We describe a procedure for alleviating the fermion sign problem in which phase fluctuations are explicitly subtracted from the Boltzmann factor. Several ansätze for fluctuations are designed and compared. In the absence of a sufficiently high-quality ansatz, a neural network can be trained to parametrize the fluctuations. Demonstrating on the staggered Thirring model in $1+1$ dimensions, we examine the performance of this method as deeper neural networks are used, and in conjunction with the well-studied contour deformation methods.

We use lattice simulations and the continuous renormalization-group method, based on the gradient flow, to study a candidate theory of composite Higgs and a partially composite top. The model is an SU(4) gauge theory with four Dirac fermions in each of the fundamental and two-index antisymmetric representations. We find that the theory has an infrared fixed point at $g^2\simeq 15.5$ in the gradient flow scheme. The mass anomalous dimension of each representation is large at the fixed point. On the other hand, the anomalous dimensions of top-partner operators do not exceed 0.5 at the fixed point. This may not be large enough for a phenomenologically successful model of partial compositeness.

The recently developed resummation technique known as renormalization group optimized perturbation theory (RGOPT) is employed in the evaluation of the equation of state (EOS) describing nonstrange cold quark matter at next-to leading order. Inspired by recent investigations, which suggest that stable quark matter can be made only of up and down quarks, the mass-radius relation for two flavor pure quark stars is evaluated and compared with the predictions from perturbative QCD (pQCD) at next-to-next-to leading order. This comparison explicitly shows that by being imbued with renormalization group properties, and a variational optimization procedure, the method allows for an efficient resummation of the perturbative series. Remarkably, when the renormalization scale is chosen so as to reproduce maximum mass stars with $\mathrm{M}=2-2.3M_{\odot }$, one obtains a mass-radius curve compatible with the masses and radii of the pulsars PSR $\mathrm{J}0740+6620$, PSR $\mathrm{J}0030+0451$, and the compact object HESS J1731-347. Moreover, the scale dependence of the EOS (and mass-radius relation) obtained with the RGOPT is greatly improved when compared to that of pQCD. This seminal application to the description of quark stars shows that the RGOPT represents a robust alternative to pQCD when describing compressed quark matter.

We carry out the calculation of kinematical higher-twist corrections to the cross section of ${\gamma }^{*}\to M_1{M}_2\gamma$ up to twist 4, where $M_i$ is a scalar or pseudoscalar neutral meson. The three independent helicity amplitudes are presented in terms of the twist-2 generalized distribution amplitudes (GDAs), which are important nonperturbative quantities for understanding the 3D structure of hadrons. Since this process can be measured by BESIII in $e^{+}{e}^{-}$ collisions, we perform the numerical estimate of the kinematical higher-twist corrections by using the kinematics of BESIII. We adopt the $\pi \pi$ GDA extracted from Belle measurements and the asymptotic $\pi \pi$ GDA to study the size of the kinematical corrections in the case of pion meson pair, and a model $\eta \eta$ GDA is used to see the impact of target mass corrections $\mathcal{O}(m^2/s)$ for ${\gamma }^{*}\to \eta \eta \gamma$. Our results show that the kinematical higher-twist corrections account for $\sim 20\%$ of the cross sections at BESIII on the average, and it is necessary to include them if one tries to extract GDAs from experimental measurements precisely. We also comment the case of ${\pi }^0\eta$ production which is important for the search of hybrid mesons.

Using the coalescence model we compute the multiplicity of $Z_{cs}(3985{)}^{-}$ (treated as a compact tetraquark) at the end of the quark gluon plasma phase in heavy ion collisions. Then we study the time evolution of this state in the hot hadron gas phase. We calculate the thermal cross sections for the collisions of the $Z_{cs}(3985{)}^{-}$ with light mesons using effective Lagrangians and form factors derived from QCD sum rules for the vertices $Z_{cs}{\overline{D}}_s^{*}D$ and $Z_{cs}{\overline{D}}_s{D}^{*}$. We solve the kinetic equation and find how the $Z_{cs}(3985{)}^{-}$ multiplicity is affected by the considered reactions during the expansion of the hadronic matter. A comparison with the statistical hadronization model predictions is presented. Our results show that the tetraquark yield increases by a factor of about 2–3 from the hadronization to the kinetic freeze-out. We also make predictions for the dependence of the $Z_{cs}(3985{)}^{-}$ yield on the centrality, the center-of-mass energy and the charged hadron multiplicity measured at midrapidity $[d{N}_{ch}/d\eta (\eta <0.5)]$.

