The dressed metric and the hybrid approach to perturbations are the two main approaches to capture the effects of quantum geometry in the primordial power spectrum in loop quantum cosmology. Both consider Fock quantized perturbations over a loop quantized background and result in very similar predictions except for the modes which exit the horizon in the effective spacetime in the Planck regime. Understanding precise relationship between both approaches has so far remained obscured due to differences in construction and technical assumptions. We explore this issue at the classical and effective spacetime level for linear perturbations, ignoring backreaction, which is the level at which practical computations of the power spectrum in both of the approaches have so far been performed. We first show that at the classical level both the approaches lead to the same Hamiltonian up to the second order in perturbations and result in the same classical mass functions in the Mukhanov-Sasaki equation on the physical solutions. At the effective spacetime level, the difference in phenomenological predictions between the two approaches in the Planck regime can be traced to whether one uses the Mukhanov-Sasaki variable $Q_{\overrightarrow{k}}$ (the dressed metric approach) or its rescaled version ${\nu }_{\overrightarrow{k}}=a{Q}_{\overrightarrow{k}}$ (the hybrid approach) to write the Hamiltonian of the perturbations, and associated polymerization ambiguities. It turns out that if in the dressed metric approach one chooses to work with ${\nu }_{\overrightarrow{k}}$, the effective mass function can be written exactly as in the hybrid approach, thus leading to identical phenomenological predictions in all regimes. Our results explicitly show that the dressed metric and the hybrid approaches for linear perturbations, at a practical computational level, can be seen as two sides of the same coin.

An effective description is presented for a Brownian particle in a magnetized plasma. In order to systematically capture various corrections to linear Langevin equation, we construct effective action for the Brownian particle, to quartic order in its position. The effective action is first derived within nonequilibrium effective field theory formalism, and then confirmed via a microscopic holographic model consisting of an open string probing magnetic fifth-dimensional anti–de Sitter (${\mathrm{AdS}}_5$) black brane. For practical usage, the non-Gaussian effective action is converted into Fokker-Planck-type equation, which is an Euclidean analog of Schrödinger equation and describes time evolution of probability distribution for particle’s position and velocity.

Black holes hold a tremendous discovery potential. In this paper the extent to which the Event Horizon Telescope and its next generation upgrade can resolve their structure is quantified. Black holes are characterized by a perfectly absorptive boundary, with a specific area determined by intrinsic parameters of the black hole. We use a general parametrization of spherically symmetric spacetimes describing deviations from this behavior, with parameters controlling the size of the central object and its interaction with light, in particular through a specular reflection coefficient $\mathrm{\Gamma }$ and an intrinsic luminosity measured as a fraction $\eta$ of that of the accretion disc. This enables us to study exotic compact objects and compare them with black holes in a model-independent manner. We determine the image features associated with the existence of a surface in the presence of a geometrically thin and optically thick accretion disc, identifying requirements for very large baseline interferometry observations to be able to cast meaningful constraints on these parameters, in particular regarding angular resolution and image dynamic range. For face-on observations, constraints of order $\eta \lesssim {10}^{-4}$, $\mathrm{\Gamma }\lesssim {10}^{-1}$ are possible with an enhanced Event Horizon Telescope array, imposing strong constraints on the nature of the central object.

Recent work on improved efficiency of calculations for extreme mass ratio inspirals has produced the useful byproduct of comparisons of inspirals of comparable mass by particle perturbation (PP) methods and by numerical relativty (NR). Here we point out: (1) In choosing the rescaling of the masses, consideration must be given to the differences in the PP and NR methods even in the earliest, least nonlinear regime—in particular barycenter effects must be addressed; (2) Care must be given to the comparison of the nonspinning remnant in PP and the rapidly spinning remnant in NR.

We propose two frequency-domain filters to analyze ringdown signals of binary black hole mergers. The first rational filter is constructed based on a set of (arbitrary) quasinormal modes (QNMs) of the remnant black holes, whereas the second full filter comes from the transmissivity of the remnant black holes. The two filters can remove corresponding QNMs from original time-domain ringdowns, while changing early inspiral signals in a trivial way—merely a time and phase shift. After filtering out dominant QNMs we can visualize the existence of various subdominant effects. For example, by applying our filters to a GW150914-like numerical relativity (NR) waveform, we find second-order effects in the $(l=4,m=4),(l=5,m=4)$, and $(l=5,m=5)$ harmonics; the spherical-spheroidal mixing mode in the $(l=2,m=2)$ harmonic; and a mixing mode in the $(l=2,m=1)$ harmonic due to a gravitational recoil. In another NR simulation where two component spins are antialigned with the orbital angular momentum we also find retrograde modes. The filters are sensitive to the remnant properties (i.e., mass and spin) and thus have a potential application to future data analyses and parameter estimations. We also investigate the stability of the full filter. Its connection to the instability of QNM spectra is discussed.

