Recently, it has been shown that the radial stability of a light ring (LR) in a spacetime generated by a stationary, axisymmetric, asymptotically flat object with a ${\mathbb{Z}}_2$ symmetry determines the possibility and radial stability of timelike circular orbits (TCOs) around the LR. In this paper, we generalize this result by also considering the vertical (angular) stability of the orbits through the study of the radial and vertical epicyclic frequencies. We show that the vertical stability of the LR only determines the vertical stability of the TCOs around it. A relation between the sum of the squared epicyclic frequencies and the Ricci tensor is also provided. With such relation, we show that objects with radially and vertically unstable LRs (TCOs) violate the null (strong) energy condition.

In general relativity, it is difficult to localize observables such as energy, angular momentum, or center of mass in a bounded region. The difficulty is that there is dissipation. A self-gravitating system, confined by its own gravity to a bounded region, radiates some of the charges away into the environment. At a formal level, dissipation implies that some diffeomorphisms are not Hamiltonian. In fact, there is no Hamiltonian on phase space that would move the region relative to the fields. Recently, an extension of the covariant phase space has been introduced to resolve the issue. On the extended phase space, the Komar charges are Hamiltonian. They are generators of dressed diffeomorphisms. While the construction is sound, the physical significance is unclear. We provide a critical review before developing a geometric approach that takes into account dissipation in a novel way. Our approach is based on metriplectic geometry, a framework used in the description of dissipative systems. Instead of the Poisson bracket, we introduce a Leibniz bracket—a sum of a skew-symmetric and a symmetric bracket. The symmetric term accounts for the loss of charge due to radiation. On the metriplectic space, the charges are Hamiltonian, yet they are not conserved under their own flow.

The excitation of $f$-mode in a neutron star member of coalescing binaries accelerates the merger course, and thereby introduces a phase shift in the gravitational waveform. Emphasizing the tidal phase shift by aligned, rotating stars, we provide an accurate, yet economical, method to generate $f$-mode-involved, premerger waveforms using realistic spin-modulated $f$-mode frequencies for some viable equations of state. We find for slow-rotating stars that the dephasing effects of the dynamical tides can be uniquely, equation-of-state-independently determined by the direct observables (chirp mass $\mathcal{M}$, symmetric ratio $\eta$, and the mutual tidal deformability $\tilde{\mathrm{\Lambda }}$), while this universality is gradually lost for increasing spin. For binaries with fast rotating members ($\gtrsim 800\mathrm{Hz}$) the phase shift due to the $f$-mode will exceed the uncertainty in the waveform phase at reasonable signal-to-noise ratio ($\rho =25$) and cutoff frequency of $\gtrsim 400\mathrm{Hz}$. Assuming a high cutoff frequency of ${10}^3\mathrm{Hz}$ and fast ($\gtrsim 800\mathrm{Hz}$) members, a significant phase shift of $\gtrsim 100$ rads has been found. For systems involving a rapidly spinning star (potentially the secondary of GW190814), neglecting the $f$-mode effect in the waveform templates can therefore lead to considerable systemic errors in the relevant analysis. In particular, the dephasing due to $f$-mode is larger than that caused by equilibrium tides by a factor of $\sim 5$, which may lead to a considerably overestimated tidal deformability if dynamical tidal contribution is not accounted. The possibility of accompanying precursors flares due to $f$-mode excitation is also discussed.

According to the Belinski-Khalatnikov-Lifshitz conjecture, close to a spacelike singularity different spatial points decouple, and the dynamics can be described in terms of the mixmaster (vacuum Bianchi IX) model. In order to understand the role played by quantum-gravity effects in this context, in the present work we consider the semiclassical behavior of this model. Classically, this system undergoes a series of transitions between Kasner epochs, which are described by a specific transition law. This law is derived based on the conservation of certain physical quantities and the rotational symmetry of the system. In a quantum scenario, however, fluctuations and higher-order moments modify these quantities, and consequently also the transition rule. In particular, we perform a canonical quantization of the model and then analytically obtain the modifications of this transition law for semiclassical states peaked around classical trajectories. The transition rules for the quantum moments are also obtained, and a number of interesting properties are derived concerning the coupling between the different degrees of freedom. More importantly, we show that, due to the presence of quantum-gravity effects and contrary to the classical model, there appear certain finite ranges of the Kasner parameters for which the system will not undergo further transitions and will follow a Kasner regime until the singularity. Even if a more detailed analysis is still needed, this feature points toward a possible resolution of the classical chaotic behavior of the model. Finally, a numerical integration of the equations of motion is also performed in order to verify the obtained analytical results.

