We present the numerical code precession, a new open-source python module to study the dynamics of precessing black-hole binaries in the post-Newtonian regime. The code provides a comprehensive toolbox to (i) study the evolution of the black-hole spins along their precession cycles, (ii) perform gravitational-wave-driven binary inspirals using both orbit-averaged and precession-averaged integrations, and (iii) predict the properties of the merger remnant through fitting formulas obtained from numerical-relativity simulations. precession is a ready-to-use tool to add the black-hole spin dynamics to larger-scale numerical studies such as gravitational-wave parameter estimation codes, population synthesis models to predict gravitational-wave event rates, galaxy merger trees and cosmological simulations of structure formation. precession provides fast and reliable integration methods to propagate statistical samples of black-hole binaries from/to large separations where they form to/from small separations where they become detectable, thus linking gravitational-wave observations of spinning black-hole binaries to their astrophysical formation history. The code is also a useful tool to compute initial parameters for numerical-relativity simulations targeting specific precessing systems. precession can be installed from the python Package Index, and it is freely distributed under version control on github, where further documentation is provided.

We discuss various modified dispersion relations motivated by quantum gravity which might affect the propagation of the recently observed gravitational-wave signal of the event GW150914. We find that the bounds set by the data on the characteristic quantum-gravity mass scale $M$ are too weak to constrain these scenarios and, in general, much weaker than the expected $M>{10}^4\mathrm{eV}$ for a correction to the dispersion relation linear in $1/M$. We illustrate this issue by giving lower bounds on $M$, plus an upper bound coming from constraints on the size of a quantum ergosphere. We also show that a phenomenological dispersion relation ${\omega }^2=k^2(1+\alpha k^n/M^n)$ is compatible with observations and, at the same time, has a phenomenologically viable mass $M>10\mathrm{TeV}$ only in the quite restrictive range $0<n<0.68$. Remarkably, this is the domain of multiscale spacetimes but not of known quantum-gravity models.

The geometrical localization mechanism in Randall-Sundrum (RS) scenarios is extended by considering the coupling between a quadratic mass term and geometrical tensors. Since the quadratic term is symmetric, tensors with two symmetric indices have to be taken into account. These are the Ricci and the Einstein tensors. For the Ricci tensor, it is shown that a localized zero mode exists while that is not possible for the Einstein tensor. It is already known that the Ricci scalar generates a localized solution but the metrics do not. Therefore, it can be concluded that divergenceless tensors do not localize the zero mode of the gauge fields. The result is valid for any warp factor recovering the RS metrics at the boundaries and, therefore, is valid for RS I and II models. We also compute resonances for all couplings. These are calculated using the transfer matrix method. The cases studied consider the standard RS with deltalike branes and branes generated by kinks and domain walls as well. The parameters are changed to control the thickness of the smooth brane. We find that, for all cases considered, geometrical coupling does not generate resonances. This enforces similar results for the coupling with the Ricci scalar and points to the existence of some unidentified fundamental structure of these couplings.

We study the scope of the Large Hadron Collider in accessing a neutral Higgs boson of the $B-L$ supersymmetric standard model. After assessing the surviving parameter space configurations following the Run 1 data taking, we investigate the possibilities of detecting this object during Run 2. For the model configurations in which the mixing between such a state and the discovered standard-model-like Higgs boson is non-negligible, there exist several channels enabling its discovery over a mass range spanning from $\approx 140$ to $\approx 500\mathrm{GeV}$. For a heavier Higgs state, with mass above 250 GeV (i.e., twice the mass of the Higgs state discovered in 2012), the hallmark signature is its decay in two such 125 GeV scalars, $h^{\prime }\to hh$, where $hh\to b\overline{b}\gamma \gamma$. For a lighter Higgs state, with mass of order 140 GeV, three channels are accessible: $\gamma \gamma$, $Z\gamma$, and $ZZ$, wherein the $Z$ boson decays leptonically. In all such cases, significances above discovery can occur for already planned luminosities at the CERN machine.

Numerical approaches to higher-order calculations often employ subtraction terms, both for the real emission and the virtual corrections. These subtraction terms have to be added back. In this paper we show that at NLO the real subtraction terms, the virtual subtraction terms, the integral representations of the field renormalization constants and—in the case of initial-state partons—the integral representation for the collinear counterterm can be grouped together to give finite integrals, which can be evaluated numerically. This is useful for an extension towards next-to-next-to-leading order.

