We study the motion of particles in the background of a four-dimensional linear dilaton black hole. We solve analytically the equations of motion of the test particles, and we describe their motion. We show that the dilaton black hole acts as a particle accelerator by analyzing the energy in the center of mass frame of two colliding particles in the vicinity of its horizon. In particular, we find that there is a critical value of the angular momentum, which depends on the string coupling, and a particle with this critical angular momentum can reach the inner horizon with an arbitrarily high c.m. energy. This is known as the Bañados, Silk, and West process. We also show that the motion and collisions of particles have behavior similar to the three-dimensional Bañados-Teitelboim-Zanelli black hole. In fact, the photons can plunge into the horizon or escape to infinity, and they cannot be deflected, while for massive particles there are no confined orbits of the first kind, like planetary or circular orbits.

Is gravity parity violating? Given the recent observations of gravitational waves from coalescing compact binaries, we develop a strategy to find an answer with current and future detectors. We identify the key signatures of parity violation in gravitational waves: amplitude birefringence in their propagation and a modified chirping rate in their generation. We then determine the optimal binaries to test the existence of parity violation in gravity, and prioritize the research in modeling that will be required to carry out such tests before detectors reach their design sensitivity.

We consider the properties and dynamics of black holes within a family of alternative theories of gravity, namely Einstein-Maxwell-dilaton theory. We analyze the dynamical evolution of individual black holes as well as the merger of binary black hole systems. We do this for a wide range of parameter values for the family of Einstein-Maxwell-dilaton theories, investigating, in the process, the stability of these black holes. We examine radiative degrees of freedom, explore the impact of the scalar field on the dynamics of merger, and compare with other scalar-tensor theories. We argue that the dilaton can largely be discounted in understanding merging binary systems and that the end states essentially interpolate between charged and uncharged, rotating black holes. For the relatively small charge values considered here, we conclude that these black hole systems will be difficult to distinguish from their analogs within General Relativity.

We use the Fisher information matrix to investigate the angular resolution and luminosity distance uncertainty for coalescing binary neutron stars (BNSs) and neutron star-black hole binaries (NSBHs) detected by the third-generation (3G) gravitational-wave (GW) detectors. Our study focuses on an individual 3G detector and a network of up to four 3G detectors at different locations including the United States, Europe, China, and Australia for the proposed Einstein Telescope (ET) and Cosmic Explorer (CE) detectors. In particular, we examine the effect of the Earth’s rotation, as GW signals from BNS and low-mass NSBH systems could be hours long for 3G detectors. In this case, an individual detector can be effectively treated as a detector network with long baselines formed by the trajectory of the detector as it rotates with the Earth. Therefore, a single detector or two-detector networks could also be used to localize the GW sources effectively. We find that a time-dependent antenna beam-pattern function can help better localize BNS and NSBH sources, especially edge-on ones. The medium angular resolution for one ET-D detector is around $150{\mathrm{deg}}^2$ for BNSs at a redshift of $z=0.1$, which improves rapidly with a decreasing low-frequency cutoff $f_{\mathrm{low}}$ in sensitivity. The medium angular resolution for a network of two CE detectors in the United States and Europe, respectively, is around $20{\mathrm{deg}}^2$ at $z=0.2$ for the simulated BNS and NSBH samples. While for a network of two ET-D detectors, the similar angular resolution can be achieved at a much higher redshift of $z=0.5$. The angular resolution of a network of three detectors is mainly determined by the baselines between detectors regardless of the CE or ET detector type. The medium angular resolution of BNS for a network of three detectors of the ET-D or CE type in the United States, Europe, and Australia is around $10{\mathrm{deg}}^2$ at $z=2$. We discuss the implications of our results for multimessenger astronomy and, in particular, for using GW sources as independent tools to constrain the Hubble constant $H_0$, the deceleration parameter $q_0$, and the equation-of-state (EoS) of dark energy. We find that, in general, if 10 BNSs or NSBHs at $z=0.1$ with known redshifts are detected by 3G networks consisting of two ET-like detectors, $H_0$ can be measured with an accuracy of 0.9%. If 1000 face-on BNSs at $z<2$ are detected with known redshifts, we are able to achieve $\mathrm{\Delta }{q}_0=0.002$ for the deceleration parameter, or $\mathrm{\Delta }{w}_0=0.03$ and $\mathrm{\Delta }{w}_a=0.2$ for EoS of dark energy, respectively.

We report the effect of the cosmological constant and the internal energy density of a cosmic string on the deflection angle of light in the spacetime of a rotating cosmic string with internal structure. We first revisit the deflection angle by a rotating cosmic string and then provide a generalization using the geodesic equations and the Gauss-Bonnet theorem. We show there is an agreement between the two methods when employing higher-order terms of the linear mass density of the cosmic string. By modifying the integration domain for the global conical topology, we resolve the inconsistency between these two methods previously reported in the literature. We show that the deflection angle is not affected by the rotation of the cosmic string; however, the cosmological constant $\mathrm{\Lambda }$ strongly affects the deflection angle, which generalizes the well-known result.

