Recent baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI) Collaboration have renewed interest in dynamical dark energy models, particularly those that cross the “phantom divide” ($w_{\mathrm{DE}}=-1$). We present leading observational constraints on monodromic k-essence, a physically motivated scalar field dark energy scenario capable of realizing rapid oscillations about the phantom divide. Using cosmic microwave background (CMB) information, DESI DR2 BAO measurements, and type Ia supernova observations, we constrain the amplitude, frequency, phase, and power-law index describing the monodromic k-essence scenario at the background level. We find that the monodromic dark energy scenario can fit these datasets with a ${\chi }^2$ that is comparable to the phenomenological $w_0\text{−}{w}_a$ parametrization. While the CMB and BAO data alone are consistent with the standard $\mathrm{\Lambda }\mathrm{CDM}$ model, the inclusion of DESY5 supernovae shows a preference for a nonzero amplitude, $A=0.44_{-0.12}^{+0.16}$ (fully marginalized 68% CL). Conversely, inclusion of the Pantheon-Plus supernovae provides no evidence for monodromic k-essence, with $A<0.43$ (95% CL). We show that constraints on both monodromic dark energy and $w_0\text{−}{w}_a$ models are sensitive to the DESI DR2 LRG2 BAO distance, especially in the absence of supernova data.

A fast-rolling axion can transfer its kinetic energy to gauge fields via the Chern-Simons coupling, leading to copious production of gauge quanta during inflation. The amplified gauge fields act as a source for both scalar and tensor perturbations. In this work, we propose a mechanism for suppressing scalar perturbations while sourcing strong tensor perturbations. We present an implementation of such a mechanism, demonstrating that sourced tensor perturbations are expected to be detected by upcoming next-generation cosmic microwave background experiments.

The interaction of gravitational waves (GWs) with matter is thought to be typically negligible in the Universe. We identify an exception in the case of resonant interactions, where GWs emitted by a background binary system, such as an inspiraling supermassive black hole (SMBH) binary, cause a resonant response in a stellar-mass foreground binary and the frequencies of the two systems become, and remain, synchronized. We point out that this previously unexplored dynamical phenomenon is not only possible, but can lead to $\mathcal{O}(30)$ binary systems becoming resonantly locked in the host galaxy of merging SMBHs of mass ${10}^{8.5-11}{M}_{\odot }$, each of which has a significantly reduced merger time. We predict $\mathcal{O}({10}^{10})$ binary systems have been locked in the Universe’s history. Resonant locking could be detected through anomalous inspiral of binary systems.

Recently, it has been suggested that the spectrum of physical states in the Standard Model may include an ultralight pseudoscalar, denoted by ${\eta }_{\mathrm{w}}$, in analogy with the ${\eta }^{\prime }$ state arising from the strong interactions. We find that typical expectations for the properties of ${\eta }_{\mathrm{w}}$ get challenged by astrophysical constraints on the couplings of ultralight bosons. Our strongest limit sets a lower bound of $\mathcal{O}(100\mathrm{TeV})$ on the decay constant of the hypothesized pseudoscalar. We also briefly discuss whether ${\eta }_{\mathrm{w}}$ could be a dark matter candidate, or the origin of dark energy, but conclude that those identifications appear unlikely. Given the important implications of a potentially overlooked ${\eta }_{\mathrm{w}}$ state for a more complete understanding of the electroweak interactions and a fundamental description of nature, further theoretical and phenomenological investigations of this possibility and its associated physics are warranted.

