In this paper, some subtleties in the measurement of the transverse polarization of the produced hadrons on symmetric colliders—such as the Large Hadron Collider when conducting the $pp$ collisions—are revealed. It can be proved that the transverse polarization of the produced particles with opposite pseudorapidity takes exactly opposite values if the normal vector of the production plane is defined in a convention-dependent way, regardless of whether parity is conserved or not in the production process. The analysis shows that, due to the symmetry of the initial state, the ${\mathrm{\Lambda }}_b$ transverse polarization measured by the CMS Collaboration in Phys. Rev. D 97, 072010 (2018) should be exactly equal to zero. A modified measurement of the ${\mathrm{\Lambda }}_b$ polarization for CMS and ATLAS is proposed, the result of which can be compared to the LHCb measurement.

With a data sample corresponding to an integrated luminosity of $11.5{\mathrm{fb}}^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring, for the first time the light hadron decay ${\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}\eta$ is searched for. While no significant signal is observed, the upper limits at the 90% confidence level for $\sigma [e^{+}{e}^{-}\to \gamma {\chi }_{c1}(3872)]\mathcal{B}[{\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}\eta ]$ at center of mass energies from 4.13 GeV to 4.34 GeV are determined. By normalizing to the ${\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$ decay channel, a 90% confidence level upper limit for the branching fraction ratio $\mathcal{R}=\mathcal{B}[{\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}\eta ]/\mathcal{B}[{\chi }_{c1}(3872)\to {\pi }^{+}{\pi }^{-}J/\psi ]<0.12$ is given. These measurements provide important inputs for understanding the internal structure of the ${\chi }_{c1}(3872)$ resonance.

We describe the application of the quantum mechanical bootstrap to the solution of one-dimensional scattering problems. By fixing a boundary and modulating the Robin parameter of the boundary conditions we are able to extract the reflection coefficient for various potentials and compare to physical expectations. This includes an application of semidefinite programming to solving a half line Schrodinger problem with arbitrary Robin boundary conditions. Finally, the WKB approximation is used to numerically determine the scattering behavior of the exponential potential of Liouville theory.

Null cosmic strings disturb electromagnetic (EM) fields of charged sources and sources with magnetic moments. As has been recently shown by the authors, these perturbations result in a self-force acting on the sources and create EM waves outgoing from the sources. We develop an analytic approximation for the asymptotic of the EM waves at the future null infinity and calculate radiation fluxes for sources of both types. For magnetic-dipole-like sources the radiation flux depends on orientation of the magnetic moment with respect to the string. Estimates show that the peak power of the radiation can be quite large for null strings moving near pulsars and considerably larger in the case of magnetars. The string generated variations of the luminosities of the stars can be used as a potential experimental signature of null cosmic strings.

We explore how quantum gravity effects, manifested through the breaking of discrete symmetry responsible for both dark matter and domain walls, can have observational effects through cosmic microwave background observations and gravitational waves. To illustrate the idea we consider a simple model with two scalar fields and two ${\mathcal{Z}}_2$ symmetries, one being responsible for dark matter stability, and the other spontaneously broken and responsible for domain walls, where both symmetries are assumed to be explicitly broken by quantum gravity effects. We show the recent gravitational wave spectrum observed by several pulsar timing array projects can help constrain such effects.

The uniqueness of the static, asymptotically flat, nonextremal photon sphere in Einstein-Maxwell spacetime with electric and magnetic charges has been proved. Using the conformal positive energy theorem, as well as the positive mass theorem and adequate conformal transformations, we envisage the two alternative ways of proving that the exterior region of a certain radius of the studied static photon sphere is characterized by Arnowitt-Deser-Misner mass, electric, and magnetic charges.

