The celebrated holographic entropy bound asserts that, within the framework of a self-consistent quantum theory of gravity, the maximal entropy (information) content of a physical system is given by one quarter of its circumscribing area: $S\le S_{\max }=\mathcal{A}/4{\ell }_P^2$ (here ${\ell }_P$ is the Planck length). An intriguing possible counterexample to this fundamental entropy bound, which involves homogenous weakly self-gravitating confined thermal fields in higher-dimensional spacetimes, was proposed almost a decade ago. Interestingly, in the present paper we shall prove that this composed physical system, which at first sight seems to violate the holographic entropy bound, actually conforms to the entropy-area inequality $S\le \mathcal{A}/4{\ell }_P^2$. In particular, we shall explicitly show that the homogeneity property of the confined thermal fields sets an upper bound on the entropy content of the system. The present analysis therefore resolves the apparent violation of the holographic entropy bound by confined thermal fields in higher-dimensional spacetimes.

We calculate a finite momentum–dependent part of the photon polarization operator in a simple model of Lorentz-violating quantum electrodynamics nonperturbatively at all orders of Lorentz-violating parameters. We sum one-particle reducible diagrams into the modified photon propagator and determine the physical photon dispersion relation as the location of its pole. The photon dispersion relation, as well as its group velocity, acquires the one-loop momentum-dependent radiative correction. We constrain the Lorentz-violating parameters for heavy charged fermions (muon, $\tau$ lepton, and top quark) from the photon timing observations.

BOOST (BOOst Symmetry Test) is a proposed satellite mission to search for violations of Lorentz invariance by comparing two optical frequency references. One is based on a long-term stable optical resonator, and the other is based on a hyperfine transition in molecular iodine. This mission will allow us to determine several parameters of the standard model extension in the electron sector up to 2 orders of magnitude better than with the current best experiments. Here, we will give an overview of the mission, the science case, and the payload.

We discuss a new perturbation method to study the dynamics of massive vector fields on extremal and near-extremal static black hole spacetimes. We start with, as our background, a rather generic class of warped-product metrics that consist of an $m$-dimensional spacetime and an $n$-dimensional Einstein space, and with respect to the behavior on the latter space, we classify the components of massive vector fields into the vector (axial)- and scalar (polar)-type components. On this generic background spacetime, we show that for the vector-type components the Proca equation reduces to a single homogeneous master equation, whereas the scalar-type components remain coupled. Then, focusing on the case of extremal and near-extremal static black holes in four dimensions, we consider the near-horizon expansion of both the background geometry and massive vector field by a scaling parameter $\lambda$ with the leading-order geometry of $\lambda \to 0$ being the so-called near-horizon geometry. We show that on the near-horizon geometry, thanks to its enhanced symmetry, the Proca equation for the scalar-type components also reduces to a set of two mutually decoupled homogeneous wave equations for two scalar variables, plus a coupled equation through which the remaining third variable is determined from one of the first two. Therefore, together with the vector-type master equation for a single variable, we obtain the set of three decoupled master wave equations, each of which governs each of the three independent dynamical degrees of freedom of the massive vector field in four dimensions. We further expand the geometry and massive vector field with respect to $\lambda$ and show that at each order of $\lambda$ the Proca equation for the scalar-type components can reduce to a set of two mutually decoupled inhomogeneous wave equations of which the source terms consist only of the lower-order variables, plus one coupled equation that determines the remaining third variable. Therefore, if one solves the master equations on the leading-order near-horizon geometry, then in principle, one can successively solve the Proca equation at any order.

