Dynamical captures of black holes are unique events that provide an exceptional opportunity to probe the strong-field regime of gravitational physics. In this article, we perform numerical relativity simulations to study the events of dynamical capture of two equal-mass nonspinning black holes. We consider a suite of scenarios within a range of initial linear momenta ($p/M=0.095–0.75$) and incidence angles ($\theta =6.36°-2.83°$), and study the emitted Weyl scalar (${\mathrm{\Psi }}_4$) of each case, as well as the spins and masses of the black holes before and after they merge. We provide a simple analytical model which accurately fits the gravitational-wave emission. We study the dependence of the time interval between the capture and the merger emissions with respect to the incidence angle, which can be well parametrized by a first-order divergent behavior, allowing us to find the angle that separates a scattering event from a dynamical capture. We also find that, in general, the parameters that model the first emission can be well described by linear or exponentially decaying functions in terms of the incidence angle, while others display more complex behaviors that offer valuable insights into the nature of these events.

We present a new, first-order, flux-conservative formulation of relativistic viscous hydrodynamics in the Bemfica-Disconzi-Noronha-Kovtun (BDNK) framework, applicable to conformal and nonconformal fluids at zero chemical potential. Focusing on the conformal case in $1+1$ dimensions, we numerically solve the equations of motion for two classes of consistent initial data and assess the robustness of the resulting solutions with respect to changing the hydrodynamic frame. Our flux-conservative formulation does not exhibit spurious oscillatory structures within the regime of validity of BDNK theory (the hydrodynamic-frame–robust regime), corresponding to sufficiently small Knudsen numbers. Using this flux-conservative approach, we numerically investigate the potential formation of shocks and their fate in BDNK in $1+1\mathrm{D}$ using smooth initial data known to produce shocks in the relativistic Euler equations. For the type of initial data we consider, we show that the sharp features formed in Euler equations are prevented by the hyperbolic viscous BDNK equations. The prevention of shock formation we observe occurs in the frame-robust regime of BDNK. This, however, does not preclude the formation of shocks in BDNK for different smooth initial data. The reliability of our results is supported by systematic numerical convergence testing, which is used to assess shock indicators, simulation performance, and the robustness of solutions for different hydrodynamic frames.

We recently described a cosmological quantum spacetime of vanishing spatial curvature, which can be considered as background for the Ishibashi-Kitazawa-Kawai-Tsuchiya (IKKT) matrix model, assuming that the resulting gauge theory couples weakly. Building on this example, we construct a large class of spatially flat cosmological quantum spacetimes. We also elaborate on various details of their algebraic and semiclassical structure as well as the higher spin modes present in these models. In particular, we introduce the notion of approximate diffeomorphisms on the cosmological quantum spacetimes that stem from gauge transformations of the underlying matrix model, and investigate how different gauges are related in the semiclassical regime by approximate diffeomorphisms. Finally, we briefly outline how the described quantum spacetimes could be incorporated into the full IKKT model.

In particle physics, axions and axionlike particles are ubiquitous. Remarkably, ultralight axions could constitute dark matter or dark energy. Therefore, it is important to detect axions experimentally. In the presence of a magnetic field, a photon can be converted into an axion, and vice versa. Utilizing the conversion phenomenon, several methods for detecting axions have been proposed. To improve detectability, it is desirable to use quantum sensing. However, since the conversion process is usually treated as classical wave dynamics, it is unclear how to incorporate quantum effects such as entanglement. In this work, we formulate the photon-axion conversion in a quantum field theoretical manner. As a result, we succeed in evaluating the conversion probability from a photon quantum state to an axion quantum state. In particular, it turns out that squeezed coherent states can enhance the conversion probability.