This study investigates the sensitivity of the radio interferometers to identify imprints of spatially inhomogeneous dark matter annihilation signatures in the 21-cm signal during the prereionization era. We focus on the upcoming low-mode survey of the Square Kilometre Array (SKA-Low) telescope. Using convolutional neural networks (CNNs), we analyze simulated 3D 21-cm differential brightness temperature maps generated via the dm21cm code, which is based on 21cmfast and darkhistory, to distinguish between spatially homogeneous and inhomogeneous energy injection/deposition scenarios arising from dark matter annihilation. The inhomogeneous case accounts for local dark matter density contrasts and gas properties, such as thermal and ionization states, while the homogeneous model assumes uniform energy deposition. Our study focuses on two primary annihilation channels to electron-positron pairs $(e^{+}{e}^{-})$ and photons $(\gamma \gamma )$, exploring dark matter masses from 1 MeV to 100 MeV and a range of annihilation cross sections. For the $\gamma \gamma$ channel, the distinction across dark matter models is less pronounced due to the larger mean free path of the emitted photons, resulting in a more uniform energy deposition. For $e^{+}{e}^{-}$ channel, the results indicate that the CNNs can effectively differentiate between the inhomogeneous and homogeneous cases. Despite observational challenges, the results demonstrate that these effects remain detectable even after incorporating noise from next-generation radio interferometers, such as the SKA. We find that the inhomogeneous dark matter annihilation models can leave measurable imprints on the 21-cm signal maps distinguishable from the homogeneous scenarios for the dark matter masses $m_{\mathrm{DM}}=1\mathrm{MeV}$ and the annihilation cross sections of $⟨\sigma v⟩\ge 5\times {10}^{-30}{\mathrm{cm}}^3/\mathrm{s}$ ($⟨\sigma v⟩\ge 5\times {10}^{-29}{\mathrm{cm}}^3/\mathrm{s}$ for $m_{\mathrm{DM}}=100\mathrm{MeV}$) for moderate SKA-Low noise. Our results demonstrate the potential of machine learning techniques, such as CNNs, to extract subtle features from complex astrophysical data and sensitivity to probe exotic sources of energy injections, offering a novel approach to exploring the nature of dark matter and the early Universe with future 21-cm observations.

We analyze the sensitivity of the Large Hadron Collider (LHC) and the Future Circular Collider-hadron-hadron (FCC-hh) to the existence of pseudoscalar Higgs boson $A_0$ predicted by the bestest little Higgs model. We study the tree-level (two and three body) and one-loop decays of the pseudoscalar, $A_0\to b\overline{b},t\overline{t},\gamma t\overline{t},\gamma b\overline{b},Zt\overline{t},Zb\overline{b},Wt\overline{b},h_{0}t\overline{t},h_{0}b\overline{b}$, and $A_0\to \gamma \gamma ,\gamma Z,ZZ,gg,WW$, respectively. In addition, we perform a phenomenological study of the production of the pseudoscalar $A_0$ via gluon-fusion $gg\to A_0\to Y$ processes, where $Y\equiv b\overline{b},t\overline{t},\gamma \gamma ,\gamma Z,ZZ,gg,WW$. From the cross section of the processes of interest and the expected integrated luminosity of the LHC and FCC-hh, we determined the number of events that could be produced in both colliders.

Inelastic dark matter scenarios have attracted considerable attention in contemporary particle physics. In this study, we investigate the phenomenology of sub-GeV inelastic dark matter interacting via a lepton-specific scalar portal. By solving the Boltzmann equations, we obtain thermal target curves for several inelastic DM mass splittings in the sub-GeV mediator-mass range. We study the discovery potential of lepton fixed-target experiments, particularly NA64e, Light Dark Matter eXperiment (LDMX), and $\mathrm{NA}64\mu$, via their missing-energy signatures. Our analysis focuses on the $\varphi$-strahlung process, $lN\to lN\varphi$, followed by the invisible decay of the scalar mediator into Majorana dark matter particles $\varphi \to {\chi }_1{\chi }_2$. We use this channel to probe the mediator coupling to charged leptons of the Standard Model. For phenomenologically viable parameters of the inelastic dark matter scenario, we derive projected sensitivities for NA64e, LDMX, and $\mathrm{NA}64\mu$, assuming that the boosted state ${\chi }_2$ decays visibly via ${\chi }_2\to {\chi }_1{e}^{+}{e}^{-}$ outside the detector acceptance. Our results demonstrate the complementary roles of electron and muon beam experiments in exploring the sub-GeV inelastic dark matter sector interacting via a scalar portal.