Continuous gravitational waves from spinning deformed neutron stars have not been detected yet and are one of the most promising signals for future detection. All-sky searches for continuous gravitational waves from unknown neutron stars in binary systems are the most computationally challenging search type. Consequently, very few search algorithms and implementations exist for these sources, and only a handful of such searches have been performed so far. In this paper, we present a new all-sky binary search method, BinarySkyHou$\mathcal{F}$, which extends and improves upon the earlier BinarySkyHough method and which was the basis for a recent search [Covas et al., Astrophys. J. Lett. 929, L19 (2022)]. We compare the sensitivity and computational cost to the previous method, showing that it is both more sensitive and computationally efficient, which allows for broader and more sensitive searches.

We consider the problem of matching two spacetimes, the previous and present aeons, in the conformal cyclic cosmology model. The common boundary between them inherits two sets of constraints—one for each solution of the Einstein field equations extended to the conformal boundaries. The previous aeon is assumed to be an asymptotically de Sitter spacetime, so the standard conformal formulation of the Einstein field equations suffice to derive the constraints on the future null infinity. For the future aeon, which is supposed to evolve from an initial singularity, they are obtained with the use of the Bach-type equation. This equation is regular at the past conformal infinity for conformally flat and conformally Einstein spacetimes, so we will mostly focus on them here. An example of the electrovacuum spacetime which does not fall into this class and has a regular conformal Bach tensor will be discussed in the Appendix.

We present a novel gravitational-wave detection algorithm that conducts a matched-filter search stochastically across the compact binary parameter space rather than relying on a fixed bank of template waveforms. This technique is competitive with standard template-bank-driven pipelines in both computational cost and sensitivity. However, the complexity of the analysis is simpler, allowing for easy configuration and horizontal scaling across heterogeneous grids of computers. To demonstrate the method we analyze approximately one month of public LIGO data from July 27 00:00 2017 UTC–Aug 25 22:00 2017 UTC and recover eight known confident gravitational-wave candidates. We also inject simulated binary black hole signals to demonstrate the sensitivity.

We propose a generalization of the photon surfaces of Claudel, Virbhadra and Ellis to the case of massive charged particles, considering a timelike hypersurface such that any worldline of a particle with mass $m$, electric charge $q$ and a fixed total energy $\mathcal{E}$, initially touching it, will forever remain in this hypersurface. Such surfaces can be defined not only with particle motion equations, but instead using the partially umbilic nature of the surface geometry. Such an approach should be especially useful in the case of nonintegrable equations of motion. It can be applied to the theory of nonthin accretion disks, and can also serve as a new tool for some general problems such as uniqueness theorems, Penrose inequalities, and hidden symmetries. A condition for the stability of worldlines is derived, which reduces to differentiation along the flow of surfaces of a certain energy. A number of examples of electrovacuum and dilaton solutions are considered; conditions are found for marginally stable surfaces of massive particles, regions of stable or unstable surfaces of massive particles and photons, as well as solutions that satisfy the no-force condition.

We fully explore the thermal freeze-out histories of a vector-portal dark matter model in the region of parameter space in which the ratio of masses of the dark photon $A^{\prime }$ and dark matter $\chi$ is in the range $1\lesssim m_{A^{\prime }}/m_{\chi }\lesssim 2$. In this region, $2\to 2$ and $3\to 2$ annihilation processes within the dark sector, as well as processes that transfer energy between the dark sector and the Standard Model, play important roles in controlling the thermal freeze-out of the dark matter. We carefully track the temperatures of all species, relaxing the assumption of previous studies that the dark and Standard Model sectors remain in thermal equilibrium throughout dark matter freeze-out. Our calculations reveal a rich set of novel pathways which lead to the observed relic density of dark matter, and we develop a simple analytic understanding of these different regimes. The viable parameter space in our model provides a target for future experiments searching for light (MeV–GeV) dark matter, and includes regions where the dark matter self-interaction cross section is large enough to affect the small-scale structure of galaxies.