The recent findings from the Dark Energy Spectroscopic Instrument (DESI) indicate a preference for dynamical dark energy at a significance level above $2.5\sigma$, with baryon acoustic oscillation (BAO) combined with cosmic microwave background (CMB) data and type Ia supernovae (SNe) data, favoring a time-dependent equation of state $w(z)$ rather than the cosmological constant ($w=-1$). We introduce the bound dark energy (BDE) model, in which dark energy arises from the lightest meson field $\varphi$ in a dark SU(3) gauge group, developing dynamically through nonperturbative interactions. Governed by an inverse power law potential $V(\varphi )={\mathrm{\Lambda }}_c^{4+2/3}{\varphi }^{-2/3}$, BDE features no dark energy free parameters: one less than $\mathrm{\Lambda }\mathrm{CDM}-(\mathrm{\Lambda })$ and three less than the $w_0{w}_a\mathrm{CDM}-(w_0,w_a,\mathrm{\Lambda })$ models. By integrating DESI BAO measurements, CMB data and Dark Energy Survey SN Ia distance data collected during the fifth year, BDE demonstrates a reduction of 42% and 37% in the reduced ${\chi }_{\mathrm{BAO}}^2$ as well as lower AIC and BIC values compared to the $w_0{w}_a\mathrm{CDM}$ and $\mathrm{\Lambda }\mathrm{CDM}$ models, respectively, while maintaining a comparable fit for both type Ia supernovae and the cosmic microwave background data. Although the ($w_0,w_a$) contour in BDE is 10,000 times smaller than that found in the $w_0{w}_a\mathrm{CDM}$ model, the BDE model suggests a dynamical dark energy scenario with precise values of $w_0=-0.9301\pm 0.0004$ and $w_a=-0.8085\pm 0.0053$ while providing a consistency on the six Planck and derived parameters at the $1\sigma$ level between BDE, $\mathrm{\Lambda }\mathrm{CDM}$ and $w_0{w}_a\mathrm{CDM}$ models. The critical parameters—condensation energy scale ${\mathrm{\Lambda }}_c=43.806\pm 0.190\mathrm{eV}$ and epoch $a_c=(2.497\pm 0.011)\times {10}^{-6}$—are consistent with predictions from high-energy physics. Through a detailed analysis of our results, which are consistent with current observational data, the BDE model effectively elucidates the origins and dynamics of dark energy without free parameters in the dark energy sector, providing an interpretation from contemporary astrophysical experiments within a particle physics framework.

The spatial curvature of the Universe remains a central question in modern cosmology. In this work, we explore the potential of localized fast radio bursts (FRBs) as a novel tool to constrain the cosmic curvature parameter ${\mathrm{\Omega }}_k$ in a cosmological model-independent way. Using a sample of 120 FRBs with known redshifts and dispersion measures, we reconstruct the Hubble parameter $H(z)$ via artificial neural networks, and use it to obtain angular-diameter distances $D_A(z)$ through two complementary approaches. First, we derive the comoving distance $D_C(z)$ and $D_A(z)$ directly from FRBs without assuming a fiducial cosmology. Then, we combine the FRB-based $H(z)$ with baryon acoustic oscillation (BAO) DESI DR2 measurements to infer $D_A(z)$. By comparing the FRB-derived and $\mathrm{BAO}+\mathrm{FRB}$-derived $D_A(z)$, we constrain spatial curvature. Our covariance-based likelihood (accounting for correlated uncertainties) yields ${\mathrm{\Omega }}_k=-0.31\pm 0.57$, while a diagonal (Gaussian) treatment gives ${\mathrm{\Omega }}_k=-0.13\pm 0.46$. Both estimations are consistent with spatial flatness at the $1\sigma$ level, albeit with a mild preference for negative curvature. Explicitly accounting for the full covariance broadens the intervals and avoids underestimation of uncertainties. These results highlight the growing relevance of FRBs in precision cosmology and their synergy with BAO as a powerful, cosmological model-independent probe of the large-scale geometry of the Universe.

We use the dynamical heating of stars in ultrafaint dwarf (UFD) galaxies to set limits on Massive Compact Halo Objects (MACHOs). In our analysis we study the robustness of the bounds under uncertainties in key UFD parameters, such as the half-light radius, stellar velocity dispersion, total halo mass and dark matter and stellar density profiles. We apply this framework to both well-established UFD candidates, as well as the recently discovered UFD candidate Ursa Major III/UNIONS 1. We find that multiple UFDs yield consistently strong limits in the mass range $10M_{\odot }\lesssim M_{\mathrm{MACHO}}\lesssim {10}^9{M}_{\odot }$, underscoring the robustness of a previous analysis solely based on Segue I. We also demonstrate that Ursa Major III, if confirmed as an UFD, would improve the constraints significantly, providing the strongest constraints on MACHO dark matter in the mass range $1M_{\odot }\lesssim M_{\mathrm{MACHO}}\lesssim {10}^5{M}_{\odot }$.