In this paper we compute the Arnowitt-Deser-Misner (ADM) mass, the angular momentum, and the charge of the Kerr black hole solution in the scalar-tensor-vector gravity theory [known as the Kerr-MOG (modified gravity) black hole configuration]; we study in detail as well several properties of this solution such as the stationary limit surface, the event horizon, and the ergosphere, and conclude that the new deformation parameter $\alpha$ affects the geometry of the Kerr-MOG black hole significantly in addition to the ADM mass and spin parameters. Moreover, the ADM mass and black hole event horizon definitions allow us to set a novel upper bound on the deformation parameter and to reveal the correct upper bound on the black hole spin. We further find the geodesics of motion of stars and photons around the Kerr-MOG black hole. By using them we reveal the expressions for the mass and the rotation parameter of the Kerr-MOG black hole in terms of the red- and blueshifts of photons emitted by geodesic particles, i.e., by stars. These calculations supply a new and simple method to further test the general theory of relativity in its strong field limit: If the measured red- and blueshifts of photons exceed the bounds imposed by the general theory of relativity, then the black hole is not of Kerr type. It could also happen that the measurements are allowed by the Kerr-MOG metric, implying that the correct description of the dynamics of stars around a given black hole should be performed using MOG or another modified theory of gravity that correctly predicts the observations. In particular, this method can be applied to test the nature of the putative black hole hosted at the center of the Milky Way in the near future.

In the first part of the paper we construct the metric of a tidally deformed, nonrotating black hole. The metric is presented as an expansion in powers of $r/b\ll 1$, in which $r$ is the distance to the black hole and $b$ the characteristic length scale of the tidal field—the typical distance to the remote bodies responsible for the tidal environment. The metric is expanded through order $(r/b{)}^4$ and written in terms of a number of tidal multipole moments, the gravitoelectric moments ${\mathcal{E}}_{ab}$, ${\mathcal{E}}_{abc}$, ${\mathcal{E}}_{abcd}$, and the gravitomagnetic moments ${\mathcal{B}}_{ab}$, ${\mathcal{B}}_{abc}$, ${\mathcal{B}}_{abcd}$. It differs from the similar construction of Poisson and Vlasov in that the tidal perturbation is presented in Regge-Wheeler gauge instead of the light-cone gauge employed previously. In the second part of the paper we determine the tidal moments by matching the black-hole metric to a post-Newtonian metric that describes a system of bodies with weak mutual gravity. This extends the previous work of Taylor and Poisson (Paper I in this sequence), which computed only the leading-order tidal moments, ${\mathcal{E}}_{ab}$ and ${\mathcal{B}}_{ab}$. The matching is greatly facilitated by the Regge-Wheeler form of the black-hole metric, and this motivates the work carried out in the first part of the paper. The tidal moments are calculated accurately through the first post-Newtonian approximation, and at this order they are independent of the precise nature of the compact body. The moments therefore apply equally well to a rotating black hole, or to a (rotating or nonrotating) neutron star. As an application of this formalism, we examine the intrinsic geometry of a tidally deformed event horizon and describe it in terms of a deformation function that represents a quadrupolar and octupolar tidal bulge.

We argue that there may exist spacetime defects embedded in Minkowski spacetime, which have negative active gravitational mass. One such spacetime defect then repels a test particle, corresponding to what may be called “antigravity.”

We determine the binding energy, the total gravitational wave energy flux, and the gravitational wave modes for a binary of rapidly spinning black holes, working in linearized gravity and at leading orders in the orbital velocity, but to all orders in the black holes’ spins. Though the spins are treated nonperturbatively, surprisingly, the binding energy and the flux are given by simple analytical expressions which are finite (respectively third- and fifth-order) polynomials in the spins. Our final results are restricted to the important case of quasicircular orbits with the black holes’ spins aligned with the orbital angular momentum.

We construct and train an artificial neural network called the backpropagation neural network to describe the evolution of the type Ia supernova spectrum by using the data from the CfA Supernova Program. This network method has many attractive features, and one of them is that the constructed model is differentiable. Benefiting from this, we calculate the absorption velocity and its variation. The model we constructed can well describe not only the spectrum of SNe Ia with wavelength range from 3500 Å to 8000 Å but also the light-curve evolution with phase time from $-15$ to 50 with different colors. Moreover, the number of parameters needed during the training process is much less than the usual methods.