Despite the impressive success of the standard cosmological model, several anomalies defy its triumph. Among them is the so-called lensing anomaly: The Planck satellite observes stronger cosmic microwave background (CMB) gravitational lensing than expected. The role of neutrinos in this anomaly has been mostly overlooked, despite their key role in CMB lensing, because in the standard scenario they tend to increase the tension. Here, we show that this strongly depends on the assumed neutrino equation of state. We demonstrate that if neutrinos have yet undiscovered long-range interactions, the lensing pattern is significantly affected, rendering the lensing anomaly as a statistical fluctuation. Our results, thus, open up a window to link anomalous CMB lensing with present and future cosmological, astrophysical, and laboratory measurements of neutrino properties.

We perform binary neutron star (BNS) merger simulations in full dynamical general relativity with illinoisgrmhd, on a Cartesian grid with adaptive-mesh refinement. After the remnant black hole has become nearly stationary, the evolution of the surrounding accretion disk on Cartesian grids over long timescales ($\sim 1\mathrm{s}$) is suboptimal, as Cartesian coordinates over-resolve the angular coordinates at large distances, and the accreting plasma flows obliquely across coordinate lines dissipating angular momentum artificially from the disk. To address this, we present the handoff, a set of computational tools that enables the transfer of general relativistic magnetohydrodynamic (GRMHD) and spacetime data from illinoisgrmhd to harm3d, a GRMHD code that specializes in modeling black hole accretion disks in static spacetimes over long timescales, making use of general coordinate systems with spherical topology. We demonstrate that the handoff allows for a smooth and reliable transition of GRMHD fields and spacetime data, enabling us to efficiently and reliably evolve BNS dynamics well beyond merger. We also discuss future plans, which involve incorporating advanced equations of state and neutrino physics into BNS simulations using the handoff approach.

We present a survey of more than a half-thousand thunderstorm ground enhancements (TGEs, fluxes of electrons, and gamma rays associated with thunderstorms) registered in 2008–2022 at Aragats space environmental center (ASEC). We analyze correlations between various measured parameters characterizing TGEs measured on Aragats. Two special cases of TGE events are considered: one, terminated by nearby lightning flashes, and another one—with a sufficiently large ratio of electrons to gamma rays. On the basis of the analysis, we summarize the most important results obtained during 12 years of TGE study, which include the following statements: (i) TGEs originated from multiple relativistic runaway electron avalanches starting with seed electrons from the ambient population of cosmic rays, which enter an extended region of the electric field with strength exceeding the critical value; (ii) quite frequently, TGEs occur prior to lightning flashes and are terminated by them; (iii) the energy spectra of avalanche electrons observed on Aragats indicate that the strong electric field region can extend very low above the ground covering a large area on the earth’s surface.

Accelerated charges emit both electromagnetic and gravitational radiation. Classically, it was found that the electromagnetic energy spectrum radiated by an electron in a monochromatic plane wave is proportional to the corresponding gravitational one. Quantum mechanically, it was shown that the amplitudes of graviton photoproduction and Compton scattering are proportional to each other at tree level. Here, by combining strong-field QED and quantum gravity, we demonstrate that the amplitude of nonlinear graviton photoproduction in an arbitrary plane wave is proportional to the corresponding amplitude of nonlinear Compton scattering. Also, introducing classical amplitudes we prove that the proportionality relies on the semiclassical nature of the electron’s motion in a plane wave and on energy-momentum conservation laws, leading to the same proportionality constant in the classical and quantum case. These results deepen the intertwine between gravity and electromagnetism into both a nonlinear and a quantum level.

The contribution of the $CP$ violating three-gluon interaction, proposed by Weinberg, to the short-range $CP$-odd nuclear force is evaluated in the nonrelativistic quark model. We first show that the naive leading contribution generated by the quark exchange process vanishes at sufficiently short distance within the resonating group method by considering the one-loop level gluon exchange $CP$-odd interquark potential induced by the Weinberg operator with massive quarks and gluons. We then estimate the true leading contribution by evaluating the gluonic correction to the $CP$-odd interquark potential in the closure approximation. It is found that the resulting irreducible $CP$-odd nuclear force is comparable to that generated by the chiral rotation of the $CP$-even short-range nuclear force, where the $CP$-odd mass calculated with QCD sum rules is used as input. The explicit calculation of the electric dipole moment (EDM) of the ${}^3\mathrm{He}$ nucleus yields $d_{{}^3\mathrm{He}}^{(\mathrm{irr})}(w)=-1.5we\mathrm{MeV}$. The total ${}^3\mathrm{He}$ EDM, accounting for the intrinsic nucleon EDM, the pion-exchange and the short-range $CP$-odd nuclear force, is $d_{{}^3\mathrm{He}}^{(\mathrm{tot})}(w)={20}_{-11}^{+14}we\mathrm{MeV}$, with the dominant effect coming from the intrinsic nucleon EDM.

