高能暂现源 · 每日文献综述

Standard frequency-domain searches for quasi-periodic oscillations (QPOs) in active galactic nuclei generally assume sinusoidal variability. However, $γ$-ray blazar emission often shows asymmetric flares and localized bursts, causing spectral leakage that can reduce the sensitivity of conventional methods to non-sinusoidal periodic signals. We analyze a blind sample of 100 high-cadence (7-day binned) Fermi-LAT blazar light curves. After baseline detrending with Singular Spectrum Analysis, we apply the Fast Template Periodogram using three template families: a sinusoid, a Gaussian burst, and an empirical asymmetric template derived from PG 1553+113. Candidate signals are then evaluated with a Random Forest classifier trained on $5\times10^4$ simulated light curves to distinguish genuine periodic phase structure from stochastic red noise. We identify nine $>3σ$ periodicity candidates. Three persistent QPOs, including PG 1553+113, are recovered by all template models, whereas six additional candidates are strongly suppressed under the standard sinusoidal assumption but become detectable with morphology-aware templates. Machine learning validation rejects five of these as lacking stable phase coherence. The remaining candidate, PKS 1424$-$418, shows a structurally stable 4.8-year periodicity with a source-specific significance of $3.76σ$ (approximately $2.4σ$ after accounting for the trial factor of the 100-source sample). These results demonstrate that morphology-aware periodograms, combined with structural machine learning validation, improve the detection of burst-dominated QPOs that are difficult to identify with traditional harmonic searches.

We consider the emission of gravitational waves (GW) from a compact binary in a spacetime with compactified extra dimensions. We solve the homogeneous and non-homogeneous wave equation, proving that there is an infinite sum of exponentially decaying pseudo-massive modes which add to the usual one which behaves as 1/r at infinity. We calculate the metric potentials, the equations of motion and the energy flux. We find that in the equations of motion there is a new term at -1PN order. This implies a modification of the energy flux.

We show that, for stationary geometries whose linearized fluctuation equations separate into radial and angular Heun equations, a pair of diffeomorphisms projects the full problem onto two coupled, isospectral Gauss hypergeometric problems in complementary spacetime regions. This projection requires Robin boundary conditions to be imposed at the intersection between the complementary regions, which are uniquely fixed by requiring the two diffeomorphisms to match there. The method provides an independent derivation of recent results obtained from the correspondence between Heun connection coefficients and instanton partition functions in the Nekrasov-Shatashvili limit. As an application, we identify a subset of modes in Kerr-de Sitter and Kerr-anti-de Sitter black holes that, in the near-extremal limit, continuously reduce to a basis of the Schwarzian/Jackiw-Teitelboim functional space of gravitational fluctuations.

While General Relativity remains our most rigorously tested framework for gravitation, the theoretical persistence of singularities within standard black hole solutions continues to motivate the exploration of mathematically regular alternatives. Gravitational vacuum stars (gravastars) offer a non-singular model, substituting the event horizon with a physical, ultra-stiff thin shell. Recent studies have demonstrated that extended theories, such as $f(R, L_m, T)$ gravity, can structurally support these objects by utilizing the non-minimal coupling between geometry and matter. Building upon these static foundations, this paper presents a phenomenological propositional model to explore the dynamic interactions between modified-gravity gravastars and equatorial accretion flows. By numerically solving the modified Tolman-Oppenheimer-Volkoff equations and applying a non-complexifying algorithm, we construct a mathematically regular rotating metric ansatz. We demonstrate that the modified gravity coupling parameter systematically alters the effective potential, shifting the location of the Innermost Stable Circular Orbit (ISCO). Furthermore, we explore the idealized thermodynamics of plasma colliding with the gravastar surface, suggesting a distinct thermal emission that could theoretically produce a ``filled-in'' central shadow in interferometric observations. While acknowledging the challenges of observational degeneracy and the deliberate omission of complex radiation pressure feedback, we offer these geometric and thermal signatures as a transparent conceptual baseline to motivate future general relativistic magnetohydrodynamic (GRMHD) campaigns.

