In this paper we study properties that the vacuum must possess in the minimal extension to the teleparallel equivalent of general relativity (TEGR) where the action is supplemented with a quadratic torsion term. No assumption is made about the weakness of the quadratic term although in the weak-field regime the validity of our previously derived perturbative solution is confirmed. Regarding the exact nature of the vacuum, it is found that if the center of symmetry is to be regular, the mathematical conditions on the tetrad at the isotropy point mimic those of general relativity. With respect to horizons it is found that, under very mild assumptions, a smooth horizon cannot exist unless the quadratic torsion coupling, $\alpha$, vanishes, which is the TEGR limit (with the Schwarzschild tetrad as its solution). This analysis is then supplemented with computational work utilizing asymptotically Schwarzschild boundary data. It is verified that in no case studied does a smooth horizon form. For $\alpha >0$ naked singularities occur which break down the equations of motion before a horizon can form. For $\alpha <0$ there is a limited range of $\alpha$ where a vacuum horizon might exist but, if present, the horizon is singular. Therefore physically acceptable black hole horizons are problematic in the studied theory at least within the realm of vacuum static spherical symmetry. These results also imply that static spherical matter distributions generally must have extra restrictions on their spatial extent and stress-energy bounds so as to render the vacuum solution invalid in the singular region and make the solutions finite.

We search for evidence of primordial chirality violation in the galaxy data from the Sloan Digital Sky Survey by comparing how strongly directions of galaxy angular momenta correlate with left and right helical components of a spin vector field constructed from the initial density perturbations. Within uncertainties, galaxy spins correlate with these two helical components identically, which is consistent with universe without primordial chirality violation. Given current data, it is not yet possible to rule out maximal chiral violation, although the case of vanishing correlation with the right helical component is ruled out at about $3.8\sigma$.

In this work, we propose a new subclass of extreme-mass-ratio-inspirals (EMRIs): mass-gap EMRIs, consisting of a compact object in the lower mass gap $\sim (2.5-5)M_{\odot }$ and a massive black hole (MBH). The mass-gap object (MGO) may be a primordial black hole or produced from a delayed supernova explosion. We calculate the formation rate of mass-gap EMRIs in both the (dry) loss-cone channel and the (wet) active galactic nucleus disk channel by solving Fokker-Planck-type equations for the phase-space distribution. In the dry channel, the mass-gap EMRI rate is strongly suppressed compared to the EMRI rate of stellar-mass black holes (SBHs) as a result of mass segregation effect. In the wet channel, the suppression is roughly equal to the mass ratio of SBHs over MGOs, because the migration speed of a compact object in an active galactic nucleus disk is proportional to its mass. We find that the wet channel is much more promising to produce mass-gap EMRIs observable by spaceborne gravitation wave detectors. (Non)detection of mass-gap EMRIs may be used to distinguish different supernova explosion mechanisms and constrain the abundance of primordial black holes around MBHs.

We study four-dimensional $N=4$ gauged supergravity with $SO(4)\times SO(4)\sim SO(3)\times SO(3)\times SO(3)\times SO(3)$ gauge group in the presence of symplectic deformations. There are in general four electric-magnetic phases corresponding to each $SO(3)$ factor, but two phases of the $SO(3)$ factors embedded in the $SO(6)$ R-symmetry are fixed. One phase can be set to zero by $SL(2,\mathbb{R})$ transformations. The second one gives equivalent theories for any nonvanishing values and can be set to $\frac{\pi }{2}$ resulting in gauged supergravities that admit $N=4$ supersymmetric ${\mathrm{AdS}}_4$ vacua. The remaining two phases are truly deformation parameters leading to different $SO(4)\times SO(4)$ gauged supergravities. As in the $\omega$-deformed $SO(8)$ maximal gauged supergravity, the cosmological constant and scalar masses of the ${\mathrm{AdS}}_4$ vacuum at the origin of the scalar manifold with $SO(4)\times SO(4)$ symmetry do not depend on the electric-magnetic phases. We find $N=1$ holographic RG flow solutions between $N=4$ critical points with $SO(4)\times SO(4)$ and $SO(3{)}_{\mathrm{diag}}\times SO(3)\times SO(3)$ or $SO(3)\times SO(3{)}_{\mathrm{diag}}\times SO(3)$ symmetries. We also give $N=2$ and $N=1$ RG flows from these critical points to various nonconformal phases. However, contrary to the $\omega$-deformed $SO(8)$ gauged supergravity, there exist nontrivial supersymmetric ${\mathrm{AdS}}_4$ critical points only for particular values of the deformation parameters within the scalar sectors under consideration.

I consider three-point functions of twist-two operators in $\mathcal{N}=4$ SYM, two of which endowed with spin. I supply perturbative data up to twelve units of spins and second perturbative order at weak coupling.

