We propose that, within the standard model, the correlation between the $t\overline{t}$ forward-backward asymmetry $A_{t\overline{t}}$ and the corresponding lepton-based asymmetry $A_l$—at the differential level—is strong and rather clean both theoretically and experimentally. Hence a combined measurement of the two distributions as a function of the lepton $p_T$, a direct and experimentally clean observable, would lead to a potentially unbiased and normalization-free test of the standard model prediction. To check the robustness of our proposal, we study how the correlation is affected by mismeasurement of the $t\overline{t}$ system transverse momenta, acceptance cuts, and scale dependence and compare the results of mcfm, powheg (with and without pythia showering), and sherpa’s csshower in first-emission mode. We find that the shape of the relative differential distribution $A_l(p_T^l)[A_{t\overline{t}}(p_T^l)]$ is only moderately distorted, hence supporting the usefulness of our proposal. Beyond the first emission, we find that the correlation is not accurately captured by lowest-order treatment. We also briefly consider other differential variables such as the system transverse mass and the canonical $t\overline{t}$ invariant mass. Finally, we study new physics scenarios where the correlation is significantly distorted and therefore can be more readily constrained or discovered using our method.

The Penner type $\beta$ ensemble for $\Omega$-deformed $\mathcal{N}=2SU(2)$ gauge theory with two massless flavors arising as a limiting case from the Alday, Gaiotto and Tachikawa conjecture is considered. The partition function can be calculated perturbatively in a saddle-point approximation. A large $N$ limit reproduces the gauge theory partition function expanded in a strong coupling regime, for any $\beta$ and beyond tree level, confirming previous results obtained via special geometry and the holomorphic anomaly equation. The leading terms and gap of the gauge theory free energy at the monopole/dyon point follow as a corollary.

The heavy quark potential is calculated in the framework of gauge/gravity duality using the large-$D$ approximation, where $D$ is the number of dimensions transverse to the flux tube connecting a quark and an antiquark in a flat $D+2$-dimensional spacetime. We find that in the large-$D$ limit the leading correction to the ground-state energy, as given by an effective Nambu-Goto string, arises not from the heavy modes but from the behavior of the massless modes in the vicinity of the quark and the antiquark. We estimate this correction and find that it should be visible in the near-future lattice QCD calculations of the heavy quark potential.

Bonnor’s map in general relativity is the duality between (dimensionally reduced) vacuum gravity and static truncation of electrovacuum theory. It was used as a tool to generate an exact electrovacuum solution from some vacuum solution. It can be expected that similar dualities will be useful for solution generation in higher-dimensional theories too. Here we study such maps within a class of theories in dimensions $D\le 6$ using oxidation of $D=3$ cosets and consistent truncation of the corresponding theories. Our class includes those theories whose $D=3$ symmetries are subgroups of $G=O(5,4)$. It contains six-dimensional minimal supergravity, five-dimensional minimal and $U(1{)}^3$ supergravities and a number of four-dimensional theories which attracted attention recently in the search of exact solutions. We give explicit reduction/truncation formulas relating different theories in dimensions $D=4$, 5, 6 in terms of metrics and matter fields and discuss various alternative duality chains between them.

In this article we analyze the geodesics of test particles and light in the five-dimensional (charged) doubly spinning black ring spacetime. Apparently it is not possible to separate the Hamilton-Jacobi equation for (charged) doubly spinning black rings in general, so we concentrate on special cases: null geodesics in the ergosphere and geodesics on the two rotational axes of the (charged) doubly spinning black ring. We present analytical solutions to the geodesic equations for these special cases. Using effective potential techniques we study the motion of test particles and light and discuss the corresponding orbits.

The coupling of conserved $p$-brane currents with non-Abelian gauge theories is done consistently by using Chern-Simons forms. Conserved currents localized on $p$-branes that have a gravitational origin can be constructed from Killing-Yano forms of the underlying spacetime. We propose a generalization of the coupling procedure with Chern-Simons gravities to the case of gravitational conserved currents. In odd dimensions, the field equations of coupled Chern-Simons gravities that describe the local curvature on $p$-branes are obtained. In special cases of three and five dimensions, the field equations are investigated in detail.