Real astrophysical lenses typically lack axisymmetry, necessitating the study of gravitational-wave (GW) lensing by elliptical mass distributions to accurately assess detectability and waveform interpretation. We investigate strong lensing using the singular isothermal ellipsoid model, which produces two or four images depending on the source’s position relative to lens caustics. Employing a quasi-geometrical-optics framework, we determine that the geometrical-optics approximation holds reliably for lens masses above approximately ${10}^5{M}_{\odot }$ at GW frequencies relevant for ground-based detectors $(\sim {10}^2\mathrm{Hz})$, though wave-optics effects become significant for lower masses or sources near caustics. Our waveform mismatch analysis demonstrates that the use of three-image templates significantly improves our ability to distinguish source signals, reducing mismatches from $\mathcal{O}({10}^{-1})$ to $\mathcal{O}({10}^{-2})$, typically by factors between 1.5 and 5 compared to the standard two-image template model. At lens masses above ${10}^7{M}_{\odot }$, diffraction effects become negligible for ground-based detectors, resulting in an additional mismatch reduction by a factor of approximately 3. These findings highlight the critical need for multi-image templates in GW searches to enhance detection efficiency and accuracy.

Force-free electrodynamics describes the electromagnetic field of the magnetically dominated plasma found near pulsars and active black holes but gives no information about the underlying particles that ultimately produce the observable emission. Working in the two-fluid approximation, we show how particles can be “painted on” to a force-free solution as a function of boundary conditions that encode the particle output of “gap regions” where the force-free approximation does not hold. These boundary conditions also determine the leading parallel electric field in the entire magnetosphere. Our treatment holds in a general (possibly curved) spacetime and is phrased in language intrinsic to the $1+1$ dimensional “field sheet spacetimes” experienced by particles stuck to magnetic field lines. Besides the new results, this provides an elegant formulation of some standard equations; for example, we show that the zero-gyroradius guiding center approximation is just the Lorentz force law on the field sheet. We derive a general perturbative method and apply it to pulsar and black hole magnetospheres with radial magnetic fields to produce fully analytic models that capture key features of the full problem. When applied to more realistic magnetic field configurations together with simulation-informed boundary conditions for the gap regions, this approach has the potential to provide global magnetosphere models without the need for global particle-in-cell simulations.

With the significantly improved sensitivity and a wider frequency band, the next-generation gravitational-wave (GW) detectors are anticipated to detect $\sim {10}^5\mathrm{GW}$ signals per year with durations from hours to days, leading to inevitable signal overlaps in the data stream. While a direct fitting for all signals may be challenging, extracting only one signal will be biased by its overlap with other signals. From this perspective, understanding how the biases arise from the overlapping and their dependence on the signal parameters is crucial for developing effective algorithms. In this work, we extend the anatomy of biases in single-detector cases [Z. Wang et al., Classical Quantum Gravity 41, 055011 (2024)] to a detector network. Specifically, we examine how the biases of the chirp mass, symmetric mass ratio, luminosity distance, and coalescence time depend on the source’s sky position and orientation, as well as on the coalescence time and phase. We propose a new quantity, named the bias integral, as a useful tool, and establish a relationship between the biases in a single detector and that in the entire network, with explicit dependence on extrinsic parameters. Using a three-detector network as an example, we further explore the potential of a network to suppress biases due to the detectors’ different locations and orientations. We find that location generally has a smaller effect than orientation, and becomes significant only when the time separation between signals is below subseconds. Through a population-level simulation over the extrinsic parameters, we find that nearly half of overlapping signals will lead to larger biases in the network compared to a single detector, highlighting the need to cope with overlapping biases in a detector network.

