We consider a class of Lorentz-violating theories of gravity involving a timelike unit vector field (the aether) coupled to a metric, two examples of which are Einstein-aether theory and Hořava gravity. The action always includes the Ricci scalar of the metric and the invariants quadratic in covariant derivatives of the aether, but the theories differ in how the aether is constructed from other fields, and whether those fields are varied in the action. Fields that are not varied define background structures breaking diffeomorphsim invariance, including threadings, folations, and clocks, which generally produce novel degrees of freedom arising from the violation of what would otherwise be initial value constraints. The principal aims of this paper are to survey the nature of the theories that arise and to understand the consequences of breaking diffeomorphism invariance in this setting. In a companion paper [A. J. Speranza, arXiv:1504.03305], we address some of the phenomenology of the “ponderable aether” case in which the presence of a background clock endows the aether with a variable internal energy density that behaves in some respects like dark matter.

We study the possibility of realizing a growth rate of matter density perturbations lower than that in general relativity. Using the approach of the effective field theory of modified gravity encompassing theories beyond Horndeski, we derive the effective gravitational coupling $G_{\mathrm{eff}}$ and the gravitational slip parameter $\eta$ for perturbations deep inside the Hubble radius. In Horndeski theories we derive a necessary condition for achieving weak gravity associated with tensor perturbations, but this is not a sufficient condition due to the presence of a scalar-matter interaction that always enhances $G_{\mathrm{eff}}$. Beyond the Horndeski domain it is possible to realize $G_{\mathrm{eff}}$ smaller than Newton’s gravitational constant $G$, while the scalar and tensor perturbations satisfy no-ghost and stability conditions. We present a concrete dark energy scenario with varying $c_{\mathrm{t}}$ and numerically study the evolution of perturbations to confront the model with the observations of redshift-space distortions and weak lensing.

We investigate properties of material ejected dynamically in the merger of black hole-neutron star binaries by numerical-relativity simulations. We systematically study the dependence of ejecta properties on the mass ratio of the binary, spin of the black hole, and equation of state of the neutron-star matter. Dynamical mass ejection is driven primarily by tidal torque, and the ejecta is much more anisotropic than that from binary neutron star mergers. In particular, the dynamical ejecta is concentrated around the orbital plane with a half opening angle of 10°–20° and often sweeps out only a half of the plane. The ejecta mass can be as large as $\sim 0.1M_{\odot }$, and the velocity is subrelativistic with $\sim 0.2–0.3c$ for typical cases. The ratio of the ejecta mass to the bound mass (disk and fallback components) is larger, and the ejecta velocity is larger, for larger values of the binary mass ratio, i.e., for larger values of the black-hole mass. The remnant black hole-disk system receives a kick velocity of $O(100)\mathrm{km}{\mathrm{s}}^{-1}$ due to the ejecta linear momentum, and this easily dominates the kick velocity due to gravitational radiation. Structures of postmerger material, velocity distribution of the dynamical ejecta, fallback rates, and gravitational waves are also investigated. We also discuss the effect of ejecta anisotropy on electromagnetic counterparts, specifically a macronova/kilonova and synchrotron radio emission, developing analytic models.

We discuss a new scenario for early cosmology when the inflationary de Sitter phase emerges dynamically. This genuine quantum effect occurs as a result of dynamics of the topologically nontrivial sectors in a strongly coupled QCD-like gauge theory in an expanding universe. We test these ideas by explicit computations in hyperbolic space ${\mathbb{H}}_{\kappa }^3\times {\mathbb{S}}_{{\kappa }^{-1}}^1$. We argue that the key element for this idea to work is the presence of nontrivial holonomy computed along ${\mathbb{S}}_{{\kappa }^{-1}}^1$. The effect is nonlocal in nature, nonanalytical in coupling constant and cannot be described in terms of any local propagating degree of freedom such as scalar inflaton field $\mathrm{\Phi }(x)$. We discuss some profound phenomenological consequences of this scenario for inflationary cosmology. We also suggest to test these ideas in a tabletop experiment by measuring some specific corrections to the Casimir pressure in the Maxwell theory formulated on a topologically nontrivial manifold.

