of nonlinear electrodynamics, dyonic charge, quintessence, and AdS pressure substantially reshape both the macroscopic phase structure and the effective microscopic interactions of the black hole.

The baryon acoustic oscillations (BAO) is a vital probe to measure cosmological distances and constrain dark energy. The ongoing and near-future space-based telescopes, including the Chinese Space Station Survey Telescope (CSST), will perform galaxy redshift surveys using slitless spectroscopy. Due to the relatively low spectral resolution and observational effects, there will be uncertainties and interloper contamination in measured redshifts. In this study, we consider the Gaussian-distributed redshift uncertainty and [O III]-H$β$ interlopers in the CSST-like slitless spectroscopic redshift (spec-z) samples, which are simulated using the approximate $N$-body code FastPM. We study the effect of spec-z errors on BAO before and after density field reconstruction. Both the redshift uncertainty and interlopers can damp the BAO signal, and the latter can further induce oscillations in the broadband shape of the power spectrum. We model the interloper effect on the propagator, i.e. the cross-correlation between the observed and initial density fields, as well as on the BAO power spectrum. We study the influence of the spec-z errors on the fitted anisotropic BAO parameters $α_{\perp}$ and $α_{\parallel}$. The resulting systematic bias on $α_{\perp}$ and $α_{\parallel}$ is mild, mostly within $0.1$ per cent and $0.2$ per cent, respectively. Even with the spec-z errors, BAO reconstruction can still significantly reduce the systematic bias and statistical errors on the $α$ parameters. Furthermore, we vary the redshift uncertainty and study the reconstruction performance.

We present the first self-consistent theoretical study of the competing $^{14}\mathrm{C}(n,γ)^{15}\mathrm{C}$ and $^{14}\mathrm{C}(p,γ)^{15}\mathrm{N}$ reactions within the same modified potential cluster model (MPCM). For the $^{14}$C$(p,γ_{0})^{15}$N reaction, total cross sections, astrophysical $S$ factors, and reaction rates are calculated using interaction potentials constrained by the available scattering and bound-state data. The astrophysical $S$-factor is estimated as $S(0)=4.5(1)$~keV$\cdot \text{b}$. Combining these results with our recent MPCM calculations for $^{14}\mathrm{C}(n,γ)^{15}\mathrm{C}$, we determine the transition temperature at which proton capture overtakes neutron capture in the production of $^{15}\mathrm{N}$. The self-consistent comparison predicts a transition temperature $T_9^{\rm c.p.}=2.5$ under Maxwell--Boltzmann statistics, significantly higher than previous estimates. The analysis is extended to Tsallis statistics, demonstrating that deviations from thermal equilibrium produce substantial shifts of the transition temperature. These results provide improved nuclear-physics input for astrophysical nucleosynthesis calculations.

In both collisional and collisionless plasmas the presence of a broad range of electromagnetic and plasma fluctuations provides anomalous electric fields that can be important for the dynamical evolution of the system as it is the case of magnetic reconnection, plasma turbulence and dynamo theory. In the context of plasma turbulence at scales larger than the ion's inertial length, the plasma satisfies the frozen-in condition, and the anomalous electric fields are produced by correlations between turbulent velocity and magnetic fields. Conversely, for collisionless plasmas and at kinetic scales, the total electric field has additional contributions that arise from kinetic phenomena, namely, charge separation, ambipolar electric fields and electron inertia, and each of these terms presents an anomalous counterpart. In this work we characterize the anomalous electric fields. We present a framework that can explain partial balance between the anomalous resistivity and anomalous transport, and we use it to study anomalous electric fields at kinetic scales. We establish how the different contributions to the anomalous electric field couple to the large-scale electric fields and show that the anomalous terms act back-reacting on magnetic-field organization and they may contribute to effective turbulent magnetic diffusion or shielding. Finally, we test two Sub-Grid-Scale models including anisotropic transport coefficients and show that although these models partially recover the spectral information, the phase coherence is not entirely recovered by these models suggesting a more complex non-linear contribution of the anomalous terms to the resolved scales.

