In quantum secret sharing protocols, the usual presumption is that the distribution of quantum shares and players’ collaboration are both performed inertially. Here we develop a quantum secret sharing protocol that relaxes these assumptions wherein we consider the effects due to the accelerating motion of the shares. Specifically, we solve the (2,3)-threshold continuous-variable quantum secret sharing in noninertial frames. To this aim, we formulate the effect of relativistic motion on the quantum field inside a cavity as a bosonic quantum Gaussian channel. We investigate how the fidelity of quantum secret sharing is affected by nonuniform motion of the quantum shares. Furthermore, we fully characterize the canonical form of the Gaussian channel, which can be utilized in quantum-information-processing protocols to include relativistic effects.

We show that the gravitational quasinormal modes (QNMs) of a Schwarzschild black hole play the role of a multimode squeezer that can generate particles. For a minimally coupled scalar field, the QNMs “squeeze” the initial state of the scalar field (even for the vacuum) and produce scalar particles. The maximal squeezing amplitude is inversely proportional to the cube of the imaginary part of the QNM frequency, implying that the particle generation efficiency is higher for lower decaying QNMs. Our results show that the gravitational perturbations can amplify Hawking radiation.

We study the quasinormal modes of asymptotically anti–de Sitter black holes in a class of shift-symmetric Horndeski theories where a gravitational scalar is derivatively coupled to the Einstein tensor. The spacetime differs from exact Schwarzschild–anti–de Sitter, resulting in a different effective potential for the quasinormal modes and a different spectrum. We numerically compute this spectrum for a massless test scalar coupled both minimally to the metric, and nonminimally to the gravitational scalar. We find interesting differences from the Schwarzschild–anti–de Sitter black hole found in general relativity.

The dynamical evolution of self-interacting scalars is of paramount importance in cosmological settings and can teach us about the content of Einstein’s equations. In flat space, nonlinear scalar field theories can give rise to localized, nonsingular, time-dependent, long-lived solutions called “oscillons.” Here, we discuss the effects of gravity on the properties and formation of these structures, described by a scalar field with a double well potential. We show that oscillons continue to exist even when gravity is turned on, and we conjecture that there exists a sequence of critical solutions with an infinite lifetime. Our results suggest that a new type of critical behavior appears in this theory, characterized by modulations of the lifetime of the oscillon around the scaling law and the modulations of the amplitude of the critical solutions.

Relativistic ultracompact objects without an event horizon may be able to form in nature and merge as binary systems, mimicking the coalescence of ordinary black holes. The postmerger phase of such processes presents characteristic signatures, which appear as repeated pulses within the emitted gravitational waveform, i.e., echoes with variable amplitudes and frequencies. Future detections of these signals can shed new light on the existence of horizonless geometries and provide new information on the nature of gravity in a genuine strong-field regime. In this work we analyze phenomenological templates used to characterize echolike structures produced by exotic compact objects, and we investigate for the first time the ability of current and future interferometers to constrain their parameters. Using different models with an increasing level of accuracy, we determine the features that can be measured with the largest precision, and we span the parameter space to find the most favorable configurations to be detected. Our analysis shows that current detectors may already be able to extract all the parameters of the echoes with good accuracy, and that multiple interferometers can measure frequencies and damping factors of the signals at the level of percent.

Quasinormal modes (QNMs) or the ringdown phase of gravitational waves provide critical information about the structure of compact objects like black holes. Thus, QNMs can be a tool to test general relativity (GR) and possible deviations from it. In the case of GR, it has been known for a long time that a relation between two types of black hole perturbations—scalar (Zerilli) and vector (Regge-Wheeler)—leads to an equal share of emitted gravitational energy. With the direct detection of gravitational waves, it is now natural to ask whether the same relation (between scalar and vector perturbations) holds for modified gravity theories, and if not, whether one can use this as a way to probe deviations from general relativity. As a first step, we show explicitly that the above relation between Regge-Wheeler and Zerilli perturbations breaks down for a general $f(R)$ model and hence the two perturbations do not share equal amounts of emitted gravitational energy. We discuss the implication of this imbalance for observations and the no-hair conjecture.

We generalize the classical junction conditions for constructing impulsive gravitational waves by the Penrose “cut and paste” method. Specifically, we study nonexpanding impulses which propagate in spaces of constant curvature with any value of the cosmological constant (that is, Minkowski, de Sitter, or anti–de Sitter universes) when additional off-diagonal metric components are present. Such components encode a possible angular momentum of the ultrarelativistic source of the impulsive wave—the so-called gyraton. We explicitly derive and analyze a specific transformation that relates the distributional form of the metric to a new form which is (Lipschitz) continuous. Such a transformation automatically implies an extended version of the Penrose junction conditions. It turns out that the conditions for identifying points of the background spacetime across the impulse are the same as in the original Penrose cut and paste construction, but their derivatives now directly represent the influence of the gyraton on the axial motion of test particles. Our results apply both for vacuum and nonvacuum solutions of Einstein’s field equations and can also be extended to other theories of gravity.