We extend the formalisms developed in Gair et al. [1] and Cornish and van Haasteren [2] to create maps of gravitational-wave backgrounds using a network of ground-based laser interferometers. We show that in contrast to pulsar timing arrays, which are insensitive to the curl modes of the background, a network of ground-based interferometers is sensitive to both the gradient and curl components. The spatial separation of a network of interferometers, or of a single interferometer at different times during its rotational and orbital motion around the Sun, allows for recovery of both components. We derive expressions for the response functions of a laser interferometer in the small-antenna limit and use these expressions to calculate the overlap reduction function for a pair of interferometers. We also construct maximum-likelihood estimates of the $+$- and $\times$-polarization modes of the gravitational-wave sky in terms of the response matrix for a network of ground-based interferometers, evaluated at discrete times during Earth’s rotational and orbital motion around the Sun. We demonstrate the feasibility of this approach for some simple simulated backgrounds (a single point source and two spatially extended distributions having only gradient or curl components), calculating maximum-likelihood sky maps and uncertainty maps based on the (pseudo)inverse of the response matrix. The distinction between this approach and standard methods for mapping gravitational-wave power is also discussed.

We investigate scenarios in which electroweak baryogenesis can occur during an exotic stage of electroweak symmetry breaking in the early Universe. This transition is driven by the expectation value of a new electroweak scalar instead of the standard Higgs field. A later, second transition then takes the system to the usual electroweak minimum, dominated by the Higgs boson, while preserving the baryon asymmetry created in the first transition. We discuss the general requirements for such a two-stage electroweak transition to be suitable for electroweak baryogenesis and present a toy model that illustrates the necessary ingredients. We then apply these results to construct an explicit realization of this scenario within the inert two Higgs doublet model. Despite decoupling the Higgs from the symmetry-breaking transition required for electroweak baryogenesis, we find that this picture generically predicts new light states that are accessible experimentally.

In the most recent measurements of the reaction $e^{+}{e}^{-}\to p\overline{p}$ by the BABAR collaboration, new structures have been found with unknown origin. We examine a possible relation of the most distinct peak to the recently observed $\varphi (2170)$. Alternatively, we analyze possible explanations due to the nucleon $\overline{\mathrm{\Delta }}$ and $\mathrm{\Delta }\overline{\mathrm{\Delta }}$ thresholds. The latter could explain a periodicity found in the data.

We study the electromagnetic form factors, decay constants and charge radii of the pion and kaon within the framework of light-front field theory formalism where we use an ansatz for the quark-meson interaction bound-state function which is symmetric under exchange of quark and antiquark momentum. The above-mentioned observables are evaluated for the $+$ component of the electromagnetic current, $J^{+}$, in the Breit frame. We also check the invariance of these observables in other frames, whereby both the valance and the nonvalence contributions have to be taken into account, and study the sensitivity of the electromagnetic form factors and charge radius to the model’s parameters; namely, the quark masses, $m_u=m_{\overline{d}}$, $m_{\overline{s}}$, and the regulator mass, $m_R$. It is found that after a fine-tuning of the regulator mass, i.e. $m_R=0.6\mathrm{GeV}$, the model is suitable to fit the available experimental data within the theoretical uncertainties of both the pion and kaon.

We measure the particle-level forward-backward production asymmetry in $b\overline{b}$ pairs with masses ($m_{b\overline{b}}$) larger than $150\mathrm{GeV}/c^2$, using events with hadronic jets and employing jet charge to distinguish $b$ from $\overline{b}$. The measurement uses $9.5{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV recorded by the CDF II detector. The asymmetry as a function of $m_{b\overline{b}}$ is consistent with zero, as well as with the predictions of the standard model. The measurement disfavors a simple model including an axigluon with a mass of $200\mathrm{GeV}/c^2$, whereas a model containing a heavier $345\mathrm{GeV}/c^2$ axigluon is not excluded.

We point out that the discovery of a right-handed charged gauge boson $W_R^{\pm }$ with mass of around a few TeV, for example through a signal of two leptons and two jets that has been reported by CMS to have a $2.8\sigma$ local excess or through a signal of a resonance decaying into a pair of standard model (SM) gauge bosons showing a local excess of $3.4\sigma$ ($2.5\sigma$ global) reported by ATLAS search, will rule out all possibilities of leptogenesis in all classes of the left-right symmetric extensions of the Standard Model (LRSM) with both triplet and doublet Higgs scalars due to the unavoidable fast gauge mediated $B-L$ violating interactions $e_R^{\pm }{W}_R^{\mp }\to e_R^{\mp }{W}_R^{\pm }$. Our conclusions are very general in the sense that they do not necessarily demand for a lepton number violating detection signal of $W_R^{\pm }$.

