In this work we analyze asymptotically flat, spherically symmetric spacetimes in which an event horizon is present without any trapped surfaces. We identify two types of such spacetimes, each related to the asymptotic behavior (in time) of one of the two degrees of freedom of the metric. We study the causal structure of both types, showing that one almost always has a Cauchy horizon beyond which it is extendable, while the other is inextendable but has two separate future null infinity regions on either side of the horizon. We also study what energy conditions can be satisfied by the matter around the horizon. Some of these spacetimes were first introduced in an earlier work in which semiclassical effects near black hole horizons were analyzed. Here, we generalize this analysis to a larger family of geometries.

In this paper, evolving wormholes in the context of braneworld scenario are investigated. We have studied the possible dynamic solutions with different forms of Ricci scalar. The possibility of the existence of dynamic traversable wormholes, without resorting to an exotic matter, has been studied. By using the fact that the Einstein field equations are modified in $3+1$ dimensions due to the brane corrections, we investigate the exact solutions which satisfy the null energy condition. Asymptotic flatness is an important property of these solutions. We discuss some physical and mathematical properties of the solutions.

Following an existing procedure in general relativity, the turnaround radius of a spherical structure is studied in scalar-tensor gravity using a new prescription for the analog of the Hawking-Hayward quasilocal mass in this class of theories.

We consider a very simple model for gravitational wave echoes from black hole merger ringdowns which may arise from local Lorentz symmetry violations that modify graviton dispersion relations. If the corrections are sufficiently soft so they do not remove the horizon, the reflection of the infalling waves which trigger the echoes is very weak. As an example, we look at the dispersion relation of a test scalar field corrected by rotonlike operators depending only on spatial momenta, in Gullstrand-Painlevé coordinates. The near-horizon regions of a black hole do become reflective, but only very weakly. The resulting “bounces” of infalling waves can yield repetitive gravity wave emissions but their power is very small. This implies that to see any echoes from black holes we really need an egregious departure from either standard GR or effective field theory, or both. One possibility to realize such strong echoes is the recently proposed classical firewalls which replace black hole horizons with material shells surrounding timelike singularities.

Given the recent advances in gravitational-wave detection technologies, the detection and characterization of gravitational-wave backgrounds (GWBs) with the Laser Interferometer Space Antenna (LISA) is a real possibility. To assess the abilities of the LISA satellite network to reconstruct anisotropies of different angular scales and in different directions on the sky, we develop a map-maker based on an optimal quadratic estimator. The resulting maps are maximum likelihood representations of the GWB intensity on the sky integrated over a broad range of frequencies. We test the algorithm by reconstructing known input maps with different input distributions and over different frequency ranges. We find that, in an optimal scenario of well understood noise and high frequency, high SNR signals, the maximum scales LISA may probe are ${\ell }_{\max }\lesssim 15$. The map-maker also allows to test the directional dependence of LISA noise, providing insight on the directional sky sensitivity we may expect.

Modified gravity (MG) scenarios have been advocated to account for the dark energy phenomenon in the universe. These models predict departures from general relativity on large cosmic scales that can be tested through a variety of probes such as observations of galaxy clusters among others. Here, we investigate the imprint of MG models on the internal mass distribution of clusterlike halos as probed by the dark matter halo sparsity. To this purpose we perform a comparative analysis of the properties of the halo sparsity using N-body simulation halo catalogs of a standard flat $\mathrm{\Lambda }\mathrm{CDM}$ model and MG scenarios from the DUSTGRAIN-pathfinder simulation suite. We find that the onset of the screening mechanism leaves a distinct signature in the redshift evolution of the ensemble average halos sparsity. Measurements of the sparsity of galaxy clusters from currently available mass estimates are unable to test MG models due to the large uncertainties on the cluster masses. We show that this should be possible in the future provided large cluster samples with cluster masses determined to better than 30% accuracy level.

We present the astrophysical science case for a space-based, decihertz gravitational-wave (GW) detector. We particularly highlight an ability to infer a source’s sky location, both when combined with a network of ground-based detectors to form a long triangulation baseline, and by itself for the early warning of merger events. Such an accurate location measurement is the key for using GW signals as standard sirens for constraining the Hubble constant. This kind of detector also opens up the possibility to test type Ia supernovae progenitor hypotheses by constraining the merger rates of white dwarf binaries with both super- and sub-Chandrasekhar masses separately. We will discuss other scientific outcomes that can be delivered, including the constraint of structure formation in the early Universe, the search for intermediate-mass black holes, the precise determination of black hole spins, the probe of binary systems’ orbital eccentricity evolution, and the detection of tertiary masses around merging binaries.