We demonstrate that the scalaron, a scalar degree of freedom, emerging from the $f(R)$ theory of gravity, can account for the observed dark matter (DM) abundance if its mass is around the MeV scale, to ensure its cosmological stability. Focusing on two well-known $f(R)$ gravity models, we systematically show that if scalaron production proceeds via the freeze-in mechanism, the right relic abundance is satisfied over a very narrow window of reheating temperature ${10}^{14}\lesssim T_{\mathrm{rh}}\lesssim {10}^{16}\mathrm{GeV}$. We delineate the viable parameter space of the $f(R)$ models consistent with the observed DM abundance, and highlight relevant experimental constraints from searches targeting DM decay signatures.

We perform a detailed analysis of the fermionic sign problem in a series of one-dimensional integrals, that are achieved as extreme (one-site) limits of genuine physics models. Altogether we studied a Hubbard-like, a Gross-Neveu-like, a Thirring-like, and a Chern-Simons-like integral. We compare the Lefschetz-thimble structure for these integrals with contours obtained with the holomorphic flow equations at different flow times and with numerically optimized continuous integration contours, defined by a maximal value of the expectation values of the phases. With the holomorphic flow equation, we perform the large flow-time limit, so that the average phase corresponds to its value on the thimbles. In all of these integrals we observe that the convergence to this value is not monotonic, meaning that there is an optimal flow time where the sign problem is weaker than it is on the thimbles. Furthermore, we find that for all of these toy models, numerical optimization can find continuous contours on which the sign problem is considerably weaker than it is both on the thimbles and at flowed integration contours at the optimal flow time.

We present the spectrum generating algebra for the hybrid string with manifest $\mathcal{N}=1$ super Poincaré symmetry in ${\mathbb{R}}^{3,1}\times {\mathbb{R}}^6$. Our Del-Giudice–Di-Vecchia–Fubini operators establish a one-to-one correspondence with the conventional superstring spectrum, while making its four-dimensional structure manifest. We also discuss part of the antifield spectrum, and introduce a simple realization of the supersymmetry charges involving the ${\mathbb{R}}^6$ directions. As an application, we algebraically compute the helicity partition function. These results provide new tools for analyzing four-dimensional on-shell superspaces and may extend naturally to phenomenologically relevant compactifications.

The LIGO-Virgo-KAGRA collaboration recently reported an exceptional gravitational-wave event, GW231123. This gravitational-wave signal was assumed to be generated from the merger of a binary black hole system, with source frame masses of ${137}_{-17}^{+22}{M}_{\odot }$ and ${103}_{-52}^{+20}{M}_{\odot }$ (90% credible intervals). As seen by the two LIGO detectors, the signal has only $\sim 5$ cycles, between 30 and 80 Hz, over $\sim 10\mathrm{ms}$. It is of critical importance to confirm the origin of this signal. Here we present the results of a Bayesian model comparison to test whether the gravitational-wave signal was actually generated by a binary black hole merger, or emitted from cusps or kinks on a cosmic string. We find significant evidence for a binary black hole merger origin versus a cosmic string origin of the signal.

As pointed out in recent research, the near extremal black hole entropy with one-loop effect exhibits universal $\log T$ behavior at sufficiently low temperature. In this paper, we discuss the low-temperature quantum corrections to the thermodynamics of four-dimensional accelerating black holes with rotation and charges by using the method of Euclidean path integral. The one-loop path integral for the black hole thermal partition function near extremality is dominated by zero modes defined with respect to the extremal background. For the accelerating black holes without rotation, the near horizon extremal geometry is a direct product of two dimensional anti-de Sitter space (${\mathrm{AdS}}_2$) and two sphere (${\mathrm{S}}^2$) with warping factors, and the gravitational zero modes contain both tensor and vector types, with the respective contributions to the near extremal black hole entropy being $(3/2)\log T$ and $(1/2)\log T$. While in the presence of rotation, the near horizon extremal geometry is a warped and twisted product of ${\mathrm{AdS}}_2$ and ${\mathrm{S}}^2$ and the gravitational vector modes are absent. For the accelerating black holes with charges, we also consider the one-loop path integral of the gauge field, where the photon zero modes are found to contribute an additional $(1/2)\log T$ term to the near extremal black hole entropy.

