There are a number of theoretical predictions for astrophysical and cosmological objects, which emit high frequency ($10^6-10^9\mathrm{Hz}$) gravitation waves (GW) or contribute somehow to the stochastic high frequency GW background. Here we propose a new sensitive detector in this frequency band, which is based on existing cryogenic ultrahigh quality factor quartz bulk acoustic wave cavity technology, coupled to near-quantum-limited SQUID amplifiers at 20 mK. We show that spectral strain sensitivities reaching $10^{-22}$ per $\sqrt{\mathrm{Hz}}$ per mode is possible, which in principle can cover the frequency range with multiple ($>100$) modes with quality factors varying between $10^6$ and $10^{10}$ allowing wide bandwidth detection. Due to its compactness and well-established manufacturing process, the system is easily scalable into arrays and distributed networks that can also impact the overall sensitivity and introduce coincidence analysis to ensure no false detections.

We study the asymptotic dynamics of the mixmaster universe, near the cosmological singularity, considering $f(R)$ gravity up to a quadratic correction in the Ricci scalar $R$. The analysis is performed in the scalar-tensor framework and adopting Misner-Chitré-like variables to describe the mixmaster universe, whose dynamics resembles asymptotically a billiard ball in a given domain of the half-Poincaré space. The form of the potential well depends on the spatial curvature of the model and on the particular form of the self-interacting scalar field potential. We demonstrate that the potential walls determine an open domain in the configuration region, allowing the point universe to reach the absolute of the considered Lobachevsky space. In other words, we outline the existence of a stable final Kasner regime in the mixmaster evolution, implying chaos removal near the cosmological singularity. The relevance of the present issue relies both on the general nature of the considered dynamics, allowing its direct extension to the Belinski-Khalatnikov-Lifshitz conjecture too, as well as the possibility to regard the considered modified theory of gravity as the first correction to the Einstein-Hilbert action as a Taylor expansion of a generic function $f(R)$ (as soon as a cutoff on the space-time curvature takes place).

In this paper, we present a precise and model-independent method to extract resonance pole parameters from phase-shift scattering data. These parameters are defined from the associated poles in the second Riemann sheet, unfolded by the analytic continuation to the complex pole using Padé approximants. Precise theoretical parametrizations of pion-pion scattering phase shifts based on once—and twice—subtracted dispersion relations are used as input, whose functional form allows us to show the benefit and accuracy of the method. In particular, we extract from these parametrizations the pole positions of the $f_0(500)$ at $\sqrt{s}=(453\pm 15)-i(297\pm 15)\mathrm{MeV}$, the $\rho (770)$ at $\sqrt{s}=(761.4\pm 1.2)-i(71.8\pm 1.0)\mathrm{MeV}$, and the pole of the $f_2(1270)$, located at $\sqrt{s}=(1267.3\pm 1.7)-i(95.0\pm 2.3)\mathrm{MeV}$. The couplings of the resonances to two pions are also determined with high precision, obtaining, respectively, $3.8\pm 0.4\mathrm{GeV}$, $5.92\pm 0.15$ and $4.41\pm 0.23{\mathrm{GeV}}^{-1}$. Special attention is dedicated to the systematic treatment of the theoretical and statistical uncertainties, together with their comparison with previous determinations.

Phase transition in $U(n)\times U(n)$ models is investigated for arbitrary flavor number $n$. We present a nonperturbative, $3+1$ dimensional finite temperature treatment of obtaining the effective potential, based on a chiral invariant expansion of the functional renormalization group flows. The obtained tower of equations is similar but not identical to that of the Dyson-Schwinger hierarchy and has to be truncated for practical purposes. We investigate the finite temperature behavior of the system in an expansive set of the parameter space for $n=2,3,4$ and also perform a large-$n$ analysis. Our method is capable of recovering the one-loop $\beta$ functions of the coupling constants of the $\epsilon$ expansion; furthermore, it shows direct evidence that regardless of the actual flavor number, within our approximation, the system undergoes a fluctuation induced first order phase transition.

