We revisit critical behavior and phase structure of charged anti–deSitter (AdS) dilaton black holes for arbitrary values of dilaton coupling $\alpha$, and realize several novel phase behavior of this system. We adopt the viewpoint that cosmological constant (pressure) is fixed and treat the charge of the black hole as a thermodynamical variable. We study critical behavior and phase structure by analyzing the phase diagrams in $T-S$ and $q–T$ planes. We numerically derive the critical point in terms of $\alpha$ and observe that for $\alpha =1$ and $\alpha \ge \sqrt{3}$, the system does not admit any critical point, while for $0<\alpha <1$, the critical quantities are not significantly affected by $\alpha$. We find that unstable behavior of the Helmholtz free energy for $q<q_c$ exhibits a first order (discontinuous) phase transition between small and large black holes for $0\le \alpha <1$, where $q_c$ is the value of charge at the critical point. For $1<\alpha <\sqrt{3}$ and $q>q_c$, however, a novel first order phase transition occurs between small and large black hole, which has not been observed in the previous studies on phase transition of charged AdS black holes.

We study quasinormal modes (QNMs) in a five-dimensional electrically charged Bardeen black hole spacetime by considering the scalar and electromagnetic field perturbations. The black hole spacetime is an exact solution of Einstein gravity coupled to nonlinear electrodynamics in five dimensions, which has nonsingular behavior. To calculate QNMs, we use the WKB approximation method up to sixth order. Due to the presence of electric charge $q_e>0$, both the scalar and electromagnetic field perturbations decay more slowly when compared to the Schwarzschild-Tangherlini black holes. We discover that the scalar field perturbations oscillate more rapidly compared to the electromagnetic field perturbations. In terms of damping, the scalar field perturbations damp more rapidly. We graphically show that the transmission (reflection) coefficients decrease (increase) with an increase in the magnitude of the electric charge $q_e$. The emission of gravitational waves allows the spacetime to undergo damped oscillations due to the nonzero value of the imaginary part, which is always negative. The imaginary part of the QNM frequencies continuously decreases with an increase in the magnitude of the electric charge $q_e$ for a given mode ($l$, $n$). A connection between the QNM frequencies and the black hole shadow, as well as the geometric cross section in the eikonal limit, is also described.

We show that the introduction of two worldline parameters defines a different approach to computations in the effective field theory approach to the two-body problem in general relativity and present some preliminary evidence for a reduction in computational complexity. These parameters obey a polynomial equation whose perturbative expansion recovers an infinite series of diagrams. Furthermore, we show that our equations define an effective two-body horizon for interacting particles in general relativity; in the circular orbit case, it corresponds to the smallest conceivable separation up to which the orbit can remain circular. We expect our results to simplify higher-order computations in the two-body problem, as well as to give insights on the nonperturbative properties of interacting binaries.

The phase structure and critical phenomena of the $3+1$ dimensional charged black holes in asymptotically flat spacetime are investigated within the Rényi statistics. As the nonextensive parameter $\lambda$ above zero, a charged black hole can be in thermodynamic equilibrium with surrounding thermal radiation and have a Hawking–Page phase transition. This gives more evidence supporting the proposed conjectured equivalence between the black hole thermodynamics in asymptotically flat spacetime via Rényi statistics and that in asymptotically anti–de Sitter (AdS) spacetime via Gibbs–Boltzmann statistics. The present work also provides another aspect of supporting evidence through exploring the extended phase space within the Rényi statistics. Working on a modified version of the Smarr formula, the thermodynamic pressure $P$ and volume $v$ of a charged black hole are found to be related to $\lambda$. The thermodynamics of asymptotically flat charged black holes via Rényi statistics has the Van der Waals phase structure, $P-v$ criticality and universal constant, in a similar way as that of asymptotically AdS charged black hole via Gibbs–Boltzmann statistics. This raises an interesting question of how $\lambda$ in the former system relates to $|\mathrm{\Lambda }|$ in the latter one.