We refine previous investigations on de Sitter space and extremal surfaces anchored at the future boundary $I^{+}$. Since such surfaces do not return, they require extra data or boundary conditions in the past (interior). In entirely Lorentzian de Sitter spacetime, this leads to future-past timelike surfaces stretching between $I^{\pm }$. Apart from an overall $-i$ factor (relative to spacelike surfaces in $AdS$) their areas are real and positive. With a no-boundary type boundary condition, the top half of these timelike surfaces joins with a spacelike part on the hemisphere giving a complex-valued area. Motivated by these, we describe two aspects of “time-entanglement” in simple toy models in quantum mechanics. One is based on a future-past thermofield double type state entangling timelike separated states, which leads to entirely positive structures. Another is based on the time evolution operator and reduced transition amplitudes, which leads to complex-valued entropy.

We propose a model of communication employing two harmonic oscillator detectors interacting through a scalar field in a background Minkowski spacetime. In this way, the scalar field plays the role of a quantum channel, namely a bosonic Gaussian channel. The classical and quantum capacities of the communication channel are found, assuming that the detectors’ spatial dimensions are negligible compared to their distance. In particular, we study the evolution in time of the classical capacity after the detectors-field interaction is switched on for various detectors’ frequencies and coupling strengths with the field. As a result, we find a finite value of these parameters optimizing the communication of classical messages. Instead, a reliable communication of quantum messages turns out to be always inhibited.

We study the classical and quantum “properties” of Galilean fermions in $3+1$ dimensions. We have taken the case of massless Galilean fermions minimally coupled to the scalar field. At the classical level, the Lagrangian is obtained by null reducing the relativistic theory in one higher dimension. The resulting theory is found to be invariant under infinite Galilean conformal symmetries. Using Noether’s procedure, we construct the corresponding infinite conserved charges. Path integral techniques are then employed to probe the quantum properties of the theory. The theory is found to be renormalizable. A novel feature of the theory is the emergence of mass scale at the first order of quantum correction. The conformal symmetry of the theory breaks at quantum level. We confirm this by constructing the beta function of the theory.

In this paper, we study the relation between entanglement and global internal symmetries in de Sitter space. We consider two symmetric causally disconnected regions in the hyperbolic chart on de Sitter space. Since entanglement measures characterizes correlations, the study of entanglement between the two causally disconnected regions gives information about the long range correlations in de Sitter space. When a theory possesses an additive global internal symmetry, the entanglement measures for a state with fixed global charge may be decomposed into local charge sectors in either subsystem and thus providing a finer resolution of entanglement. Here, we will consider two theories: free complex scalar field and free Dirac field on de Sitter space. Both theories possess global internal $U(1)$ symmetry. We study the symmetry resolved entanglement entropy for both theories in the Bunch-Davies vacuum state. We find that the symmetry resolved entanglement entropy has equipartition into local charge sectors up to the terms that scale as $V_{H_3}^0$ in the limit of large $V_{H_3}$, where $V_{H_3}$ is the volume of either region. This equipartition however is only broken by the terms of order $O(1/V_{H_3})$. Consequently, we have equipartition of symmetry resolved entanglement entropy in the limit of infinite volume.

In the $\mathcal{N}=2$, $d=3$ superspace, we consider a higher-derivative generalization of the supersymmetric quantum electrodynamics, where the higher-derivative operator is a polynomial function of the d’Alembertian with arbitrary degree. For this theory, we use the background field quantization in a higher-derivative $R_{\xi }$ gauge to explicitly calculate the superfield effective potential up to two loops in the Kählerian approximation. This superfield effective potential is obtained in a closed form and in terms of elementary functions.

We consider the motion of a point particle with spin in a stationary spacetime. We define, following Witzany et al. [Classical Quantum Gravity 36, 075003 (2019)] and later Ramond [arXiv:2210.03866], a 12-dimensional Hamiltonian dynamical system whose orbits coincide with the solutions of the Mathisson-Papapetrou-Dixon equations of motion with the Tulczyjew-Dixon spin supplementary condition, to linear order in spin. We then perturb this system by adding the conservative pieces of the leading order gravitational self-force and self-torque sourced by the particle’s mass and spin. We show that this perturbed system is Hamiltonian and derive expressions for the Hamiltonian function and symplectic form. This result extends a previous result for spinless point particles [F. M. Blanco and E. E. Flanagan, Phys. Rev. Lett. 130, 051201 (2023)].