Recently, as a generalization of general relativity, a gravity theory has been proposed in which gravitational field equations are described by the Cotton tensor. That theory allows an additional contribution to the gravitational potential of a point mass that rises linearly with radius as $\mathrm{\Phi }=-GM/r+\gamma r/2$, where $G$ is the Newton constant. The coefficients $M$ and $\gamma$ are the constants of integration and should be determined individually for each physical system. When applied to galaxies, the coefficient $\gamma$, which has the dimension of acceleration, should be determined for each galaxy. This is the same as having to determine the mass $M$ for each galaxy. If $\gamma$ is small enough, the linear potential term is negligible at short distances, but can become significant at large distances. In fact, it may contribute to the extragalactic systems. In this paper, we derive the effective field equation for Cotton gravity applicable to extragalactic systems. We then use the effective field equation to numerically compute the gravitational potential of a sample of 84 rotating galaxies. The 84 galaxies span a wide range, from stellar disk-dominated spirals to gas-dominated dwarf galaxies. We do not assume the radial density profile of the stellar disk, bulge, or gas; we use only the observed data. We find that the rotation curves of 84 galaxies can be explained by the observed distribution of baryons. This is due to the flexibility of Cotton gravity to allow the integration constant $\gamma$ for each galaxy. In the context of Cotton gravity, “dark matter” is in some sense automatically included as a curvature of spacetime. Consequently, even galaxies that have been assumed to be dominated by dark matter do not need dark matter.

The gravitationally enhanced friction can reduce the speed of the inflaton to realize an ultraslow-roll inflation, which will amplify the curvature perturbations. The amplified perturbations can generate a sizable amount of primordial black holes (PBHs) and induce simultaneously a significant background gravitational waves (SIGWs). In this paper, we investigate the primordial non-Gaussianity of the curvature perturbations in the inflation with gravitationally enhanced friction. We find that when the gravitationally enhanced friction plays a role in the inflationary dynamics, the non-Gaussianity is noticeably larger than that from the standard slow-roll inflation. During the regime in which the power spectrum of the curvature perturbations is around its peak, the non-Gaussianity parameter changes from negative to positive. When the power spectrum is at its maximum, the non-Gaussianity parameter is near zero [$\sim \mathcal{O}(0.01)$]. Furthermore, the primordial non-Gaussianity promotes the formation of PBHs, while its effect on SIGWs is negligible.

To combine information from measurements of the redshift-space power spectrum from spectroscopic data with angular weak lensing, galaxy clustering, and galaxy-galaxy lensing power spectra from photometric surveys (i.e., the $3\times 2$ point statistics), we must account for the covariance between the two probes. Currently any covariance between the two types of measurements is neglected as existing photometric and spectroscopic surveys largely probe different cosmological volumes. This will cease to be the case as data arrive from Stage-IV surveys. In this paper we derive an analytic expression for the covariance between photometric two-dimensional angular power spectra and the three-dimensional redshift-space power spectrum for Gaussian fields under the plane-parallel approximation. We find that the two probes are covariant on large radial scales, but because this covariance only appears over a small fraction of the total Fourier space coverage of the two types of probes, we forecast that it is safe to neglect this covariance when performing cosmological parameter inference.

