高能暂现源 · 每日文献综述

Binary (super-)massive black holes (BHs) are expected to reside in the center of some galaxies. In this work, we re-visit accretion onto binary massive BHs, incorporating recent advances in both accretion theory and the mass transfer rate between the two massive BHs. We focus on relatively bright systems with an Eddington ratio of 0.1 for a binary with total BH mass $10^8\,M_\odot$, but consider a wide range of mass ratios $10^{-4} \le q \le 0.5$. The binary system consists of two mini-disks surrounding two individual BHs and a circumbinary disk surrounding the mass center of binary BHs. Depending on the mass ratio, the two mini-disks can be hot accretion flows, standard thin (cold) disks, or Slim disks. The radiative contributions from all three disks, each potentially in different accretion modes, are taken into account self-consistently. The spectral energy distributions of the binary BH system show universal ``notch'' features from the near-infrared to ultraviolet bands, caused by the gap or cavity in the accretion disk, consistent with previous studies. Binary with different mass ratios exhibit distinct spectral energy distribution properties, offering opportunities for testing (identifying candidates) with future broad band (infrared up to X-rays) observations. We also investigate the evolution of these binary systems, and find that, for systems with initial mass ratios $q \lesssim \text{a few} \times 10^{-3}$, the mass ratio evolves toward an equilibrium value $q \sim 10^{-3}$. For binary BH systems with a larger initial mass ratio, their mass ratio instead evolves toward unity.

There is broad consensus that Type Ia supernovae (SNe Ia) are the thermonuclear explosions of C/O white dwarfs (WDs) in binary systems, but their progenitors and explosion mechanisms remain uncertain. Their earliest light curves probe the outermost ejecta and provide important constraints on the explosion. We analyse the ZTF DR2 sample of SNe Ia to search for objects exhibiting early flux excess (EEx SNe Ia). We employ two complementary approaches: (i) identifying deviations from models without early excess using power-law and SALT2 fits, and (ii) comparing observations with double-detonation (DD) and companion-interaction (CI) models. The latter identify 145 and 199 candidates, respectively, although the methods disagree substantially on both the objects selected and the total number of candidates. Combining all methods, we identify 17 robust EEx SN Ia candidates, including six over-luminous events (five 91T-like and one 03fg-like). The strongest excesses reach ${\sim}10$--17\% of the peak flux. The best candidates have, on average, higher stretch and preferentially occur in lower-mass, bluer host galaxies, suggesting younger stellar populations. We estimate that EEx SNe Ia comprise $\lesssim25\%$ of all SNe Ia, consistent with previous work, with over-luminous subtypes showing a higher relative incidence than normal SNe Ia. Among the DD models, the preferred solutions favour intermediate WD core masses ($1 M_{\odot}$), low shell-burning fractions ($20\%$), and heavier He-burning products ($^{56}$Ni), whereas the CI models show no clear parameter trends. Overall, we find no compelling evidence that either scenario is preferred as the origin of the observed early flux excesses.

We report a clear observational evidence for jet precession and nutation manifested in the gamma-ray emissions of the blazar PKS 1424$-$41. An analysis of $\sim$16 yr of \emph{Fermi}-LAT observations reveals three distinct and superimposed quasi-periodic oscillations (QPOs), with characteristic timescales of $\sim$5.26 yr, $\sim$0.96 yr and $\sim$1.3 yr. The longer timescale is detected with a local significance of $\sim 4.1σ$ ($99.9958\%$ confidence) and a global significance of $\sim 2.45σ$ ($98.5714\%$ confidence). The shorter timescales ($\sim 0.96$ yr and $\sim 1.3$ yr) both show local significances exceeding $3σ$. To interpret the origin of these modulations, we examine two physically motivated scenarios: Lense-Thirring precession of a misaligned accretion disk and orbital-driven jet precession in a binary supermassive black hole (BSBH) system. We model the gamma-ray variability using a compound framework that incorporates jet precession together with intrinsic jet rotation (nutation), which successfully reproduces the observed year-like QPOs. Our results indicate that the long-term, persistent $\sim$5.26 yr oscillation is most consistent with a BSBH origin, while the shorter year-like QPO modulation can be naturally attributed to rotation or wobbling of the jet axis. If PKS 1424$-$41 hosts a supermassive black hole binary, it represents a promising target for future space-borne gravitational-wave observatories such as the Laser Interferometer Space Antenna (LISA), providing an independent probe of supermassive black hole binaries.

We investigate baryogenesis in the framework of rainbow cosmology employing a complex scalar field with a softly broken global $U(1)$-symmetry. The modified dispersion relation of rainbow cosmology leads to energy-dependent modification to the FLRW metric components, that modifies the Friedmann equation and the scalar field dynamics. We thereby obtain analytical solutions for the scalar field evolution in the radiation-dominated epoch, and show that baryon asymmetry is generated dynamically even from an initially baryon-symmetric state. We find that the baryon-to-photon ratio asymptotically approaches a constant value in the long-time limit, which is proportional to the symmetry-breaking coupling strength $λ$, and scales with the scalar field mass as $M^{-5/2}$. Our results demonstrate that requiring consistency with the observed baryon asymmetry constrains the $λ$ and $M$ values within reasonable ranges, thus providing a viable dynamical mechanism for baryogenesis during the radiation-dominated era without invoking supersymmetry.

Hybrid measurements at the Pierre Auger Observatory indicate that most high-energy hadronic interaction models underestimate the average depth of the shower maximum, $\langle X_{\max} \rangle$, at a center-of-mass energy of $\sqrt{s}=97.7 \pm 0.4^{+6.6}_{-6.2}\,\mathrm{TeV}$. In this Letter, the hadronic interaction models are shown to follow a universal relation between the predicted $\langle X_{\max} \rangle$ and the mean values of variables characterizing the energy spectra of secondary particles produced in the first interaction of proton-induced air showers. Assuming the validity of these relations in Nature, we map the values of $\langle X_{\max} \rangle$ favored by Auger data into mean values of these variables. All models favor an increase in the mean elasticity and in the fraction of hadronic energy in proton--air interactions. The latter must be amplified by a factor of $2.8$ to $4.6$ to account for the muon puzzle.

We developed in this work a perturbative technique to compute the deflection angle of light rays in general static and spherically symmetric spacetimes with a homogeneous non-magnetic plasma. The deflection angle is expressed as a power series of $M/b$ with $M$ and $b$ being the spacetime mass and the impact parameter of the ray. The series coefficients are polynomials of the asymptotic expansion coefficients of the metric functions and the reciprocal of the asymptotic refractive index. When the plasma is dilute, the deflection angle can also be expressed as a dual series of $M/b$ and the frequency ratio between the electron plasma frequency and the asymptotic photon frequency. The series result reveals that for general SSS spacetime, the plasma at the leading order always enhances the deflection angle and therefore increases the apparent angles of the gravitational lensing images. These series results of the deflection angle are then shown to have excellent agreement with those obtained using numerical integration. The general formula of the deflection angle is then applied to the Reissner-Nordström, charged Horndeski and charged Galileon spacetimes. The effect of the plasma and characteristic parameter of the spacetimes on the deflection angles in these spacetimes was briefly discussed. In the appendix, the deflection angles in previously attempted spacetimes are re-computed and compared with the literature.

