We compare two different approaches for quantization of the Bianchi I model: a reduced phase space quantization, in which the isotropic Misner variables is taken as time, and the Vilenkin proposal, in which a semiclassical approximation is performed for the same variable. We outline the technical and interpretative issues of these two methods and we demonstrate that they provide equivalent results only if the dynamics is essentially dictated by the isotropic matter contribution.

We investigate the stability of highly charged Reissner-Nordström black holes to charged scalar perturbations. We show that the near-horizon region exhibits a transient instability which becomes the Aretakis instability in the extremal limit. The rates we obtain match the enhanced rates for nonaxisymmetric perturbations of the near-extremal and extremal Kerr solutions. The agreement is shown to arise from a shared near-horizon symmetry of the two scenarios.

In this work we have used the recent cosmic chronometer data along with the latest estimation of the local Hubble parameter value, $H_0$ at 2.4% precision as well as the standard dark energy probes, such as the Supernovae Type Ia, baryon acoustic oscillation distance measurements, and cosmic microwave background measurements ($\text{PlanckTT}+\text{lowP}$) to constrain a dark energy model where the dark energy is allowed to interact with the dark matter. A general equation of state of dark energy parametrized by a dimensionless parameter “$\beta$” is utilized. From our analysis, we find that the interaction is compatible with zero within the $1\sigma$ confidence limit. We also show that the same evolution history can be reproduced by a small pressure of the dark matter.

Naive dimensional analysis seems to suggest possible unitarity violations in the framework of the Higgs and new Higgs inflationary scenarios. These violations seem to happen around the value in which the potential energy, per a given Higgs boson’s vacuum expectation value, crosses the perturbative cutoff scale calculated around the electroweak vacuum. Conversely to these expectations, we show that, by using an exact analysis of the background dependent cutoff scale, and by including the contribution of the phase-space volume in the perturbative scattering amplitudes of scalars, no violation of (perturbative) unitarity might ever happen during the whole Universe evolution.

We discuss the correlation function for the metric for homogeneous and isotropic cosmologies. The exact propagator equation determines the correlation function as the inverse of the second functional derivative of the quantum effective action. This formulation relates the metric correlation function employed in quantum gravity computations to cosmological observables as the graviton power spectrum. In the Einstein-Hilbert approximation for the effective action the on-shell graviton correlation function can be obtained equivalently from a product of mode functions which are solutions of the linearized Einstein equations. In contrast, the product of mode functions, often employed in the context of cosmology, does not yield the correlation function for the vector and scalar components of the metric fluctuations. We divide the metric fluctuations into “physical fluctuations,” which couple to a conserved energy momentum tensor, and gauge fluctuations. On the subspace of physical metric fluctuations the relation to physical sources becomes invertible, such that the effective action and its relation to correlation functions no longer needs to involve a gauge fixing term. The physical metric fluctuations have a similar status as the Bardeen potentials, while being formulated in a covariant way. We compute the effective action for the physical metric fluctuations for geometries corresponding to realistic cosmologies.

Results of the search for $\sim (10^{16}–10^{17.5})\mathrm{eV}$ primary cosmic-ray photons with the data of the Moscow State University (MSU) Extensive Air Shower (EAS) array are reported. The full-scale reanalysis of the data with modern simulations of the installation does not confirm previous indications of the excess of gamma-ray candidate events. Upper limits on the corresponding gamma-ray flux are presented. The limits are among the most stringent published ones at energies $\sim 10^{17}\mathrm{eV}$.

We analytically solve the next-to-leading logarithmic Balitsky-Kovchegov equation approximated in the saturation regime, which includes corrections from quark and gluon loops, and large double transverse logarithms. The analytic result for the $S$-matrix in the saturation regime shows that the $\exp (-\mathcal{O}(Y))$ rapidity dependence of the running-coupling solution is replaced by $\exp (-\mathcal{O}(Y^{3/2}))$ in the next-to-leading logarithmic solution. The collinearly improved Balitsky-Kovchegov equations are also analytically solved in the saturation regime. This shows that the double collinear logarithms do not contribute to the $S$-matrix, and the solution is the same as the one obtained from the leading-order Balitsky-Kovchegov equation. The numerical solutions to the leading-order and next-to-leading logarithmic Balitsky-Kovchegov equations are performed in order to test the analytic results derived in the saturation regime.

Dark matter which interacts strongly with itself, but only feebly with the Standard Model, is a possibility that has been entertained to solve apparent small-scale structure problems that are pertinent to the noninteracting cold dark matter paradigm. In this paper, we study the simple case in which the self-scattering rate today is regulated by kinematics and/or the abundance ratio, through the mass splitting of nearly degenerate pseudo-Dirac fermions ${\chi }_1$ and ${\chi }_2$ or real scalars ${\varphi }_1$ and ${\varphi }_2$. We calculate the relic density of these states in a scenario where self-scattering proceeds through off-diagonal couplings with a vector particle $V$ (dark photon) and where the abundance is set through number-depleting 4-to-2 reactions in the hidden sector, or, alternatively, via freeze-in. We study the implications of the considered models and their prospect of solving astrophysical small-scale structure problems. We also show how the introduction of the (meta)stable heavier state may be probed in future dark matter searches.