Primordial black holes (PBHs) provide an exciting prospect for accounting for dark matter. In this paper, we consider inflationary models that incorporate realistic features from high-energy physics—including multiple interacting scalar fields and nonminimal couplings to the spacetime Ricci scalar—that could produce PBHs with masses in the range required to address the present-day dark matter abundance. Such models are consistent with supersymmetric constructions, and only incorporate operators in the effective action that would be expected from generic effective field theory considerations. The models feature potentials with smooth large-field plateaus together with small-field features that can induce a brief phase of ultraslow-roll evolution. Inflationary dynamics within this family of models yield predictions for observables in close agreement with recent measurements, such as the spectral index of primordial curvature perturbations and the ratio of power spectra for tensor to scalar perturbations. As in previous studies of PBH formation resulting from a period of ultraslow-roll inflation, we find that at least one dimensionless parameter must be highly fine-tuned to produce PBHs in the relevant mass range for dark matter. Nonetheless, we find that the models described here yield accurate predictions for a significant number of observable quantities using a smaller number of relevant free parameters.

More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles (FCPs) still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the Dark Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2\times {10}^{-10}{\mathrm{cm}}^{-2}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays.

An important goal of the Laser Interferometer Space Antenna (LISA) is to observe a stochastic gravitational-wave background (SGWB). A study of possible correlated noise in LISA is relevant to establish limits for this future measurement. To test noise investigation methods under somewhat realistic conditions, we use the data of LISA Pathfinder. We calculate the coherence between the LISA Pathfinder differential acceleration of the two test masses with magnetic fields, temperature, and micronewton cold gas thruster activity in the spacecraft. We apply our observed correlations to LISA, and estimate how the presence of such correlated noise would affect its search for a SGWB. In the context of a figure of merit, we estimate the effect of noise on the LISA SGWB search.

The possible signatures of the presence of hyperons inside neutron stars are discussed within a Bayesian inference framework applied to a set of models based on a density dependent relativistic mean field description of hadronic matter. Nuclear matter properties, hypernuclei properties and observational information are used to constraint the models. General properties of neutron stars such as the maximum mass, radius, tidal deformability, proton fraction, hyperon fraction and speed of sound are discussed. It is shown that the two solar mass constraint imposes that neutron stars described by equations of state that include hyperons have in average a larger radius, $\gtrsim 0.5\mathrm{km}$, and a larger tidal deformability, $\gtrsim 150$, than the stars determined from a nucleonic equation of state, while the speed of sound at the center of the star is more than 25% smaller. If a $1.4{\mathrm{M}}_{\odot }$ star with a radius $\lesssim 12.5\mathrm{km}$ is measured it is quite improbable that a massive star described by the same model contains hyperons. A similar conclusion is drawn if a two solar mass star with a radius $\lesssim 11.5\mathrm{km}$ or a neutron star with a mass above $2.2{\mathrm{M}}_{\odot }$ is observed: the possible hyperon content of these stars is ruled out or very reduced. The hyperon presence inside neutron stars is compatible with the present NICER mass-radius observations of the pulsars PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$ and the gravitational wave detection GW170817. It is shown that if the polytropic index $\gamma =\partial \ln p/\partial \ln \epsilon$ takes values of the order of 1.75 at not too large densities, it may indicate the onset of some kind of exotic matter, but not necessarily of deconfined quark matter.

The EDELWEISS collaboration reports on the search for dark matter particle interactions via Migdal effect with masses between $32\mathrm{MeV}·{\mathrm{c}}^{-2}$ to $2\mathrm{GeV}·{\mathrm{c}}^{-2}$ using a 200 g cryogenic Ge detector sensitive to simultaneously heat and ionization signals and operated underground at the Laboratoire Souterrain de Modane in France. The phonon signal was read out using a transition edge sensor made of a NbSi thin film. The detector was biased at 66 V in order to benefit from the Neganov-Trofimov-Luke amplification and resulting in a resolution on the energy of electron recoils of $4.46{\mathrm{eV}}_{ee}$ (102.58 eV at 66 V) and an analysis threshold of $30{\mathrm{eV}}_{ee}$. The sensitivity is limited by a dominant background not associated to charge creation in the detector. The search constrains a new region of parameter space for cross sections down to ${10}^{-29}{\mathrm{cm}}^2$ and masses between 32 and $100\mathrm{MeV}·{\mathrm{c}}^{-2}$. The achieved low threshold with the NbSi sensor shows the relevance of its use for out-of-equilibrium phonon sensitive devices for low-mass dark matter searches.