We have analyzed the phenomenological dependence of the spin independent ($F_1^{p,n}$ and $F_2^{p,n}$) and the spin dependent ($g_1^{p,n}$) structure functions of the nucleon on the Bjorken scaling variable $x$ using the unpolarized distribution functions of the quarks $q(x)$ and the polarized distribution functions of the quarks $\mathrm{\Delta }q(x)$ respectively. The chiral constituent quark model, which is known to provide a satisfactory explanation of the proton spin crisis and related issues in the nonperturbative regime, has been used to compute explicitly the valence and sea quark flavor distribution functions of $p$ and $n$. In light of the improved precision of the world data, the $p$ and $n$ longitudinal spin asymmetries [$A_1^p(x)$ and $A_1^n(x)$] have been calculated. The implication of the presence of the sea quarks has been discussed for the ratio of polarized to unpolarized quark distribution functions for up and down quarks in the $p$ and $n$ $\frac{\mathrm{\Delta }{u}^p(x)}{u^p(x)}$, $\frac{\mathrm{\Delta }{d}^p(x)}{d^p(x)}$, $\frac{\mathrm{\Delta }{u}^n(x)}{u^n(x)}$, and $\frac{\mathrm{\Delta }{d}^n(x)}{d^n(x)}$. The ratio of the $n$ and $p$ structure functions $R^{np}(x)=\frac{F_2^n(x)}{F_2^p(x)}$ has also been presented. The results have been compared with the recent available experimental observations. The results on the spin sum rule have also been included and compared with data and other recent approaches.

We present the first detailed study of the kinematics of free relativistic particles whose symmetries are compatible with the ones described by a quantum deformation of the de Sitter algebra, known as $q$–de Sitter Hopf algebra. In such algebra, the quantum deformation parameter is a function of the Planck length $\ell$ and the de Sitter radius $H^{-1}$, such that when the Planck length vanishes, the algebra reduces to the de Sitter algebra, while when the de Sitter radius is sent to infinity, one recovers the $\kappa$-Poincaré Hopf algebra. In the first limit, the picture is that of a particle with trivial momentum space geometry moving on de Sitter spacetime; in the second one, the picture is that of a particle with de Sitter momentum space geometry moving on Minkowski spacetime. When both the Planck length and the inverse of the de Sitter radius are nonzero, effects due to spacetime curvature and nontrivial momentum space geometry are both present and affect each other. The particles’ motion is then described in a full phase-space picture. We find that redshift effects that are usually associated with spacetime curvature become energy dependent. Also, the energy dependence of the particles’ travel times that is usually associated with momentum space nontrivial properties is modified in a curvature-dependent way.

We present results on the inspiral, merger, and postmerger evolution of a neutron star-neutron star (NSNS) system. Our results are obtained using the hybrid pseudospectral-finite volume Spectral Einstein Code (SpEC). To test our numerical methods, we evolve an equal-mass system for $\approx 22$ orbits before merger. This waveform is the longest waveform obtained from fully general-relativistic simulations for NSNSs to date. Such long (and accurate) numerical waveforms are required to further improve semianalytical models used in gravitational wave data analysis, for example, the effective one body models. We discuss in detail the improvements to SpEC’s ability to simulate NSNS mergers, in particular mesh refined grids to better resolve the merger and postmerger phases. We provide a set of consistency checks and compare our results to NSNS merger simulations with the independent bam code. We find agreement between them, which increases confidence in results obtained with either code. This work paves the way for future studies using long waveforms and more complex microphysical descriptions of neutron star matter in SpEC.