We present the gravitational-wave flux balance law in an extreme mass-ratio binary with a spinning secondary. This law relates the flux of energy (angular momentum) radiated to null infinity and through the event horizon to the local change in the secondary’s orbital energy (angular momentum) for generic, nonresonant bound orbits in Kerr spacetime. As an explicit example we compute these quantities for a spin-aligned body moving on a circular orbit around a Schwarzschild black hole. We perform this calculation both analytically, via a high-order post-Newtonian expansion, and numerically in two different gauges. Using these results we demonstrate explicitly that our new balance law holds.

Particles interacting with a prescribed quasimonochromatic gravitational wave (GW) exhibit secular (average) nonlinear dynamics that can be described by Hamilton’s equations. We derive the Hamiltonian of this “ponderomotive” dynamics to the second order in the GW amplitude for a general background metric. For the special case of vacuum GWs, we show that our Hamiltonian is equivalent to that of a free particle in an effective metric, which we calculate explicitly. We also show that already a linear plane GW pulse displaces a particle from its unperturbed trajectory by a finite distance that is independent of the GW phase and proportional to the integral of the pulse intensity. We calculate the particle displacement analytically and show that our result is in agreement with numerical simulations. We also show how the Hamiltonian of the nonlinear averaged dynamics naturally leads to the concept of the linear gravitational susceptibility of a particle gas with an arbitrary phase-space distribution. We calculate this susceptibility explicitly to apply it, in a follow-up paper, toward studying self-consistent GWs in inhomogeneous media within the geometrical-optics approximation.

We construct wormholes in Einstein-scalar-Gauss-Bonnet theories with a potential for the scalar field that includes a mass term and self-interaction terms. By varying the Gauss-Bonnet coupling constant we delimit the domain of existence of wormholes in these theories. The presence of the self-interaction enlarges the domain of existence significantly. There arise wormholes with a single throat and wormholes with an equator and a double throat. We determine the physical properties of these wormholes including their mass, their size and their geometry.

We study the dynamical properties of tracker quintessence models using a general parametrization of their corresponding potentials, and show that there is a general condition for the appearance of a tracker behavior at early times. Likewise, we determine the conditions under which the quintessence tracker models can also provide an accelerating expansion of the universe with an equation of state closer to $-1$. Apart from the analysis of the background dynamics, we also include linear density perturbations of the quintessence field in a consistent manner and using the same parametrization of the potential, with which we show the influence they have on some cosmological observables. The generalized tracker models are compared to observations, and we discuss their appropriateness to ameliorate the fine-tuning of initial conditions and their consistency with the accelerated expansion of the Universe at late times.

A multiacceleration scenario can be used to solve the cosmological coincidence problem. In this paper, after considering the early radiation era, we revisit the cosmological dynamics of the oscillating dark energy model proposed by Tián [Phys. Rev. D 101, 063531 (2020)]. We find this model allows the Universe to evolve as an oscillating scaling solution (OSS) in the radiation era and as a chaotic accelerating solution (CAS) in the matter era. Mathematically, the transition from OSS to CAS is a route of period-doubling bifurcation to chaos. Physically, there are two reasons to convince us that this scenario can be a nice picture to describe the real Universe. One is the global cosmological parameter constraints are practicable if the Universe evolves as an OSS in the radiation era. The other is the late-time Universe described by a CAS can successfully explain the observed cosmic acceleration at low redshifts.

We consider the possibility of an oscillating scalar field accounting for dark matter and dynamically controlling the spontaneous breaking of the electroweak symmetry through a Higgs-portal coupling. This requires a late decay of the inflaton field, such that thermal effects do not restore the electroweak symmetry after reheating, and so inflation is followed by an inflaton matter-dominated epoch. During inflation, the dark scalar field acquires a large expectation value due to a negative nonminimal coupling to curvature, thus stabilizing the Higgs field by holding it at the origin. After inflation, the dark scalar oscillates in a quartic potential, behaving as dark radiation, and only when its amplitude drops below a critical value does the Higgs field acquire a nonzero vacuum expectation value. The dark scalar then becomes massive and starts behaving as cold dark matter until the present day. We further show that consistent scenarios require dark scalar masses in the few GeV range, which may be probed with future collider experiments.