Ultralight axions from string compactifications carry non-canonical kinetic terms whose normalization is set by a coupling function that depends on an accompanying modulus field. As dark matter, such an axion forms a cold condensate whose quantum pressure resists gravitational collapse below a Jeans scale fixed by that coupling. One might hope that backreaction from the condensate's oscillations could shrink this Jeans length and thereby enhance structure growth. We show that it cannot. For any smooth, positive coupling function, the oscillation-averaged backreaction always drives the coupling to larger values, strengthening the quantum pressure and growing the Jeans length with time. We establish this no-go result analytically through an adiabatic- invariant analysis and confirm it by direct numerical integration. Kinetically coupled dark matter therefore cannot self-generate the conditions for enhanced gravitational collapse or the seeding of structure on sub-Jeans scales.

The Nelson-Barr mechanism solves the strong CP problem through spontaneous CP violation, but the resulting CP-conjugate vacua generically lead to stable domain walls. We propose that the Nelson-Barr scalar itself drives hilltop inflation. A CP-symmetric double-well potential for its imaginary component forms two CP-breaking valleys, with inflation proceeding along one of them. Since the lowest CP-invariant ridge is generically much higher than the energy available after inflation, transitions between the two branches are energetically inaccessible, and the domain walls cannot be regenerated after inflation. A small CP-preserving linear deformation raises the scalar spectral index of quartic hilltop inflation and yields CMB-compatible parameter regions. The Nelson-Barr sector necessarily provides a portal to visible-sector reheating. When coupled to right-handed neutrinos, it can also transmit the spontaneous CP phase to the lepton sector and, in an extension that allows a higher CP-breaking scale, even realize nonthermal leptogenesis. This establishes a unified cosmological realization of the Nelson--Barr mechanism in which the same CP-breaking dynamics solves the strong CP problem, can generate quark and lepton CP violation, drives inflation and reheating, and enables baryogenesis, while simultaneously eliminating the associated domain-wall problem.

The long-term stability of exoplanetary atmospheres depends critically on the extreme-ultraviolet (EUV) photon and high-energy particle fluxes from the host star, which are poorly constrained. To address this key gap in our understanding of atmospheric retention, we present the Extreme-ultraviolet Stellar Characterization for Atmospheric Physics and Evolution (ESCAPE) mission, a NASA Small Explorer concept proposed in 2026. ESCAPE employs extreme- and far-ultraviolet spectroscopy (80 - 1650 Ang) to provide the first comprehensive study of the stellar EUV history and stellar coronal mass ejection (CME) environments that control atmospheric mass-loss and determine the habitability of rocky exoplanets. This paper outlines both the primary science goals of the mission, the breadth of future general observer investigations, and a detailed design study of the mission's instrumentation. The ESCAPE instrument comprises a grazing incidence telescope that feeds multiple diffraction gratings and a photon-counting detector. We describe a demonstration of the Hettrick-Bowyer telescope, etched silicon diffraction gratings, the microchannel plate detector and housing, and gold and zirconium coatings. We present a STOP analysis that verifies ESCAPE's ability to meet its structural integrity, thermal stability, and optical performance requirements throughout the mission environment.

Most of the Milky Way's predicted stellar-mass black holes remain hidden, especially at high Galactic latitudes or in the Galactic halo, where traditional dense-field stellar microlensing is ineffective. We propose an alternative method to map this isolated population via the spectral microlensing of compact, extragalactic H II regions. Projected onto the source plane, the physical Einstein radius of a Galactic black hole can match the typical core sizes of H II regions in distant galaxies. Microlensing triggers an achromatic magnification, producing distinct narrow emission-line excesses in integrated galaxy spectra. Because gravitational lensing is wavelength-independent, intrinsic line ratios are preserved, offering a robust discriminant against false-positive astrophysical transients. Notably, the efficiency of this method depends critically on the size of the H II regions: while extended regions suffer from low optical depth, compact regions with a physical size $\lesssim 10$ pc offer significantly higher magnifications. These compact cores, however, are heavily dust-obscured at optical wavelengths, making infrared and radio observations the primary windows for this method. Even so, the spatial sparseness of background H II regions and the stringent alignment requirement for high magnification limit the expected event rate to $\sim 10^{-6}$ per year. Nevertheless, this method offers a unique opportunity to detect stellar-mass black holes and constrain their abundance in such low-density environments.

