We formulate an effective field theory (EFT) of coupled dark energy (DE) and dark matter (DM) interacting through energy and momentum transfers. In the DE sector, we exploit the EFT of vector-tensor theories with the presence of a preferred time direction on the cosmological background. This prescription allows one to accommodate shift-symmetric and nonshift-symmetric scalar-tensor theories by taking a particular weak coupling limit, with and without consistency conditions respectively. We deal with the DM sector as a nonrelativistic perfect fluid, which can be described by a system of three scalar fields. By choosing a unitary gauge in which the perturbations in the DE and DM sectors are eaten by the metric, we incorporate the leading-order operators that characterize the energy and momentum transfers besides those present in the conventional EFT of vector-tensor and scalar-tensor theories and the nonrelativistic perfect fluid. We express the second-order action of scalar perturbations in real space in terms of time- and scale-dependent dimensionless EFT parameters and derive the linear perturbation equations of motion by taking into account additional matter (baryons, radiation). In the small-scale limit, we obtain conditions for the absence of both ghosts and Laplacian instabilities and discuss how they are affected by the DE-DM interactions. We also compute the effective DM gravitational coupling $G_{\mathrm{eff}}$ by using a quasistatic approximation for perturbations deep inside the DE sound horizon and show that the existence of momentum and energy transfers allow a possibility to realize $G_{\mathrm{eff}}$ smaller than in the uncoupled case at low redshift.

We compute the gravitational waveform emitted during the transition from quasispherical inspiral to plunge, merger, and ringdown for a system of two black holes in the extreme mass ratio limit, where the primary is spinning and the secondary is represented by a nonspinning point-particle inspiralling along inclined orbits. The point-particle dynamics is described via a Hamiltonian formalism and the transition is driven by an effective-one-body like radiation reaction force. The gravitational waveform is obtained solving numerically, in the time-domain, the Teukolsky equation with a $\delta$-like source. The waveform is systematically characterized varying the black hole spin magnitude between (0,0.9) and the inclination angle of the orbit between $(0,\pi )$. We consider all multipoles up to $\ell =4$ and compute the energy and angular momentum losses during the plunge. The impact of the $m\ne \ell$ modes grows as the inclination angle is increased. We also use our framework to quantify the accuracy of the approximate inspiral-merger-ringdown waveform for an inclined orbit that can be obtained by applying a suitable time-dependent rotation to a given spin-aligned waveform with approximately consistent (but constant) spin-orbit coupling.

Recently, a remarkable new class of spacetimes describing black holes immersed in a nonaligned electromagnetic field has been found. While still of type D, this class goes beyond the famous Plebański-Demiański family. Here we demonstrate that the whole class admits a hidden symmetry encoded in the nondegenerate conformal Killing-Yano 2-form. Interestingly, as a direct consequence of nonalignment of the electromagnetic field and contrary to the Plebański-Demiański class (where the field is aligned), such a symmetry no longer generates the full “tower of symmetries.” Despite this, it enables one to separate variables in massless Hamilton-Jacobi, conformal wave, and massless Dirac equations, as well as allows one to tackle massless vector and tensor perturbations. These results provide a useful mathematical tool for discussing numerous (astrophysical) applications to be described by these metrics. Moreover, as we shall show, the novel spacetimes provide an interesting test ground for studying the recently defined Penrose charges whose existence is intrinsically related to hidden rather than explicit symmetries.

We examine single-field inflationary models for the formation of primordial black holes (PBHs). By analyzing the latest observations from the Atacama Cosmology Telescope [J. Cosmol. Astropart. Phys. 11 (2025) 062., J. Cosmol. Astropart. Phys. 11 (2025) 063.], we demonstrate that the observed preference for positive running (${\alpha }_s$) of the scalar spectral index $n_s$ imposes significant restrictions on the parameter space for a large class of ultra-slow-roll (USR) models. This tension becomes progressively pronounced for more massive PBHs, posing substantial challenges for USR models to yield a detectable PBH abundance, especially in the mass range probed by ongoing and future gravitational-wave experiments such as LIGO-Virgo-KAGRA and the Einstein Telescope. However, this discrepancy is minimal for asteroid-mass PBHs, which are still capable of feasibly constituting the entirety of dark matter. To numerically probe the six-dimensional parameter space of the models, we adapted a Markov Chain Monte Carlo approach to efficiently scan over the viable configurations. Our results further indicate that, in nonminimally coupled polynomial inflation, a viable cosmic microwave background (CMB) spectrum is best obtained at an inflection point for which second-order slow-roll approximation is necessary for precise CMB predictions.