We present the first experimental implementation of a polarization-circulation speed meter. In our experiment, the interferometer was reduced to a single-cavity configuration with all mirrors fixed. A green-locking scheme was employed to stabilize the polarization-circulation cavity, and a lock-acquisition procedure was demonstrated to realize speed-meter operation. The system was characterized by measuring the transfer function from a pseudodisplacement signal to the photodetector output, confirming that the device measures the speed of mirror motion. These results support the feasibility of polarization-circulation speed meters and suggest that the control scheme could be extended to more complex configurations, such as Michelson interferometers and suspended-mirror systems.

The spontaneous breaking of a global lepton number symmetry can result in a (pseudo) Nambu-Goldstone boson known as the Majoron. We study a singlet Majoron model that couples to two Higgs doublets in which the lepton number current develops an electromagnetic anomaly, allowing the decay of Majorons into photons. We focus on Majorons at the eV scale with an enhanced anomaly and show that it serves as a dark matter candidate whose decay signals can be probed by space telescope observations. Furthermore, if the decay produces Lyman-Werner photons, heavy black hole seeds can be generated via the direct collapse mechanism and evolve into the active galactic nuclei we observe at high redshifts. Our framework thus simultaneously addresses the origin of neutrino masses, the baryon asymmetry of the Universe, the nature of dark matter, and the formation of high redshift supermassive black holes.

We study lepton-flavor-violation (LFV) effects occurring in the $e-\mu$ conversion in nuclei and in the rare radiative decays $\eta ({\eta }^{\prime })\to \gamma \mu e$ of the $\eta$ and ${\eta }^{\prime }$ mesons with a special impact of the sub-GeV mass vector mediator (dark photon). In the case of the lepton conversion, we make estimates for running and future experiments operating with electron beams at fixed target. Obtained results are implemented in analysis of the LFV decays $\eta ({\eta }^{\prime })\to \gamma \mu e$.

The electric dipole moment of the electron (eEDM) is typically investigated in experiments using paramagnetic molecules. However, the physical observable in these searches consists of a linear combination of $CP$-violating interactions, rather than the eEDM alone, which is commonly referred to as the equivalent EDM of the system. Assuming the presence of new $CP$-odd physics from heavy degrees of freedom, we parametrize its effects within the Standard Model effective field theory (SMEFT) framework. We systematically compute the contributions to the full low-energy direction probed by EDM searches, focusing on leading-order effects at dimension six and one-loop level, while also discussing selected two-loop and dimension-eight contributions. We find that eEDM experiments are sensitive to a broader class of SMEFT operators than previously recognized.

The particle-physics nature of dark matter (DM) remains one of the central open questions in modern physics. A widely used framework to investigate DM properties is provided by $s$-channel simplified models (DMSimps), which extend the Standard Model with a DM particle and a mediator that connects the visible and dark sectors. Much of the DMSimps parameter space is already constrained by direct and indirect detection, collider searches, and the measured DM relic abundance. We show, however, that the resonant regime ($m_{\mathrm{DM}}\simeq m_{\mathrm{med}}/2$) remains viable under current bounds and will be stringently tested by forthcoming experiments. Using a full Boltzmann treatment that allows for departures from kinetic equilibrium near resonance, we demonstrate that this regime can reproduce the observed relic density with couplings compatible with direct-detection limits. We also show that models with $s$-wave dominated annihilation can explain the Fermi-LAT Galactic Center Excess with couplings consistent with relic-density and direct-detection constraints. Finally, we propose two minimal constructions that naturally realize $m_{\mathrm{med}}\approx 2m_{\mathrm{DM}}$, making the resonant scenario generic rather than fine-tuned.

We consider models of chaotic inflation driven by the real parts of a conjugate pair of Higgs superfields involved in the spontaneous breaking of a grand unification symmetry at a scale assuming its value within the minimal supersymmetric Standard Model (MSSM). We combine a superpotential, which is uniquely determined by applying a continuous $R$ symmetry, with two fractional shift-symmetric Kähler potential s introducing two free parameters $(p,N)$. The inflationary observables provide an excellent match to the recent Atacama Cosmology Telescope data for $1.355\le p\le 6.7$ and $6\times {10}^{-5}\le N\le 0.7$. The attainment of inflation allows for sub-Planckian inflaton values and possibly detectable primordial gravitational waves with $(p,N)$ values of order unity. A solution to the $\mu$ problem of MSSM and baryogenesis via nonthermal leptogenesis can be also accommodated by embedding the model into a $B-L$ extension of the MSSM.