The $U(1)$ extension of the supersymmetric standard model is the extension of the minimal supersymmetric standard model, and its local gauge group is $SU(3{)}_C\times SU(2{)}_L\times U(1{)}_Y\times U(1{)}_X$. We study lepton flavor violating (LFV) decays $Z\to {l_i}^{\pm }{l_j}^{\mp }$ ($Z\to e\mu$, $Z\to e\tau$, and $Z\to \mu \tau$) and $h\to {l_i}^{\pm }{l_j}^{\mp }$ ($h\to e\mu$, $h\to e\tau$, and $h\to \mu \tau$) in this model. In the numerical results, the branching ratios of $Z\to {l_i}^{\pm }{l_j}^{\mp }$ are from ${10}^{-9}$ to ${10}^{-13}$, and the branching ratios of $h\to {l_i}^{\pm }{l_j}^{\mp }$ are from ${10}^{-3}$ to ${10}^{-9}$, which can approach the present experimental upper bounds. Based on the latest experimental data, we analyze the influence of different sensitive parameters on the branching ratio and make reasonable predictions for future experiments. The main sensitive parameters and LFV sources are the nondiagonal elements corresponding to the initial and final generations of leptons, which can be seen from the numerical analysis.

Light sub-GeV dark matter (DM) particles in the Milky Way or macroscopic objects such as primordial black holes (PBHs) become attractive DM candidates due to null results of the weakly interacting massive particle from direct detection experiments. We explore the possibility in which the present PBHs play as a novel source to produce light boosted DM and confine light PBHs with current and future terrestrial facilities. We study the electron elastic scattering data and obtain the current constraints from Super-Kamiokande and XENON1T on the boosted DM from PBH evaporation. The prospective bounds on the sub-GeV DM-electron scattering cross section and the fraction of DM composed of PBHs $f_{\mathrm{PBH}}$ are also imposed for future Xenon experiments.

Two-body open charm strong decays of the $2P$ and $3P$ charmonium states are studied by the Bethe-Salpeter method combined with the ${}^3{P}_0$ model. The wave functions and mass spectra of the $2P$ and $3P$ charmonium states are obtained by solving the Bethe-Salpeter equation with the relativistic correction. The strong decay widths and relative ratios of the $2P$ and $3P$ charmonium states are calculated. Comparing our results with the experimental data, we obtain some interesting results. Considering the $X^{*}(3860)$ as the ${\chi }_{c0}(2P)$, the total strong decay width is smaller than the experimental data. But the strong decay width depends on the parameter $\gamma$ in the ${}^3{P}_0$ model, and the mass and width of the $X^{*}(3860)$ have large errors, we cannot rule out the possibility that the $X^{*}(3860)$ is the ${\chi }_{c0}(2P)$. The $X(4160)$ is a good candidate for the ${\chi }_{c0}(3P)$, not only the strong decay width of the ${\chi }_{c0}(3P)$ is same as the experimental data, but the relative ratios $\frac{\mathrm{\Gamma }({\chi }_{c0}(3P)\to D\overline{D})}{\mathrm{\Gamma }({\chi }_{c0}(3P)\to D^{*}{\overline{D}}^{*})}\approx 0.0019<0.09$, and $\frac{\mathrm{\Gamma }({\chi }_{c0}(3P)\to D{\overline{D}}^{*})}{\mathrm{\Gamma }({\chi }_{c0}(3P)\to D^{*}{\overline{D}}^{*})}=0<0.22$ are consistent with the experimental results of the $X(4160)$. Taking the $X(4274)$ as the ${\chi }_{c1}(3P)$, the strong decay width is consistent with the experimental data, so the $X(4274)$ is a good candidate for the ${\chi }_{c1}(3P)$. Assigning the $X(4350)$ as the ${\chi }_{c2}(3P)$, the corresponding strong decay width is slightly larger than the experimental data. To identify if the $X(4350)$ is ${\chi }_{c2}(3P)$, many more investigations are needed. All of the strong decay widths and relative ratios of the $2P$ and $3P$ charmonium states can provide the useful information to discover and confirm these particles in the future.

