We discuss the generalization of the Weyl double copy to higher spin “multicopies,” showing how the natural linearized higher spin field strengths can be related to sums of powers of the Maxwell tensor. The tracelessness of the field strength involves the appropriate Fronsdal equations of motion for the higher spin field. We work with spacetimes admitting Kerr-Schild coordinates and give a number of examples in different dimensions. We note that the multicopy is particularly transparent in four dimensions if one uses spinor descriptions of the fields, relating this to the Penrose transform. The higher dimensional spinor multicopy is also explored and reveals some interesting new features arising from the little group based identification of higher spin field strengths and Maxwell tensor types. We then turn to the vector superspace formalism describing higher spin and “continuous” spin representations given by Schuster and Toro, based on symmetric tensor fields. Here the Kerr-Schild higher spin fields we have used earlier naturally package into a simple expression involving an arbitrary function, when the continuous spin scale $\rho$ is set to zero. Further, we discuss the case of an anti–de Sitter background, where there is also a vector space formalism given by Segal and we clarify this approach using a different definition of the covariant derivative. We give a general solution of Kerr-Schild type and finally we describe some of the obstacles to a continuous spin formulation.

Sidney Coleman has noted that superluminal particles or observers would be able to go back in time and have no definite trajectory according to subluminal observers, while not violating Lorentz invariance [Sidney Coleman’s Lectures on Relativity (Cambridge University Press, Cambridge, England, 2022)]. Recently, Dragan and Ekert have significantly developed similar ideas even further, which led to formulation of a “quantum principle of relativity” that intimately links the two theories [New J. Phys. 22, 033038 (2020); New J. Phys.25, 088002(E) (2023)]. However, field theory descriptions of an on-shell tachyon, described by scalar field $\varphi$ with negative mass squared parameter, lead to violation of basic principles of relativity or quantum mechanics. In this work, we investigate whether purely virtual tachyons can be consistent within the fakeon framework—the only known viable formulation of purely virtual particles. We identify two fatal obstructions. First, Lorentz boosts mix creation and annihilation operators, rendering the canonical commutation relations noninvariant despite formal invariance of the vacuum. Second, the real part of the tachyon Feynman propagator and Wheeler propagator have disjoint support, preventing application of both the fakeon prescription and Wheeler-Feynman absorber mechanism. Interactions with stable Standard Model fields further violate Lorentz invariance and the equivalence principle, and we provide a quantitative limit on the coupling strength of such a scenario. Our analysis excludes the possibility of formulating a covariant quantum field theory of interacting virtual tachyons.

We study slowly rotating black hole solutions in the Einstein-Bel-Robinson gravity (EBR) in four dimensions. At the leading order in the rotation parameter, the only modification with respect to the static case is the appearance of a nonvanishing $g_{t\varphi }$ component. We construct approximate solutions to these equations and study how physical properties of the solutions, such as the angular velocity, photon sphere, black hole shadow, and innermost stable circular orbit, are modified, working to leading order in the coupling constant and the rotation parameter. Finally, we study the superradiance of a massive scalar wave scattering off slowly rotating black holes. Using direct integration, we derive the superradiant conditions and compute the energy flux through the event horizon. We demonstrate how the flux will change as a function of the black hole rotation and frequency of the incident wave. Finally, we showed how black hole parameters, including the gravitational coupling of EBR, change during superradiance. We study the impact of the superradiant evolution on the black hole shadow and show that the shadow radius can either shrink or grow depending on the competition between the involved components during the evolution.

We examine whether the Schwarzschild black hole can emerge as the continuous end state of gravitational collapse from a nonsingular configuration. Employing a time-dependent extension of the regular Schwarzschild metric, we track the evolution of the geometry during collapse and find that the process cannot remain continuous. The metric function develops a discontinuity at the origin, marking a breakdown of spacetime smoothness, an effect identified as “Minkowski breaking.” Before the Schwarzschild point source can form at $r=0$, curvature singularities appear, and the Cauchy horizon disappears. These results strongly suggest that spacetime may not evolve smoothly toward the Schwarzschild geometry. Instead, the formation of a Schwarzschild black hole appears to entail a discrete change in the structure of spacetime, pointing to the need for a noncontinuous, possibly quantized, framework to describe the emergence or regularization of gravitational singularities.