We consider heterotic ${\mathrm{E}}_8\times {\mathrm{E}}_8$ supergravity compactified on smooth Calabi-Yau manifolds with line bundle gauge backgrounds. Infinite sets of models that satisfy the Bianchi identities and flux quantization conditions can be constructed by letting their background flux quanta grow without bound. Even though we do not have a general proof, we find that all examples are at the boundary of the theory’s validity: the Donaldson-Uhlenbeck-Yau equations, which can be thought of as vanishing D-term conditions, cannot be satisfied inside the Kähler cone unless a growing number of scalar vacuum expectation values is switched on. As they are charged under various line bundles simultaneously, the gauge background gets deformed by these VEVs to a non-Abelian bundle. In general, our physical expectation is that such infinite sets of models should be impossible, since they never seem to occur in exact conformal field theory constructions.

Polymer quantization (PQ) is a background independent quantization scheme that arises in loop quantum gravity. This framework leads to a new short-distance (discretized) structure characterized by a fundamental length. In this paper we use PQ to analyze the problem of a particle bouncing on a perfectly reflecting surface under the influence of Earth’s gravitational field. In this scenario, deviations from the usual quantum effects are induced by the spatial discreteness, but not by a new short-range gravitational interaction. We solve the polymer Schrödinger equation in an analytical fashion, and we evaluate numerically the corresponding energy levels. We find that the polymer energy spectrum exhibits a negative shift compared to the one obtained for the quantum bouncer. The comparison of our results with those obtained in the GRANIT experiment leads to an upper bound for the fundamental length scale, namely $\lambda \ll 0.6\AA$. We find polymer corrections to the transition probability between levels, induced by small vibrations, together with the probability of spontaneous emission in the quadrupole approximation.

The fermion and total currents generated by a gauge field are derived in the framework of a self-consistent consideration of the Dirac and Yang-Mills equations. Under the condition of gauge invariance, the obtained currents are found to be expressible in terms of the massive vector field generated by the initial gauge field. The mass of this vector field depends strongly on the occupancy numbers of the fermion subsystem, whereas the arisen mass term holds the gauge invariance of the modified Lagrangian. We show that such a modified Lagrangian can be reduced to the pure gluodynamic Lagrangian containing a mass term. By breaking the initial $SU(N)$ symmetry, we derive the Lagrangian governing the dynamics of the massive scalar particles, which can be treated as the octet of the pseudoscalar mesons. The contribution of both the quark-gluon interaction and the self-interaction gluon field to the masses of the octet particles is considered. Provided that the hadronization of the confinement matter into the pion triplet occurs, the QCD coupling constant is evaluated in this case in the developed model.

In this paper, we will generalize the Gauss-Bonnet gravity to an energy-dependent Gauss-Bonnet theory of gravity, which we shall call the Gauss-Bonnet gravity’s rainbow. We will also couple this theory to a Maxwell’s theory. We will analyze black hole solutions in this energy-dependent Gauss-Bonnet gravity’s rainbow. We will calculate the modifications to the thermodynamics of black holes in the Gauss-Bonnet’s gravity’s rainbow. We will demonstrate that even though the thermodynamics of the black holes get modified in the Gauss-Bonnet gravity’s rainbow, the first law of thermodynamics still holds for this modified thermodynamics. We will also comment on the thermal stability of the black hole solutions in this theory.

After inflation, a period of preheating may have produced a stochastic background of high frequency gravitational waves (GWs) that would persist until today. The nature of the inflaton’s coupling to standard model or other fields is unknown, so it is useful to ask what features such fields may typically have, and how these affect predictions for the GWs produced. Here we consider the inflaton to be coupled to a light scalar field, and show that even a very small quartic self-interaction term will reduce the amplitude of the GW spectrum. For self-coupling ${\lambda }_{\chi }\gtrsim g^2$, where $g^2$ is the inflaton-scalar coupling, the peak energy density goes as ${\mathrm{\Omega }}_{\text{gw}}^{({\lambda }_{\chi })}/{\mathrm{\Omega }}_{\text{gw}}^{({\lambda }_{\chi }=0)}\sim (g^2/{\lambda }_{\chi }{)}^2$. A consequence is that if the universe reheats through an inflaton-Higgs coupling then the spectrum would be suppressed but the dynamics would be sensitive to the Higgs potential near the energy scale of inflation.