We study a large-$p_T$ three-photon production in the proton-proton collisions at the LHC. We use the leading order (LO) approximation of the parton Reggeization approach consistently merged with the next-to-leading order corrections originating from the emission of the additional jet. For numerical calculations, we apply the parton-level generator KaTie and the modified Kimder-Martin-Ryskin-type unintegrated parton distribution functions, which satisfy the exact normalization conditions for arbitrary $x$. We compare our prediction with data from the ATLAS collaboration at the center-of-mass energy $\sqrt{s}=8\mathrm{TeV}$. We find that the inclusion of the real next-to-leading-order corrections leads to a good agreement between our predictions and data with the same accuracy as for the next-to-next-to-leading calculations based on the collinear parton model of QCD. At higher energies ($\sqrt{s}=13$ and 27 TeV) the parton Reggeization approach predicts larger cross sections, up to $\sim 15\%$ and $\sim 30\%$, respectively.

We calculate the one-loop corrections to dihadron production in deep inelastic scattering (DIS) at small $x$ using the color glass condensate formalism. We show that all UV and soft singularities cancel while the collinear divergences are absorbed into quark and antiquark-hadron fragmentation functions. Rapidity divergences lead to Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov and Kovner evolution of dipoles and quadrupoles describing multiple scatterings of the quark antiquark dipole on the target proton/nucleus. The resulting cross section is finite and can be used for phenomenological studies of dihadron angular correlations at small $x$ in a future Electron-Ion Collider.

We construct the spectral functions for light vector mesons at finite density and temperature in the presence of a novel mixing between parity partners, induced by baryon density via the Wess-Zumino-Witten action. As the main origin of in-medium broadening, a set of baryon resonances that strongly couple to the vector mesons and the modifications of kaons and antikaons due to the Kaplan-Nelson term are included. It is shown that the vector spectra, even with the broadening effects, exhibit sizable signatures of chiral symmetry restoration thanks to the chiral mixing depending on three-momenta carried by the vector mesons. Those spectral functions are used to calculate the integrated production rates of lepton pairs, and a proper binning in momenta and potential decrease in the vector-meson masses due to chiral symmetry restoration are discussed in quantifying the signatures.

Using data samples collected with the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{D}^{+}{D}^{-}$ process at center-of-mass energies from 4.190 to 4.946 GeV with a partial reconstruction method. Resonance structures are seen and the cross section line shape can be described by the coherent sum of either two Breit-Wigner functions or a Breit-Wigner function and a phase space term. The mass and width of the resonance at about 4.4 GeV are determined to be $(4371.6\pm 2.5\pm 9.2)\mathrm{MeV}/c^2$ and $(167\pm 4\pm 29)\mathrm{MeV}$, respectively, which are in agreement with those of the $\psi (4360)$ or $Y(4390)$ state. The spin-$3D$-wave charmonium state $X(3842)$ is searched for through the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}X(3842)\to {\pi }^{+}{\pi }^{-}{D}^{+}{D}^{-}$ process, and evidence with a significance of $4.2\sigma$ is found in the data samples with center-of-mass energies from 4.6 to 4.7 GeV.

The detection of collider neutrinos will provide new insights about neutrino production, propagation, and interactions at TeV energies, the highest human-made energies ever observed. During run 3 of the LHC, the FASER experiment is expected to detect roughly ${10}^4$ collider neutrinos using its emulsion-based neutrino detector $\mathrm{FASER}\nu$. In this study, we show that, even without processing the emulsion data, low-level input provided by the electronic detector components of FASER and $\mathrm{FASER}\nu$ will be able to establish a $5\sigma$ discovery of collider neutrinos with as little as $5{\mathrm{fb}}^{-1}$ of integrated luminosity. These results foreshadow the possible early discovery of collider neutrinos in LHC run 3.