Circular polarization of the cosmic microwave background arises in the standard cosmological model from Faraday conversion of the linear polarization generated at the surface of last scatter by various sources of birefringence along the line of sight. If the sources of birefringence are generated at linear order in primordial density perturbations, the principal axes of the index-of-refraction tensor are determined by gradients of the primordial density field. Since linear polarization at the surface of last scatter is generated at linear order in density perturbations, the circular polarization thus arises at second order in primordial perturbations. Here, we revisit the calculation of the circular polarization using the total-angular-momentum formalism, which allows for some simplifications in the calculation of the angular power spectrum of the circular polarization—especially for the dominant photon-photon scattering contribution—and also provides some new intuition.

The decays of the ground-state charmed baryon ${\mathrm{\Lambda }}_c$ are now close to being completely mapped out. In this paper we discuss some remaining open questions, whose answers can help shed light on weak processes contributing to those decays, calculations of such quantities as transition form factors in lattice QCD, and missing decay modes such as ${\mathrm{\Lambda }}_c\to {\mathrm{\Lambda }}^{*}{\ell }^{+}{\nu }_{\ell }$, where ${\mathrm{\Lambda }}^{*}$ is an excited resonance. The discussion is in part a counterpart to a previous analysis of inclusive $D_s$ decays.

We present a calculation of the planar two-loop five-gluon amplitudes. The amplitudes are obtained in a variant of the generalized unitarity approach suitable for numerical computations, which we extend for use with finite field arithmetics. Employing a new method for the generation of unitarity-compatible integration-by-parts identities, all helicity amplitudes are reduced to a linear combination of master integrals for the first time. The approach allows us to compute exact values for the integral coefficients at rational phase-space points. All required master integrals are known analytically, and we obtain arbitrary-precision values for the amplitudes.

In this paper, we revisit the dimension-7 neutrino mass generation mechanism based on the addition of an isospin $3/2$ scalar quadruplet and two vectorlike isotriplet leptons to the standard model. We discuss the LHC phenomenology of the charged scalars of this model, complemented by the electroweak precision and lepton flavor violation constraints. We pay particular attention to the triply charged and doubly charged components. We focus on the same-sign-trilepton signatures originating from the triply charged scalars and find a discovery reach of 600–950 GeV at $3{\mathrm{ab}}^{-1}$ of integrated luminosity at the LHC. On the other hand, doubly charged Higgs has been an object of collider searches for a long time, and we show how the present bounds on its mass depend on the particle spectrum of the theory. Strong constraints on the model parameter space can arise from the measured decay rate of the standard model Higgs to a pair of photons as well.

A weak singlet charged scalar exists in many new physics models beyond the Standard Model. In this work, we show that a light singlet charged scalar with mass above 65 GeV is still allowed by the LEP and LHC data. The interactions of the singlet charged scalar with the Standard Model particles are described by operators up to dimension 5. Dominant decay modes of the singlet charged scalar are obtained, and a subtlety involving field redefinition and gauge fixing due to a dimension-5 operator is also clarified. We demonstrate that it is promising to observe the singlet charged scalar at the LHC.

The full solution of technicolor (TC) Schwinger-Dyson equations should include radiative corrections induced by extended technicolor (ETC) (or other) interactions. We verify that when TC is embedded into a larger theory including also QCD, these radiative corrections couple the different strongly interacting Schwinger-Dyson equations, providing a tiny mass to technifermions and changing the ultraviolet behavior of the gap equation solution. We argue about the origin of the different quark masses without appealing for different ETC boson masses, in one scenario where most of the new physics will appear in interactions with the third fermion generation and with a TC scalar boson possibly lighter than the TC characteristic scale (${\mathrm{\Lambda }}_{\mathrm{TC}}$).