Stellar binary disruptions through the Hills mechanism produce two fossils: a hypervelocity star (HVS), and a star tightly bound to the supermassive black hole. Among known galactic HVSs, only S5-HVS1 has unambiguous galactic-centre origin. Its measured mass and velocity determine a relation between the mass and semi-major axis of its captured companion. GRAVITY has now discovered S301, whose orbit and photometrically inferred mass satisfy this relation, making it the only compelling candidate for the captured companion of S5-HVS1. We build a forward model for the Hills origin and compare it to the null hypothesis. This confirms that S301's orbit aligns much more closely with that of S5-HVS1's companion than a typical S-star. However, the catalog-level Bayes factor remains of order unity and dependent on the probabilities of survival and detection. S301 is thus a compelling candidate, but establishing its association with S5-HVS1 will require improved mass measurements, chemical comparisons and GRAVITY-calibrated selection functions.

Multi-wavelength observations of quadruply lensed quasars constitute a powerful probe of cosmology, dark matter substructure along the line of sight, and the structure of X-ray emitting regions in high-redshift quasars. These investigations are conditional on acquiring an accurate model for the surface mass density of matter lensing these quasars. We propose a simulation-based machine learning method to accelerate parameter inference in real quadruply lensed systems by several orders of magnitude. We simulate a grid of quadruply lensed sources with Singular Isothermal Ellipsoid (SIE) lenses and use the projected positions of the four lensed images to train two fully connected neural networks that predict the mass parameter and ellipticity. For a large fraction of simulated systems, the neural network-initialised mass models converge in time-scales of a few minutes and recover the source position at the <0.''005 level for a broad range of lens masses and ellipticities. We apply our neural networks to seven quadruply lensed quasars, lensed by isolated galaxies or a galaxy-perturber pair, which have archival Chandra observations. The final optimised mass models for each quasar predict the observed lensed image positions in Gaia Data Release 3. These mass models enable the caustic method, which locates the X-ray-to-optical emission regions to milliarcsecond precision in these otherwise unresolvable systems, improving the effective angular resolution of Chandra at high-z by up to two orders of magnitude. Our approach accelerates this mass modelling by supplying informed initial parameters, enabling application to the many new quadruply lensed systems expected from forthcoming surveys.

Most cataclysmic variables (CVs) are discovered when they have an outburst generating an inherent selection bias against CVs that rarely, or never, outburst. CVs discovered by virtue of their spectroscopic characteristics are particularly valuable to offset this bias and we have used an established machine-learning technique to assist in searching 98 966 000 spectra obtained by the Dark Energy Spectroscopic Survey (DESI) to find such CVs. DESI observations are much deeper than previous spectroscopic surveys and we have identified 1029 CVs, 221 of which are new including ten of the AM CVn subtype. We have spectroscopically confirmed 441 CV candidates and obtained 84 new or improved orbital periods. We present revised space density estimates based upon this new data. We have also added ten more to the eight known examples of an intriguing class of CVs which exhibit peculiar changes in accretion.

This paper presents a convolutional neural network (CNN) approach to classifying the nuclear equation of state (EOS). As illustrative examples, we use five two-dimensional core-collapse supernova (CCSN) simulations that differ only in their EOS. We analyze estimates of the initial slope of the high-frequency feature (HFF) reconstructed in real interferometric data from the O3b LIGO-Virgo-KAGRA (LVK) observing run at Galactic source distances of 1, 5, and 10 kpc. The CNN classifier achieves an overall accuracy of 98.58% at 1 kpc and 52.43% at 5 kpc. At 10 kpc, its ability to distinguish among the EOS classes is effectively lost. The successful EOS classification at 1 kpc suggests that this approach may be scalable to next-generation observatories. The expected order-of-magnitude sensitivity improvements of Cosmic Explorer and the Einstein Telescope could enable comparable classification performance at approximately ten times the current distance. More detailed performance metrics, including the macro-averaged one-vs-rest (OvR) area under the curve (AUC), yield values of 0.97 and 0.98 at 1 kpc. These results indicate strong classification performance both across the complete set of EOS classes and for the individual classes.

In these notes, we extend a formalism for computing the amplitude of gravitational-waves (GWs) beyond null-geodesic propagation, as may arise in alternative theories of gravity. We derive the wavevector divergence governing the amplitude evolution in this more general setting and apply the formalism to GWs with a frequency-independent subluminal group velocity and to massive gravitons. We show that, in both cases, a naive interpretations of the resulting amplitudes can lead to significant apparent distortions. This formalism opens the door for amplitude interactions with extra degrees of freedom in the presence of dispersion.

We report the discovery and characterisation of MKT J032848.4-271904.6, a new radio transient identified in the LADUMA field using SARAO Science Data Processor (SDP) UHF-band images from approximately one year of MeerKAT observations. Using the Transient Pipeline (TraP) and advanced filtering techniques, we identified a number of candidate variable radio sources in the field. All but one show variability consistent with refractive interstellar scintillation, leaving MKT J032848.4-271904.6 as the sole source exhibiting intrinsic variability. In addition, MKT J032848.4-271904.6 shows intrinsic variability at 0.816 GHz, with 13 radio detections across 41 epochs and a peak flux density of 1.041+/-0.043 mJy. We associate this emission with a low-mass M-dwarf star LP 888-63, located 23 pc from the Sun and identified as a companion to the white dwarf binary system LAWD 14 / WD 0326-273. LP 888-63 displays active flaring behaviour across the electromagnetic spectrum, including multi-band optical data from MeerLICHT. TESS photometry reveals a periodic modulation in the blended light curve of 5.780+/-0.507 days, consistent with rotational variability of a mid-M dwarf. Archival ESO spectra reveal Halpha emission, confirming magnetic activity. These findings highlight the capability of MeerKAT's SDP imaging and facilities like MeerLICHT for real-time detection and characterisation of stellar transients.

We present the optical design of VIPER: a high-resolution, multimode fiber-fed, narrowband, cross-dispersed, seeing-limited spectrograph based on a Virtually Imaged Phased Array (VIPA), a spectral disperser that provides higher dispersion and a more compact form factor than conventional diffraction gratings. VIPER is specifically designed to probe exoplanet atmospheric escape through the helium 1083 nm triplet line, with a resolving power of 300,000 over a 10 nm wavelength range. VIPER is intended for operation at the 1.5 m Tillinghast Telescope at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona, USA, and is matched to this telescope's 100 $μ$m circular-core multimode optical fiber feed at f/6. VIPER's optical design is specifically optimized for high throughput, which, in a VIPA spectrograph, is more challenging with a multimode fiber feed than a single-mode fiber feed because of the larger etendue. To address this challenge, our design implements a novel use of a cylindrical beam expander and pupil slicer. We validate our design using analytic calculations and simulations in Zemax OpticStudio non-sequential mode. Our results demonstrate the feasibility of multimode fiber-fed VIPA spectrographs as compact, high-throughput alternatives to conventional grating-based spectrographs for exoplanet science and other astronomical applications.