Einstein-bumblebee gravity, as a class of massive nonminimally coupled vector-tensor theories, provides a useful framework for constraining Lorentz symmetry breaking through astrophysical observations, largely due to the existence of exact static and spherically symmetric black hole solutions. These solutions are typically obtained under the assumption that the vector-field potential vanishes everywhere once the vector field acquires a nonzero radial vacuum expectation value. However, imposing this assumption globally obstructs the construction of self-consistent compact-star solutions. In this work, we elucidate the origin of this inconsistency through a detailed analysis of the field equations and construct neutron-star configurations by abandoning the global vanishing-potential assumption. Crucially, we show that even without enforcing this condition everywhere, it is violated only in the strong-field interior region and is dynamically restored in the weak-field regime by asymptotic boundary conditions at spatial infinity. As a result, consistency with existing black hole solutions and observational constraints is preserved. Our results establish massive vector-tensor gravity as a unified, natural, and self-consistent framework for compact objects, significantly extending its astrophysical viability beyond black holes and Solar System tests.

Boundary conditions play a key role in determining the perturbation behavior of a black hole. Motivated by two guiding principles for single-field perturbations—the nondeformation of the boundary metric and the vanishing of electromagnetic energy flux at the anti–de Sitter (AdS) boundary—we impose a boundary condition for Reissner-Nordström-AdS (RN-AdS) black holes requiring both the metric and electromagnetic field-strength perturbations to vanish at the AdS boundary, which we term the physical field-vanishing (PFV) condition. Using the formulas for perturbation reconstruction, we translate the PFV condition into boundary conditions on the master functions: Dirichlet-type for odd-parity modes and Robin-type for even-parity modes. With these boundary conditions, we compute the quasinormal frequencies of RN-AdS black holes and identify new spectral features. The PFV prescription introduced here could be applied to other multifield perturbation systems in asymptotically AdS spacetimes.

We present a comprehensive study of galaxy intrinsic alignment (IA) as a probe of parity-violating primordial non-Gaussianity (PNG). Within the effective field theory (EFT) framework, we show that the parity-odd IA power spectrum is sensitive to the collapsed limit of the parity-odd primordial trispectrum. For a $U(1)$-gauge inflationary model, the IA power spectrum is proportional to the power spectrum of the curvature perturbation, $P_{\zeta }(k)\propto k^{-3}$. However, the proportionality constants contain not only the PNG amplitude but also undetermined EFT bias parameters. We use $N$-body simulations to determine the bias parameters for dark matter halos. Using these bias parameters, we forecast IA’s constraining power, assuming data from the Dark Energy Spectroscopic Instrument and the Rubin Observatory Legacy Survey of Space and Time. We find that the IA power spectrum can improve the current limits on the amplitude of parity-violating PNG derived from galaxy four-point correlation and cosmic microwave background trispectrum analyses. Moreover, galaxy shapes are complementary to these probes, as they are sensitive to different scales and trispectrum configurations. Beyond galaxy shapes, we develop a new method to generate initial conditions for simulations and forward models from the parity-odd trispectrum with an enhanced collapsed limit.

We study the phase shift that free-streaming neutrinos imprint on the 21-cm power spectrum during cosmic dawn, computing for the first time its effect on both density- and velocity-induced acoustic oscillations. Neutrinos are known to generate a characteristic phase shift in the acoustic oscillations of the photon–baryon plasma before recombination, a signature already detected in the cosmic microwave background (CMB) as well as the spectrum of baryon acoustic oscillations (BAOs) extracted from galaxy surveys. We show that in the 21-cm signal this phase shift is distinct from that observed in the CMB and BAO spectra, exhibiting a characteristic mode and redshift dependence arising from the additional contribution of the so-called velocity acoustic oscillations (VAOs), sourced by the baryon–dark matter relative velocities. Our results establish the phase of acoustic oscillations in the 21-cm spectrum as a promising new avenue for probing free-streaming light relics at cosmic dawn, complementary to existing CMB and BAO measurements.

We study the $(w_0,w_a)$ parametrization of the dark energy (DE) equation of state, with and without the effective field theory of dark energy (EFTofDE) framework to describe the DE perturbations, parametrized here by the braiding parameter ${\alpha }_B$ and the running of the Planck mass ${\alpha }_M$. We combine the effective field theory of large-scale structure full-shape analysis of the power spectrum and bispectrum of BOSS data with the tomographic angular power spectra $C_{\ell }^{gg}$, $C_{\ell }^{\kappa g}$, $C_{\ell }^{Tg}$, and $C_{\ell }^{T\kappa }$, where $g$, $\kappa$, and $T$ stand for the DESI luminous red galaxy map, Planck Public Release 4 (PR4) lensing map and Planck PR4 temperature map, respectively. To analyze these angular power spectra, we go beyond the Limber approximation, allowing us to include large-scale data in $C_{\ell }^{gg}$. The combination of all these probes with Planck PR4, Dark Energy Spectroscopic Instrument (DESI) second data release of baryon acoustic oscillation (BAO), and DES Year 5 improves the constraint on the two-dimensional posterior distribution of $\{w_0,w_a\}$ by $\sim 50\%$ and increases the preference for evolving dark energy over $\mathrm{\Lambda }$ from $3.8\sigma$ to $4.6\sigma$. When we remove BAO and supernovae data, we obtain a hint for evolving dark energy at $2.3\sigma$. Regarding the EFTofDE parameters, we improve the constraints on ${\alpha }_B$ and ${\alpha }_M$ by $\sim 40\%$ and 50%, respectively, finding results compatible with general relativity at $\sim 2\sigma$. We show that these constraints do not depend on the choice of the BAO and supernovae likelihoods.