We merge two leading beyond standard model scenarios, namely compositeness and left-right symmetry, and probe the resulting collider signatures in the leptonic case. The constraints on composite models for fermions leave open the possibility of vectorlike excitations of standard model fermions. Here we consider the possibility of low scale left-right gauge symmetry $SU(2{)}_R\times SU(2{)}_L\times U(1{)}_{B-L}$, with the simplifying assumption that the rightlike excited sector of fermions is significantly heavier than the excitations of the left chiral fermions. It is found that the right-hand currents still contribute to observable processes, and alter the existing bounds on the scale of compositeness. The cross section times branching ratio of the photon decay channel is strongly depressed, bringing down the exclusion limit of the mass of excited electrons from about 2 TeV to below 1 TeV. On the other hand, cross section times branching ratio of the Z decay channel is significantly enhanced and remains greater than that of the photon channel. We thus propose analyzing the Z decay channel in existing collider data in order to search for signature of left-right symmetry as well as excited leptons with masses above 1 TeV.

We determine the phase diagram and pion spectrum for Wilson and twisted-mass fermions in the presence of nondegeneracy between the up and down quarks and discretization errors, using Wilson and twisted-mass chiral perturbation theory. We find that the $CP$-violating phase of the continuum theory (which occurs for sufficiently large nondegeneracy) is continuously connected to the Aoki phase of the lattice theory with degenerate quarks. We show that discretization effects can, in some cases, push simulations with physical masses closer to either the $CP$-violating phase or another phase not present in the continuum, so that at sufficiently large lattice spacings physical-point simulations could lie in one of these phases.

Experimentally several charged axial-vector hidden-charm states were reported. Within the framework of the color-magnetic interaction, we have systematically considered the mass spectrum of the hidden-charm and hidden-bottom tetraquark states. It is impossible to accommodate all of the three charged states $Z_c(3900)$, $Z_c(4025)$, and $Z_c(4200)$ within the axial-vector tetraquark spectrum simultaneously. Not all of these three states are tetraquark candidates. Moreover, the eigenvector of the chromomagnetic interaction contains valuable information of the decay pattern of the tetraquark states. The dominant decay mode of the lowest axial-vector tetraquark state is $J/\psi \pi$ while its $D^{*}\overline{D}$ and ${\overline{D}}^{*}{D}^{*}$ modes are strongly suppressed, which is in contrast with the fact that the dominant decay mode of $Z_c(3900)$ and $Z_c(4025)$ is $\overline{D}{D}^{*}$ and ${\overline{D}}^{*}{D}^{*}$, respectively. We emphasize that all the available experimental information indicates that $Z_c(4200)$ is a very promising candidate of the lowest axial-vector hidden-charm tetraquark state.

Electromagnetic form factors obtained from the overlap of light front wave functions have been used to study the transverse densities of charge and magnetization. The calculations have been carried out to develop a relation between the charge distribution of the quarks inside the nucleon in the transverse coordinate space as well as in the impact parameter space. When a comparison is carried out, it is found that the transverse distribution in the impact parameter space, where the longitudinal momentum fraction $x$ can be fixed, falls off faster than the spatial distribution in the transverse coordinate space where there is some contribution from the longitudinal momentum as well. The anomalous magnetization density of the nucleon has also been discussed. Further, we have also presented the results of the QCD transverse Anti–de Sitter charge density inspired from the holographic QCD model.

In this paper we provide a physical picture for the QCD phase transition in terms of qualitative changes in the spectral functions. Our approach takes into account the crossover nature of this transition and counts for the observed strong correlation seen in higher-order susceptibilities. We demonstrate that the hadron resonance gas, which alone describes the thermodynamics at temperatures $T<T_c$, will appreciably contribute to the total pressure until $T\lesssim 3T_c$. In this intermediate regime the QCD matter consists of strongly correlated excitations, interpretable as either hadrons or partons. As hadronic spectral peaks gradually vanish, the partonic excitations start to form a stand-alone quasiparticle gas. The conventional picture of a quark gluon plasma emerges only at $T\gtrsim 3T_c$.

We calculate the rate of the decay of a metastable vacuum state in $SU(N)$ gauge theory on ${\mathbb{R}}^3\times {\mathbb{S}}^1$ space with a double trace deformation suggested by Ünsal and Yaffe. The derived analytical expression for the exponential factor in the decay rate, including the dependence on the parameter $\theta$, gives the exact behavior in the leading power of $N$ in the limit of large $N$ and provides a better approximation than a numerical result recently found in the literature.