The existence of supermassive black holes with masses $M\gtrsim10^9\,M_{\odot}$ and large dimensionless spins $χ\sim0.9-0.99$ at high redshift remains a challenge to our understanding of the early Universe. In this work, we study the adiabatic co-evolution of a Kerr black hole seed surrounded by two ultralight scalar dark matter clouds occupying different bound states, and show that this configuration allows the black hole to grow into the supermassive mass range while imprinting a characteristic final spin. The evolution proceeds through two stages. During the first stage, a spherical cloud described by the $\ell=0$ mode is completely depleted through a runaway dark-to-black accretion mechanism on a timescale of hundreds of millions of years for boson masses $μ\sim10^{-18}-10^{-17}\,\mathrm{eV}$. Since the accreted material does not carry angular momentum, the black hole spin is universally driven to $χ\simeq0$, independently of its initial spin. Throughout this stage, the second cloud, described by the $\ell=m=1$ mode, remains in the superradiant regime with negligible evolution. However, once the first stage is completed, this cloud transitions to the accreting regime, rapidly transferring both mass and angular momentum to the black hole. Starting from $χ\simeq0$, the black hole spin increases until the evolution self-consistently saturates close to the threshold $χ_{\rm sat}$, defined by the condition $Ω_H(χ_{\rm sat})=μ$, on an e-folding timescale of thousands of years, orders of magnitude shorter than the first stage. This final saturation spin is largely independent of both the initial black hole spin and the mass of the secondary cloud, providing a spin-imprinting mechanism in which the primordial spin is first erased by spherical accretion and then reset to a value determined only by the boson mass and the final black hole mass.

Magnetic fields play a fundamental role in the dynamics and radiation of jets associated with active galactic nuclei (AGNs), where they accelerate and collimate the relativistic plasma and produce the observed synchrotron emission. Faraday tomography is a powerful technique for probing the three-dimensional distribution of magnetic fields and synchrotron-emitting plasma along the line of sight, by reconstructing the Faraday Dispersion Function (FDF) from the observed polarization spectrum. To explore what aspects of AGN-jet structure can be revealed by Faraday tomography, we construct a simple three-dimensional model of an AGN jet that captures its essential features, and compute the resulting FDF for a range of model parameters. The jet is represented as a cylindrical region of uniform thermal-electron density threaded by a coherent helical magnetic field, to which a random turbulent component can optionally be added. The parameters varied include the inclination angle θ between the jet axis and the line of sight, the wavenumber of the helical field, and the amplitude of the random magnetic-field component. By systematically varying these parameters, we examine how the underlying magnetic geometry and turbulence are encoded in the observable Faraday and polarization structures. The main observational signatures identified by our model include top-bottom asymmetry across the jet, curved or double peaked FDF profiles and increasingly fragmented Faraday depth structure along longer lines of sight, providing potential diagnostics of large scale helical magnetic fields and small scale turbulent components. These signatures providing a physical framework for interpreting future polarimetric observations of AGN jets from instruments such as LOFAR, MeerKAT, and the VLA.

We explore the phenomenological viability of non-minimally coupled Weyl connection gravity by confronting its static, spherically symmetric black hole solutions with classical weak-field Solar System tests and stellar-orbit observations near Sgr A*. In this geometric framework, non-metricity is encoded via a Weyl vector field, giving rise to two distinct families of Schwarzschild-like vacuum solutions characterized by a free parameter \(ω\) with dimensions of length. We compute the corrections to four classical observables---gravitational redshift, Mercury's perihelion advance, light deflection, and radar echo delay---and derive stringent lower bounds on \(ω\) using current observational data. For Solution I (purely radial Weyl vector), the leading metric corrections scale as \(1/ω\), yielding bounds as strong as \(ω\gtrsim 10^{30}\) m from perihelion precession. For Solution II (time-radial Weyl vector), the corrections scale as \(1/ω^2\), resulting in weaker constraints, with \(ω\gtrsim 10^{20}\) m from the same test. This marked difference arises from the distinct behavior of the linear corrections in each solution: while Solution I exhibits an unsuppressed linear term \(2r/ω\) that dominates in the Solar System regime, Solution II features a linear term suppressed by an additional factor of \(M/ω\), making the quadratic term \(-r^2/4ω^2\) dominant throughout. We then analyze stellar orbits near the Galactic Center, finding that current observations of the S2 star provide complementary constraints on both solutions. (...)

Galactic binaries are expected to be the most numerous long-lived sources in the Laser Interferometer Space Antenna (LISA) data stream and are commonly modeled as quasi-circular, nearly monochromatic systems. In this work we present \texttt{eGB-multi}, a fast time-domain eccentric Galactic-binary waveform package for LISA. The package combines a post-Newtonian-accurate quasi-Keplerian eccentric source model with a time-domain LISA response, evaluating the signal on the retarded one-way links and then constructing time-delay interferometry observables. Its modular implementation allows the user to switch between different levels of orbital description, ranging from Newtonian closed eccentric orbits and relativistically precessing eccentric orbits incorporating the 1PN-accurate periastron advance, to precessing and shrinking eccentric orbits that additionally account for gravitational radiation reaction at leading quadrupolar order. The framework also provides an automatic evolution mode, in which the appropriate level of orbital dynamics is selected based on a pre-defined mismatch tolerance. We employ this framework to quantify the regimes in which orbital eccentricity renders the commonly adopted quasi-circular approximation for Galactic binaries inadequate.