Unimodular gravity (UG) is an interesting theory that may explain why the cosmological constant is extremely small, in contrast to general relativity (GR). The theory has only the transverse diffeomorphism invariance and this causes a lot of debate as to the equivalence of UG to GR in the covariant quantization. We study the covariant BRST quantization of UG by gauge fixing only the transverse diffeomorphism and show that the remaining physical degrees of freedom are two, the same number as GR. This is achieved by using antisymmetric tensor ghost fields which automatically satisfy the transverse condition without nonlocal projection operator. The theory exhibits the ghosts for ghosts phenomenon, which requires further gauge fixing and introduction of more ghosts. We identify the BRST quartet structure among the various fields and single out the remaining physical degrees of freedom.

In this work, we have investigated the phenomenon of acceleration radiation exhibited by an atom falling into a quantum corrected Schwarzschild black hole. We observe that the excitation probability of an atom with the simultaneous emission of a photon satisfies the equivalence principle when we compare it to the excitation probability of a mirror accelerating with respect to an atom. We also demonstrate the validity of the equivalence principle for a generic black hole geometry. Then we calculate the horizon brightened acceleration radiation entropy for this quantum corrected black hole geometry. We observe that the horizon brightened acceleration radiation entropy has a form identical to that of Bekenstein-Hawking black hole entropy along with universal quantum gravity corrections.

An additional scalar degree of freedom for a gravitational wave is often predicted in theories of gravity beyond general relativity and can be used for a model-agnostic test of gravity. In this article, we report the direct search for the scalar-tensor mixed polarization modes of gravitational waves from compact binaries in a strong regime of gravity by analyzing the data of GW170814 and GW170817, which are the merger events of binary black holes and binary neutron stars, respectively. Consequently, we obtain the constraints on the ratio of scalar-mode amplitude to tensor-mode amplitude: $\lesssim 0.10$ for GW170814 and $\lesssim 0.034$ for GW170817, which are the tightest constraints on the scalar amplitude in a strong regime of gravity before merger.

Starting from a formulation of correlated worldline (CWL) theory in terms of functional integrals over paths, we define propagators for particles and matter fields in this theory. We show that the most natural formulation of CWL theory involves a rescaling of the generating functional for the theory; correlation functions then simplify, and all loops containing gravitons disappear from perturbative expansions. The spacetime metric obeys the Einstein equation, sourced by all of the interacting CWL paths. The matter paths are correlated by gravitation, thereby violating quantum mechanics for large masses. We derive exact results for the generating functional and the matter propagator, and for linearized weak-field theory. For the example of a two-path experiment, we derive the CWL matter propagator, and show how the results compare with conventional quantum theory and with semiclassical gravity. We also exhibit the structure of low-order perturbation theory for the CWL matter propagator.

Equations of motion of null cosmic strings near black holes, or other massive sources, are solved exactly in the weak-field approximation. The stress-energy tensor of a null string in a curved spacetime is introduced and used to show how scattering by black holes transforms linear and angular momenta of the string. The corresponding recoil effect of a black hole and change of its angular momentum caused by a null cosmic string are calculated. For a null string, its energy $\mu$ per unit length evolves along the null direction of the string trajectory. The evolution of $\mu$ is connected with a string optical scalar $Z$. Optical properties of null strings are that their energy is concentrated on caustics, where $Z$ has poles. String parameters $\mu$ and $Z$ capture important features of the spacetime where strings move. Explicit dependence of $\mu$ and $Z$ on the strain and Bondi news tensors of gravitational wave background, mass and angular momentum aspects are established, near the future-null infinity, up to the fourth order in expansion in an inverse null parameter in asymptotically flat spacetimes.

Intermediate redshifts between galaxy surveys and the cosmic microwave background (CMB) remain unexplored territory. Line intensity mapping (LIM) offers a way to probe the $z\gtrsim 1$ Universe, including the epoch of reionization and the dark ages. Via exact nulling of the lensing kernel, we show that LIM lensing, in combination with galaxy (and, respectively, CMB) lensing, can uniquely probe the $z\gtrsim 1$ (respectively, pre-reionization) Universe. However, LIM foregrounds are a key hurdle to this futuristic technique. While continuum foregrounds can be controlled by discarding modes perpendicular to the line of sight (low-$k_{\parallel }$ modes), interloper foregrounds have not been addressed in the context of LIM lensing. In this paper, we quantify the interloper bias to LIM lensing for the first time and derive a “LIM pair” estimator which avoids it exactly after cross-correlating with CMB lensing. This new quadratic lensing estimator works by combining two intensity maps in different lines, from the same redshift, whose interlopers are uncorrelated. As a result, this foreground avoidance method is robust to even large changes in the amplitude of the interloper power and non-Gaussianity. The cross spectrum of the LIM-pair estimator with CMB lensing is thus robust to the currently large theoretical uncertainties in LIM modeling at high redshift.

