Gravitational waves (GWs) from tens of millions of compact binaries in our Milky Way enter the millihertz band of space-based detection. The majority of them cannot be resolved individually, resulting in foreground confusion noise for the Laser Interferometer Space Antenna (LISA). The concept of the Taiji mission is similar to LISA’s with slightly better sensitivity, which means that Galactic GW signals will also affect detection with Taiji. Here, we generate GW signals from 29.8 million Galactic binaries for Taiji and subtract the “resolvable” sources. The confusion noise is estimated and fitted in an analytic form with 6-month, 1-year, 2-year, and 4-year observation times. We find that the full sensitivity curve is slightly lower for Taiji than for LISA at frequencies of $\le 0.8\mathrm{mHz}$ and around 2 mHz. For a 4-year lifetime, more than 29 thousand sources are resolvable with Taiji. Compared to LISA, Taiji can subtract $\sim 20\%$ more sources, and the distribution of them in our Milky Way is consistent with that of the resolvable sources with LISA. At frequencies around 2 mHz or with the chirp masses ranging from 0.2 to $0.4M_{\odot }$, more sources become resolvable with Taiji.

We consider possible perturbations of the black hole event horizon induced by matter with spin, extending the derivation of the Hawking-Hartle formula (tidal heating) in the presence of torsion. When specialized to theories with a nonvanishing (pseudo-)traceless component of the (con)torsion tensor, we remarkably find that the tidal heating phenomenon gets modified by additional torsion-dependent terms, in agreement with previous investigations based on Jacobson’s spacetime thermodynamics approach. These results lead to relevant phenomenological and theoretical consequences: modifications in the Hawking-Hartle term change the Bondi mass associated with the gravitational radiation observed at infinity, and modify the Hawking radiation spectrum of evaporating black holes.

In this work, we present a new scheme to study the tachyon-dark-energy model using dynamical systems analysis by considering parametrization of the equation of state (EOS) of the dark energy. Both the canonical and phantom field dynamics are investigated. In our method, we do not require any explicit form of the tachyon potential. Instead of the potential, we start with an approximate form of the EOS of the tachyon field. This EOS is phenomenologically motivated and contains some dimensionless parameters. Using our method, we can construct the dynamical system which gives rise to the time evolution of the Universe. We have considered two different parametrizations of the EOS and studied the phase space dynamics in detail. Our analysis shows Taylor series parametrization of the EOS has serious cosmological limitations. We have also provided an example of how this method can be applied to coupled tachyon models with a specific form of interaction. Our proposal is generic in nature and can be applied to other scalar field dark energy models.

Motivated by constraining the neutron star properties and eliminating their uncertainties based on the constraints on nuclear matter parameters extracted from the terrestrial experiments, the correlations between a mount of nuclear matter parameters and neutron star properties have been analyzed by the selected equation of states within the relativistic mean-field theory and used to constrain the neutron star properties. It is found that the radius $R$, tidal deformability $\mathrm{\Lambda }$, and other neutron star properties have a notable correlation with the slope of symmetry energy $L$ for the typical neutron stars, and the $R_{1.4}$ and ${\mathrm{\Lambda }}_{1.4}$ restricted by the constraint on $L=54\pm 8\mathrm{MeV}$ can be consistent with the GW170817 and NICER observation constraints. Furthermore, it is shown that $L$ also has a good correlation with the properties of low-mass neutron stars, such as the gravitational binding energy $|E_g|$. The $|E_g|$ of low-mass neutron stars can be theoretically well constrained with the constraint range of $L$.

One of the most crucial areas of gravity research, after the direct observation of gravitational waves, is the possible modification of general relativity at ultraviolet and infrared scales. In particular, the possibility of parity violation should be considered in strong field regime. The Chern-Simons gravity takes into account parity violation in strong gravity regime. For all conformally flat spacetimes and spacetimes with a maximally symmetric two-dimensional subspace, Chern-Simons gravity is identical to general relativity. Specifically, the (anti–)de Sitter [(A)dS]-Kerr/Kerr black hole is not a solution for Chern-Simons gravity. Slow-rotating black holes up to the quadratic order in spin are some of the known solutions in the framework of dynamical Chern-Simons gravity. In the present study, for the (A)dS slow-rotating situation (correct to the first order in spin), we derive the linear perturbation equations controlling the metric and the dynamical Chern-Simons field equation corrected to the linear order in spin and to the second order in the Chern-Simons coupling parameter. We show that the black hole of the (A)dS-Kerr solution is stronger (i.e., more compact and energetic) than the Kerr black hole solution and the reason for this feature comes form contributions at Planck scales. Moreover, we calculate the thermodynamical quantities related to this black hole. Finally, we calculate the geodesic equation and derive the effective potential of the black hole. We show that as the numerical value of the rotation parameter increases, there is a peak, and as the rotation parameter increases further, the peak becomes positive, preventing the photons from outside to fall into the black hole.