Although gravitational radiation causes inspiralling compact binaries to circularize, a variety of astrophysical scenarios suggest that binaries might have small but non-negligible orbital eccentricities when they enter the low-frequency bands of ground- and space-based gravitational-wave detectors. If not accounted for, even a small orbital eccentricity can cause a potentially significant systematic error in the mass parameters of an inspiralling binary [M. Favata, Phys. Rev. Lett. 112, 101101 (2014)]. Gravitational-wave search templates typically rely on the quasicircular approximation, which provides relatively simple expressions for the gravitational-wave phase to 3.5 post-Newtonian (PN) order. Damour, Gopakumar, Iyer, and others have developed an elegant but complex quasi-Keplerian formalism for describing the post-Newtonian corrections to the orbits and waveforms of inspiralling binaries with any eccentricity. Here, we specialize the quasi-Keplerian formalism to binaries with low eccentricity. In this limit, the nonperiodic contribution to the gravitational-wave phasing can be expressed explicitly as simple functions of frequency or time, with little additional complexity beyond the well-known formulas for circular binaries. These eccentric phase corrections are computed to 3PN order and to leading order in the eccentricity for the standard PN approximants. For a variety of systems, these eccentricity corrections cause significant corrections to the number of gravitational-wave cycles that sweep through a detector’s frequency band. This is evaluated using several measures, including a modification of the useful cycles. By comparing to numerical solutions valid for any eccentricity, we find that our analytic solutions are valid up to $e_0\lesssim 0.1$ for comparable-mass systems, where $e_0$ is the eccentricity when the source enters the detector band. We also evaluate the role of periodic terms that enter the phasing and discuss how they can be incorporated into some of the PN approximants. While the eccentric extension of the PN approximants is our main objective, this work collects a variety of results that may be of interest to others modeling eccentric relativistic binaries. This includes a consistent eccentricity expansion of the Newtonian-order polarizations and a comparison of quasi-Keplerian results with numerical simulations. In addition to applications in gravitational-wave data analysis, the formulas derived here could be of use in comparing PN theory with numerical relativity or self-force calculations of eccentric binaries. They could also be useful in the construction of phenomenological inspiral-merger-ringdown waveforms that include eccentricity effects.

We numerically study the scattering coefficients of linear water waves on stationary flows above a localized obstacle. We compare the scattering on trans- and subcritical flows, and then focus on the latter which have been used in recent analog gravity experiments. The main difference concerns the magnitude of the mode amplification: whereas transcritical flows display a large amplification (which is generally in good agreement with the Hawking prediction), this effect is heavily suppressed in subcritical flows. This is due to the transmission across the obstacle for frequencies less than some critical value. As a result, subcritical flows display high- and low-frequency behaviors separated by a narrow band around the critical frequency. In the low-frequency regime, transmission of long wavelengths is accompanied by nonadiabatic scattering into short wavelengths, whose spectrum is approximately linear in frequency. By contrast, in the high-frequency regime, no simple description seems to exist. In particular, for obstacles similar to those recently used, we observe that the upstream slope still affects the scattering on the downstream side because of some residual transmission.

Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant $\alpha$. Here we take advantage of recent observational progress and use a combination of background cosmological observations of type Ia supernovas and astrophysical and local measurements of $\alpha$ to improve constraints on this class of models. We show that the constraints on $\alpha$ imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state $(1+w_0)<2.4\times {10}^{-7}$ at the 99.7% confidence level. Therefore current and forthcoming standard background cosmology observational probes cannot distinguish this class of models from a cosmological constant, while detections of $\alpha$ variations could possibly do so since they would have a characteristic redshift dependence.

The production of particle-antiparticle pairs from the quantum field theoretic ground state in the presence of an external electric field is studied. Starting with the quantum-kinetic Boltzmann-Vlasov equation in four-dimensional spacetime, we obtain the corresponding equations in lower dimensionalities by way of spatial compactification. Our outcomes in $2+1$ dimensions are applied to bandgap graphene layers, where the charge carriers have the particular property of behaving like light massive Dirac fermions. We calculate the single-particle distribution function for the case of an electric field oscillating in time and show that the creation of particle-hole pairs in this condensed matter system closely resembles electron-positron pair production by the Schwinger effect.

We investigate the isospin symmetry breaking effects within a recently derived Nambu-Jona-Lasinio related model by fitting the measured pseudoscalar meson masses and weak decay couplings $f_{\pi }$, $f_K$. Our model contains the next to leading order terms in the $1/N_c$ expansion of the effective multiquark Lagrangian, including the ones that break the chiral symmetry explicitly. We show the important phenomenological role of these interactions: (1) They lead to an accurate fit of the low-lying pseudoscalar nonet characteristics. (2) They account for a very good agreement of the current quark masses with the present PDG values. (3) They reduce by 40% the ratio $\epsilon /{\epsilon }^{\prime }$ of the ${\pi }^0-\eta$ and ${\pi }^0-{\eta }^{\prime }$ mixing angles, as compared to the case that contemplates explicit breaking only in the leading order, bringing it in consonance with the quoted values in the literature. The conventional NJL-type models fail in the joint description of these parameters.