Bondi showed in 1957 that bodies of opposite active gravitational mass self-accelerate: the negative chases the positive it repels, and the pair runs off together. We evolve this "Bondi dipole" in $3+1$ numerical relativity: two complex scalars share identical Klein-Gordon dynamics; only the phantom enters Einstein's equations with a minus sign -- inertial and passive masses positive, active mass negative. Across a matrix of thirty-four evolutions -- runaway pairs, controls, and parameter scans -- a mass-matched pair released at rest accelerates as a unit. The midpoint moves $3.00\pm0.01$ by $t=200$ with the separation held to 1%, and reaches a speed of $0.056c$ by $t=400$ with the acceleration steady to 2%; the total signed momentum holds at zero to $\lesssim 1$%. The force is gravity on both of its axes: $a\propto d^{-2.03\pm0.01}$ over $d=8$ to $20$, $a\propto M^{0.97\pm0.06}$ over a factor $2.5$ in mass, and $a\,d^2/\bar{M}=1$ within 2.4% on the equal-mass ladder. Swapping the sectors inverts the acceleration to two parts in $10^5$; gauge, solver-depth and mesh variations move the drift by $\lesssim 0.01$% and box doubling by 4%; same-sign control pairs hold their centroids to $\lesssim 8\times10^{-4}$ even while merging. The runaway carries no detectable gravitational radiation: the signed dipole cannot radiate, the quadrupole's $\ddot{Q}$ is constant, and the measured $\ell=2$ amplitude falls as $r^{-4.8}$ -- near zone, not flux. The phantom star is, to our knowledge, the first asymptotically flat body of negative ADM mass evolved in numerical relativity; alone it survives to $t=1000$, slowly relaxing outward.

In low-regularity spacetimes and Lorentzian length spaces, achronal causal curves play the role of null (pre-)geodesics. Because of the lack of a geodesic equation, they do not come with a canonical parametrization. In this context, we discuss a notion of affine parametrization via limits of affinely parametrized timelike geodesics. However, we point out a major drawback: an example where this approximation procedures gives a non-unique result, in a way that even completeness or incompleteness of the limit null geodesic is not well-defined. This example involves discontinuous gluing of two Lorentzian metrics across a null hypersurface to give a well-behaved Lorentzian length space and as such is, just like the parametrization problem itself, manifestly Lorentzian. In view of this, we explore possibilities for a Penrose-type singularity theorem using timelike geodesics.

Recently initiated and upcoming spectroscopic surveys, such as DESI and WST, will provide more than $10^6$ high-$z$ quasar spectra, enabling dense sky coverage by the Ly$α$ forest. This is expected to establish the three-dimensional (3D) Ly$α$ forest power spectrum, $P_{\rm 3D,α}$, as a probe of the thermal and ionization history of the intergalactic medium (IGM). To exploit this opportunity, we quantify the imprints of reionization on the post-reionization IGM using high-fidelity numerical models. We use the Sherwood and Sherwood-Relics cosmological hydrodynamical simulations with box sizes up to $160\,h^{-1}\,\rm cMpc$ to investigate the impact of box size, mass resolution, and extracted grid resolution on $P_{\rm 3D,α}$ over $2.4\leq z\leq4.8$. After applying a Zel'dovich control variate correction, simulation volume has a modest impact over most scales and orientations, whereas degrading the mass resolution produces differences of up to $\sim13\%$. Insufficient resolution of the grid used for the optical-depth calculation can artificially enhance small-scale power by up to $\sim35\%$. The timing of $\mathrm{H\,I}$ reionization leaves only a percent-level imprint on $P_{\rm 3D,α}$ at $z=2.4$, whereas varying the photoheating rate by a factor of two changes the large-scale power by $\sim4-8\%$. Our results demonstrate that numerical effects can be comparable to, or exceed, the relic astrophysical signatures encoded in $P_{\rm 3D,α}$, making numerical convergence essential for interpreting precise Ly$α$ forest measurements. The strongest astrophysical imprint arises from spatially inhomogeneous $\mathrm{H\,I}$ reionization, which enhances the large-scale power by up to $\sim70\%$ at $z=4.2$. This highlights the potential of post-reionization Ly$α$ forest measurements as a probe of the thermal history and spatial morphology of cosmic reionization.