The effects of anisotropy on the fluid pulsation modes when adopting the so-called Cowling approximation and the tidal deformability of strange-quark stars are investigated by numerically integrating the hydrostatic equilibrium, nonradial oscillation, and tidal deformability equations, all of which are modified from their standard form to include the anisotropic effects. The fluid matter inside compact stars is described by the MIT bag model equation of state. For the anisotropy profile, we consider a local anisotropy that is both regular at the center and null at the star’s surface. We find that the effect of anisotropy is reflected in the fluid pulsation modes and tidal deformability. Finally, we analyze the correlation between the tidal deformability of the GW170817 event and anisotropy.

The standard model extension (SME) is an effective field theory framework that can be used to study the possible violations of Lorentz symmetry in the gravitational interaction. In the SME’s gauge invariant linearized gravity sector, the dispersion relation of gravitational waves (GWs) is modified, resulting in anisotropy, birefringence, and dispersion effects in the propagation of GWs. In this paper, we mainly focus on the nonbirefringent and anisotropic dispersion relation in the propagation of GWs due to the violation of Lorentz symmetry. With the modified dispersion relation, we calculate the corresponding modified waveform of GWs generated by the coalescence of compact binaries. We consider the effects from the operators with the lowest mass dimension $d=6$ in the gauge invariant linearized gravity sector of the SME which are expected to have the dominant Lorentz-violating effect on the propagation of GWs. For this case, the Lorentz-violating effects are presented by 25 coefficients and we constrain them independently by the “maximal-reach” approach. We use 90 high-confidence GW events in the GWTC-3 catalog and use bilby, an open source software, and dynesty, a nested sampling package, to perform parameter estimation with the modified waveform. We do not find any evidence of Lorentz violation in the GWs data and give a 90% confidence interval for each Lorentz violating coefficient.

We investigate the motions of charged particles in the near horizon region of an extreme Kerr black hole with weak electromagnetic fields. There is an enhanced symmetry in the near-horizon-extreme-Kerr geometry. We find that when the electromagnetic field respects this enhanced symmetry, which we refer to as the maximally symmetric electromagnetic field, the equations of motion of charged particles get simplified into a set of decoupled first-order differential equations. We discuss the motions of charged particles in two maximally symmetric electromagnetic fields, one being the force-free field and the other being the vacuum fields. Even though the radial motions are similar to the geodesics in near-horizon-extreme-Kerr geometry, the angular motions could be affected by the electromagnetic field significantly. In particular, for the vacuum solution that is produced by a weakly charged black hole, there exist stable vortical motions if the electromagnetic parameter is above the critical value ${\mathfrak{B}}_c=\sqrt{3}$. These vortical motions do not cross the equatorial planes, and the charged particles in them radiate nonthermally. We discuss the corresponding astrophysical implications.

It is usually thought that the $e$-folds number of inflation must be bounded by its de Sitter entropy, otherwise we will have an information paradox. However, in light of the island rule for computing the entanglement entropy, we show that such a bound might be nonexistent, while the information flux of primordial perturbation modes the observer after inflation is able to detect follows a Page curve. In corresponding eternally inflating spacetime, it seems that our slow-roll inflation patch is accompanied with a neighborly collapsed patch (eventually developing into a black hole) so that its Hawking radiation might be just our primordial perturbations. Accordingly, the perturbation spectrum we observed will present a “Page-like” suppression at large scale.

We investigate the production of a spectator scalar dark matter field that is directly coupled to the inflaton during inflation and reheating. We consider two specific inflationary potentials, namely the Starobinsky and T model of inflation, which satisfy the constraints on the scalar tilt, $n_s$, and tensor-to-scalar ratio, $r$, measured by the Planck satellite. Excitation of light scalar dark matter during inflation may result in large isocurvature perturbations, which can be avoided by inducing a sizable effective dark matter mass during the inflationary phase. For purely gravitational production, the Planck isocurvature constraints require the dark matter mass to be larger than the Hubble scale at horizon exit, with $m_{\chi }\gtrsim 0.5H_{*}$. For small bare dark matter masses $m_{\chi }\ll H_{*}$, these constraints translate into a lower bound on the dark matter coupling to the inflaton. We argue that these constraints can be applied to a wide class of single-field slow-roll inflation models. We also derive isocurvature, dark matter abundance, and Lyman-$\alpha$ constraints on the direct coupling and bare dark matter mass.