The sensitivity of conventional direct dark matter searches for weakly interacting massive particles (WIMPs) is ultimately limited by coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$), which produces nuclear recoils indistinguishable from WIMP signals and defines the so-called neutrino floor. While the effects of solar neutrinos, geoneutrinos, diffuse supernova neutrinos, and atmospheric neutrinos have been extensively studied in this context, the contribution from reactor antineutrinos has received comparatively little attention. We present the first systematic evaluation of how reactor antineutrino fluxes, modeled as a function of reactor-detector distance, modify the neutrino floor for low-mass WIMP searches using SuperCDMS-like high-voltage germanium detectors. Both discovery-limit and opacity-based formulations of the neutrino floor are examined under consistent assumptions. We find that proximity to gigawatt-scale reactors within $\sim 10\mathrm{km}$ can raise the neutrino floor by up to a few orders of magnitude, significantly reducing the sensitivity to sub-$10\mathrm{GeV}/c^2$ dark matter. $\mathrm{Beyond}\sim 100\mathrm{km}$, the reactor contribution becomes negligible. These conclusions hold for both definitions of the neutrino floor and remain stable under reasonable variations in detector quenching, site-dependent geoneutrino flux, and reactor antineutrino flux uncertainties, emphasizing reactor proximity as a critical factor in site selection for future low-threshold dark matter experiments.

A massive “dark companion”—such as an intermediate-mass black hole or other compact dark object—orbiting the supermassive black hole at the Galactic Center can dynamically reshape the surrounding dark matter spike. Through gravitational heating and angular momentum exchange, the companion excavates a “scoured” region that lowers the inner density and suppresses the expected annihilation signal. We quantify this effect by computing the suppression of the dark matter annihilation $J$ factor induced by such a companion, combining an analytic scouring radius model with full numerical integrations of the modified density profile. We scan the parameter space of companion mass, orbital separation, system age, and spike slope, explicitly including the interplay with the annihilation plateau. For canonical Gondolo-Silk spikes with ${\gamma }_{\mathrm{sp}}\gtrsim 2$, the scouring radius grows only weakly with injected energy because the binding energy is concentrated at small radii, however, once scouring occurs, the $J$-factor suppression can be substantial, for sufficiently massive or long-lived companions. In the shallower spike regime with ${\gamma }_{\mathrm{sp}}\lesssim 2$, the same companion drives $r_{\text{scour}}$ to much larger multiples of $R_{\mathrm{core}}$, and even a modest $\sim {10}^4{M}_{\odot }$ companion on a $\mathcal{O}(100)\mathrm{AU}$ orbit and $\mathcal{O}(\mathrm{Gyr})$ age can suppress the annihilation flux by 1 to 2 orders of magnitude. Whether a steep spike is significantly suppressed, therefore, depends on the companion’s mass and lifetime, not merely on the sign of $(2-{\gamma }_{\mathrm{sp}})$. The numerical results are accurately captured (typically at the $\lesssim 10\%$ level) by a simple fitting formula in terms of a dimensionless scouring parameter that measures the ratio between the scoured region and the annihilation core. Our findings demonstrate that neglecting a dark companion can lead to substantial overestimates of the Galactic Center $J$ factor, with direct consequences for interpreting gamma-ray, neutrino, and antimatter searches for annihilating dark matter.