${\gamma }^{*}\gamma \to B\overline{B}$ is the golden process to access chiral-even di-baryon generalized distribution amplitudes (GDAs) as deeply virtual Compton scattering has proven to be for the generalized parton distributions. In the framework of colinear quantum chromodynamics factorization, where the leading twist amplitude is the convolution of GDAs and a perturbatively calculable coefficient function, we study the scattering amplitude for the baryonic channels where $B$ is a spin $1/2$ baryon such as the nucleon or hyperon $\mathrm{\Lambda }$, $\mathrm{\Sigma }$. Taking into account the interfering quantum electrodynamics amplitude, we calculate the cross section of the $e^{\pm }\gamma \to e^{\pm }B\overline{B}$ process, which can be experimentally studied in $e^{-}{e}^{+}$ as well as in electron-ion facilities. We explore both the final state polarization summed case and the polarization dependent effects. Numerical estimates are presented for $e^{-}\gamma \to e^{-}p\overline{p}$ using motivated models for GDAs. Our results show that a first extraction of baryon-antibaryon GDAs from experimental measurements is feasible at Belle II.

We employ the two-flavor quark-meson diquark model as a low-energy model for QCD at nonzero quark and isospin chemical potentials $\mu$ and ${\mu }_I$, and at zero temperature. We map out the phase diagram in the $\mu –{\mu }_I$ plane, which has four phases: a vacuum phase, a phase with condensed charged pions/Cooper pairs of $u$ and $\overline{d}$ quarks, a normal quark matter (NQM) phase, and a color superconducting phase (2SC phase). The global symmetry breaking $SU(3{)}_c\to SU(2{)}_c$ in the 2SC phase gives rise to a number of Nambu-Goldstone bosons. We classify them and briefly discuss their properties. We calculate the speed of sound $c_s$ in the two special cases, finite ${\mu }_I$ and $\mu =0$, and finite $\mu$ and ${\mu }_I=0$. In both cases, the speed of sound exhibits a maximum and approaches the conformal limit from above as the density increases. For nonzero isospin ${\mu }_I$, this behavior is in agreement with the speed of sound obtained from lattice simulations. In the 2SC phase, the behavior is qualitatively the same if we impose local charge neutrality. Finally, we discuss the possibility of having a mixed phase of negatively charged NQM and positively charged 2SC matter with global color charge neutrality imposed on the latter.

We investigate energy correlators in semi-inclusive electron-positron annihilation as precision probes of parton hadronization dynamics. Using soft-collinear effective theory, we analyze the correlation patterns between the examined hadron and the rest of QCD radiations in both large-angle and small-angle limits, which establishes a direct correspondence with transverse-momentum-dependent fragmentation functions and fragmentation energy correlators. The two complementary regimes encode the transition from perturbative parton branching to nonperturbative confinement, enabling a unified description of hadron formation across all kinematic regimes. Using renormalization group evolution, we obtain joint ${\mathrm{N}}^3\mathrm{LL}$/NNLL quantitative predictions for energy correlations both in the sudakov and jet fragmentation region. Our results demonstrate that semi-inclusive energy correlators provide direct, theoretically controlled access to QCD dynamics underlying hadronization, opening new avenues for precision studies at future lepton colliders as well as through reanalyses of archival LEP data.

We examine the effects of soft gluons on Higgs boson production in association with a $Z$ boson at the Large Hadron Collider (LHC). Utilizing the universal cusp anomalous dimensions and splitting kernels, we analyze effects of soft gluons on the gluon fusion $ZH$ process, focusing on the total production cross section as well as the invariant mass distribution at the next-to-leading logarithmic level. Additionally, we estimate the next-to-soft effects on this subprocess to the same level of accuracy. A detailed phenomenological analysis is performed for the 13.6 TeV LHC. Finally, combining these results with those from other subprocesses, we provide comprehensive predictions for the $ZH$ production cross section and the invariant mass distribution that will be valuable for comparison with experimental data from the upcoming LHC run as well as the future hadron colliders.