We study scalar, electromagnetic, and gravitational test fields in the Hayward, Bardeen, and Ayón-Beato-García regular black hole spacetimes and demonstrate that the test fields are stable in all of these spacetimes. Using the sixth order WKB approximation of the linear “axial” perturbative scheme, we determine dependence of the quasinormal mode (QNM) frequencies on the characteristic parameters of the test fields and the spacetime charge parameters of the regular black holes. We give also the grey body factors, namely, the transmission and reflection coefficients of scattered scalar, electromagnetic, and gravitational waves. We show that the damping of the quasinormal modes in regular black hole spacetimes is suppressed compared to the case of Schwarzschild black holes, and increasing the charge parameter of the regular black holes increases reflection and decreases the transmission factor of the incident waves for each of the test fields.

Tests of gauge coupling unification require knowledge of thresholds between the weak scale and the high scale of unification. If these scales are far separated, as is the case in most unification scenarios considered in the literature, the task can be factorized into IR and UV analyses. We advocate “$\mathrm{\Delta }\lambda$ plots” as an efficient IR analysis projected to the high scale. The data from these plots gives an immediate qualitative guide to the size of threshold corrections needed at the high scale (e.g., the indices of high-scale representations) and provides precise quantitative data needed to test the viability of hypothesized high-scale unification theories. Such an approach shows more clearly the reasonable prospects of nonsupersymmetric grand unification in large rank groups, and also shows the low summed values of high-scale threshold corrections required for supersymmetric unification. The latter may imply tuned cancellations of high-scale thresholds in theories based on weak-scale supersymmetry. For that reason we view nonsupersymmetric unification to be just as viable as supersymmetric unification when confining ourselves only to the question of reasonable high-scale threshold corrections needed for exact unification. We illustrate these features for a nonsupersymmetric $SO(10)$ grand unified theory and a supersymmetric $SU(5)$ theory.

Inspired by the abundant experimental observation of axial-vector states, we study whether the observed axial-vector states can be categorized into the conventional axial-vector meson family. In this paper we carry out an analysis based on the mass spectra and two-body Okubo-Zweig-Iizuka-allowed decays. Besides testing the possible axial-vector meson assignments, we also predict abundant information for their decays and the properties of some missing axial-vector mesons, which are valuable for further experimental exploration of the observed and predicted axial-vector mesons.

We compute the correction to the photon emission rate in the first order of shear components of fluid velocity gradients, ${\sigma }_{ij}$, in near-equilibrium hydrodynamic plasma at the strong coupling regime, using the real-time Schwinger-Keldysh formalism in AdS/CFT correspondence. Our result is an integral of an analytic expression. We observe that the gradient correction to the photon emission rate at strong coupling is about 0.3–0.4 times the equilibrium rate in units of ${\sigma }_{ij}/T$.

We study certain classes of $g_{++}$ deformations of theories arising in gauge/string realizations of nonrelativistic holography, some of which pertain to $z=2$ Lifshitz theories while others (pertaining to hyperscaling violation) comprise certain classes of excited states. Building on previous work, we consider holographic entanglement entropy for spacelike strip subsystems in a highly boosted (lightlike) limit, where the strip is stretched along the null $x^{+}$ plane. The leading divergence in entanglement in this null limit for these excited states is milder than the usual area law for spacelike subsystems in ground states. For ground states, the entanglement vanishes, perhaps consistent with ultralocality. We discuss this briefly from a field theory perspective. We also present some simple free lightfront field theory examples in excited states where correlators are nonvanishing.

Consider the Euclidean functional integral representation of any physical process in the electroweak model. Integrating out the fermion degrees of freedom introduces 24 fermion determinants. These multiply the Gaussian functional measures of the Maxwell, $Z$, $W$, and Higgs fields to give an effective functional measure. Suppose the functional integral over the Maxwell field is attempted first. This paper is concerned with the large amplitude behavior of the Maxwell effective measure. It is assumed that the large amplitude variation of this measure is insensitive to the presence of the $Z$, $W$, and $H$ fields; they are assumed to be a subdominant perturbation of the large amplitude Maxwell sector. Accordingly, we need only examine the large amplitude variation of a single QED fermion determinant. To facilitate this the Schwinger proper time representation of this determinant is decomposed into a sum of three terms. The advantage of this is that the separate terms can be nonperturbatively estimated for a measurable class of large amplitude random fields in four dimensions. It is found that the QED fermion determinant grows faster than $\exp [c{e}^2\int {\mathrm{d}}^{4}x{F}_{\mu \nu }^2]$, $c>0$, in the absence of zero mode supporting random background potentials. This raises doubt on whether the QED fermion determinant is integrable with any Gaussian measure whose support does not include zero mode supporting potentials. Including zero mode supporting background potentials can result in a decaying exponential growth of the fermion determinant. This is prima facie evidence that Maxwellian zero modes are necessary for the nonperturbative quantization of QED and, by implication, for the nonperturbative quantization of the electroweak model.