In the present paper, we consider a rotating black hole moving in a homogeneous massless scalar field. We assume that the field is weak and neglect its backreaction so that the metric at far distance from the black hole is practically flat. In this domain, one can introduce two reference frames, $K$ and $\tilde{K}$. The frame $\tilde{K}$ is associated with the homogeneous scalar field, in which its constant gradient has only time component. The other frame, $K$, is the frame in which the black hole is at rest. To describe the Kerr metric of the black hole, we use its Kerr-Schild form $g_{\mu \nu }={\eta }_{\mu \nu }+\mathrm{\Phi }{l}_{\mu }{l}_{\mu }$, where ${\eta }_{\mu \nu }$ is the (asymptotic) flat metric in $K$ frame. We find an explicit solution of the scalar field equation, which is regular at the horizon, and properly reproduce the asymptotic form of the scalar field at the infinity. Using this solution, we calculate the fluxes of the energy, momentum and the angular momentum of the scalar field into the black hole. This allows us to derive the equation of motion of the rotating black hole. We discuss main general properties of solutions of these equations and obtain explicit solutions for special type of the motion of the black hole.

Although Lorentz symmetry is a staple of general relativity (GR), there are several reasons to believe it may not hold in a more advanced theory of gravity, such as quantum gravity. Einstein-aether theory is a modified theory of gravity that breaks Lorentz symmetry by introducing a dynamical vector field called the aether. The theory has four coupling constants that characterize deviations from GR and that must be determined through observations. Although three of the four parameters have been constrained by various empirical observations and stability requirements, one, called $c_{\omega }$, remains essentially unconstrained. The aim of this work is to see if a constraint on $c_{\omega }$ can be derived from the I-Love-Q universal relations for neutron stars, which connect the neutron star moment of inertia (I), the tidal Love number (Love), and the quadrupole moment (Q) in a way that is insensitive to uncertainties in the neutron star equation-of-state. To understand if the theory can be constrained through such relations, we model slowly rotating or weakly tidally deformed neutron stars in Einstein-aether theory, derive their I-Love-Q relations, and study how they depend on $c_{\omega }$. We find that the I-Love-Q relations in Einstein-aether theory are insensitive to $c_{\omega }$ and that they are close to the relations in GR. This means that the I-Love-Q relations in Einstein-aether theory remain universal but cannot be used to constrain the theory. These results indicate that to constrain the theory with neutron stars, it is necessary to investigate relations involving other observables.

The number of gravitational wave signals from the merger of compact binary systems detected in the network of advanced LIGO and Virgo detectors is expected to increase considerably in the upcoming science runs. Once a confident detection is made, it is crucial to reconstruct the source’s properties rapidly, particularly the sky position and chirp mass, to follow up on these transient sources with telescopes operating at different electromagnetic bands for multimessenger astronomy. In this context, we present a rapid parameter estimation (PE) method aided by mesh-free approximations to accurately reconstruct properties of compact binary sources from data gathered by a network of gravitational wave detectors. This approach builds upon our previous algorithm [L. Pathak et al., Fast likelihood evaluation using meshfree approximations for reconstructing compact binary sources, Phys. Rev. D 108, 064055 (2023)] to expedite the evaluation of the likelihood function and extend it to enable coherent network PE in a ten-dimensional parameter space, including sky position and polarization angle. Additionally, we propose an optimized interpolation node placement strategy during the start-up stage to enhance the accuracy of the marginalized posterior distributions. With this updated method, we can estimate the properties of binary neutron star sources in approximately 2.4 (2.7) min for the TaylorF2 (IMRPhenomD) signal model by utilizing 64 CPU cores on a shared memory architecture. Furthermore, our approach can be integrated into existing parameter estimation pipelines, providing a valuable tool for the broader scientific community. We also highlight some areas for improvements to this algorithm in the future, which includes overcoming the limitations due to narrow prior bounds.

Finite-energy particles in free fall can collide with diverging center-of-mass energy near rapidly rotating black holes. What are the most salient observational signatures of this remarkable geometric effect? Here we revisit the problem from the standpoint of the near-horizon extreme Kerr geometry, where these collisions naturally take place. It is shown that the ingoing particle kinematics admits a simple, universal form. Given a scattering cross section, determination of emission properties is reduced to evaluation of particular integrals on the sky of a near-horizon orbiting particle. We subsequently apply this scheme to the example of single-photon bremsstrahlung, substantiating past results which indicate that ejected particles are observable, but their energies are bounded by the rest masses of the colliding particles. Our framework is readily applicable for any scattering process.