We construct and analyze stationary, axisymmetric vacuum metrics obtained by magnetic Ernst inversion of Kerr-NUT with Manko-Ruiz parameter $C$ and pre-inversion twist constant $β$. The transformation lies in the Ehlers orbit; our contribution is the NUT-dependent geometry and the roles of $C$ and $β$ in its axis, horizon, singularity, and azimuthal-CTC structure. The inversion preserves the canonical Weyl radius, the signed WLP numerator $F$, and the sign of $g_{φφ}$ on regular domains. At the selected pole $x=σ$, $C=-σ$, the local axis condition and conicity are controlled by $χ_σ^{(β)}=β-2m(2σa+3l)$. Exterior zeros of the chosen seed Ernst representative obey the exact criterion $-β\in\mathcal{R}_C$; for the sampled families numerical traces yield half-line ranges with closed-form corner endpoints. For $D=a^2+l^2-2alC\ne0$, $Λ_βΣ$ has a finite nonzero seed-ring limit. High-precision calculations find direction-independent finite limits of both quadratic Weyl invariants along the sampled rays, without establishing $C^2$-extendibility. At $β=0$, exterior simple Ernst zeros are found for the sampled $C=-1,0$ cases but not for $C=+1$, consistently with the computed ranges. Near one zero the Kretschmann scalar has a generic sixth-order blow-up; a numerical angular scan identifies exceptional directions of lower order. All sampled points in the regular ($g_{φφ}>0$) exterior are Petrov type I. Candidate horizon locations remain those of Kerr-NUT, and the asymptotics are Levi-Civita type.

Interpreting the observed properties of intermediate-mass stars requires accounting for rotation, binarity, intrinsic population diversity, and measurement uncertainty. We combine these effects in population-synthesis models of 1.4-2.5 M$_{\odot}$ stars that include pulsation properties of $δ$ Sct variables. The synthetic populations successfully reproduce the distributions of stars observed in young associations, validating the mapping between intrinsic and observed stellar properties. Using these models, we infer a semi-empirical $δ$ Sct instability strip by matching synthetic and observed populations. The resulting instability strip is systematically hotter than widely used theoretical prescriptions, implying that $δ$ Sct stars are on average 0.1 M$_{\odot}$ more massive than previously assumed, with 95% of the population spanning approximately 1.50-2.30 M$_{\odot}$. We then investigate the $δ$ Sct period-luminosity relation and reproduce its recently identified second ridge with mixture models in which roughly one-third of stars have the fifth or sixth radial overtone as their dominant mode; the fraction increases in younger populations. In contrast, unresolved binarity does not account for the second ridge. Finally, we predict the population-wide distribution of asteroseismic large separations, $Δν$, finding a peak between 6 and 7 d$^{-1}$, in agreement with recent observations. We also demonstrate that $Δν$ is most reliably measured with the échelle technique, while autocorrelation methods can produce spurious detections when used in isolation. These results show that population synthesis provides a powerful framework for interpreting populations of $δ$ Sct stars and for linking stellar evolution, pulsation, and observation.

Comparison of the spectra obtained at different observing dates shows significant variations in the complex H$α$ and H$β$ line profiles, such as a systematic increase in their emission peak strengths in 2025$÷$2026 compared to those observed in 2013 as well as a strong variability in their wind component. A detected variable radial velocity $V_{\odot}$ from $-20$ to $-68$ km/s with a standard deviation of the mean value of K$\sim$8.0 km/s can be interpreted as a result of pulsations or the presence of a companion. The stationary positions of forbidden lines with a mean radial velocity of $V_{\odot}=-51.38\pm0.26$ km/s are taken as an improved systemic velocity. Overall, a set of properties of IRAS 01005+7910 points to its status as a post-AGB star, which has undergone the hot-bottom burning phase.

We ask when a spinless spherical extended test body in vacuum general relativity moves as its point-particle counterpart. In Newtonian gravity, harmonicity of the external potential gives an all-order cancellation: in source-free regions all spherical multipole forces beyond the monopole vanish. Using Dixon's covariant multipole formalism, with spherical symmetry defined as $O(3)$ invariance in the Tulczyjew-Dixon momentum rest space, we show that the relativistic analogue holds through quadrupole order in any Ricci-flat spacetime. At this order the torque vector vanishes, the force reduces to Ricci contractions, and the representative worldline is geodesic; the spherical octupole is forbidden by symmetry. This universality, however, is not an all-order effacement principle. At hexadecapole (16-pole) order the torque vector still vanishes, so the spinless sector remains dynamically consistent, but curvature-squared terms generate Weyl-driven forces that can survive in vacuum. In Schwarzschild spacetime we compute the resulting force for radial infall and the invariant leading correction to the infall proper time. We also show that periodic modulations of the hexadecapole moments act as an internal drive: Melnikov's method gives transverse homoclinic splitting and local chaotic layers near the geodesic separatrix for generic driving frequencies. The analysis is restricted to the small-body regime of Dixon's finite multipole expansion.

We investigate the spontaneous scalarization of brane-localized charged black holes, focusing on the role of quantum-enhanced tachyonic instabilities. By solving the coupled bulk-brane equations numerically within the Einstein-DeTurck formulation, we construct fully backreacted static black hole solutions and map the system from the semi-classical limit to the strongly coupled quantum-dominated regime. We demonstrate that the holographic quantum effects, parameterized by $κ$, significantly modify the background geometry. Stability analysis, conducted via both effective potential diagnostics and quasinormal mode calculations, confirms that this geometric deformation deepens the negative well of the effective potential, thereby triggering a tachyonic instability. Integrating these results, we establish the global phase diagram of spontaneous scalarization in the $T_h/μ-κ$ parameter space. The results reveal that these quantum-enhanced instabilities promote scalarization by substantially raising the critical temperature, providing a clear quantitative signature of quantum effects on black hole hair formation.