We study the vacuum topology of $2+1$ flavor QCD above the chiral crossover transition, at $T\lesssim 1.2T_c$, on lattices of size ${32}^3\times 8$. Since overlap fermions have exact chiral symmetry and an index theorem even on a finite lattice, we use them to detect the topological content of gauge fields generated using domain wall fermion discretization for quarks. We further use different periodicity phases along the temporal direction for the valence overlap quarks, which allows us to probe different topological structures present in the gauge field ensembles, through their zero modes. Through this procedure we provide some first evidences that fermion zero modes can be understood to arise due to different species of instanton-dyons. We resolve the so-called “topological clusters” via multiparameter fits to their density, providing therefore an understanding of the interactions between instanton-dyons. The typical separation between dyons we obtain, is $\sim 0.3\mathrm{fm}$. Surprisingly, it emerges out from this study that a semiclassical description of the fermionic zero modes in the QCD vacuum may be possible, just above $T_c$.

The spin alignment of vector mesons produced in high energy reactions is determined by the spin-dependent fragmentation function $D_{1LL}(z,{\mu }_f)$ that is shown to be independent of the polarization of the fragmenting quark. In this paper, we extract the spin-dependent fragmentation function $D_{1LL}(z,{\mu }_f)$ from data on the spin alignment of $K^{*0}$ in $e^{+}{e}^{-}$ annihilation at the large electron-position collider (LEP) in two different scenarios and apply them to make predictions in $pp$ collisions. We make detailed analysis of contributions from different subprocesses and show that the spin alignment should be quite significant also in high energy $pp$ collisions.

We develop an analytic approximation for the coincidence limit of a massive scalar propagator in an arbitrary spatially flat, homogeneous and isotropic geometry. We employ this to compute the one loop corrections to the inflaton effective potential from a quadratic coupling to a minimally coupled scalar. We also extend the Friedmann equations to cover potentials that depend locally on the Hubble parameter and the first slow roll parameter.

We compute the first-order self-force contribution to Detweiler’s redshift invariant for extended bodies endowed with both dipolar and quadrupolar structure (with spin-induced quadrupole moment) moving along circular orbits on a Schwarzschild background. Our analysis includes effects which are second order in spin, generalizing previous results for purely spinning particles. The perturbing body is assumed to move on the equatorial plane, the associated spin vector being orthogonal to it. The metric perturbations are obtained by using a standard gravitational self-force approach in a radiation gauge. Our results are accurate through the 6.5 post-Newtonian order, and are shown to reproduce the corresponding post-Newtonian expression for the same quantity computed by using the available Hamiltonian from an effective field theory approach for the dynamics of spinning binaries.

We study analytically the spacetime geometry of the black-hole formation and evaporation. As a simplest model of the collapse, we consider a spherical thin shell, and take the backreaction from the negative energy of the quantum vacuum state. For definiteness, we will focus on quantum effects of s-waves. We obtain an analytic solution of the semiclassical Einstein equation for this model, that provides an overall description of the black hole geometry form the formation to evaporation. As an application of this result, we find its interesting implication that, after the collapsing shell enters the apparent horizon, the proper distance between the shell and the horizon remains as small as the Planck length even when the difference in their areal radii is of the same order as the Schwarzschild radius. The position of the shell would be regarded as the same place to the apparent horizon in the semiclassical regime of gravity.

LISA is considered to be launched alongside the Athena to probe the energetic astrophysical processes. LISA can determine the direction of sources for Athena’s follow-up observation. As another space gravitational wave mission, TAIJI is expected to be launched in the 2030s. The LISA-TAIJI network would provide abundant merits for sources understanding. In this work, we simulate the joint LISA-TAIJI observations for gravitational waves from coalescing supermassive black hole binaries and monochromatic sources. By using the numerical mission orbits, we evaluate the performances of sky localization for various time-delay interferometry channels. For 30 days observation until coalescence, the LISA-TAIJI network in optimal operation can localize all simulated binary sources, $({10}^7,3.3\times {10}^6)M_{\odot }$, $({10}^6,3.3\times {10}^5)M_{\odot }$, and $({10}^5,3.3\times {10}^4)M_{\odot }$ at redshift $z=2$, in $0.4{\mathrm{deg}}^2$ (field of view of Wide Field Imager on Athena). The angular resolution can be improved by more than ten times comparing to LISA or TAIJI single detector at a given percentage of population. The improvements for monochromatic sources at 3 and 10 mHz are relatively moderate in one year observation. The precision of sky localization could be improved by a factor of 2 to 4 comparing to single LISA at a given percentage of sources. For a simulated 90 days observation for monochromatic waves, the LISA-TAIJI network still represents a considerable localization advantage which could be more than ten times better.