The simulation of lattice gauge theories with tensor network (TN) methods is becoming increasingly fruitful. The vision is that such methods will, eventually, be used to simulate theories in ($3+1$) dimensions in regimes difficult for other methods. So far, however, TN methods have mostly simulated lattice gauge theories in ($1+1$) dimensions. The aim of this paper is to explore the simulation of quantum electrodynamics (QED) on infinite lattices with TNs, i.e., fermionic matter fields coupled to a $U(1)$ gauge field, directly in the thermodynamic limit. With this idea in mind we first consider a gauge-invariant infinite density matrix renormalization group simulation of the Schwinger model—i.e., QED in $(1+1)\mathrm{d}$. After giving a precise description of the numerical method, we benchmark our simulations by computing the subtracted chiral condensate in the continuum, in good agreement with other approaches. Our simulations of the Schwinger model allow us to build intuition about how a simulation should proceed in ($2+1$) dimensions. Based on this, we propose a variational ansatz using infinite projected entangled pair states (PEPS) to describe the ground state of $(2+1)\mathrm{d}$ QED. The ansatz includes $U(1)$ gauge symmetry at the level of the tensors, as well as fermionic (matter) and bosonic (gauge) degrees of freedom both at the physical and virtual levels. We argue that all the necessary ingredients for the simulation of $(2+1)\mathrm{d}$ QED are, a priori, already in place, paving the way for future upcoming results.

Precise predictions for Higgs production via vector-boson fusion (VBF) play an important role when testing the properties of the Higgs boson and probing new-physics effects. While the inclusive cross section changes little when including next-to-next-to-leading order (NNLO) and next-to-next-to-next-to-leading order QCD corrections, a differential NNLO calculation with typical VBF cuts [1] shows large corrections of up to 10% in distributions. In this article, we investigate the dependence of the differential NNLO QCD calculation on the jet definition. Starting from the known results at a fixed jet clustering choice, we use the electroweak $H+3$ jets production cross section at NLO precision to derive NNLO results for $H+2$ jets production for other jet definitions. We find that larger clustering radii significantly reduce the impact of NNLO corrections. The sizable NNLO corrections for distributions are largely caused by the broader energy flow inside jets at NNLO and are to be expected generally for processes with jets at leading order.

We present a combination of measurements of the top quark mass by the D0 experiment in the $\mathrm{lepton}+\text{jets}$ and dilepton channels. We use all the data collected in Run I (1992–1996) at $\sqrt{s}=1.8\mathrm{TeV}$ and Run II (2001–2011) at $\sqrt{s}=1.96\mathrm{TeV}$ of the Tevatron $p\overline{p}$ collider, corresponding to integrated luminosities of $0.1{\mathrm{fb}}^{-1}$ and $9.7{\mathrm{fb}}^{-1}$, respectively. The combined result is: $m_t=174.95\pm 0.40(\mathrm{stat})\pm 0.64(\mathrm{syst})\mathrm{GeV}=174.95\pm 0.75\mathrm{GeV}$.

We investigate the holographic Rényi entropy for two-dimensional $\mathcal{N}=(2,2)$ superconformal field theory (SCFT), which is dual to $\mathcal{N}=2$ supergravity in an ${\mathrm{AdS}}_3$ background. In SCFT we have the stress tensor, the current, and their supersymmetric partners, and in supergravity we have the graviton, the vector field, and two gravitinos. We get the Rényi mutual information of two short intervals on the complex plane in expansion by the cross ratio $x$ to order $x^4$, and the Rényi entropy of one interval on a torus in expansion by $q=\exp (-2\pi \beta /L)$, with $\beta$ being the inverse temperature and $L$ being the spatial period, to order $q^2$. We calculate on both the supergravity and SCFT sides, and we find matches of the results.

We analyze geometric terms and scaling properties of the Shannon mutual information in the continuum. This is done for a free massless scalar field theory in $d$-dimensions, in a coherent state reduced with respect to a general differentiable manifold. As a by-product, we find an expression for the reduced probability density of finding a certain field on a ball. We will also introduce and compute the Fisher information that this probability carries about the location of the observation region. This is an interesting information measure that refers to points in physical space, although in relativistic quantum field theory they are labels and not fluctuating quantum observables.

Assuming the hypothesis of the entropic nature of gravity, we calculate generalized Newtonian forces, their associated potentials and field equations, when other, in general nonextensive, entropies are considered instead of the usual Boltzmann entropy. Some comments about the nature of the correction terms presented are given, and a calculation of corrections to the Bekenstein-Hawking temperature is performed using the arguments which lead to what can be called a Michell-Laplace black hole.