While hundreds of protoplanetary discs have been studied in great detail, the detection of protoplanets still embedded in their native discs remains rare. WISPIT 2 is only the second laboratory allowing for direct study of planet formation while in progress. The recently discovered system hosts two giant protoplanets in a multi-ringed disc. Here, we aim at characterising the WISPIT 2 host star spectroscopically to determine its stellar properties, accretion rate, and inner disc diagnostics, providing a more complete picture of the system. We present optical and near-infrared spectroscopic observations obtained with the ESO VLT/X-Shooter and 2.2 m/FEROS instruments. We model the stellar spectrum to determine the spectral type and effective temperature, analyse the emission lines to estimate the accretion rate, and search for evidence of a close stellar companion using radial velocity measurements. Our observations reveal that WISPIT 2 is a spectroscopic binary. The binary has a period of $4.8\pm 0.1$ days, which corresponds to a semi-major axis of $0.072$ au or $15.54 R_\odot$, assuming co-planarity with the disc and a circular orbit. The binary system consists of a $\sim 0.97 M_{\odot}$ primary of spectral type K3 ($T_{\rm eff} \sim 4700K$), and a $\sim 0.33M_\odot$ secondary (mass ratio $\sim$0.34). We detect weak H$α$ emission, implying an accretion rate of $\sim 2 \times 10^{-11}\,M_{\odot}\,\mathrm{yr}^{-1}$. However, this value is below the chromospheric level, suggesting little to no ongoing accretion onto the young stars. This discovery makes the WISPIT 2 disc the first circumbinary system with directly imaged protoplanets, establishing this system as a unique benchmark for studying planet formation and disc evolution around binary stars.

HRMOS (High-Resolution Multi-Object Spectrograph) is a proposed new instrument for the ESO Very Large Telescope (VLT) developed in the context of the ESO VLT Beyond 2030 call. It is designed to fill a unique and currently unoccupied region in the observational landscape: the combination of very high spectral resolution (R=80,000) with multi-object capability (50-60 simultaneous targets), a radial-velocity (RV) precision of 10m/s, and coverage of three key spectral windows (385-421nm, 480-522nm, 623-677nm). Scientifically, HRMOS will address a rich portfolio of high-priority astrophysical questions spanning from f giant exoplanet formation, to nucleocosmochronology and constraints on cosmological parameter, to probing hierarchical galaxy assembly outside the Milky Way. The instrument is based on a modular approach and it consists in four primary subsystems, the Front End with a hybrid fiber-positioning and atmospheric dispersion correction (ADC) architecture, the Fiber Link with double-scrambling and the image slicers, three spectrographs based on volume phase holographic (VPH) gratings covering the three spectral ranges and a Calibration Unit.

We consider a cosmological model where dark matter and baryons interact via a pure momentum transfer. We present the foundations of the interaction and derive its main equations. In this framework, only the Euler equations for the two interacting components differ from those in the standard scenario. We also explain how this interaction relates with the common Tight-Coupling Approximation schemes typically used in many Boltzmann solver. After that, we implement the model in CLASS and CAMB Boltzmann solvers, which relay on those Tight-Coupling Approximation schemes and in SymBoltz, which is free from any approximation scheme. We demonstrate full consistency among all the implementations in the difference codes. We demonstrate how this type of interactions are useful regarding the $σ_8$ tension by producing a reduced clustering on smaller scales. Using cosmic microwave background, baryon acoustic oscillations, supernovae type Ia data and low-redshift constraints from Sunyaev-Zeldovich cluster counts and from DES year 6 results, we show the interacting scenario is mildly preferred when those low-redshift datasets are included.

For over a century, following the work of Eddington, Kapteyn, Malmquist and others, astronomers have wrestled with selection biases when making inferences from samples of objects. Typically, selection is performed on the same observations used to make the measurements of interest. However, selecting objects using one observable while analyzing another can also lead to a selection bias when the observables are correlated. Within a Bayesian framework, unmodelled selection effects correspond to a misspecified generative model. We derive the likelihood for truncated selection in correlated observables and demonstrate its usefulness by searching for residual selection effects of this form in Cepheid variable star brightness measurements used in recent distance-ladder measurements of the Hubble constant H0. We specifically look for the form of bias where the selection correction depends on the photometric uncertainties, which the Cepheid data can constrain while simultaneously measuring H0. We find only weak evidence for non-zero residual selection corrections, at a significance of (1.2sigma) to (1.9sigma), depending on the distance prior adopted. Including a single extra parameter to model the unknown cut-off lowers the recovered H0 by -0.7km/s/Mpc to -1.1km/s/Mpc, again depending on the distance prior. Allowing for a different selection for each host galaxy can decrease H0 further, although this becomes very sensitive to the distance prior applied. While introducing a new selection correction cannot by itself explain the Hubble tension, it may be a component of a multi-faceted solution that includes the choice of priors on distances and other effects.

The majority of spectroscopic surveys assume local thermodynamic equilibrium (LTE) during the modeling of stellar spectra. This assumption begins to break down for luminous stars, like the red giants targeted by SDSS-V's Milky Way Mapper Survey in its Galactic Genesis program. In this work, we present non-LTE (NLTE) abundances for 360,000 red giant stars in Milky Way Mapper DR19, from infrared APOGEE spectra. We generate NLTE spectra using precomputed departure coefficient grids for Na, Mg, Si, Al, Ca, Ti, Mn, and Ni. To fit APOGEE spectra at scale, we train neural network emulators (NNEs) to synthesize LTE and NLTE H-band spectra. After verifying that the NNEs are accurate, we fit the APOGEE spectra with ASPCAP results that fall within the same parameter range as the training data. We find strong NLTE effects on the order of 0.1\,dex for Al, Mn, and Ti, and smaller effects for Si and Ni. We provide a catalog of the results of our LTE and NLTE fits, as well as NLTE-corrected ASPCAP abundances using a polynomial fit correction.

We present a spectroscopic survey of young stellar objects (YSOs) in Sh2-284, a distant (~4.5 kpc), low-metallicity (Z~1/3 Zsun) star-forming region (SFR) toward the Galactic anticenter. Candidate YSOs were selected using mid-infrared Spitzer/IRAC data with optical and near-infrared photometry. Follow-up spectroscopy was conducted with MODS at the Large Binocular Telescope. We characterize the stellar and accretion properties of the disk-bearing population in a metal-poor environment, probing stellar masses from ~2.95 Msun to ~0.35 Msun. This work constitutes the first wide-field (~45'x45') spectroscopic investigation of YSOs in Sh2-284, providing a comprehensive view of star formation in this Galactic environment. We provide tentative first estimates of iron abundance for three low-mass targets and lithium abundance for a limited number of objects, offering an initial characterization of the chemical properties of these stars. We adopt a multi-diagnostic approach based on nine tracers, exploiting the spectral coverage of the instrument, using H_alpha, H_beta, H_gamma, CaII infrared triplet, Pa_eta, Pa_zeta, and Pa_epsilon emission lines. We derive key accretion properties and compare them with those measured in nearby, solar-metallicity SFRs to explore potential metallicity-driven differences in accretion behavior and disk evolution. We tentatively find indications of a flattening in the flux-flux relations of the metal-poor YSOs compared to solar-metallicity samples, a behavior that is recovered across diagnostics. Our observations indicate that the selected disk-bearing YSOs in this metal-poor environment exhibit resilient accretion activity, spanning from ~2.3x10^(-10) Msun/yr and ~1.0x10^(-6) Msun/yr, and a median rate of ~2.2x10^(-8) Msun/yr. Overall, this demonstrates that gas accretion can be efficiently sustained in sub-solar metallicity environments.