We have witnessed some flavor anomalies appearing in the past years, and explanations based on extended gauge sectors are among the most popular solutions. These beyond the Standard Model (SM) theories often assume flavor-changing interactions mediated by new vector bosons. Still, at the same time, they could yield deviations from the SM in the $K^0-{\overline{K}}^0$, $D^0-{\overline{D}}^0$, $B_d^0-\overline{B}{{}^0}_d$, and $B_s^0-\overline{B}{{}^0}_s$ meson systems. Using up-to-date data on the mass difference of these meson systems, we derive lower mass bounds on vector mediators for two different parametrizations of the quark mixing matrices. Focusing on a well-motivated model based on the fundamental representation of the weak SU(3) gauge group, we put our findings into perspective with current and future hadron colliders to conclude that meson mass systems can give rise to bounds much more stringent than those from high-energy colliders and that recent new physics interpretations of the $b\to s$ and $R(D^{*})$ anomalies are disfavored.

We present a measurement of the momentum spectra of ${\pi }^{\pm }$, ${\mathrm{K}}^{\pm }$, ${\mathrm{p}}^{\pm }$, $\mathrm{\Lambda }$, $\overline{\mathrm{\Lambda }}$, and ${\mathrm{K}}_{\mathrm{S}}^0$ produced in interactions of negatively charged pions with carbon nuclei at beam momenta of 158 and $350\mathrm{GeV}/c$. The total production cross sections are measured as well. The data were collected with the large-acceptance spectrometer of the fixed target experiment NA61/SHINE at the CERN SPS. The obtained double-differential $p\text{−}{p}_{\mathrm{T}}$ spectra provide a unique reference dataset with unprecedented precision and large phase-space coverage to tune models used for the simulation of particle production in extensive air showers in which pions are the most numerous projectiles.

We show that the Proca equation in vacuum, as well as its plausible modifications in dielectric media, is incompatible with experimental evidence, no matter how small the Proca mass is.

We study the semimetal-insulator phase transition in graphene using a Schwinger-Dyson approach. We consider various forms of vertex Ansätze to truncate the hierarchy of Schwinger-Dyson equations. We define a Ball-Chiu-type vertex that truncates the equations without violating gauge invariance. We show that there is a family of these vertices, parametrized by a continuous parameter that we call $a$, all of which satisfy the Ward identity. We have calculated the critical coupling of the phase transition using different values of $a$. We have also tested a common approximation in which only the first term in the Ball-Chiu Ansatz is included. This vertex is independent of $a$, and, although it is not gauge invariant, it has been used many times in the literature because of the numerical simplifications it provides. We have found that, with a one-loop photon polarization tensor, the results obtained for the critical coupling from the truncated vertex and the full vertex with $a=1$ agree very well, but other values of $a$ give significantly different results. We have also done a fully self-consistent calculation, in which the photons are backcoupled to the fermion degrees of freedom, for one choice $a=1$. Our results show that when photon dynamics are correctly taken into account, it is no longer true that the truncated vertex and the full Ball-Chiu vertex with $a=1$ agree well. The conclusion is that traditional vertex truncations do not really make sense in a system that does not respect Lorentz invariance, like graphene, and the need to include vertex contributions self-consistently is likely inescapable.

