We derive a master equation for the reduced density matrix of a uniformly accelerating quantum detector in arbitrary dimensions, generically coupled to a field initially in its vacuum state, and analyze its late time regime. We find that such density matrix asymptotically reaches a Gibbs state. The particularities of its evolution towards this state are encoded in the response function, which depends on the dimension, the properties of the fields, and the specific coupling to them. We also compare this situation with the thermalization of a static detector immersed in a thermal field state, pinpointing the differences between both scenarios. In particular, we analyze the role of the response function and its effect on the evolution of the detector towards equilibrium. Furthermore, we explore the consequences of the well-known statistics inversion of the response function of an Unruh-DeWitt detector linearly coupled to a free scalar field in odd spacetime dimensions. This allows us to specify in which sense accelerated detectors in Minkowski vacuum behave as static detectors in a thermal bath and in which sense they do not.

Cosmological and astrophysical observations indicate the presence of a magnetic field over all scales. In order to explain these magnetic fields, it is assumed that there exists a seed magnetic field which gets amplified by dynamos. These seed fields may have been produced during inflation, at phase transitions, or during some turbulent phase of the early Universe. One well-known mechanism to get the seed field is the Biermann battery, which was originally discussed in the context of generation in an astrophysical object. Requirements for this mechanism to work are (i) a nonzero gradient of the electron number density and pressure, and (ii) they are nonparallel to each other. In the present article we propose a similar mechanism to generate the seed field but in an inhomogeneous chiral plasma. Our mechanism works, in the presence of chiral anomaly, by the virtue of inhomogeneity in the chiral chemical potential and temperature. We discuss various scenarios where inhomogeneities in the chemical potential and temperature can arise. We find that, depending on the epoch of generation, the strength of the seed magnetic fields varies from a few nanogauss (nG) to a few hundred nG.

We study an expanding two-fluid model of nonrelativistic dark matter and radiation, which are allowed to interact during a certain time span and to establish an approximate thermal equilibrium. Such an interaction, which generates an effective bulk viscous pressure at background level, is expected to be relevant for times around the transition from radiation to matter dominance. We quantify the magnitude of this pressure for dark-matter particle masses within the range $1\mathrm{eV}\lesssim m_{\chi }\lesssim 10\mathrm{eV}$ around the matter-radiation equality epoch (i.e., redshift $z_{\mathrm{eq}}\sim 3400$) and demonstrate that the existence of a transient bulk viscosity has consequences which may be relevant for addressing current tensions of the standard cosmological model: (i) the additional (negative) pressure contribution modifies the expansion rate around $z_{\mathrm{eq}}$, yielding a larger $H_0$ value, and (ii) large-scale structure formation is impacted by suppressing the amplitude of matter overdensity growth via a new viscous friction-term contribution to the Mészáros effect. As a result, the $H_0$ and $S_8$ tensions of the current standard cosmological model are both significantly alleviated.

In astrophysical scenarios with large neutrino density, like supernovae and the early universe, the presence of neutrino-neutrino interactions can give rise to collective flavor oscillations in the out-of-equilibrium collective dynamics of a neutrino cloud. The role of quantum correlations in these phenomena is not yet well understood, in large part due to complications in solving for the real-time evolution of the strongly coupled many-body system. Future fault-tolerant quantum computers hold the promise to overcome much of these limitations and provide direct access to the correlated neutrino dynamic. In this work, we present the first simulation of a small system of interacting neutrinos using current generation quantum devices. We introduce a strategy to overcome limitations in the natural connectivity of the qubits and use it to track the evolution of entanglement in real-time. The results show the critical importance of error-mitigation techniques to extract meaningful results for entanglement measures using noisy, near term, quantum devices.