We show the emission of the Nambu-Goldstone (NG) bosons from the cosmological evolution of global monopoles. The NG bosons are non-thermally produced from the dynamics of global monopoles such as the pair annihilation of monopole and anti-monopole. Our numerical lattice simulations demonstrate that the spectrum of NG bosons emitted from the scaling evolution of global monopoles has a peak around the horizon scale, as in the case with the global string and the semilocal string. We also estimate the abundance of the pseudo-Nambu-Goldstone (pNG) dark matter when one (or both) of the NG modes has a soft mass.

Strong lensing changes the phase of a gravitational-wave signal as well as its amplitude and arrival time. We study whether this phase information can distinguish three dark-matter structures in the lens: a Navarro--Frenk--White halo (NFW), a self-interacting halo (SIDM), and a fuzzy-dark-matter field (FDM). We generate waveforms for the detectable lensed massive-black-hole-binary population of a four-year LISA mission and fit every signal with the same smooth singular-isothermal-ellipsoid lens with external shear. In 132 lens systems, 311 images are resolved as separate signals in time. NFW and SIDM produce real waveform changes, but their slowly varying part is largely degenerate with the constant, gradient, and curvature of a smooth lens. The coherent density fluctuations of FDM leave a larger frequency-dependent residual after this fit. The NFW--FDM and SIDM--FDM populations become distinguishable with about 60 and 110 resolved image waveforms, respectively. These results show that repeated lensed LISA signals can probe the spatial form of dark matter in lens galaxies, rather than only the total lensing mass.

We present an audio gate plugin that uses real gravitational wave strain data from the LIGO and Virgo detectors as low frequency oscillator (LFO) modulation sources. Conventional audio gates rely on synthetic waveforms, sine, triangle, sawtooth, whose fixed harmonic content produces predictable pumping effects. By contrast, gravitational wave chirps from compact binary coalescences sweep through frequency and amplitude on subsecond timescales; when time scaled to LFO rates (0.1 to 10)Hz, these chirps yield modulation signals with continuously evolving harmonic structure. The plugin demonstrates that astrophysical signals can serve as musically compelling modulation sources, bridging sonification and creative audio processing.

Persistent discrepancies between early- and late-Universe measurements have made cosmological tensions a major test of the standard $Λ$CDM model. We investigate whether an entropic generalized Chaplygin-gas cosmology, describing a unified dark sector, can modify the parameter degeneracies associated with these tensions. The model is constrained using Type Ia supernova data from PantheonPlus+SH0ES and DES--Dovekie, DESI BAO measurements, RSD growth data, compressed Planck 2018 distance priors, and a Planck lensing-amplitude prior. We find that the entropic gCg model closely reproduces the $Λ$CDM background expansion while introducing a controlled late-time deformation of the distance--redshift relation. This shifts the preferred $(H_0,Ω_m,S_8)$ region and partially reduces background-driven discrepancies, especially those involving $H_0$. Using \texttt{Tensiometer} to quantify posterior shifts in the common derived parameter space $(H_0,Ω_m,S_8)$, we show that the displacement relative to $Λ$CDM occurs mainly along background-sensitive directions. The model therefore modifies the late-time expansion sector more effectively than the growth sector, leaving residual $S_8$ discrepancies comparatively robust. These results support the possibility that the $H_0$ and $S_8$ tensions arise from distinct physical sectors.

We present a linear instability in magnetized plasmas with charge fluctuations. It is driven by an electric current proportional to the charge chemical potential $μ$ and the bulk velocity. This charge-flow (C-flow) instability has hitherto not been considered in standard magnetohydrodynamics or its chiral extensions. We derive its dispersion relation and maximum growth rate, and confirm them with direct numerical simulations. We also show that the C-flow instability persists even for zero-mean fluctuations of $μ$, vanishing resistivity, and a magnetic Prandtl number of unity.

We present a systematic derivation of the equations of relativistic chiral magnetohydrodynamics (MHD) for a plasma of charged fermions in an expanding universe. Through a combination of a coordinate transformation and a rescaling of the dynamical variables, we bring the full system to the same form as in the Minkowski metric, with the Hubble expansion surviving only in the chirality-flipping rate and the kinematic viscosity. Retaining all four contributions to both the electric and the axial current yields terms absent from standard chiral MHD: charge-density corrections to the evolution equations for the chemical potentials, and an electric current proportional to the charge chemical potential $μ$ and the bulk velocity. The latter is mandated by current conservation, requires no chirality imbalance, and drives the charge-flow instability studied in a companion paper. For the radiation-dominated era, we evaluate all the coefficients in physical units and use them to estimate the magnetic Reynolds number, the attainable magnetic field strength, and the minimum temperature at which the chiral dynamo can operate. The resulting equations are cast in a form ready for direct numerical implementation.

We introduce Solar Neutrinos for Direct Detection ($\texttt{SNuDD}$): an open-source Python package that enables the computation of the solar neutrino rate spectrum at direct detection experiments. $\texttt{SNuDD}$ can be used to determine the differential rate for both nuclear and electron recoils within the Standard Model and in the presence of beyond Standard Model physics effects, such as those arising from neutral-current non-standard interactions (NSI). The package accounts for matter effects during neutrino propagation through both the Sun and the Earth and for modifications to the scattering cross sections at the interaction site. We employ $\texttt{SNuDD}$ to place new limits on the effective NSI couplings using results from the xenon-based direct detection experiments LZ, XENONnT, and PandaX-4T, and we project the sensitivity of a future xenon detector based on the planned XLZD and PandaX-xT observatories. We find that current direct detection experiments are rapidly approaching sensitivities comparable to those of dedicated neutrino experiments and that future xenon detectors can provide leading constraints. We recommend that $\texttt{SNuDD}$ be used to combine incoming direct detection data with those from neutrino experiments in future global fits, placing direct detection within the broader landscape of neutrino physics.

Large spectroscopic surveys require robust pipelines capable of inferring stellar parameters over a wide range of the Hertzsprung-Russell (HR) diagram from data of varying quality. SDSS-V is one such survey, where the data from the lower-resolution, optical BOSS spectrograph will provide a large dataset covering a wide range of Galactic stellar populations. To better analyze these data, we present BOSS-CLAM, a generative, forward modeling pipeline for inferring effective temperature ($T_\mathrm{eff}$), surface gravity ($\log g$), metallicity ($[\mathrm{Fe/H}]$), and $α-$abundance ($[α/\mathrm{M}]$) from continuum-normalized BOSS spectra. BOSS-CLAM maps stellar labels to Non-negative Matrix Factorization (NMF) basis vector weights via a polynomial mapping jointly optimized with the spectral decomposition, which provides a more flexible framework for working with the lower-resolution BOSS data. Additionally, training labels are drawn from four complementary sources (ASPCAP, BOSS-MINESweeper, wide binaries, and a hot star validation sample), which enables coverage from cool M dwarfs through hot OB stars, and across a wide range of metallicity. We infer parameters for 1,708,214 BOSS spectra, with a recommended clean catalog of 915,514 sources. Validation against open and globular clusters demonstrates homogeneous, accurate abundances across a wide range of metallicity. Wide binary tests yield abundance uncertainties of $σ_{[\mathrm{Fe/H}]} \approx 0.15$ dex and $σ_{[α/\mathrm{M}]} \approx 0.06$ dex at SNR = 10. Finally, we demonstrate that the BOSS-CLAM catalog recovers known chemical structure of the Milky Way disk and is well-suited for Galactic archaeology, chemical tagging, and stellar population modeling. The pipeline, trained model, and catalog are publicly released as part of SDSS-V DR20.