The classical theory of space-time, namely general relativity, suggests but does not demonstrate the existence of so-called wormholes allowing for interstellar journeys. Alternative proposals such as quantum gravity theories are developed nowadays to allow for wormhole travels by assuming hypothetical trans-Planckian effects at tiny scales. Here we show experimentally that analogue traversable and bidirectional wormholes exist in hydrodynamics following a suggestion by Wheeler. Using a water channel, we sent free surface waves on a countercurrent in an analogue gravity setup aiming at showing that hydrodynamic wormhole travels are controlled by a cascade of dispersive scales including surface tension effects: the capillary wavelength plays the role of a Planckian scale below which long gravity waves are transformed into short capillary waves that are able to move at speeds higher than the “flow” of space-time. Whereas our results do not apply to putative astrophysical wormholes per se, we anticipate that they will trigger new ideas to explore quantum gravity physics.

We investigate the evolution of cosmological perturbations in models of dark energy described by a timelike unit normalized vector field specified by a general function $\mathcal{F}(\mathcal{K})$, so-called generalized Einstein-Aether models. First we study the background dynamics of such models via a designer approach in an attempt to model this theory as dark energy. We find that only one specific form of this designer approach matches $\mathrm{\Lambda }\mathrm{CDM}$ at background order, and we also obtain a differential equation which $\mathcal{F}(\mathcal{K})$ must satisfy for general $w\mathrm{CDM}$ cosmologies, where CDM refers to cold dark matter. We also present the equations of state for perturbations in generalized Einstein-Aether models, which completely parametrize these models at the level of linear perturbations. A generic feature of modified gravity models is that they introduce new degrees of freedom. By fully eliminating these we are able to express the gauge invariant entropy perturbation and the scalar, vector, and tensor anisotropic stresses in terms of the perturbed fluid variables and metric perturbations only. These can then be used to study the evolution of perturbations in the scalar, vector, and tensor sectors, and we use these to evolve the Newtonian gravitational potentials.

Subhorizon perturbations under the extreme initial condition of the axion model are investigated, where initial axion angles start near the potential maximum and the mass oscillation is substantially delayed. This work focuses on a few new features found in the extreme axion model but absent in the free-particle model. A particularly novel new feature is the spectral excess relative to the cold dark matter model in some wave number range, where the excess may be so large that landscapes of high-redshift universe beyond $z=10$ can be significantly altered. For axions of particle mass ${10}^{-22}\mathrm{eV}$, this range of wave number corresponds to first galaxies of few times $10^9–{10}^{10}{M}_{\odot }$. We demonstrate that subhorizon perturbations are accurately described by Mathieu’s equation and subject to parametric instability, which explains this novel feature. Actually the axion model is not a special one; perturbations in a wide range of scalar field models can share the similar characteristic.

We show that the stochastic evolution of an interacting system of the Higgs field and a spectator scalar field naturally gives rise to an enhanced probability of settling down at the electroweak vacuum at the end of inflation. Subsequent destabilization due to parametric resonance between the Higgs field and the spectator field can be avoided in a wide parameter range. We further argue that the spectator field can play the role of dark matter.

The self-annihilation of dark matter particles with mass in the MeV range can produce gamma rays via prompt or secondary radiation. The annihilation rate for such light dark matter particles is however tightly constrained by cosmic microwave background (CMB) data. Here we explore the possibility of discovering MeV dark matter annihilation with future MeV gamma-ray telescopes taking into account the latest and future CMB constraints. We study the optimal energy window as a function of the dominant annihilation final state. We consider both the (conservative) case of the dwarf spheroidal galaxy Draco and the (more optimistic) case of the Galactic center. We find that for certain channels, including those with one or two monochromatic photon(s) and one or two neutral pion(s), a detectable gamma-ray signal is possible for both targets under consideration and compatible with CMB constraints. For other annihilation channels, however, including all leptonic annihilation channels and two charged pions, CMB data rule out any significant signal of dark matter annihilation at future MeV gamma-ray telescopes from dwarf galaxies, but possibly not for the Galactic center.

Multifrequency gravitational wave (GW) observations are useful probes of the formation processes of coalescing stellar-mass binary black holes (BBHs). We discuss the phase drift in the GW inspiral waveform of the merging BBH caused by its center-of-mass acceleration. The acceleration strongly depends on the location where a BBH forms within a galaxy, allowing observations of the early inspiral phase of Laser Interferometer Gravitational Wave Observatory (LIGO)-like BBH mergers by the Laser Interferometer Space Antenna (LISA) to test the formation mechanism. In particular, BBHs formed in dense nuclear star clusters or via compact accretion disks around a nuclear supermassive black hole in active galactic nuclei would suffer strong acceleration, and produce large phase drifts measurable by LISA. The host galaxies of the coalescing BBHs in these scenarios can also be uniquely identified in the LISA error volume, without electromagnetic counterparts. A nondetection of phase drifts would rule out or constrain the contribution of the nuclear formation channels to the stellar-mass BBH population.