In this article, we study the on-shell production of low-mass vector mediators from neutrino-antineutrino coalescence in the core of protoneutron stars. Taking into account the radial dependence of the density, energy, and temperature inside the protoneutron star, we compute the neutrino-antineutrino interaction rate in the star interior in the well-motivated $U(1{)}_{L_{\mu }-L_{\tau }}$ model. First, we determine the values of the coupling above which neutrino-antineutrino interactions dominate over the Standard Model neutrino-nucleon scattering. We argue that, although in this regime a redistribution of the neutrino energies might take place, making low-energy neutrinos more trapped, this only affects a small part of the neutrino population and it cannot be constrained with the SN 1987A data. Thus, contrary to previous claims, the region of the parameter space where the $U(1{)}_{L_{\mu }-L_{\tau }}$ model explains the discrepancy in the muon anomalous magnetic moment is not ruled out. We then focus on small gauge couplings, where the decay length of the new gauge boson is larger than the neutrino-nucleon mean free path, but still smaller than the size of protoneutron star. We show that in this regime, the on-shell production of a long-lived $Z^{\prime }$ and its subsequent decay into neutrinos can significantly reduce the duration of the neutrino burst, probing values of the coupling below $\mathcal{O}({10}^{-7})$ for mediator masses between 10 and 100 MeV. This disfavors new areas of the parameter space of the $U(1{)}_{L_{\mu }-L_{\tau }}$ model.

Investigations on the resonancelike phenomenon in the collisional flavor instability (CFI) of neutrinos, which were observed in the linear phase recently, are reported. We show that it occurs not only for the isotropy-preserving modes as pointed out in the previous work but also for the isotropy-breaking modes and that it enhances the linear growth rate of the CFI. Employing linear analysis and nonlinear numerical simulations in the two-flavor scheme and under the relaxation approximation for the collision term, we discuss the criterion for the resonancelike phenomenon observed in the linear phase, its effect on the subsequent nonlinear evolution as well as the influences of homogeneity-breaking ($k\ne 0$) perturbations and of anisotropy in the background on the resonancelike structure. We will also touch on idea the cohabitation of the resonancelike structure with the fast-flavor conversion.

The idea of self-interacting bosonic dark matter capable of exhibiting superfluidity is revisited. We show that the most interesting parameter space of the theory corresponds to fully thermalized dark matter halos. As a result the entire halo undergoes Bose-Einstein condensation due to high degeneracy. Since it is observationally preferable for the dark matter density profile to be similar to cold dark matter in the outskirts of the halo, we argue that the Jeans wavelength must be at least few times shorter than the virial radius. This entails that, upon condensation, a dark matter halo fragments into superfluid clumps. However, we demonstrate that these wouldbe solitons experience strong tidal disruption and behave as virialized weakly interacting streams. An exception is the central soliton, which can be as large as few tens of kiloparsecs in size without contradicting observational bounds. As a result, in dwarf galaxies, the observed rotation curves can be completely contained within the superfluid soliton. In this case, the dark matter distribution is expected to be strongly sensitive to the baryonic density profile. We argue that the diversity of rotation curves observed for dwarf galaxies is a natural consequence of the superfluid dark matter scenario.

The optical characteristics of the Kazakov-Solodukhin black hole (BH) surrounded by a thin disk is investigated. By utilizing the ray-tracing method, we derive the direct and secondary images to illustrate the influence of observational inclination angle (${\theta }_0$) and quantum correction parameter ($a$) on the observable properties. Our calculation involves determining the effective potential, light deflection, and azimuthal angle of the BH as well as the radiation flux of the accretion disk. By assuming three function models, we determine that the exponential function is the most suitable for describing the relationship between the observed flux and the quantum deformation parameter. Our research reveals that the observable characteristics of a BH are affected not only by the shape of the accretion disk but also by its spatiotemporal properties and the observer’s inclination angle. We observe that a BH encircled by an optically thick accretion disk yields different results from those of an optically thin disk.