The early spectra of the kilonova AT2017gfo following the binary neutron star merger GW170817 exhibit numerous features shaped by r-process nucleosynthesis products. Although a few species were tentatively detected, no third-peak elements were unambiguously identified, as the amount of atomic data required for radiative transfer modeling is immense. Although comprehensive atomic data, including atomic opacities, is now available for many elements, wavelength-calibrated data remain limited to a few selected ions. To examine the atomic opacities of all singly and doubly ionized lanthanides, from La ($Z=57$) to Yb ($Z=70$), we perform atomic structure calculations using the fac code. Our calculations incorporate an innovative optimization of the local central potential and the number of configurations considered, alongside a calibration technique aimed at enhancing agreement between theoretical and experimental atomic energy levels. We assess the accuracy of the computed data, including energy levels and electric dipole (E1) transition strengths, as well as their impact on kilonova opacities. We find that strong transitions [$\log (gf)>-1$] are in good agreement with both experiments and semiempirical calculations. For ions with substantial experimental data, the computed opacities exhibit good agreement with prior calculations. By calibrating low-lying energy levels with experimental data, we have identified 66 722 transitions with experimentally calibrated wavelength information, rendering future lanthanide line identifications through radiative transfer modeling feasible. In total, our calculations encompass 28 ions, yielding 146 849 energy levels below the ionization threshold and 29 337 507 transitions among these levels.

Space-based gravitational-wave observatories will detect the early inspiral of stellar-mass binary black holes and can track their eccentricity evolution. However, untargeted searches in the space band are computationally demanding and require relatively high detection thresholds (signal-to-noise ratio $\sim 15$). Information from ground-based detections can significantly shrink the parameter space for space-band analyses and thereby substantially reduce the detection threshold. We present a Bayesian inference pipeline for ground-triggered archival space-band analyses that includes eccentricity. Using ground-informed priors, we demonstrate that with one year of LISA or TianQin data a GW190521-like source with signal-to-noise ratio $\sim 7$ can be distinguished and tightly constrained. In this setup, space observations sharpened the redshifted chirp mass from $\mathcal{O}({10}^{-3})M_{\odot }$ to $\mathcal{O}({10}^{-5})M_{\odot }$, and constrain the eccentricity to $\mathcal{O}({10}^{-5})$ around the injected value $e_{0.01\mathrm{Hz}}=0.1$. These results demonstrate that inference of eccentric stellar-mass binary black holes in noisy space-band data is practically feasible, supports an expanded yield of multiband detections, and strengthens prospects for future astrophysical and gravitational tests.

The Jiangmen Underground Neutrino Observatory (JUNO) experiment has recently released its first measurement results based on 59.1 days of data, achieving unprecedented precision in measuring the lepton mixing angle ${\theta }_{12}$. This significant improvement places stringent constraints on certain neutrino mass models and flavor mixing patterns. In this work, we examine the impact of the latest JUNO results on the two trimaximal (i.e., TM1 and TM2) mixing patterns. They are two well-motivated variants of the tribimaximal mixing pattern and predict specific correlations between ${\theta }_{12}$ and ${\theta }_{13}$. After taking into account the first JUNO results, the TM1 mixing pattern sits on the edge of the experimentally allowed $1\sigma$ region, while the TM2 mixing pattern lies outside the $3\sigma$ region. To reconcile these TM mixing patterns with the latest experimental data, we further investigate the renormalization group (RG) running effects on them in the both Majorana and Dirac neutrino cases. Our analytical and numerical results show that RG corrections can bring the two TM mixing patterns into excellent agreement with the latest JUNO data if neutrino masses are quasidegenerate. However, the Majorana case faces severe constraints from neutrinoless double beta decay limits, and particularly, the TM2 mixing pattern with Majorana neutrinos has been essentially ruled out. In the Dirac case, the TM1 mixing pattern is fully consistent with current data including beta decay results, whereas the TM2 pattern is strongly constrained by the KATRIN limit and even could be largely ruled out if the KATRIN experiment reaches its final sensitivity without any discovery. Future high-precision measurements of lepton mixing parameters and absolute neutrino masses in both oscillation and nonoscillation experiments will provide decisive tests of these mixing patterns.

This work explores the discovery potential of the first-generation weak-isosinglet vectorlike leptons, denoted by $E^{\pm }$, via pair production at future electron-positron colliders. Our analysis adopts a comprehensive framework that incorporates beam polarization configurations and leverages detailed detector simulations. We focus on two distinct multilepton signatures: the $2\ell +2j+{\cancel{E}}_T$ and $3\ell +2j+{\cancel{E}}_T$ final states ($\ell =e$, $\mu$). Both signatures arise from the decay $E^{\pm }\to Z{e}^{\pm }/W^{\pm }{\nu }_{\ell }$ and are distinguished by the decay patterns of the associated gauge bosons. By applying optimized selection criteria to both signal and background events, we establish exclusion sensitivities and discovery prospects across the vectorlike lepton mass spectrum. Our findings demonstrate that, for integrated luminosities of 25, 90, and $1000{\mathrm{fb}}^{-1}$ at corresponding center-of-mass energies of 1, 1.5, and 3 TeV, the accessible mass range extends to approximately 490, 740, and 1440 GeV, respectively, which represents a substantially improvement over the detection limits of existing hadron collider experiments.