Dark sectors lying beyond the Standard Model and containing sub-GeV particles which are bilinearly coupled to nucleons would induce quantum forces of the Casimir-Polder type in ordinary matter. Such new forces can be tested by a variety of experiments over many orders of magnitude. We provide a generic interpretation of these experimental searches and apply it to a sample of forces from dark scalars behaving as $1/r^3$, $1/r^5$, $1/r^7$ at short range. The landscape of constraints on such quantum forces differs from the one of modified gravity with Yukawa interactions and features, in particular, strong short-distance bounds from molecular spectroscopy and neutron scattering.

Flavor models typically rely on flavons—scalars that break the family symmetry by acquiring vacuum expectation values in specific directions. We develop the idea of effective alignments, i.e., cases where the contractions of multiple flavons give rise to directions that are hard or impossible to obtain directly by breaking the family symmetry. Focusing on the example where the symmetry is $S_4$, we list the effective alignments that can be obtained from flavons vacuum expectation values that arise naturally from $S_4$. Using those effective alignments as building blocks, it is possible to construct flavor models, for example by using the effective alignments in constrained sequential dominance models. We illustrate how to obtain several of the mixing schemes in the literature, and explicitly construct renormalizable models for three viable cases, two of which lead to trimaximal mixing scenarios.

Attempts to extract the order of the chiral transition of QCD at zero chemical potential, with two dynamical flavors of massless quarks, from simulations with progressively decreasing pion mass, have remained inconclusive because of their increasing numerical cost. In an alternative approach to this problem, we consider the path integral as a function of continuous number $N_{\mathrm{f}}$ of degenerate quarks. If the transition in the chiral limit is first order for $N_{\mathrm{f}}\ge 3$, a second-order transition for $N_{\mathrm{f}}=2$ then requires a tricritical point in between. This, in turn, implies tricritical scaling of the critical boundary line between the first-order and crossover regions as the chiral limit is approached. Noninteger numbers of fermion flavors are easily implemented within the staggered fermion discretization. Exploratory simulations at $\mu =0$ and $N_{\mathrm{f}}=2.8$, 2.6, 2.4, 2.2, 2.1, on coarse $N_{\tau }=4$ lattices, indeed show a smooth variation of the critical mass mapping out a critical line in the ($m$, $N_{\mathrm{f}}$) plane. For the smallest masses, the line appears consistent with tricritical scaling, allowing for an extrapolation to the chiral limit.

In situations where the low-lying eigenmodes of the Dirac operator are suppressed one observed degeneracies of some meson masses. Based on these results a hidden symmetry was conjectured, which is not a symmetry of the Lagrangian but emerges in the quantization process. We show here how the difference between classes of meson propagators is governed by the low modes and shrinks when they disappear.

One of the remarkable features of high-multiplicity hadronic events in proton-proton collisions at the LHC is the fact that the produced particles appear as two “ridges”, opposite in azimuthal angle $\varphi$, with approximately flat rapidity distributions. This phenomenon can be identified with the inelastic collision of gluonic flux tubes associated with the QCD interactions responsible for quark confinement in hadrons. In this paper, we analyze the ridge phenomena when the collision involves a flux tube connecting the quark and antiquark of a high energy real or virtual photon. We discuss gluonic tube string collisions in the context of two examples: electron-proton scattering at a future electron-ion collider or the peripheral scattering of protons accessible at the LHC. A striking prediction of our analysis is that the azimuthal angle of the produced ridges will be correlated with the scattering plane of the electron or proton producing the virtual photon. In the case of $ep\to eX$, the final state $X$ is expected to exhibit maximal multiplicity when the elliptic flow in $X$ is aligned with the electron scattering plane. In the $pp\to ppX$ example, the multiplicity and elliptic flow in $X$ are estimated to exhibit correlated oscillations as functions of the azimuthal angle $\mathrm{\Phi }$ between the proton scattering planes. In the minimum-bias event samples, the amplitude of oscillations is expected to be on the order of 2% to 4% of the mean values. In the events with highest multiplicity, the oscillations can be three times larger than in the minimum-bias event samples.