Cosmological defects result from cosmological phase transitions in the early Universe and the dynamics reflects their symmetry-breaking mechanisms. These cosmological defects may be probed through weak lensing effects because they interact with ordinary matters only through the gravitational force. In this paper, we investigate global textures by using weak lensing curl and B modes. Nontopological textures are modeled by the nonlinear sigma model (NLSM) and induce not only the scalar perturbation but also vector and tensor perturbations in the primordial plasma due to the nonlinearity in the anisotropic stress of scalar fields. We show angular power spectra of curl and B modes from both vector and tensor modes based on the NLSM. Furthermore, we give the analytic estimations for curl and B-mode power spectra. The amplitude of weak lensing signals depends on a combined parameter ${\epsilon }_v^2=N^{-1}{(v/m_{\mathrm{pl}})}^4$ where $N$ and $v$ are the number of the scalar fields and the vacuum expectation value, respectively. We discuss the detectability of the curl and B modes with several observation specifications. In the case of the CMB lensing observation without including the instrumental noise, we can reach ${\epsilon }_v\approx 2.7\times {10}^{-6}$. This constraint is about 10 times stronger than the current one determined from the Planck. For the cosmic shear observation, we find that the signal-to-noise ratio depends on the mean redshift and the observing number of galaxies as $\propto z_{\mathrm{m}}^{0.7}$ and $\propto N_{\mathrm{g}}^{0.2}$, respectively. In the study of textures using cosmic shear observations, the mean redshift would be one of the key design parameters.

A non singular cosmological bounce in the Einstein frame can only take place if the null energy condition (NEC) is violated. We explore situations where a single scalar field drives the NEC violation and derive the constraints imposed by demanding tree level unitarity on a cosmological background. We then focus on the explicit constraints that arise in $P(X)$ theories and show that constraints from perturbative unitarity make it impossible for the NEC violation to occur within the region of validity of the effective field theory without also involving irrelevant operators that arise at a higher scale that would enter from integrating out more massive degrees of freedom. Within the context of $P(X)$ theories we show that including such operators allows for a bounce that does not manifestly violate tree level unitarity, but at the price of either imposing a shift symmetry or involving technically unnatural small operator coefficients within the low-energy effective field theory.

The assumption that we are typical observers plays a core role in attempts to make multiverse theories empirically testable. A widely shared worry about this assumption is that it suffers from systematic ambiguity concerning the reference class of observers with respect to which typicality is assumed. As a way out, Srednicki and Hartle recommend that we empirically test typicality with respect to different candidate reference classes in analogy to how we test physical theories. Unfortunately, as this paper argues, this idea fails because typicality is not the kind of assumption that can be subjected to empirical tests. As an alternative, a background information constraint on observer reference class choice is suggested according to which the observer reference class should be chosen such that it includes precisely those observers who one could possibly be, given one’s assumed background information.

A hypothetical photon mass, $m_{\gamma }$, gives an energy-dependent light speed in a Lorentz-invariant theory. Such a modification causes an additional time delay between photons of different energies when they travel through a fixed distance. Fast radio bursts (FRBs), with their short time duration and cosmological propagation distance, are excellent astrophysical objects to constrain $m_{\gamma }$. Here for the first time we develop a Bayesian framework to study this problem with a catalog of FRBs. Those FRBs with and without redshift measurement are both useful in this framework, and can be combined in a Bayesian way. A catalog of 21 FRBs (including 20 FRBs without redshift measurement, and one, FRB 121102, with a measured redshift $z=0.19273\pm 0.00008$) give a combined limit $m_{\gamma }\le 8.7\times {10}^{-51}\mathrm{kg}$, or equivalently $m_{\gamma }\le 4.9\times {10}^{-15}\mathrm{eV}/c^2$ ($m_{\gamma }\le 1.5\times {10}^{-50}\mathrm{kg}$, or equivalently $m_{\gamma }\le 8.4\times {10}^{-15}\mathrm{eV}/c^2$) at 68% (95%) confidence level, which represents the best limit that comes purely from kinematics. The framework proposed here will be valuable when FRBs are observed daily in the future. Increment in the number of FRBs, and refinement in the knowledge about the electron distributions in the Milky Way, the host galaxies of FRBs, and the intergalactic medium, will further tighten the constraint.

In this work we study the sensitivity on the anomalous magnetic and electric dipole moments of the tau neutrino in the framework of the $SU(2{)}_L\times U(1{)}_Y\times U(1{)}_{B-L}$ electroweak model at future $e^{+}{e}^{-}$ linear colliders, such as the ILC and CLIC. For our study we consider the process $e^{+}{e}^{-}\to (Z,Z^{\prime },\gamma )\to {\nu }_{\tau }{\overline{\nu }}_{\tau }\gamma$. For center-of-mass energies of $\sqrt{s}=1000–3000\mathrm{GeV}$ and integrated luminosities of $\mathcal{L}=500–2000{\mathrm{fb}}^{-1}$, we derive 95% C.L. limits on the dipole moments $|{\mu }_{{\nu }_{\tau }}({\mu }_B)|\le 6.28\times {10}^{-9}$ and $|d_{{\nu }_{\tau }}(\mathrm{ecm})|\le 1.21\times {10}^{-21}$, which improve on the existing limits by 2 to 3 orders of magnitude. Our study complements other studies on the dipole moments of the tau neutrino at hadron and $e^{+}{e}^{-}$ colliders.