We investigate the parameter space of the Standard Model enhanced by a gauge singlet real scalar $S$. Taking into account all the theoretical and experimental constraints, we show the allowed parameter space for two different types of such singlet-enhanced Standard Model. For the first case, the scalar potential has an explicit $Z_2$ symmetry and may lead to a dark matter candidate under certain conditions. For the second case, the scalar potential does not respect any $Z_2$. This is again divided into two subcategories: one where the Standard Model vacuum is stable, and one where it is unstable and can decay into a deeper minimum. We show how the parameters in the scalar potential control the range of validity of all these models. Finally, we show the effect of one-loop correction on the positions and depths of the minima of the potential.

Current discussions of the allowed two-Higgs-doublet model parameter space after LHC run 1 and the prospects for run 2 are commonly phrased in the context of a quasidegenerate spectrum for the new scalars. Here, we discuss the generic situation of a two-Higgs-doublet model with a nondegenerate spectrum for the new scalars. This is highly motivated from a cosmological perspective since it naturally leads to a strongly first-order electroweak phase transition that could explain the matter-antimatter asymmetry in the Universe. While constraints from measurements of Higgs signal strengths do not change, those from searches of new scalar states get modified dramatically once a nondegenerate spectrum is considered.

We explore the possibility to explain the 750 GeV diphoton excess recently measured by ATLAS and CMS collaborations in terms of a massive spin-2 particle. In particular, we consider the case in which the top-quark loops can give similar amplitudes as the tree-level contributions to the diphoton and digluon channels. Such a scenario can be naturally realized in the generalized warped extradimension models. As a result, the parameter space favored by the diphoton data implies that the top-quark loop contribution can compete to and even dominate over the tree-level amplitude in the spin-2 particle production via the gluon-gluon fusion process. Similar results are obtained for the case in which the spin-2 particle induces large invisible decay branching ratios, as indicated by the ATLAS data.

The cross section of the double heavy diquark pair production process $pp\to (bc)+(\overline{b}\overline{c})+X$ is calculated in the leading order of the gluonic fusion channel, with all four possible color and spin combinations—$[{}^1{S}_0{]}_{\overline{3}}$, $[{}^1{S}_0{]}_6$, $[{}^3{S}_1{]}_{\overline{3}}$, and $[{}^3{S}_1{]}_6$ for each of the two final diquarks—taken into account. Several sources of relativistic corrections to the cross section are handled in the framework of the relativistic quark model. Perturbative $\mathcal{O}(v^2)$ corrections originating from the production amplitude expansions in heavy quark relative velocity $v$ depend on the color and spin states of the final particles, but can be generally considered as unimportant, giving maximally 12% improvement in numerically significant cases. Modifications of the quark-quark and antiquark-antiquark bound state wave functions caused by the appropriate generalization of the Breit interaction potential have a rather severe impact on the cross section, suppressing it almost 3 times. Under the assumption of antitriplets’ and sextuplets’ nonperturbative parameters having the same order of magnitude, it is shown that the color-sextet mechanism strongly dominates pair diquark production in both nonrelativistic and relativistic approximations.

The helicity of a Dirac neutrino with mass $m$ evolves under the influence of a $B$ field because it has a magnetic dipole moment proportional to $m$. Moreover, it was recently shown that a polarized or anisotropic medium engenders the same effect for both Dirac and Majorana neutrinos. Because a $B$ field polarizes a background medium, it instigates helicity oscillations even for Majorana neutrinos unless the medium is symmetric between matter and antimatter. Motivated by these observations, we review the impact of a $B$ field and of an anisotropic or polarized medium on helicity oscillations for Dirac and Majorana neutrinos from the common perspective of in-medium dispersion.

It is known that in contrast with the $E$-mode polarization the $B$-mode polarization of the cosmic microwave background cannot be generated by the Compton scattering in the case of the scalar mode of metric perturbation. However, it is possible to generate the $B$ mode by the Compton scattering in the case of the tensor mode of metric perturbation. For this reason, the ratio of tensor to scalar modes of metric perturbation ($r\sim C_{Bl}/C_{El}$) is estimated by comparing the $B$-mode power spectrum with the $E$ mode at least for small $l$. We study the cosmic microwave background polarization, especially the $B$ mode due to the weak interaction of the cosmic neutrino background and cosmic microwave background, in addition to the Compton scattering in both cases of scalar and tensor metric perturbations. It is shown that the power spectrum $C_{Bl}$ of the $B$-mode polarization receives some contributions from scalar and tensor modes, which have effects on the value of the $r$ parameter. We also show that the $B$-mode polarization power spectrum can be used as an indirect probe into the cosmic neutrino background.