The cosmological dynamics of generalized holographic Ricci dark energy (GHRDE) of Xu type, embedded within power-law $f(\mathcal{T})=α\mathcal{T}+β\mathcal{T}^{m}$ teleparallel gravity and driven by the Hubble-parameter-dependent deceleration law $q=b-ν/H$, are investigated. The deceleration law yields an exact closed-form Hubble function $H(z)$ that interpolates between an early decelerating phase and an asymptotic de~Sitter regime, enabling all cosmological diagnostics to be expressed as explicit analytical functions of redshift. The present-day deceleration parameter $q_{0}=-0.60$ and transition redshift $z_{t}=1.0$ are consistent with current observational estimates. The GHRDE equation-of-state parameter $ω_{G,0}=-0.81$ lies within the quintessence band, and the effective equation of state evolves monotonically toward $-1$ without phantom crossing. The geometrical statefinder pair locates the model in the quintessence region of the $r$--$s$ plane, clearly displaced from the $Λ$CDM fixed point. A phase-space analysis reveals a stable-node de~Sitter attractor with strictly negative eigenvalues, guaranteeing robust late-time acceleration for generic initial conditions. The null, weak, and dominant energy conditions are satisfied throughout the redshift range considered, while the strong energy condition is violated at low redshift, as expected for an accelerating Universe. An observational constraint methodology combining cosmic chronometer data, Pantheon$+$ supernovae, and baryon acoustic oscillation measurements is outlined as the natural continuation of this work.

This thesis investigates quantum field theoretic approaches to classical gravity beyond General Relativity. Using worldline effective field theory, worldline quantum field theory, and on shell scattering amplitudes, it investigates compact-object dynamics in dark-sector models, scalar tensor gravity, dynamical Chern Simons gravity, and Einstein Maxwell dilaton theory. The thesis derives a range of conservative and radiative observables, including impulses, waveforms, eikonal phases, two-body potentials, and scattering angles, while incorporating effects associated with spin, parity violation, infrared structure, and multi-loop integrals. It also constructs celestial eikonal amplitudes and analyzes their conformal data in gravitational theories beyond General Relativity. Collectively, these results broaden the application of modern quantum field theoretic techniques to gravitational dynamics and contribute to a more detailed understanding of gravity beyond the Einsteinian framework. (Detailed abstract in the thesis.)

Stellar spectroscopy is a robust technique for determining fundamental stellar parameters such as effective temperature, surface gravity and metallicity. Spectroscopy Made Easy (SME) has long served as a framework for spectral synthesis and parameter inference. In this paper, we introduce webSME, a web-based extension of the Python implementation of SME. webSME integrates enhancements including a non-local thermodynamic equilibrium abundance correction mode, a precomputed grid of synthetic spectra for robust determination of stellar parameters from large wavelength ranges (thousands of Angstroms wide), Markov Chain Monte Carlo sampling for uncertainty estimation, and support for recent reference abundance patterns. It enables efficient and user-friendly analysis of high-resolution spectra, making it suitable for a wide range of applications - from detailed abundance studies to education and outreach. We demonstrate the performance of webSME on synthetic and observed spectra, including benchmark stars, and validate its accuracy against classical SME-based analysis. The platform's ease of access and advanced capabilities position it as a powerful tool in the modern astrophysical toolkit.

Type Ia supernovae provide one of the principal observational probes of late-time cosmic acceleration. Recently, Son et al. [MNRAS 544, 975 (2025)] proposed that correlations between SNe Ia luminosity and progenitor age could introduce a systematic bias in the inferred luminosities, leading to revised distance moduli in the Pantheon+ and DES-SN5YR compilations. Motivated by this possibility, we test whether the age-bias-corrected SNe Ia Hubble diagrams comply with the luminosity-distance relation $d_L=c/H_0\,(1+z)\ln(1+z)$. We find that this one-parameter logarithmic relation provides a high-quality description of both datasets, with the Hubble constant $H_0$ as its sole free parameter. For Pantheon+ and DES separately, the relation yields lower $χ^2$ values than the two-parameter flat $Λ$CDM, with $Δχ^2=12.0$ and $2.1$, respectively. A joint likelihood analysis of both datasets yields $Δχ^2=17.1$, corresponding to $(Δ\text{AIC},Δ\text{BIC})=(19.1,25.2)$ in favor of the logarithmic relation. We further find that, after the age-bias correction, neither dataset requires higher-order corrections to the relation, whereas the Einstein-de Sitter cosmology is firmly rejected. These results indicate that the closed-form relation $d_L=c/H_0\,(1+z)\ln(1+z)$ provides a viable one-parameter description of progenitor age-bias-corrected SNe Ia Hubble diagrams. Its asymptotic behavior $d_L\propto z\,\ln z$ naturally accounts for the excess distance moduli observed at high redshift. Should the progenitor age-bias correction be confirmed, the logarithmic relation can be stringently tested using larger samples of SNe Ia within $1\lesssim z\lesssim2$, where it already departs markedly from flat $Λ$CDM.