We present the first chemical survey of Class I and Flat-Spectrum (I/FS) disks using JWST MIRI/MRS, targeting sixteen sources in the Ophiuchus star-forming region. Through empirical line luminosity measurements and multi-component slab modeling, we characterize the molecular reservoir of these young systems and compare them to twelve Class II disks of similar stellar mass. Water, HCN, C$_2$H$_2$, and CO$_2$ are frequently detected in I/FS sources with inclinations $i < 70^{\circ}$, whereas edge-on systems show significantly suppressed emission. Compared to Class II disks, I/FS sources show suggestive---though not yet statistically significant---evidence for elevated cold water ($\sim$200\,K) mass and lower CO$_2$ excitation temperatures. Statistical analyses identify accretion luminosity as the primary correlate of molecular mass across both evolutionary stages. Once this dependence is removed, cold water and CO$_2$ masses anti-correlate with mm-dust disk radius, while hot water remains insensitive to disk size. These patterns are qualitatively consistent with pebble drift models that predict early water enrichment followed by delayed CO$_2$ delivery, suggesting an evolutionary progression from molecular-poor Class 0 sources, through water-rich Class I/FS disks, to Class II disks with reduced cold water excess. This work provides an initial evolutionary framework for disk chemistry that requires larger, multi-region samples to confirm.

We study a modification of the model of axion inflation coupled to a $U(1)$ gauge field where the vector field is massive. In the conventional scenario with a massless gauge field, the onset of the regime where the gauge field strongly backreacts on the inflaton displays an instability whose nonlinear evolution and endpoint remain poorly understood. We argue that, if the gauge field is massive enough, the transition to the strong backreaction regime instead occurs smoothly, avoiding this instability. This observation suggests that axion inflation with massive gauge fields admits a controllable strong backreaction regime, so that a phenomenologically viable realization of inflation might be possible in this class of models.

In this article we describe a scheme for sensing both the mode mismatch and alignment of a cavity which does not require custom sensors and uses only Quadrant Photo-Detectors (QPDs). The technique is simple relying upon cylindrical lenses and thoughtful Gouy phase telescope design, and is trivial to implement alongside a Pound-Drever-Hall (PDH) locking scheme. The Gouy phase telescope design utilizes all three of the QPDs to sense each degree of freedom which also increases sensitivity and provides redundancy. The technique we show also works without RF modulation, which is useful for providing other general diagnostic information in complex optical experiments. An analytical overview of the technique as well as generic design equations for the Gouy phase telescope is provided. Finally, a detailed optical simulation is presented to verify the technique.

Here, we investigate the observational viability of fractional power law inflationary potentials, $V(\varphi) \propto \varphi^n$ ($n=$ 1/3, 2/5, 2/3), within the effective framework of Loop Quantum Cosmology (LQC) incorporating inverse volume corrections. By employing LQC modifications to the background dynamics and cosmological perturbation equations in the semi-classical regime, we analytically derive the scalar spectral index $n_{\rm s}$ and the tensor-to-scalar ratio $r$. These theoretical predictions are confronted with the latest high precision joint observational constraints, including ACT DR6, Planck 2018, DESI BAO, and BICEP/Keck datasets (P-ACT-LB-BK18). While steeper classical power law models are in severe tension with modern data, our results demonstrate that the inclusion of LQC inverse volume effects induces a prominent negative shift in $n_{\rm s}$. Consequently, for specific viable ranges of the quantum geometric parameters ($σ$ and $δ$), the theoretical predictions are translated horizontally across the $r-n_{\rm s}$ plane. This mechanism successfully steers classically disfavored models back into the tightly constrained 68\% and 95\% CLs, significantly improving their consistency with precision cosmological data.

Classical general relativity allows time travel, but Hawking [Phys. Rev. D 46, 603 (1992)] conjectured that quantum mechanics ultimately prevents it. Here we propose a feasible experiment to test Hawking's Chronology Protection Conjecture in optics. In this scheme, time travel is inherently related to lasing, and the amplified vacuum fluctuations above laser threshold establish the quantum limits of time travel

It was proposed that extra dimensions can acquire large size by higher dimensional inflation connecting two large hierarchies in particle physics and cosmology, namely the weakness of the actual gravitational force to the largeness of the observable Universe, in terms of one fundamental scale. This proposal is consistent with the observed approximate scale invariant power spectrum of primordial density perturbations only for one or two extra dimensions of around the micron size. While a cosmological history connecting the period of higher dimensional inflation to the beginning of the standard cosmology has recently been studied, we investigate here the TransPlanckian Censorship Conjecture in that context and show that it drastically constrains the parameter space of the model.

The Integrated Sachs--Wolfe (ISW) effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. We investigate whether the redshift evolution of the ISW effect can provide new constraints on the time evolution of dark energy. We consider theoretical predictions for the standard $Λ$CDM cosmology and alternative $w_0w_a$CDM models favoured by recent DESI BAO and DES Y6 constraints. We perform a tomographic cross-correlation analysis of the {\it Quaia} quasar catalogue and \textit{Planck} CMB temperature maps to measure the ISW signal over a broad redshift range, spanning about $(10h^{-1}~\mathrm{Gpc})^3$ comoving volume. We assess the robustness of the inferred ISW amplitude against variations in sky coverage, multipole range, and tomographic binning. We detect the ISW effect at a significance of $2.8 \, σ$, corresponding to an amplitude of $A_{\rm ISW}\simeq1.69\pm0.61$ relative to the \textit{Planck} $Λ$CDM prediction. The inferred signal remains stable against various analysis choices, including various CMB maps (SMICA, NILC, SEVEM), different choices of $\ell_{\rm max}$ and the number of multipole bins, and an alternative quasar bias model. The measured ISW amplitude is moderately stronger than predicted by the fiducial $Λ$CDM cosmology, and the alternative $w_0w_a$CDM models do not account for this discrepancy. Future tomographic ISW measurements with improved quasar catalogues from {\it Gaia} and forthcoming wide-area galaxy surveys such as {\it Euclid} and DESI will help clarify the origin of this difference.