We numerically study the shadows of a Bonnor black dihole through the technique of backward ray tracing. The presence of a magnetic dipole yields nonintegrable photon motion, which sharply affects the shadow of the compact object. Our results show that there exists a critical value for the shadow. When the magnetic dipole parameter is less than the critical value the shadow is a black disk, but when the magnetic dipole parameter is larger than the critical value the shadow becomes a concave disk with eyebrows possessing a self-similar fractal structure. These behaviors are very similar to those of the equal-mass and nonspinning Majumdar-Papapetrou binary black holes. However, we find that the two larger shadows and the smaller eyebrow-like shadows are joined together by the middle black zone for the Bonnor black dihole, which is different from that in the Majumdar-Papapetrou binary black hole spacetime where they are disconnected. With the increase of the magnetic dipole parameter, the middle black zone connecting the main shadows and the eyebrow-like shadows becomes narrow. Our results show that the spacetime properties arising from the magnetic dipole yield interesting patterns for the shadow cast by a Bonnor black dihole.

Although large-scale perturbations beyond a finite-volume survey region are not direct observables, these affect measurements of clustering statistics of small-scale (subsurvey) perturbations in large-scale structure, compared with the ensemble average, via the mode-coupling effect. In this paper we show that a large-scale tide induced by scalar perturbations causes apparent anisotropic distortions in the redshift-space power spectrum of galaxies in a way depending on an alignment between the tide, wave vector of small-scale modes and line-of-sight direction. Using the perturbation theory of structure formation, we derive a response function of the redshift-space power spectrum to large-scale tide. We then investigate the impact of large-scale tide on estimation of cosmological distances and the redshift-space distortion parameter via the measured redshift-space power spectrum for a hypothetical large-volume survey, based on the Fisher matrix formalism. To do this, we treat the large-scale tide as a signal, rather than an additional source of the statistical errors, and show that a degradation in the parameter is restored if we can employ the prior on the rms amplitude expected for the standard cold dark matter (CDM) model. We also discuss whether the large-scale tide can be constrained at an accuracy better than the CDM prediction, if the effects up to a larger wave number in the nonlinear regime can be included.

Searching for $\gamma$ rays from dwarf spheroidal galaxies (dSphs) is a promising approach to detect dark matter (DM) due to the high DM densities and low baryon components in dSphs. The Fermi-LAT observations from dSphs have set stringent constraints on the velocity independent annihilation cross section. However, the constraints from dSphs may change in velocity dependent annihilation scenarios because of the different velocity dispersions in galaxies. In this work, we study how to set constraints on the velocity dependent annihilation cross section from the combined Fermi-LAT observations of dSphs with the kinematic data. In order to calculate the $\gamma$ ray flux from the dSph, the correlation between the DM density profile and velocity dispersion at each position should be taken into account. We study such correlation and the relevant uncertainty from kinematic observations by performing a Jeans analysis. Using the observational results of three ultrafaint dSphs with large J-factors, including Willman 1, Reticulum II, and Triangulum II, we set constraints on the p-wave annihilation cross section in the Galaxy as an example.

Theories of dark energy and modified gravity can be strongly constrained by astrophysical or cosmological observations, as illustrated by the recent observation of the gravitational wave event GW170817 and of its electromagnetic counterpart GRB 170817A, which showed that the speed of gravitational waves, $c_g$, is the same as the speed of light, within deviations of order ${10}^{-15}$. This observation implies severe restrictions on scalar-tensor theories, in particular theories whose action depends on second derivatives of a scalar field. Working in the very general framework of degenerate higher-order scalar-tensor (DHOST) theories, which encompass Horndeski and beyond Horndeski theories, we present the DHOST theories that satisfy $c_g=c$. We then examine, for these theories, the screening mechanism that suppresses scalar interactions on small scales, namely the Vainshtein mechanism, and compute the corresponding gravitational laws for a nonrelativistic spherical body. We show that it can lead to a deviation from standard gravity inside matter, parametrized by three coefficients which satisfy a consistency relation and can be constrained by present and future astrophysical observations.

We find the general analytical solution of the viscous relativistic hydrodynamic equations (in the absence of bulk viscosity and chemical potential) for a Bjorken expanding fluid with an ideal gas equation of state and a constant shear viscosity relaxation time. We analytically determine the hydrodynamic attractor of this fluid and discuss its properties. We show for the first time that the slow-roll expansion, a commonly used approach to characterize the attractor, diverges. This is shown to hold also in a conformal plasma. The gradient expansion is found to converge in an example where causality and stability are violated.

