General relativity is expected to break down in the high-curvature regime. Beyond an effective field theory treatment with higher-order operators, it is important to identify consistent theories with higher-curvature terms at the nonperturbative level. Two well-studied examples are $f(\mathcal{R})$ gravity and Einstein-dilaton-Gauss-Bonnet (EdGB) gravity. The former shares the same vacuum solutions as general relativity, including black holes, while the latter suffers from well-posedness issues due to quadratic curvature terms in the strong-coupling regime. We show that combining these two theories leads to genuinely new phenomena beyond their simple superposition. The resulting framework falls outside Horndeski’s class, as it can be recast as a gravitational theory involving two nonminimally coupled scalar fields with nontrivial mutual interactions. This construction naturally extends EdGB gravity to include arbitrary higher-curvature terms, providing a versatile setting to address fundamental questions. Focusing on quadratic and quartic corrections, we find that: (i) black holes are modified by $f(\mathcal{R})$ terms, unlike the case without Gauss-Bonnet interactions; (ii) the resulting solutions retain the qualitative nonperturbative features of EdGB black holes with certain couplings, such as a minimum mass and multiple branches; (iii) a nontrivial mechanism suppresses the divergence of the Ricci scalar in the black-hole interior; (iv) still, even with quartic corrections, the singularity structure and elliptic regions inside the horizon remain similar to those of pure EdGB gravity. This suggests that, at the nonperturbative level, the theory’s ill-posedness cannot be resolved by adding individual higher-order terms. This conjecture could be tested by studying the nonlinear dynamics, which remains governed by second-order field equations.

Extreme mass-ratio inspirals (EMRIs), consisting of a stellar-mass compact object spiraling into a massive black hole, are key sources for future space-based gravitational wave observatories such as LISA. Accurate modeling of these systems requires incorporating the spin effects of both the primary and secondary bodies, particularly for waveforms at the precision required for LISA detection and astrophysical parameter extraction. In this work, we develop a framework for modeling flux-driven spherical inspirals (orbits of approximately constant Boyer-Lindquist radius) of a spinning secondary into a Kerr black hole. We leverage recently found solutions for the motion of spinning test particles and compute the associated gravitational wave fluxes to linear order in the secondary spin. Next, we show that spherical orbits remain spherical under radiation reaction at linear order in spin, and derive the evolution of the orbital parameters throughout the inspiral. We implement a numerical scheme for waveform generation in the frequency domain and assess the impact of the secondary spin on the gravitational wave signal. In contrast to quasicircular inspirals, we find that neglecting the secondary spin in spherical inspirals induces large mismatches in the waveforms that will plausibly be detectable by LISA.

We investigate the spontaneous scalarization of generic, static, and spherically symmetric regular black holes supported by nonlinear electrodynamics. Starting from an arbitrary seed metric, we employ the $P$-dual formalism to reconstruct the electromagnetic sector and subsequently couple a real scalar field nonminimally. As a worked example, we apply the framework to the regular Balart-Vagenas black hole, showing that scalarized and scalar-free branches can coexist in a region where the scalarized configurations are entropically preferred. We further assess possible observational imprints, finding percent-level deviations in both the shadow size and the fundamental scalar quasinormal modes ($<10\%$ for small charge-to-mass ratios), indicating that current electromagnetic and gravitational-wave observations do not rule out these solutions. Our construction thus provides a general route to explore scalarization on top of nonlinear-electrodynamics-supported spacetimes, extending beyond specific Reissner-Nordström-like cases.

We study Kerr-Schild perturbations of a ghost-free, generic nonlocal gravity theory constructed from an infinite series of higher-derivative terms in $D$ dimensions. The infinite series of higher-derivative terms are encoded by form factors, the forms of which can be restricted by requiring that the action remains perturbatively free of ghosts and tachyons around maximally symmetric backgrounds for transverse-traceless fluctuations. To demonstrate this, we obtain field equations for the anti–de Sitter plane-wave metric in Kerr-Schild form, which yield linearized field equations for transverse-traceless spin-2 field. Using unitarity and consistency requirements, we obtain, as an example, the explicit derivation of nonlocal form factors in $D$ dimensions.