We lay the groundwork for a UV-complete formulation of the Euclidean Jackiw-Teitelboim two-dimensional models of quantum gravity when the boundary lengths are finite, emphasizing the discretized approach. The picture that emerges is qualitatively new. For the disk topology, the problem reduces to counting so-called self-overlapping curves, that are closed loops that bound a distorted disk, with an appropriate multiplicity. We build a matrix model that does the correct counting. The theories in negative, zero, and positive curvatures have the same UV description but drastically different macroscopic properties. The Schwarzian theory emerges in the limit of very large and negative cosmological constant in the negative curvature model, as an effective theory valid on distance scales much larger than the curvature length scale. In positive curvature, we argue that large geometries are ubiquitous and that the theory exists only for a positive cosmological constant. Our discussion is pedagogical and includes a review of several relevant topics.

Quantum effects in the era of reheating of the Universe after inflation are considered. A semiclassical approach to gravity theory is applied within Starobinsky’s inflationary model with backreaction. Some subtleties associated with accounting for quantum effects in the one-loop approximation are clarified. An estimate of the contribution of vacuum polarization in the stress-energy tensor of matter fields to the cosmological particle creation due to the scalaron decay is presented.

The search for regular black holes with nonlinear electromagnetic fields has sprouted numerous candidates, each exhibiting certain virtues but often accompanied by significant drawbacks. We demonstrate that Komar mass, electric charge, and magnetic charge are mutually dependent in regular black holes with nonlinear electromagnetic fields, defined by a Lagrangian which is a function of both electromagnetic invariants, $F_{ab}{F}^{ab}$ and $F_{ab}{\star F}^{ab}$, regardless of the specific weak field limit of the theory. Also, we generalize one of the key no-go theorems by showing that static, spherically symmetric, electrically charged black holes in a theory respecting the relaxed Maxwellian weak field limit do not admit a bounded Kretschmann scalar. Finally, we address one of the long-standing niche questions, whether regular black hole solutions can exist when both electric and magnetic charges are present, by constructing an exotic family of regular dyonic black holes with nonlinear electromagnetic fields in theories respecting the Maxwellian weak field limit. Mounting evidence suggests that regularizing black holes through simplistic nonlinear extensions of Maxwell’s electromagnetism entails a high cost in the form of unorthodox theoretical assumptions.

Cold dark matter is one of the most compelling candidates for dark matter, and its intrinsic properties suggest that it can accumulate near the central supermassive black holes of galaxies, forming dense dark matter halos. Space-based gravitational wave (GW) detectors, with their high sensitivity, offer a promising avenue to probe the existence of dark matter through its effects on GW signals. In this work, we adopt the Navarro-Frenk-White (NFW) profile as the initial dark matter halo model and consider the adiabatic formation of a static, spherically symmetric black hole within the halo. In the final state spacetime, we took into account the gravitational perturbation effect of the dark matter halo, which resulted in the final spacetime metric being different from the Schwarzschild metric. Based on the relativistic dynamics in the resulting spacetime, we calculate the dark matter density and velocity distributions in the vicinity of the black hole. In this process, we employ the near-field approximation to derive analytical expressions for the distribution function of the NFW halo. Furthermore, we assess the dynamical friction exerted by the dark matter halo on orbiting bodies near the black hole, and investigate its impact on the orbital evolution and GW waveforms of extreme mass-ratio inspiral systems. Our results indicate that, in certain scenarios, the presence of a dark matter halo can lead to modifications in the phase of the emitted GWs.