When binary black holes are embedded in a gaseous environment, a rotating disk surrounding them, the so-called circumbinary disk, will be formed. The binary exerts a gravitational torque on the circumbinary disk and thereby transfers its orbital angular momentum to it, while the angular momentum of the circumbinary disk is transferred to the binary through mass accretion. The binary undergoes an orbital decay due to both gravitational wave emission and binary-disk interaction, driving the phase evolution of the gravitational wave signal. The precise measurement of the gravitational wave phase may therefore provide information regarding the circumbinary disk. In this paper, we assess the detectability of this signature of binary-disk interaction using future spaceborne gravitational wave detectors such as DECIGO and BBO, via standard matched filtering analysis. We find that the effect of the circumbinary disk around binary black holes in the mass range $6M_{\odot }\le M\lesssim 3\times {10}^3{M}_{\odot }$ is detectable at a statistically significant level in five years of observation, provided that gas accretes onto the binary at a rate greater than $\dot{M}\sim 1.4\times {10}^{17}[\mathrm{g}{\mathrm{s}}^{-1}]j^{-1}(M/10M_{\odot }{)}^{33/23}$ with 10% mass-to-energy conversion efficiency, where $j$ represents the efficiency of the angular momentum transfer from the binary to the circumbinary disk. We point out that the circumbinary disk is detectable, even if its mass around the inner edge is over 10 orders of magnitude less than the binary mass. We show that $O(0.1)$ coalescence events for binary stellar-mass black holes are expected to occur in sufficiently dense molecular clouds during five years of observation, and we discuss the event rate for binary intermediate-mass black holes in spite of their large uncertainties. Since the expected number of merger events for binary stellar-mass black holes is also proportional to the binary’s bulk velocity to the power of $-27/5$, the resultant coalescence events can be easily reduced by 1 order of magnitude even when the bulk velocity is twice larger than the fiducial one, $20\mathrm{km}{\mathrm{s}}^{-1}$. The feasibility of detection of circumbinary disks around binary stellar-mass black holes is significantly low, even with five years of observation with DECIGO/BBO.

In “entropic cosmology,” instead of a cosmological constant $\Lambda$, an extra driving term is added to the Friedmann equation and the acceleration equation, taking into account the entropy and the temperature on the horizon of the universe. By means of the modified Friedmann and acceleration equations, we examine a non-adiabatic-like accelerated expansion of the universe in entropic cosmology. In this study, we consider a homogeneous, isotropic, and spatially flat universe, focusing on the single-fluid- (single-component-) dominated universe at late times. To examine the properties of the late universe, we solve the modified Friedmann and acceleration equations, neglecting high-order corrections for the early universe. We derive the continuity (conservation) equation from the first law of thermodynamics, assuming nonadiabatic expansion caused by the entropy and temperature on the horizon. Using the continuity equation, we formulate the generalized Friedmann and acceleration equations, and propose a simple model. Through the luminosity distance, it is demonstrated that the simple model agrees well with both the observed accelerated expansion of the Universe and a fine-tuned standard $\Lambda \mathrm{CDM}$ (lambda cold dark matter) model. However, we find that the increase of the entropy for the simple model is likely uniform, while the increase of the entropy for the standard $\Lambda \mathrm{CDM}$ model tends to become gradually slower, especially after the present time. In other words, the simple model predicts that the present time is not a special time, unlike for the prediction of the standard $\Lambda \mathrm{CDM}$ model.

We use the so-called eikonal approximation, recently introduced in the context of cosmological perturbation theory, to compute power spectra for multicomponent fluids. We demonstrate that, at any given order in standard perturbation theory, multipoint power spectra do not depend on the large-scale adiabatic modes. Moreover, we employ perturbation theories to decipher how nonadiabatic modes, such as a relative velocity between two different components, damp the small-scale matter power spectrum, a mechanism recently described in the literature. In particular, we do an explicit calculation at one-loop order of this effect. While the one-loop result eventually breaks down, we show how the damping effect can be fully captured by the help of the eikonal approximation. A relative velocity not only induces mode damping but also creates large-scale anisotropic modulations of the matter power spectrum amplitude. We illustrate this for the Local Group environment.