Accurate modeling of gravitational waves from binary black hole mergers is essential for extracting their rich physics. A key detail for understanding the physics of mergers is predicting the precise time when the amplitude of the gravitational wave strain peaks, which can differ significantly among the different harmonic modes. We propose two semianalytical methods to predict these differences using the same three inputs from numerical relativity (NR): the remnant mass and spin and the instantaneous frequency of each mode at its peak amplitude. The first method uses the frequency evolution predicted by the backwards one-body model, while the second models the motion of an equatorial timelike geodesic in the remnant black hole spacetime. We compare our models to the Simulating eXtreme Spacetimes Collaboration’s waveform catalog for quasicircular, nonprecessing systems and find excellent agreement for $l=|m|$ modes up to $l=8$, with mean and median differences from NR below $1M$ in nearly all cases across the parameter space. We compare our results to the differences predicted by leading effective one-body and NR surrogate waveform models and find that in cases corresponding to the largest timing differences, our models can provide significant increases in accuracy.

It is important to explore the potential existence of lepton asymmetry in the neutrino sector. Conducting a joint analysis of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data and Planck 2018 cosmic microwave background data, we obtain the upper limits on the neutrino degeneracy parameter, i.e., $\xi <0.56$ for the normal mass hierarchy while $\xi <0.62$ for the inverted mass hierarchy, at 95% confidence level. Considering the influence of the dynamical dark energy, we find that these upper limits remain to be robust. This work may provide helpful implications for model buildings of the matter-antimatter asymmetry in the Universe.

Time-delay cosmology offers an alternative approach to measuring the Hubble constant ($H_0$), which is distinct from the cosmic distance ladder and cosmic microwave background radiation methods. In this study, we present an improved strong lens mass modeling analysis of the cluster-lensed supernova Refsdal, incorporating the latest spectroscopic redshift data from the MUSE on the Very Large Telescope and the James Webb Space Telescope CANUCS/Technicolor. The robustness of our lens models is confirmed using the Jackknife method. From our analysis that considers four lens mass models with different assumptions on profiles of dark matter halos and external perturbations, we derive a constraint on the Hubble constant of $H_0=66.0\pm 4.3\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ after combining best-fitted values of the four lens models.

The Atacama Cosmology Telescope (ACT) Collaboration has reported a scalar spectral index $n_s=0.9743\pm 0.0034$. This is substantially larger than the classical prediction of nonminimally coupled inflation models such as Higgs Inflation, $n_s\approx 0.965$. Here we revisit the unitarity-conserving nonminimally coupled inflation model proposed by R. N. Lerner and J. McDonald [Phys. Rev. D 82, 103525 (2010)]. We show that when the inflaton is a complex nonminimally coupled gauge singlet scalar with additional interactions in the Jordan frame to maintain unitarity, the model predicts $n_s=0.9730$ and $r\approx 9\times {10}^{-6}$ for scalar self-coupling $\lambda =0.1$.

In multimessenger high-energy astrophysics, interpreting observed spectra often hinges on understanding the underlying competition between energy gains and radiative losses within the accelerator. To progress along these lines, we report here on numerical particle-in-cell simulations of particle acceleration in relativistic, magnetized turbulent pair plasmas including synchrotron radiative losses. We investigate a regime of weak synchrotron cooling, where the maximal energy predicted by balancing the acceleration and radiation rates resides in the suprathermal tail, i.e., above the thermal bulk and below the confinement energy associated with the outer scale of the turbulence. Our key finding is that the particle energy spectrum, along with the radiated synchrotron spectral power, does not terminate at this maximal energy (or corresponding frequency), but extends significantly beyond with a steepened spectrum, up to the synchrotron burn-off limit where particles cool within a gyrotime. For our adopted parameters (turbulence magnetization parameter $\sigma \approx 1$ and amplitude $\delta B/B_0\simeq 1$), the particle distribution function follows $\mathrm{d}n/\mathrm{d}\gamma \propto {\gamma }^{-s}$ with $s\simeq 3$ below the predicted maximal energy, then steepens to $s\simeq 4$ above. The particle energy distribution and the radiated synchrotron spectra display strong variability near the cutoff energy down to timescales well below the largest eddy turn-around time. We substantiate our results by demonstrating that the acceleration rate itself displays a broken power-law-like distribution, whose mean value defines the diffusion coefficient and whose maximal value is the gyrofrequency. We perform a detailed analysis of the acceleration mechanism for the highest-energy particles and demonstrate that they are accelerated to this extreme limit by a generalized Fermi process in ideal electric fields. This process is driven by a gradient of the four-velocity field $u_E$ of the magnetic field lines of relativistic amplitude, $\delta u_E\gtrsim c$, ordered on a scale comparable to, or larger than, the particle gyroradius at the synchrotron burn-off limit. We contend that this is a generic feature of relativistic, large-amplitude turbulence. Finally, we apply our results to the case of the Crab nebula, which exhibits a hierarchy of characteristic Lorentz factors similar to that studied here. We conclude that stochastic acceleration in this environment is a promising mechanism for explaining the highest-energy part of the synchrotron spectral energy distribution and its variability.