Polymer quantization is a nonstandard approach to quantizing a classical system inspired by background-independent approaches to quantum gravity such as loop quantum gravity. When applied to field theory it introduces a characteristic polymer scale at the level of the fields’ classical configuration space. Compared with models with space-time discreteness or noncommutativity, this is an alternative way in which a characteristic scale can be introduced in a field theoretic context. Motivated by this comparison we study here localization and diffusion properties associated with polymer field observables and dispersion relation in order to shed some light on the novel physical features introduced by polymer quantization. While localization processes seems to be only mildly affected by polymer effects, we find that polymer diffusion differs significantly from the “dimensional reduction” picture emerging in other Planck-scale models beyond local quantum field theory.

Introducing a new form of scalar potential $V(\varphi )$, we derive a proper form of the rotating black hole solution in three-dimensional Einstein gravity with nonminimally coupled scalar field and find that the first law of thermodynamics of this new rotating hairy black hole can be protected, where the scalar field parameter $B$ is constrained to relate to the black hole size. We also disclose the Hawking–Page phase transition between this rotating hairy black holes and the pure thermal radiation. Moreover, we study phase transitions between this rotating hairy black hole and rotating Banados-Teitelboim-Zanelli (BTZ) black hole. Considering the matchings for the temperature and angular momentum, we find that the rotating BTZ black hole always has smaller free energy, which is a thermodynamically more preferred phase. Additionally, we evaluate the thermodynamics of the rotating black hole with minimally coupled scalar hair in three dimensions, which exhibits that the thermodynamical behaviors of this rotating hairy black hole are very similar to those of the rotating black hole with nonminimally coupled scalar hair.

In earlier work, we provided a Hilbert manifold structure for the phase space for the Einstein-Yang-Mills equations, and used this to prove a condition for initial data to be stationary [, Adv. Theor. Math. Phys. 18, 799 (2014)]. Here we use the same phase space to consider the evolution of initial data exterior to some closed 2-surface boundary, and establish a condition for stationarity in this case. It is shown that the differential relationship given in the first law of black hole mechanics is exactly the condition required for the initial data to be stationary; this was first argued nonrigorously by Sudarsky and Wald [Phys. Rev. D 46, 1453 (1992)]. Furthermore, we give evidence to suggest that if this differential relationship holds then the boundary surface is the bifurcation surface of a bifurcate Killing horizon.

We perform the Hamiltonian constraint analysis for a wide class of gravity theories that are invariant under spatial diffeomorphism. With a very general setup, we show that different from the general relativity, the primary and secondary constraints associated with the lapse function $N$ become second class, as long as the lapse function $N$ enters the Hamiltonian nonlinearly. This fact implies that there are 3 degrees of freedom are propagating, of which two correspond to the usual tensor-type transverse and traceless gravitons, and one is the scalar-type graviton. By restoring the full spacetime diffeomorphism using the Stückelberg trick, this type of spatially covariant gravity theory corresponds to a large class of single field scalar-tensor theories that possess higher order derivatives in the equations of motion, and thus is beyond the scope of the Horndeski theory.

The discovery of a “weakly turbulent” instability of anti–de Sitter spacetime supports the idea that confined fluctuations eventually collapse to black holes and suggests that similar phenomena might be possible in asymptotically flat spacetime, for example in the context of spherically symmetric oscillations of stars or nonradial pulsations of ultracompact objects. Here we present a detailed study of the evolution of the Einstein-Klein-Gordon system in a cavity, with different types of deformations of the spectrum, including a mass term for the scalar and Neumann conditions at the boundary. We provide numerical evidence that gravitational collapse always occurs, at least for amplitudes that are three orders of magnitude smaller than Choptuik’s critical value and corresponding to more than ${10}^5$ reflections before collapse. The collapse time scales as the inverse square of the initial amplitude in the small-amplitude limit. In addition, we find that fields with nonresonant spectrum collapse earlier than in the fully resonant case, a result that is at odds with the current understanding of the process. Energy is transferred through a direct cascade to high frequencies when the spectrum is resonant, but we observe both direct- and inverse-cascade effects for nonresonant spectra. Our results indicate that a fully resonant spectrum might not be a crucial ingredient of the conjectured turbulent instability and that other mechanisms might be relevant. We discuss how a definitive answer to this problem is essentially impossible within the present framework.