We propose a version of a gravitational theory with a torsion field, induced by the chameleon field. Following Hojman et al. [Phys. Rev. D 17, 3141 (1976)], the results obtained in Phys. Rev. D 90, 045040 (2014) are generalized by extending Einstein gravity to Einstein-Cartan gravity with a torsion field as a gradient of the chameleon field through a modification of the local gauge invariance of minimal coupling in the Weinberg-Salam electroweak model. The contributions of the chameleon (torsion) field to the observables of electromagnetic and weak processes are calculated. Since in our approach the chameleon-photon coupling constant ${\beta }_{\gamma }$ is equal to the chameleon-matter coupling constant $\beta$, i.e., ${\beta }_{\gamma }=\beta$, the experimental constraints on $\beta$—obtained in terrestrial laboratories by T. Jenke et al. [Phys. Rev. Lett. 112, 115105 (2014)] and by H. Lemmel et al. [Phys. Lett. B 743, 310 (2015)]—can be used for the analysis of astrophysical sources of chameleons, proposed by C. Burrage et al. [Phys. Rev. D 79, 044028 (2009)], A.-C. Davis et al. [Phys. Rev. D 80, 064016 (2009)], and in references therein, where chameleons induce photons because of direct chameleon-photon transitions in the magnetic fields.

Theories involving curved momentum space, which recently became a topic of interest in the quantum-gravity literature, can, in general, violate many apparently robust aspects of our current description of the laws of physics, including relativistic invariance, locality, causality, and global momentum conservation. Here, we explore some aspects of the pathologies arising in generic theories involving curved momentum space for what concerns causality and momentum conservation. However, we also report results suggesting that when momentum space is maximally symmetric, and the theory is formulated relativistically, most notably including translational invariance with the associated relativity of spacetime locality, momentum is globally conserved and there is no violation of causality.

We present a general expression for the values of the average kinetic energy and of the temperature of kinetic decoupling of a weakly interacting massive particle, valid for any cosmological model. We show an example of the usage of our solution when the Hubble rate has a power-law dependence on temperature, and we show results for the specific cases of kination cosmology and low-temperature reheating cosmology.

We explore the phenomenological implications of generalizing the causal patch and fat geodesic measures to a multidimensional multiverse, where the vacua can have differing numbers of large dimensions. We consider a simple model in which the vacua are nucleated from a $D$-dimensional parent spacetime through dynamical compactification of the extra dimensions, and compute the geometric contribution to the probability distribution of observations within the multiverse for each measure. We then study how the shape of this probability distribution depends on the time scales for the existence of observers, for vacuum domination, and for curvature domination ($t_{\text{obs}},t_{\mathrm{\Lambda }}$, and $t_c$, respectively.) In this work we restrict ourselves to bubbles with positive cosmological constant, $\mathrm{\Lambda }$. We find that in the case of the causal patch cutoff, when the bubble universes have $p+1$ large spatial dimensions with $p\ge 2$, the shape of the probability distribution is such that we obtain the coincidence of time scales $t_{\text{obs}}\sim t_{\mathrm{\Lambda }}\sim t_c$. Moreover, the size of the cosmological constant is related to the size of the landscape. However, the exact shape of the probability distribution is different in the case $p=2$, compared to $p\ge 3$. In the case of the fat geodesic measure, the result is even more robust: the shape of the probability distribution is the same for all $p\ge 2$, and we once again obtain the coincidence $t_{\text{obs}}\sim t_{\mathrm{\Lambda }}\sim t_c$. These results require only very mild conditions on the prior probability of the distribution of vacua in the landscape. Our work shows that the observed double coincidence of time scales is a robust prediction even when the multiverse is generalized to be multidimensional; that this coincidence is not a consequence of our particular Universe being ($3+1$)-dimensional; and that this observable cannot be used to preferentially select one measure over another in a multidimensional multiverse.