We develop a (Wilsonian) functional-renormalisation-group framework for scalar cosmology in which quantum fluctuations of a scalar field are coarse-grained on cosmological spacelike hypersurfaces. Integrating out quantum fluctuations with wavelengths smaller than the Hubble radius $H(t)^{-1}$, we obtain an effective scalar potential $U(φ(t),H(t))$ that evolves in time. We derive a non-perturbative flow equation for this potential, together with the coupled set of (modified) Friedmann equations. We then apply this formalism to the simplest possible case of a de Sitter vacuum when the scalar field is at rest, in two situations which satisfy exactly our flow equation: $(i)$ A flat potential, for which we find that the only pure de Sitter solution is unstable and corresponds to a saddle point. $(ii)$ A quadratic potential with curvature $m^2>0$, for which we find that the presence of the mass term stabilises the system. The latter case leads to a de Sitter attractor either at the Hubble scale when the mass is larger than the Hubble scale at initial time, or by introducing a new attractor located at $H=m$ in the case the mass is smaller, which may be particularly relevant to the phenomenological study of dark energy and inflation theories.

Many approaches to quantum gravity predict logarithmic corrections to the Bekenstein-Hawking entropy. Within the spacetime-thermodynamic description of gravity, such corrections lead to modified gravitational field equations. We study their effect on primordial perturbations during standard single-field slow-roll inflation. We derive the evolution equation for the comoving curvature perturbation and show that it retains the standard Mukhanov--Sasaki form, with the quantum-gravity correction entering through the time-dependent effective frequency. We compute the scalar and tensor primordial spectra at next-to-next-to-next-to-leading order ($\mathrm{N}^3\mathrm{LO}$) in the Hubble-flow parameters, keeping the leading contribution from the logarithmic correction. The scalar spectrum remains nearly scale invariant, but the quantum-gravity correction shifts its tilt and runnings. Free tensor modes still propagate as in general relativity, although on the quantum-gravity-corrected background. This different response of the two sectors shifts both the tensor-to-scalar ratio and the single-field consistency relation, which provide the starting point for tracing the model's signatures through the post-inflationary evolution and into the CMB.

The double copy relates gravitational data to gauge-theory data, most sharply through color-kinematics duality for flat-space scattering amplitudes. This review surveys the extent to which this idea can be formulated beyond asymptotically flat backgrounds. After recalling the flat-space ingredients needed for comparison, we describe curved-space constructions for boundary correlators and scattering observables in AdS, dS, and other non-trivial backgrounds. We then review classical and field-level maps, including Kerr--Schild, Weyl, Cotton, twistor, and convolutional double copies. A separate part is devoted to self-dual sectors. Throughout, we emphasize both the common structures that survive from flat space and the obstructions introduced by curvature.

Understanding a composite system through its constituents is a fundamental practice in physics. In the context of quantum reference frames (QRFs), however, combining the usual quantum-theoretic notion of composition with QRF perspectives gives rise to subtle issues, such as the 'paradox of the third particle'. Here we study in depth how to compose subsystems in QRF perspectives, building on a recent formalism for QRFs [E.Castro-Ruiz and O.Oreshkov, 2025]. We first show how the frames of external observers can be internalised and treated within the framework. This establishes a consistent hierarchy of QRF perspectives, which we use to define the adding and removing of subsystems. We then explain how, owing to the so-called 'extra-particle' degrees of freedom, the formalism gives a consistent treatment of subsystems, avoiding any paradoxes by construction. Consistency then implies that composing subsystems in a QRF perspective differs from, and generalises, the standard quantum-theoretic case. In particular, not every state can be appended in tensor-product form relative to a QRF, and we characterise the set of compatible states. Finally, we introduce 'classicalisation', a procedure that recovers a classical-like perspective from a general QRF. This procedure circumvents the aforementioned state restrictions but carries a different operational meaning, which we study through a concrete example.

The combination of cosmic microwave background (CMB) measurements with distance measurements from baryon acoustic oscillations (BAO) and type Ia supernovae (SNIa) suggests that dark energy is dynamical, with an equation of state crossing the phantom divide at low redshifts. This feature can not be described within canonically normalized, minimally coupled, self-interacting scalar field models. We investigate the possibility of achieving phantom crossing by introducing an interaction in the dark sector such that the dark matter particle mass is dependent on the dark energy field $φ$ as $m \propto φ^α$. We consider a self-interacting potential of the inverse power-law form $V \propto φ^{-β}$. We implement this model both at the background and perturbative levels in a Boltzmann solver and use a bayesian framework to constrain its parameters using using CMB, BAO and SNIa data. We find best-fits that have similar goodness-of-fits as the commonly used phenomenological $w_0-w_a$ parameterization, providing a more fundamental understanding of the dark sector.