We numerically study how the primordial magnetic field affects the first-order electroweak phase transition in the early Universe. We observe the following: 1) the phase transition process would be slowed down by the magnetic field; 2) the phenomenon of vortex structure of the Higgs condensation appears when the homogenesis hypermagentic field $g^{\prime }{B}_Y^{ex}/m_W^2\gtrsim 3.63$; and, 3) the helical hypermagnetic field can dramatically enhance the sphaleron rate and validate the generation of the baryon asymmetry through the chiral anomaly.

The complex geometry of the Lyman-alpha ($\mathrm{Ly}\alpha$) forest data has motivated the use of various two-point statistics as alternatives to the three-dimensional power spectrum ($P_{3\mathrm{D}}$), which carries cosmological information in Fourier space. On large scales, the three-dimensional correlation function (${\xi }_{3\mathrm{D}}$) has provided robust measurements of the baryon acoustic oscillation scale at 150 Mpc. On smaller scales, the one-dimensional power spectrum, $P_{1\mathrm{D}}(k_{\parallel })$, has been the primary tool for extracting information. At the same time, the cross spectrum, $P_{\times }(\theta ,k_{\parallel })$, has been introduced to incorporate angular information without the complications caused by survey window functions. We propose an analytical forward-modeling framework to reconstruct $P_{3\mathrm{D}}$ from all these observables, based on the mathematical relation between them and $P_{3\mathrm{D}}$. We demonstrate the performance of our method using a hypothetical mock data vector representative of future Dark Energy Spectroscopic Instrument measurements. We show that the monopole of $P_{3\mathrm{D}}$ can be reconstructed in $25k$ bins between $0.07{\mathrm{Mpc}}^{-1}$ and $1.8{\mathrm{Mpc}}^{-1}$, achieving an average precision of ${\sigma }_P/P=13\%$ across the bins. Our method can serve as an intermediary for consistency checks, though it is not intended to replace direct $P_{3\mathrm{D}}$ estimation.

Three black-hole low-mass x-ray binaries (LMXBs) in the Milky Way show rates of period decay which cannot be easily explained by standard mechanisms. Recently, it has been claimed that the anomalous period decays in two of these systems may be explained by dynamical friction due to very high dark matter (DM) densities around the black holes. We critically assess these claims by performing $N$-body simulations of binaries embedded in dense DM “spikes.” We simulate the previously studied systems XTE $\mathrm{J}1118+480$ and A0620–00, as well as studying the third binary Nova Muscae 1991 for the first time in this context. These simulations show that feedback on the DM distribution plays a crucial role and we rule out previously claimed shallow DM spikes. We set lower limits on the steepness $\gamma$ of DM density profiles required to explain the period decay in these LMXBs, requiring $\gamma \gtrsim 2.15–2.20$ in XTE $\mathrm{J}1118+480$ and A0620–00 and $\gamma \gtrsim 2.3$ in Nova Muscae 1991. Improved modeling of the long-term evolution of binaries embedded in DM spikes may allow us to exclude even larger densities in future.

A cosmological origin of magnetic fields in large scale structures of the Universe would require a non-negligible magnetic field in cosmic voids, which, however, remains undetected. Gamma-ray emission from gamma-ray bursts (GRBs) offers the opportunity to indirectly probe such an intergalactic magnetic field (IGMF), as $\gamma$ rays interact with cosmic radiation fields, producing electron-positron pairs, and initiate an electromagnetic cascade. The deflection of the pairs in the IGMF results in a time-delayed signal at GeV energies. Using observations with the Fermi Large Area Telescope of the GRB 221009A, we are able to derive the most stringent constraints to date from the nonobservation of the cascade and rule out magnetic fields $B<2.5\times {10}^{-17}\mathrm{G}$ at 95% confidence level for a coherence length larger than 1 Mpc. Our results are comparable to limits obtained from blazar observations but do not suffer from assumptions on the duty cycle of the $\gamma$-ray source or whether inverse-Compton scattering losses dominate over the development of plasma instabilities.

In this work, motivated by several beyond the Standard Model signal topologies, we perform detailed background mitigation analyses for the DUNE near detector. Specifically, we investigate $e^{+}{e}^{-}$, $e^{-}\gamma$, $\gamma$, and $\gamma \gamma$ final states that may arise from long-lived particles, including light mediators, dark matter, heavy neutral leptons, and axionlike particles (ALPs), decaying or scattering inside the liquid argon detector. To this end, we employ both photophilic and leptophilic ALPs as phenomenological benchmarks. The aforementioned final states leave a hard electromagnetic signature with no hadronic activity above the detector energy thresholds. Nevertheless, such signatures are not immune to backgrounds from neutrino scattering in the detector, which are in the focus of our study. In order to model realistic experimental analyses, we take into account particle misidentification rates, cross-contamination effects, and detector responses. We calculate confidence limit projections for DUNE, thereby presenting realistic capabilities for constraining or discovering new physics manifested through electromagnetic showers.