Magnetars provide natural laboratories for strong-field quantum electrodynamics processes, such as vacuum polarization, which gives rise to vacuum resonance together with the plasma response. We develop a general framework to describe vacuum resonance in a three-component plasma consisting of ions, electrons, and positrons, as expected in baryon-loaded magnetar bursts. By introducing a parametrization of the plasma composition, we establish the general criterion for the occurrence of vacuum resonance in such plasmas. Our analysis encompasses both Mikheyev-Smirnov-Wolfenstein-like adiabatic mode conversion and nonadiabatic eigenmode transition, highlighting their dependence on the plasma composition. Applying this framework to baryon-loaded fireballs in magnetar bursts, we estimate the characteristic x-ray polarization signatures. Detection of these polarizations will provide observational signatures of vacuum polarization as well as baryon loading in magnetar fireballs.

We discuss the low-frequency gravitational wave signals from three state-of-the-art three-dimensional core-collapse supernova models produced with the chimera supernova code. We provide a detailed derivation of the gravitational wave signal sourced from the anisotropic emission of neutrinos and provide the total (fluid-sourced and neutrino-sourced) gravitational waves signal generated in our models. We discuss the templatability of this low-frequency signal, which is useful for future work involving matched filtering for signal detection and parameter estimation.

We present a modification of the expected local primordial black hole (PBH) count $N(y)$, typically seen in the context of the early PBH binary merger rate as a term in the merger rate suppression. We utilize recent results in small-scale PBH clustering to formulate $N(y)$ in such a way that accounts for variations in the binary mass ratio $q$. We then examine how this change affects the projected constraints on PBH abundance from simulated Einstein Telescope (ET) and LISA mergers. Our results indicate that for broadly extended mass distributions, the merger suppression is greatly reduced for binaries with $q\gg 1$. This leads to an enhanced merger rate for binary distributions favoring a lighter average mass. This change is best reflected by an extension of the low mass end of the constraint windows derived from the resolvable merger channel, although this result is present as well in the stochastic gravitational wave background (SGWB) constraints. Our results imply that the assumption of PBH clustering is testable at abundances and mass ranges much lower than anticipated. Note however that we have only considered the two-body merger channel in this work; a more thorough analysis of our scenario will require a study on the dynamics involved in the three-body merger channel for broad mass distributions, which we leave to future work.

By reentering into laser interferometers, scattered or stray light introduces nonlinear noise. This is a major limitation of precision interferometers as preventing such parasitic light is nearly impossible. Thus, substantial effort is put into mitigating the reentering of these fields in various ways. Ground-based laser interferometric gravitational wave detectors employ such mitigation techniques to reduce otherwise restrictive stray light noise. However, they are now reaching sensitivities where conventional mitigation techniques reach limitations. Further improvements planed for future observatories are placing even more demanding constraints on tolerable stray light power. We previously presented tunable coherence as a possible technique to ease these constraints and suppress unwanted coherent interference. For these promising demonstrations, the remaining coherence length and achievable suppression in length-constrained layouts was limited, among other things, by the used pseudo-random-noise phase modulation frequency. In this work, we demonstrate stray light suppression and cavity performance at modulation frequencies up to 10 GHz. This reduces the remaining coherence to a few centimeter in an interferometer, and even to the scale of the laser wavelength in a cavity. We further present a first demonstration of tunable coherence in a power-recycled Michelson interferometer, successfully suppressing stray light in a more complex topology.