A framework based on a class of Abelian gauge symmetries is proposed in which the masses of only the third generation quarks and leptons arise at the tree level. The fermions of the first and second families receive their masses through radiative corrections induced by the new gauge bosons in the loops. It is shown that the class of Abelian symmetries which can viably implement this mechanism are flavor nonuniversal in nature. Taking the all-fermion generalization of the well-known leptonic $L_{\mu }-L_{\tau }$ and $L_e-L_{\mu }$ symmetries, we construct an explicit renormalizable model based on two $U(1)$ which is shown to reproduce the observed fermion mass spectrum of the Standard Model. The first and second generation fermion masses are loop suppressed while the hierarchy between these two generations results from a gap between the masses of two vector bosons of the extended gauge symmetries. Several phenomenological aspects of the flavorful new physics are discussed and lower limits on the masses of the vector bosons are derived.

We present a formalism for determining the cross section for exclusive heavy vector meson production ($J/\psi ,\mathrm{\Upsilon }$) as a function of rapidity, in both high-energy proton-proton and proton-heavy ion collisions, at next-to-leading order in QCD. We compare and contrast the production in $pp$ and $p$-Pb collisions and show how data for these processes can give information on the low-$x$ gluon distribution of the proton and heavy ions at a range of different scales.

We have systematically calculated the strong decays of the low-lying $\rho$-mode $1P$-wave ${\mathrm{\Lambda }}_{c(b)}$, ${\mathrm{\Sigma }}_{c(b)}$, ${\mathrm{\Xi }}_{c(b)}$, ${\mathrm{\Xi }}_{c(b)}^{\prime }$, ${\mathrm{\Omega }}_{c(b)}$ baryons using the chiral quark model within the $j\text{−}j$ coupling scheme. For the controversial states, our results indicate the following: (i) For the singly charmed heavy baryons, the newly observed ${\mathrm{\Lambda }}_c(2910{)}^{+}$ is a good candidate of the $J^P=5/2^{-}$ state ${\mathrm{\Lambda }}_c|J^P={\frac{5}{2}}^{-},2{⟩}_{\rho }$. (ii) For the singly bottom heavy baryons, the ${\mathrm{\Xi }}_b(6227{)}^{-}$ favors the $J^P=5/2^{-}$ state ${\mathrm{\Xi }}_b|J^P={\frac{5}{2}}^{-},2{⟩}_{\rho }$. (iii) The other missing $\rho$-mode $1P$-wave excitations in ${\mathrm{\Lambda }}_b$, ${\mathrm{\Sigma }}_{c(b)}$, and ${\mathrm{\Xi }}_{c(b)}^{\prime }$ families appear to be broad structures with $\mathrm{\Gamma }\sim (100–200)\mathrm{MeV}$, and their strong decay widths are sensitive to their masses. (iv) The $\rho$-mode $1P$-wave ${\mathrm{\Xi }}_{c(b)}$ and ${\mathrm{\Omega }}_{c(b)}$ baryons have a relatively narrow decay width of a few mega-electron-volts (MeV) or a few tens of MeV, and have a good potential to be observed in forthcoming experiments.

Frame-dragging effect manifests itself as polarization direction rotation when linearly polarized electromagnetic/gravitational wave scatters from a spinning point source through gravitational interactions, an effect also known as the gravitational Faraday rotation. Treating general relativity as an effective field theory, the Faraday rotation angle and its quantum corrections are computed using scattering amplitudes. While the classical rotation angle is universal as expected from the equivalence principle, the quantum corrections are found to be different between electromagnetic and gravitational waves, supporting earlier studies that some formulations of the equivalence principle may need reformulation in the quantum regime.

In this paper, we derive a soft photon theorem in the near horizon region of the Schwarzschild black hole from the Ward identity of the near horizon large gauge transformation. The flat spacetime soft photon theorem can be recovered as a limiting case of the curved spacetime. The soft photons on the horizon are indeed soft electric hairs. This accomplishes the triangle equivalence on the black hole horizon.