We develop a relativistic multifluid dynamics appropriate for describing neutron star cores at finite temperatures based on Carter’s convective variational procedure. The model includes seven fluids, accounting for both normal and superfluid/superconducting neutrons and protons, leptons (electrons and muons) and entropy. The formulation is compared to the nonvariational relativistic multifluid hydrodynamics of Gusakov and collaborators and shown to be equivalent. Vortex lines and flux tubes, mutual friction, vortex pinning, heat conduction and viscosity are incorporated into the model in steps after the basic hydrodynamics is described. The multifluid system is then considered at the mesoscopic scale where the currents around individual vortex lines and flux tubes are important, and this mesoscopic theory is averaged to determine the detailed vortex line/flux tube contributions to the macroscopic “effective” theory. This matching procedure is partially successful, though obtaining full agreement between the averaged mesoscopic and macroscopic effective theory requires discarding subdominant terms. The matching procedure allow us to interpret the magnetic $H$-field inside a neutron star in a way that is consistent with condensed matter physics literature, and to clarify the difference between this interpretation and that in previous astrophysical works.

We consider the thermal conductivity, shear viscosity, and momentum relaxation rates in the nucleon cores of the neutron stars. We study how the choice of the nuclear interaction and the model for three-body forces may affect these transport coefficients calculated within the Brueckner-Hartree-Fock many-body nuclear theory. We find that at relatively large densities the model dependence of the results is substantial. In addition we provide the analytical approximations which allow to incorporate our results in practical simulations.

We investigate the hadron-quark phase transition in cold neutron stars in light of (i) the observed limits on the maximum-mass of heavy pulsars, (ii) constraints on the tidal properties inferred from the gravitational waves emitted in binary neutron-star mergers, and (iii) mass and radius constraints derived from the observation of hot spots on neutron star observed with the Neutron Star Interior Composition Explorer instrument. Special attention is directed to the possible presence of $\mathrm{\Delta }(1232)$ baryons in neutron star matter. Our results indicate that this particle could make up a large fraction of the baryons in neutron stars and thus have a significant effect on the properties of such objects, particularly on their radii. This is partially caused by the low density appearance of $\mathrm{\Delta }\mathrm{s}$ for a wide range of theoretically defensible sets of meson-hyperon, SU(3) ESC08 model, and meson-$\mathrm{\Delta }$ coupling constants. The transition of hadronic matter to quark matter, treated in the $2\mathrm{SC}+\mathrm{s}$ condensation phase, is found to occur only in neutron stars very close to the mass peak. Nevertheless, quark matter may still constitute an appreciable fraction of the stars’ total matter if the phase transition is treated as Maxwell-like (sharp), in which case the neutron stars located beyond the gravitational mass peak would remain stable against gravitational collapse. In this case, the instability against gravitational collapse is shifted to a new (terminal) mass different from the maximum-mass of the stellar sequence, giving rise to stable compact objects with the same gravitational masses as those of the neutron stars on the traditional branch, but whose radii are smaller by up to 1 km. All models for the equation of state of our study fall comfortably within the bound established very recently by Annala et al. [Nat. Phys., 10.1038/s41567-020-0914-9 (2020)].

Advanced LIGO and Virgo have detected ten binary black hole mergers by the end of their second observing run. These mergers have already allowed constraints to be placed on the population distribution of black holes in the Universe, which will only improve with more detections and increasing sensitivity of the detectors. In this paper we develop techniques to measure the angular distribution of black hole mergers by measuring their statistical $N$-point correlations through hierarchical Bayesian inference. We apply it to the special case of two-point angular correlations using a Legendre polynomial basis on the sky. Building on the mixture model formalism introduced by Smith and Thrane [Phys. Rev. X 8, 021019 (2018)], we show how one can measure two-point correlations with no threshold on significance, allowing us to target the ensemble of subthreshold binary black hole mergers not resolvable with the current generation of ground based detectors. We also show how one can use these methods to correlate gravitational waves with other probes of large scale angular structure like galaxy counts, and validate both techniques through simulations.