Rotating black holes in Einstein-Maxwell-Chern-Simons theory possess remarkable features when the Chern-Simons coupling constant reaches a critical value. Representing single asymptotically flat black holes with horizons of spherical topology, they exhibit nonuniqueness. In particular, there even exist extremal and nonextremal black holes with the same sets of global charges. Both extremal and nonextremal black holes form sequences of radially excited solutions that can be labeled by the node number of the magnetic gauge potential function. The extremal Reissner-Nordström solution is no longer always located on the boundary of the domain of existence of these black holes, nor does it remain the single extremal solution with vanishing angular momentum. Instead a whole sequence of rotating extremal $J=0$ solutions is present, whose mass converges towards the mass of the Reissner-Nordström solution. These radially excited extremal solutions are all associated with the same near horizon solution. Moreover, there are near horizon solutions that are not realized as global solutions.

Self-accelerating solutions in massive gravity provide explicit, calculable examples that exhibit the general interplay between superluminality, the well-posedness of the Cauchy problem, and strong coupling. For three particular classes of vacuum solutions, one of which is new to this work, we construct the conformal diagram for the characteristic surfaces on which isotropic stress-energy perturbations propagate. With one exception, all solutions necessarily possess spacelike characteristics, indicating perturbative superluminality. Foliating the spacetime with these surfaces gives a pathological frame where kinetic terms of the perturbations vanish, confusing the Hamiltonian counting of degrees of freedom. This frame dependence distinguishes the vanishing of kinetic terms from strong coupling of perturbations or an ill-posed Cauchy problem. We give examples where spacelike characteristics do and do not originate from a point where perturbation theory breaks down and where spacelike surfaces do or do not intersect all characteristics in the past light cone of a given observer. The global structure of spacetime also reveals issues that are unique to theories with two metrics: in all three classes of solutions, the Minkowski fiducial space fails to cover the entire de Sitter spacetime allowing worldlines of observers to end in finite proper time at determinant singularities. Characteristics run tangent to these surfaces requiring ad hoc rules to establish continuity across singularities.

The detection of unmodeled gravitational-wave transients by ground-based interferometric gravitational-wave detectors is an important goal for the advanced detector era. These searches are commonly cast as pattern recognition problems, where the goal is to identify statistically significant clusters indicating the presence of gravitational-wave transients in spectrograms of detector strain power when the precise signal morphology is unknown. In previous work, we have introduced a clustering algorithm referred to as seedless clustering, and shown that it is a powerful tool for detecting weak and long-lived ($\sim 10–1000\mathrm{s}$) gravitational-wave transients. However, as the algorithm is currently conceived, in order to carry out a search on approximately a year of data, significant computational resources may be required for estimating background events. Currently, the use of the algorithm is limited by the computational resources required for performing background studies to assign significance to events identified by the algorithm. In this paper, we present an analytic method for estimating the background generated by the seedless clustering algorithm and compare the performance to both Monte Carlo Gaussian noise and time-shifted gravitational-wave data from a week of LIGO’s 5th Science Run. We demonstrate qualitative agreement between the model and measured distributions and argue that the approximation will be useful to supplement conventional background estimation techniques for advanced detector searches for long-duration gravitational-wave transients.

It is emphasized that a rare decay $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ becomes promising in a future search for a new particle, because the theoretical treatment is well established and the value of the branching ratio $\mathrm{Br}(K^{+}\to {\pi }^{+}\nu \overline{\nu })$ is sensitive to a search for a new particle with a TeV scale mass. As an example, according to a U(3) family gauge boson model which predicts the lowest family gauge boson with a few TeV mass $M_{11}$, the branching ratio $\mathrm{Br}(K^{+}\to {\pi }^{+}\nu \overline{\nu })$ is discussed. If we can obtain, in the future, a slightly lower value ${\mathrm{Br}}^{\text{obs}}\sim 0.9\times {10}^{-10}$ compared with the present observed value ${\mathrm{Br}}^{\text{obs}}=(1.7\pm 1.1)\times {10}^{-10}$, we can conclude $M_{11}\sim \text{a few}$ TeV.