We present a measurement of the non-Gaussian four-point correlation function (4PCF) from the DESI DR1 luminous red galaxy (LRG) sample. For the gravitationally induced parity-even 4PCF, we detect a signal with a significance of $14.7\sigma$ using our fiducial setup. We assess the robustness of this detection through a series of validation tests, including auto and cross-correlation analyses, sky partitioning across multiple patch combinations, and variations in radial scale cuts. Due to the low completeness of the sample, we find that differences in fiber assignment implementation schemes can significantly impact estimation of the covariance and introduce biases in the data vector. After correcting for these effects, all tests yield consistent results. This is one of the first measurements of the connected 4PCF on the DESI LRG sample; the good agreement between the simulation and the data implies that the amplitude of the density fluctuation inferred from the connected 4PCF is consistent with the Planck $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. The methodology and diagnostic framework established in this work provide a foundation for interpreting parity-odd 4PCF.

Quantum reflection is a fascinating signature of the quantum vacuum that emerges from inhomogeneities in the electromagnetic fields. In pursuit of the prospective real-world implementation of quantum reflection in the back-reflection channel, we provide the first numerical estimates for the light-by-light scattering with dipole pulses, which are known to provide the tightest focusing of light possible. For an all-optical setup with a dipole pump and Gaussian probe of the same frequency, we find that the dominant signal signature is related mainly to the back-reflection channel from 4-wave mixing. Focusing on this, we study the particular case of a multiple focusing pulses configuration (belt configuration) as an approximation to the idealized dipole pulse. Using Bayesian optimization methods, we determine optimal parameters that maximize the detectability of a discernible back-reflection signal. Our study indicates that the optimization favors a three-beam collision setup, which we further investigate both numerically and analytically.

We consider Sauter-Schwinger pair production by electric fields that depend on both time and space, $E(t,z)$ and $E(t,x,y)$. For space independent fields $E(t)$, momentum conservation $\delta (\mathbf{p}+{\mathbf{p}}^{\prime })$ fixes the positron momentum ${\mathbf{p}}^{\prime }$ in terms of the electron momentum $\mathbf{p}$. For $E(t,z)$, on the other hand, $p_z$ and $p_z^{\prime }$ are independent. However, previous exact-numerical studies have considered only the probability as a function of a single momentum variable, $P(p_z)$, $P(p_z^{\prime })$ or $P(p_z^{\prime }-p_z)$, but not the correlation $P(p_z,p_z^{\prime })$. In this paper, we show how to obtain $P(p_z,p_z^{\prime })$ by solving the Dirac equation numerically. To do so, we split the wave function into a background and a scattered wave, $\psi (t,\mathbf{x})={\psi }_{\mathrm{back}.}(t,\mathbf{x})+{\psi }_{\mathrm{scat}.}(t,\mathbf{x})$, where ${\psi }_{\mathrm{back}.}\propto \exp (\pm ipx+\text{gauge term})$. ${\psi }_{\mathrm{scat}\mathrm{.}}$ vanishes outside a past light cone and is obtained by solving $(i\cancel{D}-m){\psi }_{\mathrm{scat}.}=-(i\cancel{D}-m){\psi }_{\mathrm{back}.}$. backward in time starting with ${\psi }_{\mathrm{scat}.}(t\to +\infty ,\mathbf{x})=0$.

Axionlike particles (ALPs) are well-motivated examples of light, weakly coupled particles in theories beyond the Standard Model. In this work, we study long-lived ALPs coupled exclusively to leptons in the mass range between $2m_e$ and $m_{\tau }-m_e$. For anarchic flavor structure the leptophilic ALP production in tau decays or from ALP-tau bremsstrahlung is enhanced thanks to derivative couplings of the ALP and can surpass production from electron and muon channels, especially for ALPs heavier than $m_{\mu }$. Using past data from high-energy fixed-target experiments such as CHARM and BEBC we place new constraints on the ALP decay constant $f_a$, reaching scales as high as $\mathcal{O}({10}^8)\mathrm{GeV}$ in lepton-flavor-violating channels and $f_a\sim \mathcal{O}({10}^2)\mathrm{GeV}$ in lepton-flavor-conserving ones. We also present projections for the event-rate sensitivity of current and future detectors to ALPs produced at the Fermilab Main Injector, the CERN SPS, and in the forward direction of the LHC. We show that SHiP will be sensitive to $f_a$ values that are over an order of magnitude above the existing constraints.