In the search for beyond the Standard Model (SM) physics, long-lived particles (LLPs) have emerged as potential candidates and are being explored in various ongoing experiments. Future lepton colliders, such as the FCC-ee, shall provide an excellent opportunity to probe LLPs, owing to their clean environment and improved particle identification. This study investigates the potential of the proposed Innovative Detector for an Electron-Positron Accelerator (IDEA) detector at FCC-ee in the detection of LLPs produced from $B$-meson and Higgs boson decays. We explore benchmark scenarios for different final states resulting from LLP decays, including a detailed analysis of the SM long-lived hadronic background. Additionally, we propose dedicated LLP detectors with different configurations, dimensions, and locations with respect to the IDEA detector. DELIGHT B, originally proposed as a dedicated LLP detector for the FCC-hh, stands out as the detector with the maximum efficiency for detecting LLPs produced at FCC-ee. We find that cylindrical detector configurations, if feasible to construct around the IDEA detector, would also enhance sensitivity for LLPs mostly decaying outside it.

Dark matter (DM) with masses of order an electronvolt or below can have a nonzero coupling to electromagnetism while being compatible with cosmological observations. In these models, the ambient DM behaves as a new classical source in Maxwell’s equations, which can excite potentially detectable electromagnetic (EM) fields in the laboratory. We propose a new integrated-photonics–based approach to search for dark matter candidates in the 0.1–few eV mass range. This approach offers a wide range of wavelength-scale devices like resonators and wave guides that are readily fabricated in large quantities, enabling a scalable and novel search. In particular, we demonstrate that refractive index-modulated resonators, such as etched/grooved microrings, or patterned slabs, support EM modes with efficient coupling to DM. When excited by DM, these modes are read out by coupling the resonators to a wave guide that terminates on a micron-scale–sized single photon detector, such as a single pixel of a low-noise charge-coupled device or a superconducting nanowire. We then estimate the sensitivity of this experimental concept in the context of axionlike particle and dark photon models of DM, demonstrating that nanophotonic confinement and scalability can extend dark matter sensitivity into previously unexplored parameter space.

In this manuscript we extend our previous analysis of the exclusive photoproduction of the ${\chi }_c\gamma$ pairs to the high-energy (small-$x$) kinematics, evaluate in detail the cross section in the color glass condensate framework, and discuss the potential of this channel as a novel complementary probe of the hadronic interactions. In the leading order in strong coupling ${\alpha }_s$, the cross section is controlled by the dipole scattering amplitude. Using available phenomenological parametrizations of the latter, we estimated numerically the cross sections for different polarizations of ${\chi }_c$ mesons and final-state photons in the kinematics of the ultraperipheral collisions at LHC and the future Electron Ion Collider. We found that the expected number of produced and detected events is significant for experimental study. We suggest that the ratio of the cross sections with different spins ${\sigma }_{\gamma {\chi }_{c1}}/{\sigma }_{\gamma {\chi }_{c2}}$ can be used to test the validity of the heavy quark spin symmetry relations for ${\chi }_c$, and in this way resolve a long-standing ambiguity observed in hadroproduction of ${\chi }_c$ mesons. Finally, we also analyzed the role of this process as a potential background to exclusive ${\chi }_c$ photoproduction, which has been recently suggested as an alternative channel for studies of odderons.

We calculate the spin density matrix of a heavy-quark-antiquark pair ($b\overline{b}$, $c\overline{c}$ or $s\overline{s}$) diffractively produced in deep inelastic scattering and ultraperipheral collisions. We show that the Pomeron exchange leaves characteristic imprints on the entanglement pattern between the quark and the antiquark. For the longitudinally polarized virtual photon, the pair always exhibits maximal entanglement and maximal violation of the Bell-Clauser-Horne-Shimony-Holt inequality. For the transversely polarized photon, the pair is always entangled and Bell violating, reaching maximal entanglement and maximal violation simultaneously when the transverse momentum approximately equals the quark mass.