Herbig stars are intermediate mass pre-main sequence stars of 1.5 to $\sim15$~M$_\odot$ and are in between low and high-mass star formation. This work provides a catalog of all 243 known bona-fide Herbig stars with clear infrared excess and in many cases accretion signatures within 1~kpc. It contains archival, recalibrated, and newly derived stellar parameters, accretion rate properties, and disk dust mass measurements. We derive the latter by using newly obtained millimeter photometry and literature values. We find that 50\% of Herbig dust disks are more massive than 10~M$_\oplus$, while this is only true for 20\% and 5\% of the T~Tauri disks in Lupus and Upper~Scorpius respectively. Furthermore, the Herbig disk dust mass distribution is bimodal, it consists of a high and low disk mass population with a mean dust mass of 21~M$_\oplus$ and 0.45~M$_\oplus$ respectively. We find that the catalog is near complete for within 300~pc, however, this decreases to 24\% out to 1~kpc. We observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10~M$_\oplus$) disks to occur at $\sim$1-2~M$_\odot$ stars, coinciding with the peak in occurrence rate of giant exoplanets. The small number of Herbig stars with low accretion rates ($<10^{-8}$~M$_\odot$~yr$^{-1}$) or low disk dust masses ($\lesssim1$~M$_\oplus$), combined with the lack of an age dependence in the disk dust mass distribution, suggests that the observed Herbig star population represents the surviving disk-hosting phase in the optically visible late stages of intermediate-mass star formation. We argue that this is either due to the formation of deep dust traps in these disks or replenishment by late-infall, or a combination of the two.

Small-scale dark matter (DM) structure encodes key information about the particle nature of DM and therefore provides a sensitive test of competing models. Yet, it remains hidden from electromagnetic surveys and is instead inferred through its gravitational effects. Stellar aberration, the apparent shift in a light source's position induced by the observer's motion, offers a largely unexplored channel to access such signatures. DM subhalos can perturb the observer's motion, imprinting characteristic, spatially correlated shifts in stellar positions across the sky. We show that the Transiting Exoplanet Survey Satellite (TESS), with its long temporal baseline, wide sky coverage, and high-cadence observations, is well suited to search for these aberration signals. We derive Fisher-matrix-based sensitivity estimates for constant observer accelerations, forecasting a sensitivity down to $6.3\times 10^{-9}\,\mathrm{m/s^2}$ from the combined sample of TESS stars with magnitude $\mathrm{Tmag}\leq 10$. This sensitivity allows TESS to probe concentrated DM subhalos over a broad parameter space, from $\gtrsim 10^{-6}\,\mathrm{M_{\odot}}$ at AU-scale distances to $\gtrsim 10^{7}\,\mathrm{M_{\odot}}$ at $\mathcal{O}(10\,\mathrm{pc})$. TESS's sector-based observing strategy further provides intrinsic temporal resolution of potential DM-induced aberration signals. Moreover, we briefly discuss challenges for future data analysis, including the modeling of instrumental systematics and stellar astrometric foregrounds, such as parallax and proper motion. Our results establish stellar aberration as a novel probe of DM substructure, paving the way for dedicated searches in TESS and next-generation wide-field surveys.

In a generally covariant theory whose Lagrangian density contains no derivatives of the metric, the spacetime geometry is fixed algebraically by the scalar fields, and the simplest quadratic potential is known to generate exponentially expanding, recollapsing and big-rip cosmologies. We extend this emergent-gravity Higgs cosmology by one new spacelike scalar field - the vacuum-expectation-value generating field - coupled to the Higgs particle through the Standard Model potential, so that the electroweak vacuum expectation value becomes a dynamical quantity evolving with cosmological time. We show that the broken-symmetry valley of the potential is an exact and stable solution of the full nonlinear system, on which the background is solved in closed form in terms of a single conserved charge. The charge feeds the Friedmann equation with a radiation-like component of purely geometric origin, diluting with the inverse fourth power of the scale factor although no radiation fluid is present; as a consequence the universe is born at a finite cosmological time in a radiation-dominated big bang, and for vanishing constant term in the potential the expansion history realizes a spontaneous radiation-to-dark-energy sequence. The sign of the Higgs kinetic term is not an assumption of the model: the requirement that the broken phase be the physical vacuum fixes it dynamically, and the stable choice reproduces the Standard Model relation between the Higgs mass, the self-coupling and the vacuum expectation value with no adjustable parameter. Oscillations about the valley describe a Higgs condensate which is frozen at early times, begins to oscillate through a misalignment mechanism, obeys a parameter-free adiabatic amplitude law, and backreacts on the expansion history as a definite renormalization of the background constants that feeds the radiation-like component.

Recent JWST observations challenge the traditional 'cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial planets around M dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated 'cosmic sandbar' and a cooler, escape-regulated 'cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by tidal heating from secular eccentricity excitation in multi-planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M stellar types as a function of volatile inventory, planetary mass, age, and tidal heating. Lava worlds with thick atmospheres are unlikely around stars cooler than K-type unless sustained by extreme tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.