The perturbative effective potential calculated in Landau gauge suffers from infrared problems due to Goldstone boson loops. These divergences are spurious and can be removed by a resummation procedure that amounts to a shift of the mass of soft Goldstones. We prove this to all loops using an effective theory approach, providing a compact recipe for the shift of the Goldstone mass that relies on the use of the method of regions to split soft and hard Goldstone contributions.

We study three-body systems composed of $D^{(*)}$, $B^{(*)}$, and ${\overline{B}}^{(*)}$ in order to look for possible bound states or resonances. In order to solve the three-body problem, we use the fixed center approach for the Faddeev equations considering that the $B^{*}{\overline{B}}^{*}(B\overline{B})$ are clusterized systems, generated dynamically, which interact with a third particle $D(D^{*})$ whose mass is much smaller than the two-body bound states forming the cluster. In the $D{B}^{*}{\overline{B}}^{*}$, $D^{*}{B}^{*}{\overline{B}}^{*}$, $DB\overline{B}$, and $D^{*}B\overline{B}$ systems with $I=1/2$, we found clear bound state peaks with binding energies typically a few tens MeV and more uncertain broad resonant states about ten MeV above the threshold with widths of a few tens MeV.

Using a quantization of the nonassociative and noncommutative Snyder ${\varphi }^4$ scalar field theory in a Hermitian realization, we present in this article analytical formulas for the momentum-conserving part of the one-loop two-point function of this theory in $D$-, 4-, and 3-dimensional Euclidean spaces, which are exact with respect to the noncommutative deformation parameter $\beta$. We prove that these integrals are regularized by the Snyder deformation. These results indicate that the Snyder deformation does partially regularize the UV divergences of the undeformed theory, as it was proposed decades ago. Furthermore, it is observed that different nonassociative ${\varphi }^4$ products can generate different momentum-conserving integrals. Finally, most importantly, a logarithmic infrared divergence emerges in one of these interaction terms. We then analyze sample momentum nonconserving integral qualitatively and show that it could exhibit IR divergence too. Therefore, infrared divergences should exist, in general, in the Snyder ${\varphi }^4$ theory. We consider infrared divergences at the limit $p\to 0$ as UV/IR mixings induced by nonassociativity, since they are associated to the matching UV divergence in the zero-momentum limit and appear in specific types of nonassociative ${\varphi }^4$ products. We also discuss the extrapolation of the Snyder deformation parameter $\beta$ to negative values as well as certain general properties of one-loop quantum corrections in Snyder ${\varphi }^4$ theory at the zero-momentum limit.

Many grand unified theory (GUT) models conserve the difference between the baryon and lepton number, $B-L$. These models can create baryon and lepton asymmetries from heavy Higgs or gauge boson decays with $B+L\ne 0$ but with $B-L=0$. Since the sphaleron processes violate $B+L$, such GUT-generated asymmetries will finally be washed out completely, making GUT baryogenesis scenarios incapable of reproducing the observed baryon asymmetry of the Universe. In this work, we revisit the idea to revive GUT baryogenesis, proposed by Fukugita and Yanagida, where right-handed neutrinos erase the lepton asymmetry before the sphaleron processes can significantly wash out the original $B+L$ asymmetry, and in this way one can prevent a total washout of the initial baryon asymmetry. By solving the Boltzmann equations numerically for baryon and lepton asymmetries in a simplified $1+1$ flavor scenario, we can confirm the results of the original work. We further generalize the analysis to a more realistic scenario of three active and two right-handed neutrinos to highlight flavor effects of the right-handed neutrinos. Large regions in the parameter space of the Yukawa coupling and the right-handed neutrino mass featuring successful baryogenesis are identified.