A stochastic gravitational-wave background (SGWB) can arise from the superposition of many independent events. If the fraction of time that events emit in some frequency band is sufficiently high, the resulting background is Gaussian in that band, which is to say that it is characterized only by a gravitational-wave strain power spectrum. Alternatively, if this fraction is low, we expect a non-Gaussian background, characterized by intermittent subthreshold signals. Many experimentally accessible models of the SGWB, such as the SGWB arising from compact binary coalescences, are expected to be of this non-Gaussian variety. Primordial backgrounds from the early Universe, on the other hand, are more likely to be Gaussian. Measuring the Gaussianity of the SGWB can therefore provide additional information about its origin. In this paper we introduce a novel maximum likelihood estimator that can be used to estimate the non-Gaussian component of an SGWB signature measured in a network of interferometers. This method can be robustly applied to spatially separated interferometers with colored, non-Gaussian noise. Furthermore, it can be cast as a generalization of the widely used stochastic radiometer algorithm.

Magnetars have been proposed as sources of gravitational waves, potentially observable by current and future terrestrial gravitational-wave detectors. In this paper, we calculate the stochastic gravitational wave background generated by summing the contributions from all magnetars in the Universe, and we study its accessibility to the second- and third-generation gravitational-wave detector networks. We perform systematic scans of the parameter space in this model, allowing the magnetic field, the ellipticity, the initial period, and the rate of magnetars to vary over the currently believed range of values. We also consider different proposed configurations of the magnetic field (poloidal, toroidal, and twisted torus) and different proposed star-formation histories. We identify regions in the parameter space of poloidal and toroidal models that will be accessible to the second- and third-generation gravitational-wave detectors and conclude that the twisted-torus models are likely out of reach of these detectors. The poloidal field configuration with a type II superconductor equation of state in the interior, or with a highly disordered magnetic field, and the toroidal configuration with a very strong toroidal magnetic field in the interior ($>{10}^{16}\mathrm{G}$) are the most promising in terms of gravitational-wave detection.

The Earth’s density distribution can be approximately considered piecewise continuous at the scale of two-flavor oscillations of typical solar neutrinos, such as the beryllium-7 and boron-8 neutrinos. This quite general assumption appears to be enough to analytically calculate the day-night asymmetry factor for such neutrinos. Using the explicit time averaging procedure, we show that, within the leading-order approximation, this factor is determined by the electron density within about one oscillation length under the detector, namely, in the Earth’s crust (and upper mantle for high-energy neutrinos). We also evaluate the effect of the inner Earth’s structure on the observed asymmetry and show that it is suppressed and mainly comes from the neutrinos observed near the winter and summer solstices. As a result, we arrive at the strict interval constraint on the asymmetry, which is valid within quite a wide class of Earth models.

This paper examines the possibility of floating or nondecaying orbits for extreme mass ratio binary black holes. In the adiabatic approximation, valid in the extreme mass ratio case, if the orbital flux lost due to gravitational radiation reaction is compensated for by the orbital flux gained from the spins of the black holes via superradiant scattering (or, equivalently, tidal acceleration), the orbital decay would be stalled, causing the binary to “float.” We show that this flux balance is not, in practice, possible for extreme mass ratio binary black holes with circular equatorial orbits; furthermore, adding eccentricity and inclination to the orbits will not significantly change this null result, thus ruling out the possibility of floating orbits for extreme mass ratio binary black holes. We also argue that binaries consisting of material bodies dense and massive enough to generate gravitational waves detectable by any kind of gravitational wave detector are also unlikely to float. Using a multipolar analysis, we show that a non-Kerr spacetime which could produce a floating orbit (given the same amount of tidal acceleration as in the case of a Kerr black hole) would need to be a rapidly rotating prolate spheroid, which would be an exotic object indeed.