This paper presents the construction of the supersymmetric (SUSY) deformed version of the time dependent metric that describes the interior of the Schwarzschild BH. First, the noncommutative bosonic model is constructed by inducing the deformation in the minisuperspace coordinates and the associated canonical momentum. Following the methods of SUSY quantum mechanics, the supercharges of the deformed models are constructed and the deformed SUSY Wheeler-DeWitt equation is obtained. The classical dynamics are also obtained using the WKB approximation, we find the classical solutions and the conditions to satisfy the Hamiltonian constraint for both the SUSY and bosonic cases. Finally, the effects of the deformation in the context of deformed phase space cosmology and black holes are discussed.

We construct Vaidya-type solutions of quasitopological gravity coupled to nonlinear electrodynamics in arbitrary spacetime dimensions. Starting from the corresponding static spherically symmetric charged solutions, we obtain their dynamical counterparts by promoting the integration constants, in particular the mass and electric charge, to arbitrary functions of the advanced or retarded null coordinate. We show that the resulting field equations are satisfied provided suitable charge-carrying null currents and null fluid fluxes are included. The formalism applies to a broad class of nonlinear electromagnetic theories and provides a simple and systematic method for generating exact radiating charged solutions in quasitopological gravity.

Classical delay, chorus, and reverb effects model multiple pro- pagation paths using discrete delays or statistical distributions. This work proposes a model inspired by gravitational lensing, where an audio signal is treated as a wave packet traversing a temporally distorted potential rather than physical spacetime. The distortion generates multiple effective propa- gation paths with different delays, phases, and gains, producing controlled constructive and destructive interference.

White dwarf (WD) atmospheric metal pollution provides strong evidence for the presence of remnant planetary material and it can be used as an indirect tracer of outer planetary systems. We analyze whether the presence of a wide stellar companion affects the occurrence of outer planetary systems by comparing the incidence of calcium (Ca) pollution in hydrogen-atmosphere WDs in wide binaries and in apparently single stars. We construct two sample pairs: a large homogeneous SDSS low-resolution spectroscopic set and a smaller high-resolution sample. For each WD, we measure Ca abundances or upper limits and compute detectability-corrected cumulative pollution fractions that account for variations in effective temperature, signal-to-noise ratio, and spectral resolution. In the SDSS-based samples, we find pollution fractions <1%, defined as the fraction of WDs with detected Ca, for both single WDs and WDs in wide binaries. After correcting for detectability, the cumulative abundance distributions of the two populations are statistically consistent. The same conclusion is obtained for the higher-resolution samples, despite their different raw detection fractions. Our results indicate no statistically significant difference in the occurrence rate of remnant outer planetary systems between single stars and stars with wide (~200 au) companions, within the current uncertainties. These uncertainties are significant because the samples contain only a small number of polluted WDs. The corrected detectability cumulative fraction approach used here provides a framework for comparing samples with different detection sensitivities and can be extended to larger spectroscopic datasets. Such samples will be required to determine whether wide stellar companions affect the survival and delivery of planetary material and to search for more subtle trends, for example, as a function of companion separation.

We investigate the degeneracies between black hole (BH) spin effects and parametrized post-Newtonian (PPN) parameters in the relativistic orbital dynamics of S2-like and S62-like stars orbiting Sagittarius A<inline-formula><tex-math>$^{\ast }$</tex-math></inline-formula>. Using a 1PN+SO Hamiltonian framework and synthetic astrometric and radial velocity data sets, we perform Bayesian parameter inference. For current baseline observational precisions, the dominant relativistic observable ─ the Schwarzschild periapsis advance ─ allows the recovery of the effective precession parameter <inline-formula><tex-math>$\Upsilon$</tex-math></inline-formula>, while leaving the individual PPN parameters <inline-formula><tex-math>$\gamma$</tex-math></inline-formula> and <inline-formula><tex-math>$\beta$</tex-math></inline-formula> degenerate. Assuming microarcsecond-level astrometric precision, the spin-induced Lense─Thirring signal becomes partially detectable; fixing the PPN sector to General Relativity allows the BH spin magnitude to be constrained to an uncertainty of <inline-formula><tex-math>$\sim 10^{-2}$</tex-math></inline-formula>. However, simultaneously varying PPN and spin parameters reveals a strong, approximately linear covariance between <inline-formula><tex-math>$\Upsilon$</tex-math></inline-formula> and the dimensionless spin parameter <inline-formula><tex-math>$\chi$</tex-math></inline-formula>. To overcome this limitation, we demonstrate that joint multi-star inference can disentangle the degeneracy by combining a wider-orbit star, which constrains the dominant 1PN sector, with a compact relativistic orbit that is sensitive to Lense─Thirring frame dragging.

We investigate static, spherically symmetric charged black holes in Einstein gravity coupled to Euler--Heisenberg (EH) nonlinear electrodynamics, including purely electric, purely magnetic, and dyonic configurations. Rather than adopting the Hamiltonian formulation based on the auxiliary electromagnetic invariant $\mathcal{P}$, we work directly with the physical electromagnetic invariant $\mathcal{F}$ in the Einstein-Euler--Heisenberg Lagrangian, thereby describing all charged configurations without introducing auxiliary variables. Within this approach, we derive an exact analytical solution for the purely electric case, recover the purely magnetic solution directly from the field equations, and construct the dyonic solutions numerically. We systematically study the horizon structure, causal properties, and thermodynamics of these solutions. While the purely electric branch exhibits the familiar Reissner--Nordström horizon structure, the purely magnetic branch naturally admits a novel three-horizon configuration consisting of one event horizon and two inner horizons. The dyonic solutions continuously interpolate between the electric and magnetic limits and exhibit either one- or three-horizon configurations, depending on the magnetic-to-electric charge ratio and the EH coupling. We further show that the EH nonlinear interaction significantly modifies the horizon structure and thermodynamic properties of charged black holes while leaving the central curvature singularity unresolved. These results demonstrate that EH nonlinear electrodynamics gives rise to qualitatively new causal structures beyond Einstein--Maxwell theory.

We investigate cosmic evolution in generalized Nash's theory of gravity involving the quadratic Ricci invariant $χ=R_{μν}R^{μν}$. The analysis is divided into two complementary branches. First, we study the power-law family $f(R,χ)=R^α+βχ$ as a reduced autonomous system in a flat FLRW background. Because the adopted variables become singular at the Einstein--Hilbert limit $α=1$, the phase-space analysis is restricted to $α\neq1$, with $α=2$ used as a representative quadratic benchmark. This benchmark contains radiation-like boundary configurations, restricted scaling saddles, and de Sitter-like accelerating endpoints (a stable node away from $α=2$ and non-hyperbolic at the benchmark itself), but not a complete regular radiation-to-matter-to-de Sitter sequence. Second, we constrain the regular observational branch $f_{\rm obs}(R,χ)=R-2Λ+βχ$, which reduces exactly to flat $Λ$CDM when $β\to0$. The Hubble rate is obtained from the reduced $Λ$CDM-connected background branch, integrated over $0\le z\le10$ and matched at higher redshift to a standard radiation+matter+$Λ$ background. Using SNe~Ia, BAO, and Planck~2018 compressed CMB distance priors, we find an expansion history very close to $Λ$CDM, with the quadratic correction tightly constrained around the nested standard-model limit. The resulting bound on $β$ should be interpreted as a background-level constraint within this reduced prescription, not as a perturbation-level viability test of the full higher-derivative theory.