We present a new approach to the conservative dynamics of binary systems, within the effective one-body (EOB) framework, based on the use of a Lagrange multiplier to impose the mass-shell constraint. When applied to the post-Minkowskian (PM) description of the two-body problem in Einsteinian gravity, this Lagrange-EOB (LEOB) approach allows for a new formulation of the conservative dynamics that avoids the drawbacks of the recursive definition of EOB-PM Hamiltonians. Using state-of-the-art values of the waveform and radiation reaction, based on factorized and resummed post-Newtonian (PN) expressions, we apply our new formalism to the construction of an aligned-spin, quasicircular, inspiralling EOB waveform model, called leob-pm, that incorporates analytical information up to the 4PM level, completed by 4PN contributions up to the sixth order in eccentricity, in the orbital sector, and by 4.5PN contributions, in the spin-orbit sector. In the nonspinning case, we find that an uncalibrated leob-pm model delivers maximum EOB/numerical relativity (NR) unfaithfulness ${\overline{\mathcal{F}}}_{\mathrm{EOBNR}}$ (with the Advanced LIGO noise in the total mass range $10-200M_{\odot }$) varying between 0.2% and 1% over all the nonspinning dataset of the Simulating Extreme Spacetime (SXS) Numerical Relativity catalog up to mass ratio $q=15$. It also delivers excellent phasing agreement with the $q=32$ configuration of the Rochester Institute of Technology catalog. We also found consistency between binding energies within a few percent at the NR merger location. Then, when NR informing the dynamics of the model (both orbital and spinning sectors) by using only 17 SXS dataset, we find that the EOB/NR unfaithfulness (compared to 530 spin-aligned SXS waveforms) has a median value of $5.39\times {10}^{-4}$, or $6.13\times {10}^{-4}$ (depending on the chosen description of spin-spin interactions), reaching at most $\sim 1\%$ in some of the high-spin corners. Although this global performance is less good (by a factor 3.67) than some of the state-of-the-art PN-Hamiltonian-based models, our finding shows that the LEOB approach is a promising route toward robustly incorporating both PM and PN information in the EOB description of the dynamics.

Gravitational waves (GWs) can be distorted by intervening mass distributions while propagating, leading to frequency-dependent modulations that imprint a distinct signature on the observed waveforms. Bayesian inference for GW lensing with conventional sampling methods is costly, and the problem is exacerbated by the rapidly growing GW catalog. Moreover, assessing the statistical significance of lensed candidates requires thousands, if not millions, of simulations to estimate the background from noise fluctuations and waveform systematics, which is infeasible with standard samplers. We present a novel method, dingo-lensing, for performing inference on lensed GWs, extending the neural posterior estimation framework dingo. By comparing our results with those using conventional samplers, we show that the compute time of parameter estimation of lensed GWs can be reduced from weeks to seconds, while preserving accuracy both in the posterior distributions and the evidence ratios. We train our neural networks with LIGO detector noise at design sensitivity and a lens model that accommodates two overlapping images with a constant $\pi /2$ phase shift. We show that the lensing parameters are recovered with millisecond precision for the time delays. We also demonstrate that our network can identify signals diffracted by point masses, highlighting its flexibility for searches. By simulating thousands of lensed and nonlensed events, we determine how the detectability changes with different source properties. dingo-lensing provides a scalable and efficient avenue for identifying and characterizing gravitationally lensed GW events in the upcoming observing runs.

In this paper, we study asymptotic properties of static spherically symmetric black holes in quadratic gravity with a cosmological constant $\mathrm{\Lambda }$. We find that for sufficiently large values of $|\mathrm{\Lambda }|$ these black holes are generically asymptotically (A)dS and form a three-parameter family of black holes, with free parameters being the horizon radius, $\mathrm{\Lambda }$, and Bach parameter $b$. For smaller values of $|\mathrm{\Lambda }|$, fine-tuning of the Bach parameter is necessary to recover asymptotically (A)dS behavior, resulting in two distinct two-parameter families of spherically symmetric black holes with (A)dS asymptotics. One family is the (A)dS-Schwarzschild solution, the other is a fine-tuned asymptotically (A)dS-Schwarzschild-Bach solution. We also generalize the above solutions to electrically charged black holes, obtaining qualitatively similar asymptotic behavior. This adds the electric charge as an additional free parameter of these black holes. Both fine-tuned three-parameter families are distinct from Reissner-Nordström black holes.

In this study, we present a novel family of exact black hole solutions constructed in the context of five-dimensional Gauss-Bonnet gravity. These solutions add a nonlinear charge to the Bañados-Teitelboim-Zanelli-like configurations known to exist with arbitrary Thurston horizon geometry. We establish constraints on the parameter space defining physically viable black holes, aligning with the standard energy conditions. An explicit proof of the first law of thermodynamics within our scenario is provided. We also employ holographic techniques to characterize the dc conductivities for the distinct horizon geometries, identifying a critical temperature indicative of phase transitions and exploring pertinent limits.