We summarize the recent progress of the Axion Longitudinal Plasma Haloscope (ALPHA) Consortium, a new experimental collaboration to build a plasma haloscope to search for axions and dark photons. The plasma haloscope is a novel method for the detection of the resonant conversion of light dark matter to photons. ALPHA will be sensitive to QCD axions over almost a decade of parameter space, potentially discovering dark matter and resolving the strong $CP$ problem. Unlike traditional cavity haloscopes, which are generally limited in volume by the Compton wavelength of the dark matter, plasma haloscopes use a wire metamaterial to create a tuneable artificial plasma frequency, decoupling the wavelength of light from the Compton wavelength and allowing for much stronger signals. We develop the theoretical foundations of plasma haloscopes and discuss recent experimental progress. Finally, we outline a baseline design for ALPHA and show that a full-scale experiment could discover QCD axions over almost a decade of parameter space.

In this work, I analyze the structure of the QED spacetime lattice and review the Schwinger pair creation process from a thermodynamic point of view. This viewpoint enables the dynamical mean-field calculation for $3+1$-dimensional Schwinger pair creation with backreaction. As an example, I demonstrate how to evaluate pair creation in a finite volume with external electric fields turned on at $t=0$. The numerical results show how backreaction responds to the external fields and influences pair creation.

We present a careful study of the chiral symmetry breaking minima and the baryonic directions in supersymmetric QCD ($SU(N_c)$ with $N_f$ flavors) perturbed by anomaly mediated supersymmetry breaking (AMSB). For the s-confining case of $N_f=N_c+1$ and most of the free-magnetic phase ($N_f\le 1.43N_c$) we find that naive tree level baryonic runaways are stabilized by loop effects. Runaways are present, however, for the upper end of the free magnetic phase ($N_f\gtrsim 1.43N_c$) and into conformal window, signaling the existence of incalculable minima at large field values of $\mathcal{O}(\mathrm{\Lambda })$. Nevertheless, the chiral symmetry breaking points are locally stable, and are expected to continuously connect to the vacua of QCD for large SUSY breaking. The case of $N_f=N_c$ requires particular care due to the inherently strongly coupled nature of the quantum modified moduli space. Due to the incalculability of critical Kähler potential terms, the stability of the chiral symmetry breaking point along baryonic directions cannot be determined for $N_f=N_c$. With the exception of this case, all theories to which AMSB can be applied ($N_f<3N_c$) possess stable chiral symmetry breaking minima, and all theories with $N_f\lesssim 1.43N_c$ (aside from $N_f=N_c$) are protected from runaways to incalculable minima.

The properties of the $X(3872)$ and its spin partner, the $X(4014)$, are studied both in vacuum and at finite temperature. Using an effective hadron theory based on the hidden-gauge Lagrangian, the $X(3872)$ is dynamically generated from the $s$-wave rescattering of a pair of pseudoscalar and vector charm mesons. By incorporating the thermal spectral functions of open charm mesons, the calculation is extended to finite temperature. Similarly, the properties of the $X(4014)$ are obtained out of the scattering of charm vector mesons. By applying heavy-quark flavor symmetry, the properties of their bottom counterparts in the axial-vector and tensor channels are also predicted. All the dynamically generated states show a decreasing mass and acquire an increasing decay width with temperature, following the trend observed in their meson constituents. These results are relevant in relativistic heavy-ion collisions at high energies, in analyses of the collective medium formed after hadronization, or in femtoscopic studies, and can be tested in lattice-QCD calculations exploring the melting of heavy mesons at finite temperature.

The issue of resulting in the same physical observables with different current components, in particular from the minus current, has been challenging in the light-front quark model (LFQM) even for the computation of the two-point functions such as meson decay constants. At the level of one-body current matrix element computation, we show the uniqueness of pseudoscalar and vector meson decay constants using all available components including the minus component of the current in the LFQM consistent with the Bakamjian-Thomas construction. Regardless of the current components, the polarization vectors, and the reference frames, the meson decay constants are uniquely determined in the noninteracting constituent quark and antiquark basis while the interactions of the constituents are added to the meson mass operator in the LFQM.