We study static and spherically symmetric traversable wormholes in $f(T,τ)$ gravity, where the torsion scalar $T$ is coupled to the trace $τ$ of the matter energy--momentum tensor. We consider the linear model $f(T,τ)=T+βτ$ with an anisotropic fluid and the mean-pressure matter Lagrangian $\Lm=\Pmean=(p_r+2p_t)/3$. The field equations are obtained for the Morris--Thorne geometry without fixing the redshift or shape function at the outset. For a constant redshift function, the energy-condition problem takes a simple form. On the branch $β>8π$ and for $b(r)>0$, the energy density together with the null, weak, and strong energy conditions is satisfied throughout the spacetime if and only if $r b(r)$ is non-increasing. The same condition also implies asymptotic flatness, $b(r)<r$ outside the throat, and $b'(r_0)\leq -1$. The allowed geometries can therefore be written as $b(r)=r_0^2 h(r)/r$, where $h(r_0)=1$ and $h(r)$ is positive and non-increasing. For the representative family $b(r)=r_0(r_0/r)^n$, the null, weak, and strong energy conditions hold for $n\geq1$, while the dominant energy condition requires $n\geq3(β-2π)/(β-6π)$. We also separate the physical matter from the effective source and show how the trace coupling allows the physical matter to remain non-exotic although the effective source violates the null energy condition. Finally, we examine the marginal case $b(r)=r_0^2/r$ with a non-constant redshift function. A decreasing redshift function can improve the tangential null energy condition at the throat, but this improvement cannot be maintained throughout an asymptotically flat exterior. These results show that the matter--torsion coupling can support a broad class of traversable wormholes without requiring exotic physical matter.

Previous work has shown that first-order Palatini gravity may be cast as a non-conservative Herglotz Lagrangian field theory, which excludes the conformal mode from its space of dynamical variables. In the present work, we analyse the role of the $SO(1,3)$ gauge connection in the construction of this action-dependent theory. The connection may be decomposed into `shape' and `scale' pieces, where only the former is retained within the Herglotz theory, while the latter is incorporated into the action-dependent sector. It is shown that the choice of connection decomposition is a space that can be smoothly parameterised. Such an observation leads to the finding that there exists a `moduli space of frictional field theories', in which each point corresponds to a distinct splitting of the shape and scale connection dynamics. Movement within the moduli space transitions between Herglotz Lagrangians whose on-shell dynamics all reproduce first-order Palatini gravity. The distinction lies in how the reproduction of the scale dynamics of the original theory is partitioned between action dependence and dynamical torsion.

The emerging picture of radio haloes and mini-haloes in galaxy clusters is more blurred and far less distinct than once thought. While both trace cosmic ray electrons and magnetic fields in the intracluster medium (ICM), our knowledge of the mechanisms powering these sources, their properties and their connection to cluster dynamics, is incomplete. We present new deep MeerKAT L-band (856$-$1712\,MHz) observations of the sloshing cool-core cluster 2A~0335+096, performed as part of the ``MeerKAT-meets-LOFAR'' mini-halo census, as well as reprocessed LOFAR 120$-$168\,MHz LOFAR Two-metre Sky Survey data. We present highly sensitive radio continuum images, from which we perform a spectral analysis and a comparison of the thermal and non-thermal properties using reprocessed archival \textit{XMM-Newton} data. Our MeerKAT data reveal that the known mini-halo is embedded in a large-scale radio halo spanning up to 510\,kpc in this sloshing cluster, although only the inner mini-halo is detected by LOFAR. We find a typical steep spectrum of $α= -1.20 \pm 0.09$ for the mini-halo; the non-detection of the larger-scale halo by LOFAR indicates a spectral index no steeper than $-1.2$. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration powered by sloshing within the cluster potential well. This work emphasises the need for using deep, high-dynamic multi-frequency radio observations in conjunction with high-quality X-ray observations to complete our understanding of the connection between radio halo properties and cluster dynamics.

Imaging Earth-like exoplanets in the habitable zone of their host star is among the main science objectives of future ground-based and space-based observatories. However, the extreme contrast and small separations needed to image such planets cannot be reached with current technology. The Phase-Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is a promising coronagraph to reach this goal. The PIAACMC uses a set of aspheric lenses to apodize the entrance pupil without throughput losses and a phase-shifting focal plane mask for starlight suppression. These allow us to maintain high throughput and achieve a small inner-working angle (IWA), unlocking the capability to observe exoplanets at the diffraction limit. The masks are manufactured in-house at Leiden University with Nanoscribe, a micro-3D-printer that uses two-photon polymerization to achieve sub-micron precision in height. We present the first scientific results with a focal plane mask for the PIAACMC on the Magellan Adaptive Optics eXtreme (MagAO-X) instrument for the 6.5-meter Magellan Clay telescope at Las Campanas Observatory, Chile. We show laboratory and on-sky contrast curves with a broadband z' filter centered at 908 nm with a 14% bandwidth. We use the PIAACMC to detect binary companions at separations ~0.8-5 lambda/D (~23-144 mas). This demonstrates the PIAACMC's capability to observe at the diffraction limit and below, with a sub-lambda/D IWA. Future work includes exploring new mask designs to improve the contrast in broadband light and performing active focal plane wavefront sensing and control.