We derive new positivity bounds at finite momentum transfer, assuming a large separation between the mass $m$ of the lightest particle in the effective theory and the mass gap $M$ to new heavy states. Massive gravity parametrically violates these bounds unless the cutoff is within 1 order of magnitude of the graviton mass $M\lesssim O(10)m$. Nongravitational effective theories of massive spin-2 particles are similarly bounded.

Allowing for the possibility of extra dimensions, there are two paradigms: either the extra dimensions are hidden from observations by being compact and small as in Kaluza-Klein scenarios or the extra dimensions are large/noncompact and undetectable due to a large warping as in the Randall-Sundrum scenario. In the latter case, the five-dimensional background has a large curvature, and Isaacson’s construction of the gravitational energy-momentum tensor, which relies on the assumption that the wavelength of the metric fluctuations is much smaller than the curvature length of the background spacetime, cannot be used. In this paper, we construct the gravitational energy-momentum tensor in a strongly curved background such as Randall-Sundrum. We perform a scalar-vector-tensor decomposition of the metric fluctuations with respect to the $SO(1,3)$ background isometry and construct the covariantly conserved gravitational energy-momentum tensor out of the gauge-invariant metric fluctuations. We give a formula for the power radiated by gravitational waves and verify it in known cases. In using the gauge-invariant metric fluctuations to construct the gravitational energy-momentum tensor we follow previous work done in cosmology. Our framework has applicability beyond the Randall-Sundrum model.

Near-future, space-based, radio- and gravitational-wave interferometry missions will enable us to rigorously test whether the Kerr solution of general relativity accurately describes astrophysical black holes, or if it requires some kind of modification. At the same time, recent work has greatly improved our understanding of theories of gravity that modify the Einstein-Hilbert action with terms quadratic in the curvature, allowing us to calculate black hole solutions to (essentially) arbitrary order in a slow-rotation expansion. Observational constraints of such quadratic gravity theories require the calculation of observables that are robust against the expansion order of the black hole solution used. We carry out such a study here and determine the accuracy with respect to expansion order of ten observables associated with the spacetime outside a rotating black hole in two quadratic theories of gravity, dynamical-Chern-Simons and scalar-Gauss-Bonnet gravity. We find that for all but the most rapidly rotating black holes, only about the first eight terms in the spin expansion are necessary to achieve an accuracy that is better than the statistical uncertainties of current and future missions.

We cut a general, static, spherically symmetric spacetime and paste its copy to make a wormhole with a thin shell of any barotropic fluid in general relativity. We show that the stability of the thin-shell wormhole is characterized by a set of circular photon orbits called an (anti)photon sphere in the original spacetime if a momentum flux passing through a throat is prohibited. Our result will be useful to classify the stability of the thin shell on the throat against linearized spherically symmetric perturbations.

Observations of galaxy-scale strong gravitational lensing systems enable unique tests of departures from general relativity at the kilo- to megaparsec scale. In this work, the gravitational slip parameter ${\gamma }_{\mathrm{PN}}$, measuring the amplitude of a hypothetical fifth force, is constrained using 130 elliptical galaxy lens systems. We implement a lens model with a power-law total mass density and a deprojected De Vaucouleurs luminosity density, favored over a power-law luminosity density. To break the degeneracy between the lens velocity anisotropy $\beta$ and the gravitational slip, we introduce a new prior on the velocity anisotropy based on recent dynamical data. For a constant gravitational slip, we find ${\gamma }_{\mathrm{PN}}=0.90_{-0.14}^{+0.18}$ in agreement with general relativity at the 68% confidence level. Introducing a Compton wavelength ${\lambda }_g$, effectively screening the fifth force at small and large scales, the best fit is obtained for ${\lambda }_g\sim 0.2\mathrm{Mpc}$ and ${\gamma }_{\mathrm{PN}}=0.77_{-0.14}^{+0.25}$. A local minimum is found at ${\lambda }_g\sim 100\mathrm{Mpc}$ and ${\gamma }_{\mathrm{PN}}=0.56_{-0.35}^{0.45}$. We conclude that there is no evidence in the data for a significant departure from general relativity and that using accurate assumptions and having good constraints on the lens galaxy model is key to ensure reliable constraints on the gravitational slip.