The neutron portal operator provides a theoretically motivated connection between the visible and dark sectors and features in several well-studied asymmetric dark matter models. This operator leads to dark matter induced nucleon decays that mimic the experimental signature of “ordinary” nucleon decays. In this work, we reinterpret Super-Kamiokande nucleon decay searches for $n\to {\pi }^0\nu$ and $p\to {\pi }^{+}\nu$ to constrain dark matter induced nucleon decays. For GeV-scale dark matter, we obtain lower bounds of $\mathcal{O}(1\mathrm{TeV})$ on the scale of the effective neutron portal operator. We also discuss the prospects for future searches at Hyper-Kamiokande and highlight the importance of a dedicated experimental analysis with reduced systematic uncertainties.

Recently, a new framework for studying generic $2\to 3$ hard exclusive reactions, referred to as single-diffractive hard exclusive processes, has been introduced to provide a cleaner separation of the underlying physical mechanisms. In this work, we expand this formalism to the case of exclusive real-photon electroproduction off a nucleon, $e(\ell )+N(p)\to e({\ell }^{\prime })+N(p^{\prime })+\gamma (q^{\prime })$, which represents the classical channel for accessing generalized parton distributions (GPDs) in nucleons and nuclei. This extension enables a more systematic and physically transparent formulation of the reaction dynamics, paving the way for improved extractions of GPDs from experimental data as compared to existing approaches.

We develop a Gaussian model to evaluate the decorated dipole and quadrupole operators that arise beyond the eikonal approximation in the color glass condensate framework. While the method is general and applicable to arbitrary beyond-eikonal Wilson line structures, we employ it for dijet production in deep inelastic scattering at next-to-eikonal accuracy. After validating the model at the eikonal level, we compute all next-to-eikonal operator structures entering the dijet cross section. We show that some of them do not contribute to this observable, while others vanish identically. Therefore, in the Gaussian model next-to-eikonal corrections to dijet production in deep inelastic scattering originate solely from a given type of operators and from next-to-eikonal three-point correlators. The resulting expressions are provided in a form suitable for numerical implementation.

We present a detailed analysis of the proton electromagnetic form factors (FFs) using exclusive photon leptoproduction (EP) data in kinematic regions where the Bethe-Heitler (BH) contribution dominates the deeply virtual Compton scattering (DVCS) cross section. By exploiting the sensitivity of the BH amplitude to the Dirac and Pauli FFs, we extract $F_1(t)$, $F_2(t)$, and the corresponding Sachs FFs within several fitting scenarios based on dipole and $P$-pole parametrizations, and evaluate the charge and magnetic radii of the proton. In this fitting scenario, we show that EP measurements in the range $0.11<|t|<0.45{\mathrm{GeV}}^2$ can provide constraints on $F_1(t)$, while offering limited sensitivity to $F_2(t)$. The extracted charge radius values tend to be smaller than those obtained from traditional elastic electron-proton scattering measurements and are consistent, within uncertainties, with recent high-precision PRad results. These findings indicate that EP measurements, especially when covering smaller values of $|t|$, can serve as a complementary tool for determining the proton electromagnetic structure and may contribute to ongoing efforts to better understand the proton charge radius. The methodology developed here provides a framework for future combined analyses of EP and elastic electron-proton scattering data which enables a unified determination of the nucleon FFs.

We investigate the buildup of elliptic flow of charm quarks produced in the early pre-equilibrium stage of high-energy proton-nucleus collisions. The initial stage is modeled within the color glass condensate framework as an evolving glasma, initialized through the McLerran-Venugopalan model. Subnucleonic fluctuations have been implemented as constituent-quark hotspots for both the proton and the nuclear participants. Charm quarks are propagated in the evolving non-Abelian background by solving the relativistic Wong equations for their coordinates, momenta, and color charges. First, we compute the nuclear modification factor of charm quarks, finding a slight migration towards higher $p_T$ states in agreement with previous results in the literature. Then, we focus on the azimuthal anisotropies acquired through the interaction with glasma fields. We find that glasma-induced momentum anisotropies are efficiently transmitted to heavy quarks within $\tau \sim 0.4\mathrm{fm}/\mathrm{c}$, leading to a sizeable charm-quark $v_2$, with a magnitude that increases with the strength of the initial fields and with the number of nuclear participants. Remarkably, we show that the early stage contribution alone can account for a significant fraction of the experimentally observed $J/\psi$ elliptic flow in p-Pb collisions, indicating that prehydrodynamic dynamics can play a non-negligible role in the final-state heavy-flavor collectivity, especially in small systems.