We investigate the impact of a fourth sterile neutrino at reactor and Spallation Neutron Source neutrino detectors. Specifically, we explore the discovery potential of the TEXONO and COHERENT experiments to subleading sterile neutrino effects through the measurement of the coherent elastic neutrino-nucleus scattering event rate. Our dedicated ${\chi }^2$-sensitivity analysis employs realistic nuclear structure calculations adequate for high purity sub-keV threshold Germanium detectors.

The low-energy dynamics of any system admitting a continuum of static configurations is approximated by slow motion in moduli (configuration) space. Here, following Ferrell and Eardley, this moduli space approximation is utilized to study collisions of two maximally charged Reissner-Nordström black holes of arbitrary masses, and to compute analytically the gravitational radiation generated by their scattering or coalescence. The motion remains slow even though the fields are strong, and the leading radiation is quadrupolar. A simple expression for the gravitational waveform is derived and compared at early and late times to expectations.

To reflect the asymptotic freedom in the thermal direction, a temperature-dependent coupling was proposed in the literature. We investigate its effect on QCD matter with and without strong magnetic fields. Compared with the fixed coupling constant, the running coupling leads to a drastic change in the dynamical quark mass, entropy density, sound velocity, and specific heat. The crossover transition of QCD matter at finite temperature is characterized by the pseudocritical temperature $T_{\mathrm{pc}}$, which is generally determined by the peak of the derivative of the quark condensate with respect to the temperature $d\varphi /dT$, or equivalently, by the derivative of the quark dynamical mass $dM/dT$. In a strong magnetic field, the temperature- and magnetic-field-dependent coupling $G(eB,T)$ was recently introduced to account for inverse magnetic catalysis. We propose an analytical relation between the two criteria $d\varphi /dT$ and $dM/dT$ and show a discrepancy between them in finding the pseudocritical temperature. The magnitude of the discrepancy depends on the behavior of $dG/dT$.

We analyze the worldline holographic framework for fermions. Worldline holography is based on the observation that in the worldline approach to quantum field theory, sources of a quantum field theory over ${\mathrm{Mink}}_4$ naturally form a field theory over ${\mathrm{AdS}}_5$ to all orders in the elementary fields and in the sources. Schwinger’s proper time of the worldline formalism automatically appears with the physical four spacetime dimensions in an ${\mathrm{AdS}}_5$ geometry. The worldline holographic effective action in general and the proper-time profiles of the sources in particular solve a renormalization group equation. By taking into account sources up to spin one, we reconstruct seminal holographic models. Considering spin two confirms ${\mathrm{AdS}}_5$ as a consistent background.

Tunneling is a fascinating aspect of quantum mechanics that renders the local minima of a potential meta-stable, with important consequences for particle physics, for the early hot stage of the universe, and more speculatively, for the behavior of the putative multiverse. While this phenomenon has been studied extensively for systems which have canonical kinetic terms, many theories of fundamental physics contain fields with noncanonical kinetic structures. It is therefore desirable to have a detailed framework for calculating tunneling rates and initial states after tunneling for these theories. In this work we present such a rigorous formulation and illustrate its use by applying it to a number of examples.

We consider the effective field theory (EFT) treatment of two-body systems with narrow resonances. Within this approach, an $s$-wave scattering amplitude can be expanded in powers of a typical momentum scale of a system $Q\ll \mathrm{\Lambda }$, where $\mathrm{\Lambda }$ represents a hard scale of a scattering system, and an energy difference $\delta \epsilon =|E-{\epsilon }_0|\ll {\epsilon }_0$, where ${\epsilon }_0$ is a resonance peak energy. It is shown that at leading order in the double expansion a universal form of a two-body scattering amplitude is a sum of a Breit-Wigner term of order $Q^{-1}$, a smooth background term of order $Q^0$, and an interference term of order $Q^0$. The techniques developed in this paper can be used to investigate the properties of narrow resonances that are produced by short-distance dynamics.

Flows of the couplings of a theory of an $N$-component (complex) scalar field coupled to electrodynamics are investigated using the functional renormalization group formalism in $d$ dimensions in covariant gauges. We find charged fixed points for any number of components in $d=3$, in accordance with the findings of [G. Fejos and T. Hatsuda, Phys. Rev. D 93, 121701 (2016)] for $N=1$. It is argued that the appropriate choice of the regulator matrix is indispensable to obtain such a result. Ward-Takahashi identities are analyzed in the presence of the regulator, and their compatibility with the flow equation is investigated in detail.