Versions of parameterized pseudo-Newtonian gravity theories specially designed for cosmology have been introduced in recent cosmology literature. The modifications often consider the zero-pressure fluid in the context of versions of modified Poisson-like equation with two different gravitational potentials or an effective gravitational constant. We consider such modifications available in the context of relativistic gravity theories where the action is a general algebraic function of the scalar curvature, the scalar field, and the kinetic term of the field. We show that in general it is not possible to isolate the fluid component even in Einstein’s gravity. Only in the small-scale (far inside the horizon) limit, to the linear order, and assuming the quasistatic approximation, we can realize some special forms of the attempted modifications with limited validity. Theoretically motivated relativistic generalized gravity theories we are considering have much richer cosmological aspects than simply captured by some pseudo-Newtonian modifications. We show that even Einstein’s gravity with a minimally coupled scalar field as a dynamical dark energy demands similar modification in Poisson’s equation and the baryon density perturbation equation.

The expectation values of energy density and pressure of a quantum field inside a wedge-shaped region appear to violate the expected relationship between torque and total energy as a function of angle. In particular, this is true of the well-known Deutsch-Candelas stress tensor for the electromagnetic field, whose definition requires no regularization except possibly at the vertex. Unlike a similar anomaly in the pressure exerted by a reflecting boundary against a perpendicular wall, this problem cannot be dismissed as an artifact of an ad hoc regularization.

This brief report studies the behavior of entropy in two recent models of cosmic evolution by J. A. S. Lima, S. Basilakos, and F. E. M. Costa [Phys. Rev. D 86, 103534 (2012)], and J. A. S. Lima, S. Basilakos, and J. Solá [arXiv:1209.2802]. Both start with an initial de Sitter expansion, go through the conventional radiation and matter dominated eras to be followed by a final and everlasting de Sitter expansion. In spite of their outward similarities (from the observational viewpoint they are arbitrary close to the conventional Lambda cold dark matter model), they deeply differ in the physics behind them. Our study reveals that in both cases the Universe approaches thermodynamic equilibrium in the last de Sitter era in the sense that the entropy of the apparent horizon plus that of matter and radiation inside it increases and is concave. Accordingly, they are consistent with thermodynamics. Cosmological models that do not approach equilibrium at the last phase of their evolution appear in conflict with the second law of thermodynamics.

We construct the most general local solutions to 11-dimensional supergravity (or M theory), which are invariant under the superalgebra $D(2,1;c^{\prime };0)\oplus D(2,1;c^{\prime };0)$ for all values of the parameter $c^{\prime }$. The BPS constraints are reduced to a single linear partial differential equation on a complex function $G$. The physical fields of the solutions are determined by $c^{\prime }$, a freely chosen harmonic function $h$, and the complex function $G$. $h$ and $G$ are both functions on a two-dimensional compact Riemannian manifold. We obtain the expressions for the metric and the field strength in terms of $G$, $h$, and $c^{\prime }$ and show that these are indeed valid solutions of the Einstein, Maxwell, and Bianchi equations. Finally we give a construction of one parameter deformations of ${\mathrm{AdS}}_7\times S^4$ and ${\mathrm{AdS}}_4\times S^7$ as a function of $c^{\prime }$.

We consider a real massless scalar field in $3+1$ dimensions satisfying a Robin boundary condition at a nonrelativistic moving mirror. Considering vacuum as the initial field state, we compute explicitly the number of particles created per unit frequency and per unit solid angle, exhibiting in this way the angular dependence of the spectral distribution. The well-known cases of Dirichlet and Neumann boundary conditions may be reobtained as particular cases from our results. We show that the particle creation rate can be considerably reduced (with respect to the Dirichlet and Neumann cases) for particular values of the Robin parameter. Our results extend, for $3+1$ dimensions, previous results found in the literature for $1+1$ dimensions. Further, we also show that this inhibition of the dynamical Casimir effect occurs for different angles of particle emission.