The possibility of a reconstruction of the Lagrangian for the scalar field dark energy with constant effective sound speed $c_s$ is analyzed. It is found that such a reconstruction can be made with accuracy up to an arbitrary constant. The value of $c_s$ is estimated together with other dark energy parameters (${\mathrm{\Omega }}_{de}$, $w_0$, and $c_a^2$) and main cosmological ones on the basis of data including Planck-2013 results on cosmic microwave background (CMB) anisotropy, baryon acoustic oscillation distance ratios from recent galaxy surveys, the galaxy power spectrum from WiggleZ, magnitude-redshift relations for distant SNe Ia from SNLS3 and Union2.1 compilations, and the Hubble Space Telescope determination of the Hubble constant. It is shown that no value of $c_s$ from the range [0,1] is preferred by the used data because of the very weak influence of dark energy perturbations on the large scale structure formation and CMB temperature fluctuations.

Flavor SU(3) symmetry, including 30% first-order SU(3) breaking, has been shown to describe adequately a vast amount of data for charmed meson decays to two pseudoscalar mesons and to a vector and a pseudoscalar meson. We review a recent dramatic progress achieved by applying a high-order perturbation expansion in flavor SU(3) breaking and treating carefully isospin breaking. We identify a class of U-spin related $D^0$ decays to pairs involving charged pseudoscalar or vector mesons, for which high-precision nonlinear amplitude relations are predicted. Symmetry-breaking terms affecting these relations are fourth-order U-spin breaking and terms which are first order in isospin breaking and second order in U-spin breaking. The predicted relations are shown to hold within experimental errors at a precision varying between $10^{-3}$ and $10^{-4}$, in agreement with estimates of high-order terms. Improved branching ratio measurements for $D^0\to K^{+}{\rho }^{-},K^{*+}{\pi }^{-}$ and for decay modes involving three other pairs of charged pseudoscalar and vector mesons could further sharpen two of these precision tests. We also obtain amplitude relations for $D^0$ decays to pairs of neutral pseudoscalar mesons, and relations for rate asymmetries between decays involving $K_S^0$ and $K_L^0$, which hold up to second-order U-spin breaking at a level of several percent.

The search for a new source of $CP$ violation is one of the most important endeavors in particle physics. A particularly interesting way to perform this search is to probe the $CP$ phase in the $h\tau \tau$ coupling, as the phase is currently completely unconstrained by all existing data. Recently, a novel variable $\mathrm{\Theta }$ was proposed for measuring the $CP$ phase in the $h\tau \tau$ coupling through the ${\tau }^{\pm }\to {\pi }^{\pm }{\pi }^0\nu$ decay mode. We examine two crucial questions that the real LHC detectors must face, namely, the issue of neutrino reconstruction and the effects of finite detector resolution. For the former, we find strong evidence that the collinear approximation is the best for the $\mathrm{\Theta }$ variable. For the latter, we find that the angular resolution is actually not an issue even though the reconstruction of $\mathrm{\Theta }$ requires resolving the highly collimated ${\pi }^{\pm }$’s and ${\pi }^0$’s from the $\tau$ decays. Instead, we find that it is the missing transverse energy resolution that significantly limits the LHC reach for measuring the $CP$ phase via $\mathrm{\Theta }$. With the current missing energy resolution, we find that with $\sim 1000{\mathrm{fb}}^{-1}$ the $CP$ phase hypotheses $\mathrm{\Delta }=0^{°}$ (the standard model value) and $\mathrm{\Delta }=90^{°}$ can be distinguished, at most, at the 95% confidence level.

In this paper we consider Higgs boson plus jet production as a process that is sensitive to the linear polarization of gluons inside the unpolarized protons of the LHC. The leading order expressions for the transverse momentum distribution of the Higgs boson plus jet pair are provided in terms of transverse momentum dependent quark and gluon distributions. This includes both angular independent and azimuthal angular dependent contributions, presented directly in the laboratory frame. Lacking experimental constraints on the linearly polarized gluon distribution, we study its effects on Higgs boson plus jet production using two different models to illustrate the generic features and maximal effects. It is found that the $\cos 2\varphi$ distribution may be the most promising observable, as it is driven by only one initial linearly polarized gluon. The potential advantages of the Higgs boson plus jet process compared to other processes sensitive to the linear polarization of gluons are discussed.

We consider the entanglement entropy in the dS/CFT correspondence. In Einstein gravity on de Sitter spacetime we propose the holographic entanglement entropy as the analytic continuation of the extremal surface in Euclidean anti–de Sitter spacetime. Even though dual conformal field theories for Einstein gravity on de Sitter spacetime are not known yet, we analyze the free $Sp(N)$ model dual to Vasiliev’s higher spin gauge theory as a toy model. In this model we confirm the behavior similar to our holographic result from Einstein gravity.