We reconstruct the primordial power spectrum (PPS) across the full range of cosmological scales accessible to Cosmic Microwave Background (CMB) observations. Using the Modified Richardson--Lucy algorithm, we perform free-form reconstructions through deconvolution of Planck PR3 and PR4, Atacama Cosmology Telescope (ACT) DR6, and South Pole Telescope 3G (SPT-3G) D1 data. Across different regularization schemes, we find no evidence for significant deviations from a power-law primordial spectrum. The reconstructed spectra show a strong correlation between Planck and ACT, even at the level of localized features over their overlapping range, $0.07 < k < 0.14\,\mathrm{Mpc}^{-1}$, demonstrating consistency between the two observations. Using a complementary parametric Bayesian reconstruction, we find that the previously discussed preference for a blueward tilt in the ACT data at small scales is preferred only at the $1σ$ level.

Quantum simulators based on Bose-Einstein condensates (BECs) provide a powerful platform to study relativistic quantum-field phenomena in the lab and in particular emulate relativistic analog particle detectors. However, such detectors typically couple to excitations beyond the acoustic phonon regime, so that the nonlinear Bogoliubov dispersion introduces corrections that cause the effective relativistic description to break down. We propose to overcome this limitation using an intrinsically momentum-selective Unruh-DeWitt detector model in which a tweezer-trapped atom couples to the condensate through a multimode optical cavity. Although the atom is effectively pointlike, the cavity-mediated interaction kernel causes it to sample density fluctuations over a controllable finite region of the BEC equivalent to a finite-size detector. The effective detector size is tunable via the cavity mode structure determining a controllable momentum cutoff that filters out nonphononic excitations. We analytically calculate the response of such a detector for uniform linear acceleration and uniform circular motion and show that this momentum selectivity can enhance the signal at experimentally accessible accelerations. Compatible with existing cavity-QED platforms our scheme thus provides a versatile setting for analog quantum-field measurements or relativistic quantum-information protocols.

A cosmological network of axion strings may exist in the Universe today. If axion-like particles couple to electromagnetism, such a network induces spatially varying birefringence in the polarization of the cosmic microwave background (CMB), which can be probed by current and next-generation CMB experiments. We calibrate a loop-crossing model against a large-scale adaptive-mesh-refinement (AMR) simulation of axion-string network dynamics in the early Universe and use the calibrated model to predict CMB birefringence from recombination to today. We find that the non-detection of anisotropic birefringence in CMB observations places a strong upper bound on the electromagnetic anomaly coefficient $\mathcal{A}$ that enters the axion-photon coupling $g_{aγγ} = - \mathcal{A} α_\mathrm{em} / πf_a$. A joint analysis of available anisotropic birefringence measurements constrains $|\mathcal{A}| < 0.24$ at 95% C.L., which is independent of the Peccei-Quinn scale $f_a$, assuming that the axions are hyperlight so that the network survives until today. This limit strongly restricts the high-energy embedding of hyperlight axions, excluding the minimal Grand Unified Theory prediction for the electromagnetic anomaly coefficient at high significance. In addition, we discuss the implications of an axion-string origin for the recently reported evidence of isotropic birefringence.

We extend the earlier analysis of cosmic censorship and the Weak Gravity Conjecture (WGC) in Einstein--Maxwell-dilaton (EMD) theory by performing a complete higher-order Sorce--Wald gedankenexperiment on the static charged Gibbons--Maeda--Garfinkle--Horowitz--Strominger (GMG) black hole. In the probe limit, an extremal GMG black hole can apparently be overcharged by a test particle, seemingly violating the weak cosmic censorship conjecture (WCCC), which is nothing but first-order variational identity in the Iyer--Wald formalism. This window can be closed by either incorporating backreaction via the Hoop Conjecture or further including second-order variational identities. In this paper, we explicitly compute third-order variational identities. The extremality parameter eta remains non-negative to the third perturbative orders confirming WCCC protection, regardless of the apparent failure of all-order generalization, model-independent proof of Lu, et al.. We further incorporate the Swampland Distance Conjecture (SDC): the resulting infinite tower of light charged states discharges any would-be overcharged configuration on a timescale tau much less than 2M, exponentially faster than a horizon can be destroyed, reinforcing WCCC in dynamical regimes and strongly relaxing the original WGC charge-to-mass bound.