Many theories beyond the standard model involve an extra $U(1)$ gauge group. The resulting gauge boson $U$, in general mixed with the $Z$ and the photon, may be massless or very light and very weakly coupled. It may be viewed as a generalized dark photon interacting with matter through a linear combination $[{\epsilon }_{Q}Q+{\epsilon }_{B}B+{\epsilon }_{L}L]e$, involving $B-L$ in a grand-unified theory, presumably through $B-L-.61Q$, inducing effectively a very small repulsive force between neutrons. This new force, if long-ranged, may manifest through apparent violations of the equivalence principle. They are approximately proportional to ${\epsilon }_B+{\epsilon }_L/2$, times a combination involving mostly ${\epsilon }_L$. New forces coupled to $B-L$ or $L$ should lead to nearly opposite values of the Eötvös parameter $\delta$, and to almost the same limits for ${\epsilon }_{B-L}$ or ${\epsilon }_L$, as long as no indication for $\delta \ne 0$ is found. We derive new limits from the first results of the MICROSCOPE experiment testing the equivalence principle in space. A long-range force coupled to $[{\epsilon }_{Q}Q+{\epsilon }_{B-L}(B-L)]e$ or $[{\epsilon }_{Q}Q+{\epsilon }_{L}L]e$ should verify $|{\epsilon }_{B-L}|$ or $|{\epsilon }_L|<.8{10}^{-24}$, and a force coupled to $[{\epsilon }_{Q}Q+{\epsilon }_{B}B]e$, $|{\epsilon }_B|<5{10}^{-24}$. We also discuss, within supersymmetric theories, how such extremely small gauge couplings $g”$, typically $\lesssim {10}^{-24}$, may be related to a correspondingly large $\xi ”D”$ term associated with a huge initial vacuum energy density, $\propto 1/g{”}^2$. The corresponding hierarchy between energy scales, by a factor $\propto 1/\sqrt{g”}\gtrsim {10}^{12}$, involves a very large scale $\sim {10}^{16}\mathrm{GeV}$, that may be associated with inflation, or supersymmetry breaking with a very heavy gravitino, leading to possible values of $\delta$ within the experimentally accessible range.

In this paper, we compute the forward-backward asymmetry and the isospin asymmetry of the $B\to K^{*}{\mu }^{+}{\mu }^{-}$ decay. The $B\to K^{*}$ transition form factors (TFFs) are key components of the decay. To achieve a more accurate QCD prediction, we adopt a chiral correlator for calculating the QCD light cone sum rules for those TFFs with the purpose of suppressing the uncertain high-twist distribution amplitudes. Our predictions show that the asymmetries under the standard model and the minimal supersymmetric standard model with minimal flavor violation are close in shape for $q^2\ge 6{\mathrm{GeV}}^2$ and are consistent with the Belle, LHCb, and CDF data within errors. When $q^2<2{\mathrm{GeV}}^2$, their predictions behave quite differently. Thus, a careful study on the $B\to K^{*}{\mu }^{+}{\mu }^{-}$ decay within the small $q^2$ region could be helpful for searching new physics beyond the standard model. As a further application, we also apply the $B\to K^{*}$ TFFs to the branching ratio and longitudinal polarization fraction of the $B\to K^{*}\nu \overline{\nu }$ decay within different models.

We present the radiative corrections to neutrino masses in a minimal supersymmetric extension of the standard model with local $U(1{)}_{B-L}$ symmetry. At tree level, three tiny active neutrinos and two nearly massless sterile neutrinos can be obtained through the seesaw mechanism. Considering the one-loop corrections to the neutrino masses, the numerical results indicate that two sterile neutrinos obtain KeV masses and the small active-sterile neutrino mixing angles. The lighter sterile neutrino is a very interesting dark matter candidate in cosmology. Meanwhile, the active neutrinos mixing angles and mass squared differences agree with present experimental data.

We revisit the current LHC constraints on the electroweak-ino sector parameters in the minimal supersymmetric standard model (MSSM) that are relevant to explaining the $(g-2{)}_{\mu }$ anomaly via the dominant chargino and muon sneutrino loop. Since the LHC bounds on electroweak-inos become weaker if they decay via an intermediate stau or a tau sneutrino instead of the first two generation sleptons, we perform a detailed analysis of the scenario with a bino as the lightest supersymmetric particle (LSP) and a light stau as the next-to-lightest one (NLSP). Even in this scenario, the chargino sector parameters in the MSSM that can account for the $(g-2{)}_{\mu }$ anomaly within $1\sigma$ are already found to be significantly constrained by the 8 TeV LHC and the available subset of the 13 TeV LHC limits. We also estimate the current LHC exclusions in the left-smuon (and/or left-selectron) NLSP scenario from multilepton searches, and further combine the constraints from the multitau and multilepton channels for a mass spectrum in which all three generations of sleptons are lighter than the chargino. In the latter two cases, small corners of the $1\sigma$ favored region for $(g-2{)}_{\mu }$ are still allowed at present.

We discuss the extension of gauge-invariant electric and magnetic screening masses in the quark-gluon plasma to the case of a finite baryon density, defining them in terms of a matrix of Polyakov loop correlators. We present lattice results for $N_f=2+1$ QCD with physical quark masses, obtained using the imaginary chemical potential approach, which indicate that the screening masses increase as a function of ${\mu }_B$. A separate analysis is carried out for the theoretically interesting case ${\mu }_B/T=3i\pi$, where charge conjugation is not explicitly broken and the usual definition of the screening masses can be used for temperatures below the Roberge-Weiss transition. Finally, we investigate the dependence of the static quark free energy on the baryon chemical potential, showing that it is a decreasing function of ${\mu }_B$, which displays a peculiar behavior as the pseudocritical transition temperature at ${\mu }_B=0$ is approached.