We present new analytic solutions to the relativistic Boltzmann equation within the relaxation time approximation. We first obtain spherically expanding solutions which are the kinetic counterparts of the exact solutions of the Israel-Stewart equation in the literature. This allows us to compare the solutions of the kinetic and hydrodynamic equations at an analytical level. We then derive a novel boost-invariant solution of the Boltzmann equation which has an unconventional dependence on the proper time. The existence of such a solution is also suggested in second-order hydrodynamics and fluid-gravity correspondence.

The claim that an overdense (positive-curvature) region in the early Universe cannot extend beyond some maximum scale and remain part of our Universe, first made 40 years ago, has recently been questioned by Kopp et al. Their analysis is elucidating and demonstrates that one cannot constrain the form of primordial density perturbations using this argument. However, the notion of a separate universe scale still applies and there is also an upper limit on the scale of a region collapsing to a black hole at any epoch, these scales being simply related. We calculate these scales for equations of state of the form $p=k\rho c^2$ with $-1<k<\infty$, refining earlier calculations on account of the Kopp et al. criticisms. For $-1/3<k<\infty$, the scale is always of the order of the cosmological particle horizon size, with a numerical factor depending on $k$. This confirms the earlier claim that a primordial black hole cannot be much larger than the particle horizon at formation. For $-1<k<-1/3$, as expected for some periods in the history of the Universe, the situation changes radically, in that a sufficiently large positive-curvature region produces a baby universe rather than a black hole. There is still a separate universe scale but the interpretation of these solutions requires care.

In various theories of quantum gravity, one observes a change in the spectral dimension from the topological spatial dimension $d$ at large length scales to some smaller value at small, Planckian scales. While the origin of such a flow is well understood in continuum approaches, in theories built on discrete structures a firm control of the underlying mechanism is still missing. We shed some light on the issue by presenting a particular class of quantum geometries with a flow in the spectral dimension, given by superpositions of states defined on regular complexes. For particular superposition coefficients parametrized by a real number $0<\alpha <d$, we find that the spatial spectral dimension reduces to $d_{\mathrm{S}}\simeq \alpha$ at small scales. The spatial Hausdorff dimension of such class of states varies between 1 and $d$, while the walk dimension takes the usual value $d_{\mathrm{W}}=2$. Therefore, these quantum geometries may be considered as fractal only when $\alpha =1$, where the “magic number” $D_{\mathrm{S}}\simeq 2$ for the spectral dimension of spacetime, appearing so often in quantum gravity, is reproduced as well. These results apply, in particular, to special superpositions of spin-network states in loop quantum gravity, and they provide more solid indications of dimensional flow in this approach.

We study the integrated Sachs-Wolfe (ISW) effect in ghost-free, massive bigravity. We focus on the infinite-branch bigravity (IBB) model which exhibits viable cosmic expansion histories and stable linear perturbations, while the cosmological constant is set to zero and the late-time accelerated expansion of the Universe is due solely to the gravitational interaction terms. The ISW contribution to the CMB auto-correlation power spectrum is predicted, as well as the cross-correlation between the CMB temperature anisotropies and large-scale structure. We use ISW amplitudes as inferred from the WMAP 9-year temperature data together with galaxy and AGN data provided by the WISE mission in order to compare the theoretical predictions to the observations. The ISW amplitudes in IBB are found to be larger than the corresponding ones in the standard $\mathrm{\Lambda }\mathrm{CDM}$ model by roughly a factor of 1.5, but are still consistent with the observations.

Numerical simulations indicate that black holes carrying linear momentum and/or orbital momentum can power jets. The jets extract the kinetic energy stored in the black hole’s motion. This could provide an important electromagnetic counterpart to gravitational wave searches. We develop the theory underlying these jets. In particular, we derive the analogues of the Penrose process and the Blandford-Znajek jet power prediction for boosted black holes. The jet power we find is $(v/2M{)}^2{\mathrm{\Phi }}^2/(4\pi )$, where $v$ is the hole’s velocity, $M$ is its mass, and $\mathrm{\Phi }$ is the magnetic flux. We show that energy extraction from boosted black holes is conceptually similar to energy extraction from spinning black holes. However, we highlight two key technical differences: in the boosted case, jet power is no longer defined with respect to a Killing vector, and the relevant notion of black hole mass is observer dependent. We derive a new version of the membrane paradigm in which the membrane lives at infinity rather than the horizon and we show that this is useful for interpreting jets from boosted black holes. Our jet power prediction and the assumptions behind it can be tested with future numerical simulations.