In many models of inflation, reheating is realized through a coupling between the inflaton and the Higgs boson. Often, the mass of the inflaton is of order ${10}^{13}\mathrm{GeV}$ determined by the amplitude of the scalar fluctuation spectrum. However, in models where the inflaton potential is of the form $V\sim {\varphi }^k$ about its minimum, the inflaton is massless for $k\ge 4$ unless a bare mass term, $\frac{1}{2}{m}_{\varphi }^2{\varphi }^2$, is present. In this case, the inflaton mass may be of order the electroweak scale and may be subject to existing collider constraints. In particular, we investigate the constraints on the inflaton mass and reheating temperature $T_{\mathrm{rh}}$ arising from the decay of $\varphi$ into $\mathcal{H}$ through an interaction term $\mu \varphi |\mathcal{H}{|}^2$. We perform a renormalization group analysis to determine the relative values of $\mu$ and $m_{\varphi }$ such that the Higgs potential remains stable (and perturbative) at high energy. Taking into account the running of the Higgs quartic self-coupling and the experimental constraints from the LHC via the higgstools public code, we find that $3.4\times {10}^6\mathrm{GeV}\lesssim T_{\mathrm{rh}}\lesssim 3.9\times {10}^{12}\mathrm{GeV}$ with a corresponding constraint on the inflaton bare mass $260\mathrm{GeV}\lesssim m_{\varphi }\lesssim 3.8\times {10}^{10}\mathrm{GeV}$. The dependencies between $T_{\mathrm{rh}}$ and the inflaton bare mass $m_{\varphi }$ as well as between $\mu$ and $m_{\varphi }$ are provided.

Exotic interactions between fermions mediated by new bosons beyond the Standard Model may hold the key to several fundamental conundrums on the frontier of physics. However, laboratory searching for exotic interactions on small length scales is fundamentally held back by the short force range. Here we propose that the force range of exotic interactions tends to infinity when the oscillation frequency of exotic interactions approaches the mass of the new bosons, i.e., the new bosons become nearly on-shell. This is named as the near-threshold enhancement. Through the near-threshold enhancement, even fermions at distances larger than the original force range can make considerable contributions to exotic interactions. Therefore, the size of the experimental apparatus can break the limitation of the force range, and thus both the signal of exotic interactions and the sensitivity of sensors can be greatly enhanced. We also propose a method to search for the exotic interactions in the mass range between $80\mathrm{\mu }\mathrm{eV}$ and $800\mathrm{\mu }\mathrm{eV}$ taking advantage of the near-threshold enhancement. For the coupling $g_{\mathrm{A}}^{\mathrm{e}}{g}_{\mathrm{A}}^{\mathrm{e}}$, we expect an improvement on its upper bounds of ten orders of magnitude at $800\mathrm{\mu }\mathrm{eV}$. This method can be further extended to enhance the search for other types of exotic interactions and boost the study of new physics beyond the Standard Model.

In the QCD phase diagram, the dependence of the pseudocritical temperature, $T_{\mathrm{pc}}$, on the baryon chemical potential, ${\mu }_B$, is of fundamental interest. The variation of $T_{\mathrm{pc}}$ with ${\mu }_B$ is normally captured by $\kappa$, the coefficient of the leading (quadratic) term of the polynomial expansion of $T_{\mathrm{pc}}$ with ${\mu }_B$. In this work, we present the first calculation of $\kappa$ using hadronic quantities. Simulating $N_f=2+1$ flavors of Wilson fermions on fastsum ensembles, we calculate the $\mathcal{O}({\mu }_B^2)$ correction to mesonic correlation functions. By demanding degeneracy in the vector and axial-vector channels we obtain $T_{\mathrm{pc}}({\mu }_B)$ and hence $\kappa$. While lacking a continuum extrapolation and being away from the physical point, our results are consistent with previous works using thermodynamic observables (renormalized chiral condensate, strange quark number susceptibility) from lattice QCD simulations with staggered fermions.