We investigate gravitational analogue models to describe slowly rotating objects (e.g., dark-matter halos, or boson stars) in terms of Bose-Einstein condensates, trapped in their own gravitational potentials. We begin with a modified Gross-Pitaevskii equation, and show that the resulting background equations of motion are stable, as long as the rotational component is treated as a small perturbation. The dynamics of the fluctuations of the velocity potential are effectively governed by the Klein-Gordon equation of an “Eulerian metric,” where we derive the latter by the use of a relativistic Lagrangian extrapolation. Superradiant scattering on such objects is studied. We derive conditions for its occurrence and estimate its strength. Our investigations might give an observational handle to phenomenologically constrain Bose-Einstein condensates.

Why is the cosmological constant $\mathrm{\Lambda }$ observed today so much smaller than the Planck scale, and why is the Universe accelerating at present? This is the so-called cosmological constant fine-tuning problem. In this paper, we find that this problem may be solved with the help of Higgs inflation by simply assuming a variable cosmological “constant” during the inflationary epoch. Meanwhile, it could predict a large tensor-to-scalar ratio $r\approx 0.20$ and a large running of the spectral index $n_s^{\prime }\approx -0.028$ with a red-tilt spectrum $n_s\approx 0.96$, as well as a big enough number of $e$-folds $N\approx 40$, requiring that we solve the problems in big bang cosmology with the help of $\mathrm{\Lambda }$.

TeV gamma-ray emission has been recently observed from the direction of a few open clusters containing massive stars. We consider the high energy processes occurring within massive binary systems and in their dense environment by assuming that nuclei, from the stellar winds of massive stars, are accelerated at the collision region of the stellar winds. We calculate the rates of injection of protons and neutrons from fragmentation of these nuclei in collisions with stellar radiation and matter of the winds from the massive companions in a binary system. Protons and neutrons can interact with the matter, within the stellar wind cavity, and within the open cluster, producing pions which decay into $\gamma$ rays and neutrinos. We discuss the detectability of such $\gamma$-ray emission by the present and future Cherenkov telescopes for the case of two binary systems Eta Carinae, within the Carina Nebula, and WR 20a, within the Westerlund 2 open cluster. We also calculate the neutrino fluxes produced by protons around the binary systems and within the open clusters. This neutrino emission is confronted with ANTARES upper limits on the neutrino fluxes from discrete sources and with the sensitivity of IceCube.

The measured values of the Higgs and top masses and of the strong gauge coupling constant point to the near-criticality of the Standard Model, where two vacua at the electroweak and Planck scales are quasidegenerate. We argue that the criticality is required by the occurrence of an eternal topological inflation induced by the Higgs potential. The role of this inflation is to continuously create a sufficiently flat and homogeneous Universe, providing the necessary initial condition for the subsequent slow-roll inflation that generates the density perturbations of the right magnitude. While the condition for the topological Higgs inflation is only marginally satisfied in the Standard Model, it can be readily satisfied if one introduces the right-handed neutrinos and/or the nonminimal coupling to gravity; currently unknown quantum gravity corrections to the potential may also help. We also discuss the $B-L$ Higgs inflation as a possible origin of the observed density perturbations. Its necessary initial condition, the restored $B-L$ symmetry, can be naturally realized by the preceding topological Higgs inflation.

We revisit the mechanism of neutrinoless double beta ($0\nu \beta \beta$) decay mediated by the exchange with the heavy Majorana neutrino $N$ of arbitrary mass $m_N$, slightly mixed $\sim U_{\mathit{eN}}$ with the electron neutrino ${\nu }_e$. By assuming the dominance of this mechanism, we update the well-known $0\nu \beta \beta$-decay exclusion plot in the $m_N-U_{\mathit{eN}}$ plane taking into account recent progress in the calculation of nuclear matrix elements within quasiparticle random phase approximation and improved experimental bounds on the $0\nu \beta \beta$-decay half-life of ${}^{76}\mathrm{Ge}$ and ${}^{136}\mathrm{Xe}$. We also consider the known formula approximating the $m_N$ dependence of the $0\nu \beta \beta$-decay nuclear matrix element in a simple explicit form. We analyze its accuracy and specify the corresponding parameters, allowing one to easily calculate the $0\nu \beta \beta$-decay half-life for arbitrary $m_N$ for all the experimentally interesting isotopes without resorting to real nuclear structure calculations.