We study the pair production of $B_c$ mesons in the photon-photon interaction in the framework of perturbative quantum chromodynamics and the relativistic quark model. The production amplitudes of a pair of pseudoscalar and vector $B_c$ mesons are constructed in the nonrelativistic approximation and taking into account relativistic effects. Relativistic corrections related to the relative motion of heavy quarks in the production amplitude, as well as in the wave function of the bound state of heavy quarks, are taken into account. Analytical expressions are constructed for the relativistic differential and total cross sections for the pair $B_c$ meson production. Based on them, numerical values of the production cross sections are obtained for various energies and scattering angles.

The search for light and long-lived particles at the LHC will be intensified in the upcoming years with a prominent role of the new FASER experiment. In this study, we discuss how FASER could independently probe such scenarios relevant for new physics searches at kaon factories. We put an emphasis on the proposed explanations for the recently observed three anomalous events in the KOTO experiment. The baseline of FASER precisely corresponds to the proposed lifetime solution to the anomaly that avoids the NA62 bounds on charged kaons. As a result, the experiment can start constraining relevant models within the first few weeks of its operation. In some cases, it can confirm a possible discovery with up to ${10}^4$ spectacular high-energy events in FASER during LHC run 3. Further complementarities between FASER and kaon factories, which employ FASER capability to study $\gamma \gamma$ signatures, are illustrated for the model with axionlike particles dominantly coupled to $SU(2{)}_W$ gauge bosons.

We analyze the recent hints of lepton flavor universality violation in both charged-current and neutral-current rare decays of $B$ mesons in an $R$-parity-violating supersymmetric scenario. Motivated by simplicity and minimality, we had earlier postulated the third-generation superpartners to be the lightest (calling the scenario “RPV3”) and explicitly showed that it preserves gauge coupling unification and of course has the usual attribute of naturally addressing the Higgs radiative stability. Here we show that both $R_{D^{(*)}}$ and $R_{K^{(*)}}$ flavor anomalies can be addressed in this RPV3 framework. Interestingly, this scenario may also be able to accommodate two other seemingly disparate anomalies, namely, the longstanding discrepancy in the muon ($g-2$), as well as the recent anomalous upgoing ultrahigh-energy Antarctic Impulsive Transient Antenna events. Based on symmetry arguments, we consider three different benchmark points for the relevant RPV3 couplings and carve out the regions of parameter space where all (or some) of these anomalies can be simultaneously explained. We find it remarkable that such overlap regions exist, given the plethora of precision low-energy and high-energy experimental constraints on the minimal model parameter space. The third-generation superpartners needed in this theoretical construction are all in the 1–10 TeV range, accessible at the LHC and/or next-generation hadron colliders. We also discuss some testable predictions for the lepton-flavor-violating decays of the tau lepton and $B$ mesons for the current and future $B$-physics experiments, such as LHCb and Belle II. Complementary tests of the flavor anomalies in the high-$p_T$ regime in collider experiments such as the LHC are also discussed.

We present the results on the radius of the neutron distribution in ${}^{40}\mathrm{Ar}$, on the low-energy value of the weak mixing angle, and on the electromagnetic properties of neutrinos obtained from the analysis of the coherent neutrino-nucleus elastic scattering data in argon recently published by the COHERENT Collaboration, taking into account proper radiative corrections. We present also the results of the combined analysis of the COHERENT argon and cesium-iodide data for the determination of the low-energy value of the weak mixing angle and the electromagnetic properties of neutrinos. In particular, the COHERENT argon data allow us to improve significantly the only existing laboratory bounds on the electric charge $q_{\mu \mu }$ of the muon neutrino and on the transition electric charge $q_{\mu \tau }$.

Fermion pair production at $e^{-}{e}^{+}$ linear collider experiments with polarized $e^{-}$ and $e^{+}$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z^{\prime }\mathrm{s}$, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^{-}{e}^{+}$ linear collider experiments with energies 250 GeV to 1 TeV.

We investigate some properties of Karsten-Wilczek and Borici-Creutz fermions, which are the best known varieties in the class of minimally doubled lattice fermion actions. Our focus is on the dispersion relation and the distribution of eigenvalues in the free-field theory. We consider the situation in two and four spacetime dimensions, and we discuss how properties vary as a function of the Wilson-like lifting parameter $r$.

The pion transition form factor $G(q^2)$ is computed on the entire domain of spacelike and timelike momenta using a quantum field theory continuum approach. In an analytical continuation of the function $G(Q^2)$ we utilized the gauge technique with the quark propagator determined from Minkowski space solution of QCD Dyson-Schwinger equations. The scale is set up by the phenomena of dynamical chiral symmetry breaking, which is a striking feature of low energy QCD.