In this work we introduce exact cosmological solutions in General Relativity in (3+1) dimensions which take into account both the usual fluid component as well as a superfluid component describing superfluid Pionic vortices. Such superfluid vortices are source of inhomogeneities which can be treated exactly, no perturbation theory is required. These analytic solutions are relevant to obtain a non-perturbative description of inhomogeneities in cosmology. We discuss the peculiar effects of these hadronic inhomogeneities on the propagation of electromagnetic fields on such cosmological backgrounds analyzing possible observable effects. Finally, the properties that the effective superfluid satisfy for such solutions to exist are discussed, together with possible extensions of this family of solutions.

Symmetric teleparallel gravity provides an alternative description of gravitation in which non-metricity replaces curvature and torsion. Its extension through $f(Q)$ gravity offers a different geometric description of the late-time expansion of the Universe and its accelerated phase. In this work, we investigate two $f(Q)$ models, a normalized power-law model and a square-root exponential model, and test their ability to describe the late-time expansion history. We constrain the model parameters through Markov chain Monte Carlo analyses using Cosmic Chronometer measurements, DESI DR2 baryon acoustic oscillations, strong-lensing time-delay observations, and three Type Ia supernova compilations, Pantheon$^+$, Union 3.0, and DES Y5. We compare both models with the flat $Λ$CDM model using the minimum $χ^2$, Akaike information criterion, and Bayesian information criterion. The square-root exponential model provides a better statistical fit than $Λ$CDM for the combinations of Cosmic Chronometer, DESI DR2, and strong-lensing time-delay data with Pantheon$^+$ and Union 3.0, with improvements in both the goodness of fit and information criteria. The normalized power-law model remains statistically competitive with $Λ$CDM for the supernova-inclusive combinations, although the information criteria do not favor its additional parameter. We also determine the transition redshift from cosmic deceleration to acceleration for both models, obtaining consistent values across the different dataset combinations. The transition redshifts agree with observational estimates of the cosmic acceleration epoch. Overall, our results support $f(Q)$ gravity as a viable alternative to $Λ$CDM for explaining the late-time accelerated expansion of the Universe without requiring a cosmological constant.

Recent advancements in direct detection (DD) experiments stimulate the investigation of the interactions of dark matter (DM) with nucleons and nuclei. In the framework of Composite Higgs Models (CHMs) the lightest Dirac composite particle (LDCP) can be stable composing a significant fraction ξof the observed DM relic abundance. We consider the elastic scattering of the LDCP on nucleons as well as on xenon (Xe) and argon (Ar) nuclei within the CHMs in which the LDCP magnetic moment, its mass and its coupling to the Higgs doublet are suppressed by an approximate U(1) symmetry. The LDCP with non-zero magnetic dipole moment can result in a substantial enhancement of the differential event rate in the DD experiments at low recoil energies of nuclei. Assuming ξ\ge 0.1, we identify the region of the parameter space where such enhancement may be potentially observable. In addition we specify some observables that can be useful in discriminating between the DM fermions with non-zero magnetic moment and other types of dark matter particles which don't have similar electromagnetic properties.

We characterize all maximally charged black hole spacetimes in $3+1$ dimensions. More precisely, given any initial data set $(M,g,k)$ saturating the mass-charge inequality that satisfies the charged dominant energy condition, we show that $(M,g,k)$ must arise from an isometric embedding into a Majumdar-Papapetrou spacetime.

Few planetary systems form in isolation. Rather, interactions in their birth environments may sculpt their architectures or drive them into unstable configurations. Here we study the role of environmental perturbations in triggering dynamical instabilities leading to hot Jupiter formation in dense clusters, focusing on whether the elevated occurrence rate of hot Jupiters in the open cluster M67 can be explained through flyby-induced high-eccentricity migration. We develop a hybrid method for modelling the secular and tidal evolution of planetary systems under external perturbations by passing stars using a combination of analytic and numerical approaches. We evolve 10,000 realizations each of systems with either a single planet, two planets, or a planet and a stellar companion for $\sim$4 Gyr in an M67-like cluster, comparing outcome statistics against a control sample without flybys. In single- and two-planet systems, the rate of flyby-induced hot Jupiter formation is negligible. However, in systems with an initially isotropically oriented stellar companion, the cluster environment boosts hot Jupiter formation by a factor of $\sim$2, accompanied by a factor of $\sim$3 increase in the rate of planets undergoing tidal disruption. Based on observationally motivated estimates of primordial populations, our hot Jupiter yields are consistent with both field and M67 occurrence rates, provided the primordial wide binary fraction among solar-type stars is close to $\sim$50 per cent, binary-driven high-eccentricity migration is the dominant formation pathway, and a substantial fraction of tidally disrupted systems survive as hot Jupiters through partial mass loss.