The description of the $T\overline{T}$ deformation in terms of two-dimensional gravity is analyzed from the Hamiltonian point of view, in a manner analogous to the Arnowitt-Deser-Misner description of general relativity. We find that the Hamiltonian constraints of the theory imply relations between target-space momentum at finite volume that are equivalent to the $T\overline{T}$ finite-volume flow equations. This fully quantum $T\overline{T}$ result emerges already at the classical level within the gravitational theory. We exemplify the analysis for the case when the undeformed sector is a collection of $D-2$ free massless scalars, where it is shown that—somewhat nontrivially—the target-space two-dimensional Poincaré symmetry is extended to $D$ dimensions. The connection between canonical quantization of this constrained Hamiltonian system and previous path integral quantizations is also discussed. We extend our analysis to the “gravitational” description of $J\overline{T}$-type deformations, where it is found that the flow equations obtained involve deformations that twist the spatial boundary conditions.

We describe tree-level soft theorems for Chern-Simons QED and QCD in $4+1$ dimensions. Soft theorems have been studied in various context in the past. The universal behavior of the leading and subleading soft theorems is understood as a consequence of the local on-shell gauge invariance of the scattering amplitudes. Chern-Simons terms are gauge invariant only up to a boundary term. Hence, they make for an interesting case to study the relationship between gauge invariance and soft theorems. In this paper, we show that the subleading soft theorems in QED and QCD get corrected when Chern-Simons terms are introduced and also derive those corrections. We start with a discussion on soft theorems as a consequence of gauge invariance. Then we move on to derive the Chern-Simons vertices. Finally, we calculate the correction to soft theorems due to the addition of Chern-Simons terms for both QED and QCD.

When studying the Casimir effect in a quantum field theory setting, one can impose the boundary conditions by adding appropriate Dirac-$\delta$ functions to the path integral. In this paper, the limits of this approach are explored under different boundary conditions.

Recent evidence of stochastic gravitational wave background through pulsar time array (PTA) observations hint toward an alternative inflationary scenario, compared to the usual inflation, for describing the early stage of the Universe in order to be compatible with the PTA data. Moreover, currently the Atacama Cosmology Telescope (combined with the Planck 2018 and baryon acoustic oscillation) refines the constraint on inflationary observables, compared to the only-Planck 2018 measurements. In the present work, we simultaneously address these two issues by incorporating certain modification during inflation over the usual inflationary scenario. Such modification amplifies the primordial tensor perturbation over the modes that are sensitive to the NANOGrav frequency region. For this purpose, we take the thermodynamic route of cosmology where the entropy of the apparent horizon is given by a generalized form of entropy that is able to generalize the other known form of horizon entropies for suitable representations. The constraints on the model parameters coming from the ACT data also fit the NANOGrav 15-year data (based on numerical analysis), which reveal the model’s compatibility with both the ACT and the PTA data.

In recent years, several Pulsar Timing Array collaborations have reported evidence for a nanohertz gravitational wave background (GWB). Such a background signal could be produced by supermassive binary black holes, early-Universe processes such as inflation and phase transitions, or a mixture of both. One way to disentangle different contributions to the GWB is to search for anisotropic signatures. In this work, we search for anisotropy in the GWB using the third data release of the Parkes Pulsar Timing Array. Our analysis employs both the radiometer method and the spherical harmonic basis to characterize the distribution of GWB power across the sky. We calculate the angular power in the lowest five frequency bins and compare it with detection thresholds determined under the null hypothesis of isotropy. In the 5.26 nHz frequency bin, we identify a hotspot in the reconstructed sky map with a $p$ value of 0.016 (the lowest in our analysis), which we attribute to noise fluctuations. While our search reveals no statistically significant anisotropy, we expect that the precise measurement of angular power spectrum of the GWB will become instrumental in determining the origin of the nanohertz GWB signal.

Massive compact objects soften binaries. This process has been used for decades to constrain the population of such objects, particularly as a component of dark matter (DM). The effects of light compact objects, such as those in the unconstrained asteroid-mass range, have generally been neglected. In principle, low-energy perturbers can harden binaries instead of softening them, but the standard lore is that this effect vanishes when the perturber velocities are large compared to the binary’s orbital velocity, as is typical for DM constituents. Here, we revisit the computation of the hardening rate induced by light perturbers. We show that although the perturbations average to zero over many encounters, many scenarios of interest for DM constraints are in the regime where the variance cannot be neglected. We show that a few fast-moving perturbers can leave stochastic perturbations in systems that are measured with great precision, and we use this framework to revisit the constraint potential of systems such as binary pulsars and the Solar System. This opens a new class of dynamical probes with potential applications to asteroid-mass DM candidates.