Short gamma-ray bursts are believed to be produced by both binary neutron star (BNS) and neutron star-black hole (NSBH) mergers. We use current estimates for the BNS and NSBH merger rates to calculate the fraction of observable short gamma-ray bursts produced through each channel. This allows us to constrain merger rates of a BNS to ${\mathcal{R}}_{\mathrm{BNS}}=384_{-213}^{+431}{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$ (90% credible interval), a 16% decrease in the rate uncertainties from the second Laser Interferometer Gravitational Wave Observatory (LIGO)-Virgo Gravitational-Wave Transient Catalog. Assuming a top-hat emission profile with a large Lorentz factor, we constrain the average opening angle of gamma-ray burst jets produced in BNS mergers to $\approx 15°$. We also measure the fraction of BNS and NSBH mergers that produce an observable short gamma-ray burst to be ${0.02}_{-0.01}^{+0.02}$ and $0.01\pm 0.01$, respectively, and find that $\gtrsim 40\%$ of BNS mergers launch jets (90% confidence). We forecast constraints for future gravitational-wave detections given different modeling assumptions, including the possibility that BNS and NSBH jets are different. With 24 BNS and 55 NSBH observations, expected within six months of the LIGO-Virgo-Kamioka Gravitational Wave Detector network operating at design sensitivity, it will be possible to constrain the fraction of BNS and NSBH mergers that launch jets with 10% precision. Within a year of observations, we can determine whether the jets launched in NSBH mergers have a different structure than those launched in BNS mergers and rule out whether $\gtrsim 80\%$ of binary neutron star mergers launch jets. We discuss the implications of future constraints on understanding the physics of short gamma-ray bursts and binary evolution.

Recently, a tight correlation between the dynamical radial acceleration and the baryonic radial acceleration in galaxies—the radial acceleration relation—has been discovered. This has been claimed as an indirect support of the modified gravity theories. However, whether the radial acceleration relation could also be found in galaxy clusters is controversial. In this article, we derive and present an analytic radial acceleration relation for the central region of galaxy clusters. We examine the data of some large galaxy clusters and we find that the resulting radial acceleration relation has a very large scatter. Moreover, although the radial acceleration relation for galaxy clusters shows some agreement with the one discovered in galaxies for a certain range of baryonic radial acceleration, their functional forms are somewhat different from each other. This suggests that the radial acceleration relation may not be a universal relation in general.

Black hole (BH) shadows can be used to probe new physics in the form of ultralight particles via the phenomenon of superradiant instability. By directly affecting the BH mass and spin, superradiance can lead to a time evolution of the BH shadow, which nonetheless has been argued to be unobservable through very-long-baseline interferometry (VLBI) over realistic observation time scales. We revisit the superradiance-induced BH shadow evolution including the competing effects of gas accretion and gravitational wave (GW) emission and, as a first step towards modeling realistic new physics scenarios which predict the existence of multiple ultralight species, we study the system in the presence of two ultralight bosons, whose combined effect could help reduce the shadow evolution time scale. We find that accretion and GW emission play a negligible role in our results (justifying previous simplified analyses), and that contrary to our intuition the inclusion of an additional ultralight boson does not shorten the BH shadow evolution time scale and hence improve detection prospects. However, we point out an important subtlety concerning the observationally meaningful definition of the superradiance-induced BH shadow evolution time scale, which reduces the latter by about an order of magnitude, opening up the possibility of observing the superradiance-induced BH shadow evolution with upcoming VLBI arrays, provided angular resolutions just below the $\mu \mathrm{as}$ level can be reached. As a concrete example, we show that the angular size of the shadow of ${\mathrm{SgrA}}^{*}$ can change by up to $0.6\mu \mathrm{as}$ over a period as short as 16 years, which further strengthens the scientific case for targeting the shadow of ${\mathrm{SgrA}}^{*}$ with next-generation VLBI arrays.

In this paper, we present a detailed derivation of relativistic first-order spin hydrodynamics using the Chapman-Enskog method to linearize the nonlocal collision term for massive fermions proposed in Weickgenannt et al. [Phys. Rev. D 104, 016022 (2021)], which well describes spin-orbit coupling in the collision process and is relevant for the research on local spin polarization. Based on this collisional term, we provide a formal discussion about first-order spin hydrodynamics and determine the motion equations of fluid variables and nonequilibrium corrections to the energy-momentum and spin tensors. The results indicate that the motion equations show no differences compared to spinless first-order hydrodynamics and the energy-momentum tensor receives no corrections from spin as far as first-order theory is concerned, which calls for the construction of second-order theory of fluids naturally incorporating the effect of spin-orbit coupling.