Primordial black holes (PBHs) could account for all or part of dark matter, as well as for some LIGO events. We discuss the spins of primordial black holes produced in different cosmological scenarios, with the emphasis on recently discovered possibilities. PBHs produced as a horizon-size collapse of density perturbations are known to have very small spins. In contrast, PBHs resulting from assembly of matterlike objects (particles, Q-balls, oscillons, etc.) can have large or small spins depending on their formation history and the efficiency of radiative cooling. We show that scalar radiation can remove the angular momentum very efficiently, leading to slowly rotating PBHs in those scenarios for which the radiative cooling is important. Gravitational waves astronomy offers an opportunity to determine the spins of black holes, opening a new window on the early Universe if, indeed, some black holes have primordial origin.

Extreme mass ratio inspirals (EMRIs) can be classified as dry EMRIs and wet EMRIs based on their formation mechanisms. Dry (or the “loss-cone”) EMRIs, previously considered as the main EMRI sources for the Laser Interferometer Space Antenna, are primarily produced by multibody scattering in the nuclear star cluster and gravitational capture. In this work, we highlight an alternative EMRI formation channel: (wet) EMRI formation assisted by the accretion flow around accreting galactic-center massive black holes (MBHs). In this channel, the accretion disk captures stellar-mass black holes that are initially moving on inclined orbits and subsequently drives them to migrate towards the MBH—this process boosts the formation rate of EMRIs in such galaxies by orders of magnitude. Taking into account the fraction ($\mathcal{O}({10}^{-2}–{10}^{-1})$) of active galactic nuclei where the MBHs are expected to be rapidly accreting, we forecast that wet EMRIs will contribute an important or even dominant fraction of all detectable EMRIs by spaceborne gravitational wave detectors.

Space-based interferometric gravitational wave instruments such as the ESA/NASA Laser Interferometer Space Antenna (LISA) observe gravitational waves by measuring changes in the light travel time between widely separated spacecraft. One potential noise source for these instruments is interaction with the solar wind, in particular the free electrons in the interplanetary plasma. Variations in the integrated column density of free electrons along the laser links will lead to time-of-flight delays which directly compete with signals produced by gravitational waves. In this paper we present a simplified model of the solar plasma relevant for this problem, anchor key parameters of our model using data from the NASA Wind/solar wind experiment instrument, and derive estimates for the effect in the LISA measurement. We find that under normal solar conditions, the gravitational wave sensitivity limit from the free-electron effect is smaller than other noise sources that are expected to limit LISA’s sensitivity.

Measuring the triple Higgs boson coupling is a crucial task in the LHC and future collider experiments. We apply the message passing neural network (MPNN) to the study of nonresonant Higgs pair production process $pp\to hh$ in the final state with $2b+2\ell +E_{\mathrm{T}}^{\mathrm{miss}}$ at the LHC. Although the MPNN can improve the signal significance, it is still challenging to observe such a process at the LHC. We find that a $2\sigma$ upper bound (including a 10% systematic uncertainty) on the production cross section of the Higgs pair is 3.7 times the predicted Standard Model cross section at the LHC with the luminosity of $3000{\mathrm{fb}}^{-1}$, which will limit the triple Higgs boson coupling to the range of $[-3,11.5]$.

A pointlike neutron in an external electromagnetic field experiences a shift in energy that mimicks the effect of an actual structural deformation of an extended neutron, i.e., a proper polarizability. In order to be able to differentiate between the former and the latter, a Foldy-Wouthuysen transformation is constructed which yields the energy shift of a pointlike neutron quadratic in the external field in a derivative expansion, generalizing a long-known result for the dipole electric polarizability due to Foldy. The ten leading Foldy contributions to the energy are determined for a zero-momentum neutron. In addition, eliminating the momentum operator in favor of the velocity operator, analogous results are derived for a zero-velocity neutron. In this case, operator ordering ambiguities are encountered that permit only a determination of eight of the ten Foldy terms.