Prompt $\rho \propto r^{-1.5}$ density cusps are the densest and most abundant dark matter systems. If the dark matter is a weakly interacting massive particle (WIMP), recent studies have shown that prompt cusps dominate the aggregate dark matter annihilation rate. This article explores whether individual prompt cusps could be detected as gamma-ray sources. At the Fermi Telescope’s point-source sensitivity, WIMPs with the canonical annihilation cross section could form detectable prompt cusps if the particle mass is of order 10 GeV. These objects could be 10–100 pc away and weigh under a solar mass; they would subtend around 0.1 degrees on the sky. For GeV-scale dark matter particles with below-canonical cross sections, searches for individual prompt cusps can be more sensitive than searches for the annihilation signals from galactic dark matter halos.

What would a parity-violating universe look like? We present a numerical and theoretical study of mirror asymmetries in the late universe, using a new suite of $N$-body simulations: quijote-odd. These feature parity-violating initial conditions, injected via a simple ansatz for the imaginary primordial trispectrum and evolved into the nonlinear regime. We find that the realization-averaged power spectrum, bispectrum, halo mass function, and matter PDF are not affected by our modifications to the initial conditions, deep into the nonlinear regime, which we argue arises from rotational and translational invariance. In contrast, the parity-odd trispectrum of matter (measured using a new estimator), shows distinct signatures proportional to the parity-violating parameter, $p_{\mathrm{NL}}$, which sets the amplitude of the primordial trispectrum; furthermore, the statistic cannot be sourced by any conventional gravitational or baryonic processes. We additionally find intriguing signatures in the angular momentum of halos, with the primordial trispectrum inducing a nonzero correlation between angular momentum and smoothed velocity field, proportional to $p_{\mathrm{NL}}$. Our simulation suite has been made public to facilitate future analyses.

We investigate an early coupled quintessence model where a light scalar mediates a fifth force stronger than gravity among dark matter particles and leads to the growth of perturbations prior to matter-radiation equality. Using cosmological data from the Planck cosmic microwave background power spectra, the $\mathrm{Pantheon}+\text{type}$ 1a supernovae, baryon acoustic oscillations, and big bang nucleosynthesis, we constrain the coupling strength $\beta$ and the redshift $z_{\mathrm{OFF}}$ at which the interaction becomes effectively inactive, finding a firm degeneracy between these two parameters which holds regardless of when the scaling regime begins.

Gravitational waves (GWs) from stellar-mass compact binary coalescences (CBCs) are expected to be strongly lensed when encountering large agglomerations of matter, such as galaxies or clusters. Searches for strongly lensed GWs have been conducted using data from the first three observing runs of the LIGO-Virgo GW detector network. Although no confirmed detections have been reported, interesting candidate lensed pairs have been identified. In this work, we delineate a preliminary analysis that rapidly identifies pairs to be further analyzed by more sophisticated Bayesian parameter estimation (PE) methods. The analysis relies on the Gaussian/Fisher approximation to the likelihood and compares the corresponding approximate posteriors on the chirp masses of the candidate pair. It additionally cross-correlates the rapidly produced localization sky areas (constructed by Bayestar sky-localization software). The analysis was used to identify pairs involving counterparts from targeted subthreshold searches to confidently detected superthreshold CBC events. The most significant candidate “super-sub” pair deemed by this analysis was subsequently found, by more sophisticated and detailed joint-PE analyses, to be among the more significant candidate pairs, but not sufficiently significant to suggest the observation of a lensed event [J. Janquart et al., Follow-up analyses to the O3 LIGO-Virgo-KAGRA lensing searches, Mon. Not. R. Astron. Soc. 526, 3 (2023)].

The densities in the cores of the neutron stars (NSs) can reach several times that of the nuclear saturation density. The exact nature of matter at these densities is still virtually unknown. We consider a number of proposed phenomenological, relativistic mean field equations of state to construct theoretical models of NSs. We find that, based on our selected set of models, the emergence of exotic matter at these high densities restricts the mass of NSs to $\simeq 2.2M_{\odot }$. However, the presence of magnetic fields and a model anisotropy significantly increases the star’s mass, placing it within the observational mass gap that separates the heaviest NSs from the lightest black holes. Therefore, we propose that gravitational wave observations, like GW190814 and other potential candidates within this mass gap, may actually represent massive, magnetized NSs.