Recently, the Belle Collaboration reported the first measurements of the ${\tau }^{-}\to {\nu }_{\tau }{\pi }^{-}{e}^{+}{e}^{-}$ branching fraction and the spectrum of the pion-dielectron system. In an analysis previous to Belle’s results, we evaluated this branching fraction which turned out to be compatible with that reported by Belle, although with a large uncertainty. This is the motivation to seek for improvement on our previous evaluation of ${\tau }^{-}\to {\nu }_{\tau }{\pi }^{-}{\ell }^{+}{\ell }^{-}$ decays ($\ell =e$, $\mu$). In this paper we improve our calculation of the $W{P}^{-}{\gamma }^{*}$ vertex by including flavor-symmetry breaking effects in the framework of the resonance chiral theory. We impose QCD short-distance behavior to constrain most parameters and data on the ${\pi }^{-}{e}^{+}{e}^{-}$ spectrum reported by the Belle Collaboration to fix the remaining free ones. As a result, improved predictions for the branching ratios and hadronic/leptonic spectra are reported, which are in good agreement with observations. Analogous calculations for the strangeness-changing ${\tau }^{-}\to {\nu }_{\tau }{K}^{-}{\ell }^{+}{\ell }^{-}$ transitions are reported for the first time. Albeit one expects the $m_{\pi {\mu }^{+}{\mu }^{-}}$ spectrum to be measured in Belle-II and the observables with $\ell =e$ can be improved, it is rather unlikely that the $K$ channels can be measured due to the suppression factor $|V_{ud}/V_{us}{|}^2=0.05$.

If dark matter has a finite size, the intrinsic interaction responsible for the structure formation is inevitable from the perspective of dark matter self-scattering. To describe the circumstance in which the binding force realizes the finite size dark protons, we first use the eikonal approximation to simplify the convoluted scattering between dark protons into the case at the $t=0$ limit. The Chou-Yang model is then introduced to reduce the number of input parameters to one based on the simplicity and analyticity principle. A new definition of velocity dependence and the corresponding implications on the small cosmological structures from Chou-Yang dark protons are shown clearly. Even though the parameter space is not fully covered, the numerical findings show that the amplitude coefficient can alter the self-scattering cross section, allowing us to recover the excluded parameter space without using binding force. Finally, we demonstrate that the correct relic density from thermal freeze-out production prefers super heavy dark protons.

We revisit a theory that proposes a dark charge, $D$, as a dequantization of the electric charge, $Q$. We find that the general arguments of anomaly cancellation and fermion mass generation yield both $D$ and $Q$, nontrivially unified with the weak isospin $T_i$ $(i=1,2,3)$ in a novel gauge symmetry, $SU(3{)}_C\otimes SU(2{)}_L\otimes U(1{)}_Y\otimes U(1{)}_N$, where $Y$ and $N$ determine $Q$ and $D$ through the $T_3$ operator, i.e., $Q=T_3+Y$ and $D=T_3+N$, respectively. A new observation is that fundamental particles possess a dynamical dark charge, which governs both neutrino mass and dark matter, where the neutrino mass is determined via a canonical seesaw, while the dark matter stability is ensured by electric and color charge conservations. We examine the mass spectra of fermions, scalars, and gauge bosons, as well as their interactions, taking into account the kinetic mixing effect of $U(1{)}_{Y,N}$ gauge fields. The new physics phenomena at colliders are examined. The dark matter relic density and detection are discussed.

The radion equilibrium in the Randall-Sundrum (RS) model is guaranteed by the backreaction of a bulk scalar field. In this paper we study an extended scenario, where an intermediate brane exists in addition to the two branes at the fixed points, due to the discontinuity of bulk cosmology constants in two spatial regions. We conducted a complete analysis of the linearized Einstein’s equations after applying the Goldberger-Wise mechanism. Our result elucidates that in the presence of nonfixed point branes under the rigid assumption, a unique radion field is conjectured as legitimate in the RS metric perturbation. The cosmological expansion in this setup is briefly discussed.

There is a well-established connection between the higher-derivative corrections to the black hole entropy and the black hole extremality bound. The particular combination of effective field theory (EFT) coefficients $c_i$ that controls the mass shift at fixed charge and temperature also controls the entropy shift at fixed charge and mass, in the limit where the mass approaches the uncorrected value for the extremal mass. In this paper, we use the classical entropy function formalism to examine the entropy corrections at exactly zero temperature, or at the corrected value for the extremal mass. We find that the zero-temperature entropy shift (a) is unrelated to the mass shift, (b) is $\mathcal{O}(c_i)$ in the EFT coefficients, rather than $\mathcal{O}(\sqrt{c_i})$, as is the constant-mass entropy shift, and (c) is negative in the example of the EFT arising at low energies from QED plus gravity.