We determine the small-oscillation period of a simple pendulum in Schwarzschild spacetime. After transients decay, the displaced rope coincides with a geodesic of the induced spatial metric. This determines the radial lift of the bob to quadratic order in the angular amplitude and leads to the period measured by an observer at the bob's equilibrium position, $r=r_2$, with the fulcrum at $r_1$, \[ T_{(2)}=4π\frac{r_2^2}{c r_s}\sqrt{N_2(N_1-N_2)}, \] where $N_i=N(r_i)$ and $N(r)=\sqrt{1-r_s/r}$ is the Schwarzschild lapse. The result is therefore expressed in terms of the same function that determines clock rates and gravitational redshifts. In the Newtonian limit, we reproduce the classical result $T=2π\sqrt{L_0/g}$. We interpret the period close to the horizon in terms of an effective pendulum length. We compare our treatment with the coordinate-length constraint adopted in an earlier study and argue that the two problems are inequivalent away from the classical, weak-field limit.

The Black Hole Explorer (BHEX) is a next-generation space very-long-baseline interferometry (VLBI) mission concept that will extend existing ground-based millimeter/submillimeter VLBI arrays to space. The Japanese astronomical community has contributed to BHEX mission development through the BHEX Japan Consortium, established in 2023. This paper provides a high-level summary of progress in Japan since 2024, including the establishment of the Black Hole Explorer Working Group (BHEX WG) at the Institute of Space and Astronautical Science (ISAS), JAXA, to conduct the Japanese side of the Pre-Phase~A mission studies. We outline recent advances in key instrument technologies, including concept design studies of a 4.5\,K closed-cycle mechanical cryocooler and prototype development of an ultra-wideband 300\,GHz Superconductor--Insulator--Superconductor (SIS) mixer for BHEX. We also describe ongoing upgrades to Japan's ground infrastructure to support 86\,GHz observations with VERA and simultaneous 86+230\,GHz observations with the Nobeyama 45\,m Telescope.

We present a systematic reassessment of cosmological constraints beyond ΛCDM by progressively relaxing the assumptions underlying Dark Energy (DE), Curvature, Neutrinos, and Inflation. Using the latest CMB data together with DESI BAO and different SN catalogues, we show that the preference for dynamical DE persists across all the extended cosmologies considered. Ω<SUB>k</SUB> remains compatible with flatness, despite a mild 2.2σ preference for Ω<SUB>k</SUB> &gt; 0 that is substantially degraded in dynamical DE extensions. Constraints on N<SUB>eff</SUB> are broadly consistent with <mml:math><mml:mrow><mml:msub><mml:mi>N</mml:mi><mml:mrow><mml:mrow><mml:mi>e</mml:mi></mml:mrow><mml:mi>f</mml:mi><mml:mi>f</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>3.04</mml:mn></mml:mrow></mml:math>, while cosmological upper limits on the total neutrino mass vary substantially across the cosmologies explored, ranging from ∑m<SUB>ν</SUB> ≲ 0.06 eV to ≲ 0.2 eV. We quantify both the preference for the mass ordering and the apparent tension between cosmology and oscillation experiments, showing that they are strongly framework dependent. We find no evidence for inflationary tensor modes, with r ≲ 0.035. Constraints on the spectral index n<SUB>s</SUB> show significant model dependence. Allowing for the scalar runnings produces a mild shift toward α<SUB>s</SUB> &gt; 0 and β<SUB>s</SUB> &gt; 0 that can reabsorb the preference for larger n<SUB>s</SUB> found in small-scale CMB data, although both α<SUB>s</SUB> and β<SUB>s</SUB> remain consistent with zero at ~ 1.5σ. We highlight the implications for slow-roll inflation and benchmark models. None of the extensions considered here can resolve the H<SUB>0</SUB> tension. We discuss the implications for Ω<SUB>m</SUB> and S<SUB>8</SUB>. Overall, dynamical DE is the only significant deviation from ΛCDM and has the strongest impact on the inferred conclusions in the other sectors of the model.