We study the $SU(\infty )$ lattice Yang-Mills theory at the dimensions $D=2$, 3, 4 via the numerical bootstrap method. It combines the loop equations, with a cutoff $L_{\max }$ on the maximal length of loops, and positivity conditions on certain matrices of Wilson loop averages. Our algorithm is inspired by the pioneering paper of P. D. Anderson and M. Kruczenski [Nucl. Phys. B921, 702 (2017)] but it is significantly more efficient, as it takes into account the symmetries of the lattice theory and uses the relaxation procedure in line with our previous work on matrix bootstrap. We thus obtain rigorous upper and lower bounds on the plaquette average at various couplings and dimensions. For $D=4,L_{\max }=16$ the lower bound data appear to be close to the Monte Carlo data in the strong coupling phase and the upper bound data in the weak coupling phase reproduce well the 3-loop perturbation theory. Our results suggest that this bootstrap approach can provide a tangible alternative to the, so far uncontested, Monte Carlo approach.

Predictability is grounded by causality while may be practically restricted by the occurrence of chaos. To reveal the relation between these two popular notions, we study chaos in geodesic motion in generic curved spacetimes with external potentials, where causality is controlled by a scalar potential. We develop a reparametrization-independent method to analytically estimate the Lyapunov exponent $\lambda$ of particle motion. We show that causality gives the universal upper bound $\lambda \propto E(E\to \infty )$, which coincides with the chaos energy bound proposed by Murata, Tanahashi, Watanabe, and one of the authors (K. H.). We also find that the chaos bound discovered by Maldacena, Shenker, and Stanford can be violated in particular potentials, even with causality. Our estimates, although waiting for numerical confirmation, reveal the hidden nature of physical theories: causality bounds chaos.

The orbital angular momentum (OAM) of photons has shown the ability to generate high-dimensional entanglement. Here, we examine a novel kind of entanglement degradation caused by the Unruh effect. By paraxially quantizing the light field, we derive the mode functions in both inertial and noninertial reference frames and demonstrate that, from the perspective of an accelerating observer, empty inertial space may seem to be full of OAM particles. They may inundate the high-dimensional entangled OAM photons and cause them to decay. Additionally, we investigate high-dimensional entanglement in the vicinity of a Schwarzschild black hole. Our results suggest that higher-dimensional entanglement will suffer from greater adverse impacts in both instances.

As is well-known, black hole plays an important role in probing the quantum effects of gravity in the strong-field regime. In this paper, we focus on a polymerized black hole and investigate the quantum effects on the redshift, blueshift, and gravitational redshift of photons emitted by massive particles revolving around this black hole. With a general relativistic formalism, we obtain two elegant and concise expressions for the mass of the black hole and the quantum parameter in terms of few direct observables, and find that all the frequency shifts of photons decrease with the quantum parameter. By expanding the total frequency shift for large orbit of the emitter, low peculiar redshift, and small azimuthal angle, we find that the leading contributions to the frequency shift are originated from the kinematic shift and peculiar shift, and the quantum effects make a negligible contribution. In addition, we study the effects of the plasma on the redshift/blueshift for the first time, and conclude that the presence of plasma results in the decrease of the redshift/blueshift.

We introduce an analog model for the conformally coupled scalar field on the BTZ black hole. The model is based on the propagation of acoustic waves in a Laval nozzle. Since the BTZ black hole is not a globally hyperbolic spacetime, the dynamics of the scalar field is not well defined until extra boundary conditions are prescribed at its spatial infinity. We show that quasinormal modes (QNMs) satisfying Dirichlet, Neumann, and Robin boundary conditions in the BTZ black hole can be interpreted in terms of ordinary QNMs defined with respect to an appropriately extended nozzle. We also discuss the stability of our model with respect to small perturbations.

We propose a novel method to measure the $E_G$ statistic from clustering alone. The $E_G$ statistic provides an elegant way of testing the consistency of General Relativity by comparing the geometry of the Universe, probed through gravitational lensing, with the motion of galaxies in that geometry. Current $E_G$ estimators combine galaxy clustering with gravitational lensing, measured either from cosmic shear or from CMB lensing. In this paper, we construct a novel estimator for $E_G$, using only clustering information obtained from two tracers of the large-scale structure: intensity mapping and galaxy clustering. In this estimator, both the velocity of galaxies and gravitational lensing are measured through their impact on clustering. We show that with this estimator, we can suppress the contaminations that affect other $E_G$ estimators and consequently test the validity of General Relativity robustly. We forecast that with the coming generation of surveys like HIRAX and Euclid, we will measure $E_G$ with a precision of up to 7% (3.9% for the more futuristic SKA2).