Confining gauge theories contain glueballs and mesons with arbitrary spin, and these particles become metastable at large $N$. However, metastable higher-spin particles, when coupled to gravity, are in conflict with causality. This tension can be avoided only if the gravitational interaction is accompanied by interactions involving other higher-spin states well below the Planck scale $M_{\mathrm{pl}}$. These higher-spin states can come from either the QCD sector or the gravity sector, but both these resolutions have some surprising implications. For example, QCD states can resolve the problem since there is a nontrivial mixing between the QCD sector and the gravity sector, requiring all particles to interact with glueballs at tree-level. If gravity sector states restore causality, any weakly coupled UV completion of the gravity sector must have many stringy features, with an upper bound on the string scale $M_{\text{string}}\lesssim \sqrt{M_{\mathrm{pl}}{\mathrm{\Lambda }}_{\mathrm{QCD}}/N}$, where ${\mathrm{\Lambda }}_{\mathrm{QCD}}$ is the confinement scale.

We report on a search for non-Newtonian forces that couple to mass, with a characteristic scale of $\sim 10\mu \mathrm{m}$, using an optically levitated microsphere as a precision force sensor. A silica microsphere trapped in an upward-propagating, single-beam, optical tweezer is utilized to probe for interactions sourced from a nanofabricated attractor mass with a density modulation brought into close proximity to the microsphere and driven along the axis of periodic density in order to excite an oscillating response. We obtain a force sensitivity of $\lesssim {10}^{-16}\mathrm{N}/\sqrt{\mathrm{Hz}}$. Separately searching for attractive and repulsive forces results in the constraint on a new Yukawa interaction of $|\alpha |\gtrsim {10}^8$ for $\lambda >10\mu \mathrm{m}$. This is the first test of the inverse-square law using an optically levitated test mass of dimensions comparable to $\lambda$, a complementary method subject to a different set of systematic effects compared to more established techniques.

We study confinement in 4d $\mathcal{N}=1$ $SU(N)$ Super-Yang Mills (SYM) from a holographic point of view, focusing on the 1-form symmetry and its relation to chiral symmetry breaking (${\chi }_{\mathrm{SB}}$). We identify the topological couplings in the 5d truncation of the Klebanov-Strassler solution that determine the 1-form symmetry and its ’t Hooft anomalies. One coupling is a mixed 0-/1-form symmetry anomaly related to ${\chi }_{\mathrm{SB}}$ in gapped confining vacua. In the gravity dual we also identify the infrared 4d topological field theory which realizes ${\chi }_{\mathrm{SB}}$ and matches the mixed anomaly. Finally, complementing this, we derive the chiral and mixed anomalies from the little string theory realization of pure SYM.

We study the generalized minimal massive gravity (GMMG) in Compere, Song, and Strominger boundary conditions employing a semiproduct of Virasoro and $\widehat{u}(1)$ Kac-Moody current algebras as the asymptotic symmetry algebra. We calculate the entropy of Bañados-Teitelboim-Zanelli black holes via the degeneracy of states belonging to a Warped conformal field theory. We compute the linearized energy excitations by using the representations of the algebra $\widehat{u}(1)\times SL(2,R{)}_R$ and show that energies of excitations are non-negative at (two) chiral points in the parameter space. At these special points, the charge algebra is described by either Virasoro algebra or Kac-Moody algebra. We also consider some special limits of the GMMG theory which correspond to $2+1$-dimensional massive gravity theories such as new massive and minimal massive gravity theories.

We study the effects of momentum relaxation on the holographic Weyl semimetal which exhibits a topological quantum phase transition between the Weyl semimetal phase and a topological trivial phase. The conservation of momentum in the field theory is broken by the axion fields in holography. The topological Weyl semimetal phase is characterized by a nontrivial anomalous Hall conductivity. We find that the critical value of the phase transition decreases when we increase the momentum relaxation strength up to a special value, above which it goes to zero. This indicates that the Weyl semimetal phase shrinks and finally disappears as the momentum relaxation strength is increased, which is consistent with the weakly coupled field theory predictions. We also study the behavior of transverse and longitudinal conductivities and low-temperature dependence of the dc resistivities with respect to momentum relaxation strength.