We establish a sufficient one-minimum criterion for the off-shell Kerr family $Δ(r) = r^2 - 2rm(r) + a^2$ with a positive, nondecreasing mass profile $m(r)$, showing that $1 - 2m'(r) - rm''(r) > 0$ ensures strict convexity and determines root counts for $Δ$. Using a fuzzy-dark-matter-inspired benchmark satisfying this bound, we derive first-order responses for the outer horizon, extremal branch, photon sphere, and shadow functional under general deformations $m/M_{\text{ADM}} = 1 + \varepsilon h$. We demonstrate that static horizon and photon responses are profile-controlled, spin-odd shadow displacements are completion-dependent, and scale-consistent weak-field limits render local profile-gradient effects negligible ($\ll 10^{-20}$), confirming the strong-field box as a formal radial-profile benchmark rather than a self-consistent rotating scalar-field solution.

In this paper, we investigate topologically charged Morris-Thorne-type traversable wormholes by solving the Einstein field equations with an anisotropic fluid as the energy-momentum tensor and analysing the resulting solutions. In continuation to the earlier work (Eur. Phys. J C {\bf 84} (2024) 1037), we consider the shape functions such as: (i) $A(r)=r_0\,e^{r_0-r}$; (ii) $A(r)=r_0\,a^r/a^{r_0}$,\quad $0 < a<1$; (iii) $A(r)=r_0\,\left(\frac{\cosh r_0}{\cosh r}\right)^δ$,\quad $δ\geq 1$; (iv) $A(r)=\frac{1}{r}+\ln\!\frac{r}{r_0}$; (v) $A(r)=B\,r^n+(1-B)$; (vi) $A(r)=r_0\,\frac{\mbox{ln} (1+r)}{\mbox{ln} (1+r_0)}$, (vii) $A(r)=r_0+a\,r_0\,\left[\left(\frac{r}{r_0}\right)^β-1\right]$, where $β<1$ and $0 < a\,β<1$. We examine the energy conditions-namely, null, weak, strong, and dominant energy conditions and explore how topological charge influences or controls these conditions. Additionally, we calculate the anisotropy parameter to determine whether the wormhole geometry exhibits attractive or repulsive behavior. Our analysis demonstrates that the energy density of the anisotropic fluid is always positive. However, while some of the energy conditions are partially satisfied, others are violated.

We perform an observational and thermodynamic analysis of four cosmological models $Λ$CDM, CPL, MPL, and the three-parameter MmAH parametrization. All dynamical models improve the fit relative to $Λ$CDM, with $Δχ^2 \sim 6$-$6.5$, with MPL providing the best fit, while MmAH remains viable. Although Bayesian evidence mildly favors $Λ$CDM due to its lower complexity, the dynamical dark energy models remain competitive alternatives given current observations. We then reconstruct thermodynamic quantities within observationally constrained cosmological models, extending previous theoretical studies. The bestfit heat capacity reconstruction indicates that the divergence associated with a second order thermodynamic phase transition coincides with the deceleration-acceleration transition only in $Λ$CDM, whereas for the dynamical dark energy models it occurs at distinct redshifts, suggesting that this coincidence is not universal. The generalized second law is satisfied for all models over $0 \le z \le 1$, while the Hessian analysis reveals a transient instability at the phase transition; however, the late time thermodynamic stability is model dependent, with CPL and MPL remaining stable and $Λ$CDM and MmAH failing to satisfy both stability conditions simultaneously. These results show that thermodynamic properties reconstructed within observationally constrained cosmological models provide a complementary probe of dark energy, with the thermodynamic phase transition emerging as an intrinsically model dependent phenomenon.