Quantum coherence could be sustained up to interstellar distances. It is shown that the photon mean free path in certain regions of the electromagnetic spectrum, such as within the radio or x-ray ranges, could allow sustaining of the quantum state of a photon up to galactic distances. Therefore processes involving quantum entanglement, such as quantum teleportation, could be realized over very long distances in the Milky Way or other galaxies. This is of fundamental interest and offers a new direction in the role of quantum mechanics. Some limited applications of this observation are discussed.

Heterodyne laser phase measurements in the Laser Interferometer Space Antenna (LISA) are degraded by the phase fluctuations of the onboard clocks, resulting in unacceptable sensitivity performance levels of the interferometric data. The current scheme for cancellation of the clock phase noise requires 1 GHz modulation of the ranging laser beams and additional interspacecraft clock recovery heterodyne phase measurements. Here, we report experimental results for an alternative approach to clock noise cancellation based on modified second generation time-delay interferometry (TDI) with optical frequency combs (OFCs). The use of OFCs in the LISA scheme allows simultaneous cancellation of both laser and clock noises, and would eliminate the need for 1 GHz laser modulations and associated demodulation detections. Two Mach-Zehnder interferometers with acousto-optic modulators were used to simulate two LISA arms with Doppler shifts and time delays. With a self-referenced OFC locked to the laser providing the clock signal, we achieve simultaneous suppression of laser and clock noises by 7 and 1.5 orders of magnitudes, respectively, down to the setup noise floor. Based on a numerical analysis, we further show that the noise suppression performance of the OFC-based TDI scheme can meet the LISA mission requirements with an ample margin.

We calculate chiral susceptibilities in ($2+1$)-flavor QCD for different masses of the light quarks using the functional renormalization group (fRG) approach to first principles QCD. We follow the evolution of the chiral susceptibilities with decreasing masses as obtained from both the light-quark and the reduced quark condensate. The latter compares very well with recent results from the HotQCD Collaboration for pion masses $m_{\pi }\gtrsim 100\mathrm{MeV}$. For smaller pion masses, fRG and lattice results are still consistent. In particular, the estimates for the chiral critical temperature are in very good agreement. We close by discussing different extrapolations to the chiral limit.

Applications of the general theory of quantum electrodynamics with Lorentz- and $CPT$-violating operators of mass dimensions up to six are presented to Penning-trap experiments comparing charge-to-mass ratios between particles and antiparticles. Perturbation theory is used to derive Lorentz- and $CPT$-violating contributions to the energy levels and cyclotron frequencies of confined particles and antiparticles. We show that whether the experimental interpreted quantity $(|q|/m{)}_{\overline{w}}/(|q|/m{)}_w-1$ is a clean measure of a $CPT$ test depends on the context of the relevant theory. Existing experimental results of charge-to-mass ratio comparisons are used to obtain first-time constraints on 69 coefficients for Lorentz and $CPT$ violation.

Anomalies in transverse Ward-Takahashi identities are studied, allowing discussion of the feasibility of anomalies arising in general nonsymmetry Ward-Takahashi identities. We adopt the popular Fujikawa method and rigorous dimensional renormalization to verify the existence of transverse anomalies to one-loop order and any loop order, respectively. The arbitrariness of coefficients of transverse anomalies is revealed, and a way out is also proposed after relating transverse anomalies to Schwinger terms and comparing symmetry and nonsymmetry anomalies. Papers that claim the nonexistence of transverse anomalies are reviewed to find anomalies hidden in their approaches. The role played by transverse anomalies is discussed.