A foundational question in relativistic fluid mechanics concerns the properties of the hydrodynamic gradient expansion at large orders. We establish the precise conditions under which this gradient expansion diverges for a broad class of microscopic theories admitting a relativistic hydrodynamic limit, in the linear regime. Our result does not rely on highly symmetric fluid flows utilized by previous studies of heavy-ion collisions and cosmology. The hydrodynamic gradient expansion diverges whenever energy density or velocity fields have support in momentum space exceeding a critical momentum and converges otherwise. This critical momentum is an intrinsic property of the microscopic theory and is set by branch point singularities of hydrodynamic dispersion relations.

Pure Yang-Mills theory in two spacetime dimensions shows exact Casimir scaling. Thus, there are infinitely many string tensions, and this has been understood as a result of nonpropagating gluons in two dimensions. From ordinary symmetry considerations, however, this richness in the spectrum of string tensions seems mysterious. Conventional wisdom has it that it is the center symmetry that classifies string tensions, but being finite it cannot explain infinitely many confining strings. In this paper, we resolve this discrepancy between dynamics and kinematics by pointing out the existence of a noninvertible 1-form symmetry, which is able to distinguish Wilson loops in different representations. We speculate on possible implications for Yang-Mills theories in three and four dimensions.

In this article, we investigate the quantum circuit complexity and entanglement entropy in the recently studied black hole gas framework using the two-mode squeezed states formalism written in arbitrary dimensional spatially flat cosmological Friedmann-Lemaître-Robertson-Walker background space-time. We compute the various complexity measures and study the evolution of these complexities by following two different prescriptions viz the covariant matrix method and Nielsen’s method. Independently, using the two-mode squeezed states formalism we also compute the Rényi and von-Neumann entanglement entropy, which show an inherent connection between the entanglement entropy and quantum circuit complexity. We study the behavior of the complexity measures and entanglement entropy separately for three different spatial dimensions and observe various significant different features in three spatial dimensions on the evolution of these quantities with respect to the scale factor. Furthermore, we also study the underlying behavior of the equilibrium temperature with two of the most essential quantities i.e., rate of change of complexity with scale factor and the entanglement entropy. We observe that irrespective of the spatial dimension, the equilibrium temperature depends quartically on entanglement entropy.

We study the thermalization of smeared particle detectors that couple locally to any operator in a quantum field theory in curved spacetimes. We show that if the field state satisfies the Kubo-Martin-Schwinger condition with inverse temperature $\beta$ with respect to the detector’s local notion of time evolution, reasonable assumptions ensure that the probe thermalizes to the temperature $1/\beta$ in the limit of long interaction times. Our method also imposes bounds on the size of the system with respect to its proper acceleration and spacetime curvature in order to accurately probe the Kubo-Martin-Schwinger temperature of the field. We then apply this formalism to a uniformly accelerated detector probing the Minkowski vacuum of any $CPT$ symmetric quantum field theory, and show that the detector thermalizes to the Unruh temperature, independently of the operator it couples to. This exemplifies yet again the robustness of the Unruh effect, even when arbitrary smeared detectors are used to probe general operators in a quantum field theory.

We investigate the relation between the subleading soft graviton theorem and asymptotic symmetries in gravity in even dimensions $d=2+2m$ higher than four. After rewriting the subleading soft graviton theorem as a Ward identity, we argue that the charges of such identity generate $\mathrm{Diff}(S^{2m})$. In order to show that, we propose suitable commutation relation among certain components of the metric fields. As a result, all $\mathrm{Diff}(S^{2m})$ transformations are symmetries of gravitational scattering.

We discuss the energy loss due to gravitational radiation of binaries composed of exotic objects whose horizon boundary conditions are replaced with reflective ones. Our focus is on the extreme mass-ratio inspirals in which the central heavier black hole is replaced with an exotic compact object. We show, in this case, a modulation of the energy loss rate depending on the evolving orbital frequency occurs and leads to two different types of modifications to the gravitational wave phase evolution; the oscillating part directly corresponding to the modulation in the energy flux, and the nonoscillating part coming from the quadratic order in the modulation. This modification can be sufficiently large to detect with future space-born detectors.