We construct numerically two families of static five-dimensional Lorentzian metrics, solutions of vacuum Einstein equations with a negative cosmological constant, one with and one without a black hole region, with a metric at sections of conformal infinity which is conformal to any squashed three-dimensional sphere.

We present a framework for inferring stellar ages from spectroscopic stellar parameters, calibrated with ensemble kinematics by averaging over the median vertical action, $J_z$, for stars with similar atmospheric and chemical properties, yielding self-consistent age estimates across the Hertzsprung-Russell (HR) diagram. We refer to these ages as ensemble kinematic ages as the age scale is calibrated from the average kinematics of ensembles of stars with similar stellar parameters. Individual stellar kinematics are not used in assigning ages. We validate the method against subgiant ages, achieving an accuracy of ~30%, comparable to [C/N]-based estimates. We find a clear age-$J_z$ relations that enable age inference up to ~10 Gyr for both the high- and low-$α$ disks. Applying this framework to 1.5 million LAMOST stars, we derive ages for subgiants and giants with typical uncertainties of ~2 Gyr. The inferred ages agree well with literature age catalogs, with no significant systematic trends as a function of $\log g$. We also demonstrate the potential of empirical isochrones to calibrate theoretical stellar models. We identify an old (~7 Gyr) population within the low-$α$ disk but draw no firm conclusions. Although ensemble kinematic ages are statistical and sensitive to selection effects, Galactic potential assumptions, and Galactic location, they provide a robust population-level tool for Galactic archaeology, complementing traditional age indicators and extending age estimates across the full HR diagram.

In these lecture notes for the Les Houches School on Loop Quantum Gravity 2025, which took place in September 2025, we give a pedagogical review of the basics of the spinfoam framework for a quantum gravity path integral. While spin network states in loop quantum gravity describe the quantum geometry of the 3d space as dynamical networks of entangled quanta of volumes, spinfoams define transition amplitudes for those spin networks using the reformulation of general relativity as an "almost-topological" field theory and tools from quantum BF theory and topological state-sums. The lectures were a short format of three times one hour and a half, only allowing to cover the basics and offer a glimpse of more advanced lines of research. We introduce spin foam path integrals for increasing spacetime dimensions starting with 2d BF theory, then build up to 3d quantum gravity with the Ponzano-Regge state-sum and the Turaev-Viro invariant, and finally the quantization of general relativity in four dimensions.

The pre-inflationary QCD axion is often said to require low-scale inflation. We derive a general isocurvature bound for a light axion with a scale-invariant spectrum, treating its inflationary normalization $f_I$ independently of the late-time decay constant $f_a$ and allowing for an arbitrary axion dark matter fraction, nontrivial perturbation transfer, and the full anharmonic abundance response. In the minimal benchmark, where axions constitute all of the dark matter, $f_I=f_a\leq M_{\rm Pl}$, and the angular perturbation is conserved, the least restrictive CMB limit considered gives the 95% C.L. upper bound $H_I<1.25\times10^{10}\,\mathrm{GeV}$ on the inflationary Hubble scale. For an initial misalignment angle $θ_i=1$, the bound strengthens to $H_I<2.2\times10^7\,\mathrm{GeV}$, with still stronger constraints near the hilltop. Combining the isocurvature and tensor spectra yields axion-tensor and axion-conditioned Lyth bounds. If the observed curvature perturbation is generated by a canonical cold single-field slow-roll inflaton and the tensor amplitude varies slowly across the observable CMB window, these relations limit the inflaton excursion to $Δφ_{\rm CMB}/M_{\rm Pl}\lesssim10^{-7}\text{-}10^{-4}$ and require $|M_{\rm Pl}V'/V|\sim10^{-8}\text{-}10^{-5}$ while $M_{\rm Pl}^2V''/V\sim-10^{-2}$. This hierarchy favors models with independent control of the inflationary scale, potential derivatives, exit, and reheating, including hybrid, running-mass, and inflection-point models. Reheating and the requirement of Peccei-Quinn non-restoration sharpen these conditions, while nonminimal scenarios can relax them by modifying the primordial fluctuation, its transfer, or the relic abundance.

We revisit Kerr-NUT metrics and related spin-$s$ fields in $D\geq4$, and study their associated scattering amplitudes. Starting in position space, we highlight the interpretation of mass and (multiple) NUT charges as being associated to distinct solutions of the rotation-deformed radial equation, which is made explicit in Cartesian multi-Kerr-Schild coordinates. This interpretation extends to electromagnetism with magnetic-type charges, and also extends to higher-spin counterparts, in accordance with the classical double or multi copy. We then establish a notion of ``electric-magnetic" duality in higher dimensions, relating mass/electric to NUT/magnetic charges, which generalises the $D=4$ case in a novel manner. For $D\geq6$, this involves the choice where the multiple magnetic charges are equal. The duality is revealed in momentum space, by the 3-point scattering amplitudes that generate the solutions. For all spins, these amplitudes are constructed from a spin-raising operator $\mathcal S_μ$ and take the form $\varepsilon^{μ_1\cdotsμ_s}{\mathcal S}_{μ_1}\cdots {\mathcal S}_{μ_s}$ acting on a scalar seed. The scalar seed of the electric sector is dual to that of the magnetic sector: where the former's rotation dependence resums to a Bessel function $J_{\frac{D-5}{2}}$, the latter resums to a Bessel function $J_{-\frac{D-5}{2}}$. Finally, we explore the notion of self-duality that arises from this picture. Studying the classical $2\!\mapsto\!2$ amplitudes that determine leading-order scattering, we find no evidence of a higher-dimensional analogue of the integrability of $D=4$ self-dual gravity.

The Unruh effect predicts that an accelerating observer perceives the Minkowski vacuum as a thermal bath, yet direct detection remains experimentally inaccessible. Its timelike counterpart, arising from the entanglement of massless fields between the future and past light cones, offers a more feasible route but requires a detector whose transition frequency follows a specific conformal-time scaling. We propose and analyze a practical implementation of such a detector using superconducting fluxonium circuits, which naturally provide two quasi-degenerate ground states and a tunable excited state, forming an effective $Λ$-system. By modulating the excited-state transition frequency in Minkowski time, the detector accumulates a geometric phase associated with the timelike Unruh effect. Open-system simulations predict $\sim 10\%$ shift in the ground-state population within $530$ ns, representing a three-order-of-magnitude sensitivity enhancement over two-level Unruh-DeWitt detectors. These results establish a realistic quantum-circuit platform for experimentally probing the timelike Unruh effect and, more broadly, for testing fundamental nature of quantum fields using engineered quantum systems.