We derive an analytic expression for the energy spectrum of gravitational waves from a parabolic Keplerian binary by taking the limit of the Peters and Mathews spectrum for eccentric orbits. This demonstrates that the location of the peak of the energy spectrum depends primarily on the orbital periapse rather than the eccentricity. We compare this weak-field result to strong-field calculations and find it is reasonably accurate $(\sim 10\%)$ provided that the azimuthal and radial orbital frequencies do not differ by more than $\sim 10\%$. For equatorial orbits in the Kerr spacetime, this corresponds to periapse radii of $r_p\gtrsim 20M$. These results can be used to model radiation bursts from compact objects on highly eccentric orbits about massive black holes in the local Universe, which could be detected by the Laser Interferometer Space Antenna (LISA).

QED based on $\theta$-unexpanded noncomutative space-time in contrast with the noncommutative QED based on $\theta$-expanded U(1) gauge theory via the Seiberg-Witten map is one-loop renormalizable. Meanwhile it suffers from asymptotic freedom that is not in agreement with the experiment. We show that the QED part of the $U_{\star }(3)\times U_{\star }(1)$ gauge group as an appropriate gauge group for the noncommutative $\mathrm{QED}+\mathrm{QCD}$ is not only one-loop renormalizable but also has a $\beta$ function that can be positive, negative and even zero. In fact the $\beta$ function depends on the mixing parameter ${\delta }_{13}$ as a free parameter and it will be equal to its counterpart in the ordinary QED for ${\delta }_{13}=0.367\pi$.

A formalism to deal with high-order perturbations of a general spherical background was developed in earlier work [D. Brizuela, J. M. Martín-García, and G. A. Mena Marugán, Phys. Rev. D 74, 044039 (2006); D. Brizuela, J. M. Martín-García, and G. A. Mena Marugán, Phys. Rev. D 76, 024004 (2007)]. In this paper, we apply it to the particular case of a perfect fluid background. We have expressed the perturbations of the energy-momentum tensor at any order in terms of the perturbed fluid’s pressure, density, and velocity. In general, these expressions are not linear and have sources depending on lower-order perturbations. For the second-order case we make the explicit decomposition of these sources in tensor spherical harmonics. Then, a general procedure is given to evolve the perturbative equations of motions of the perfect fluid for any value of the harmonic label. Finally, with the problem of a spherical collapsing star in mind, we discuss the high-order perturbative matching conditions across a timelike surface, in particular, the surface separating the perfect fluid interior from the exterior vacuum.

We investigate strong nonlinear damping effects which occur during high amplitude oscillations of neutron stars, and the gravitational waves they produce. For this, we use a general relativistic nonlinear hydrodynamics code in conjunction with a fixed spacetime (Cowling approximation) and a polytropic equation of state (EOS). Gravitational waves are estimated using the quadrupole formula. Our main interest are $l=m=2$ $f$ modes subject to the CFS (Chandrasekhar, Friedman, Schutz) instability, but we also investigate axisymmetric and quasiradial modes. We study various models to determine the influence of rotation rate and EOS. We find that axisymmetric oscillations at high amplitudes are predominantly damped by shock formation, while the nonaxisymmetric $f$ modes are mainly damped by wave breaking and, for rapidly rotating models, coupling to nonaxisymmetric inertial modes. From the observed nonlinear damping, we derive upper limits for the saturation amplitude of CFS-unstable $f$ modes. Finally, we estimate that the corresponding gravitational waves for an oscillation amplitude at the upper limit should be detectable with the advanced LIGO (Laser Interferometer Gravitational Wave Observatory) and VIRGO interferometers at distances above 10 Mpc. This strongly depends on the stellar model, in particular, on the mode frequency.

The halo-galaxy lensing correlation function or the average tangential shear profile over sampled halos is a very powerful means of measuring the halo masses, the mass profile, and the halo-mass correlation function of very large separations in the linear regime. We reformulate the halo-galaxy lensing correlation in harmonic space. We find that, counterintuitively, errors in the conventionally used flat-sky approximation remain at a percent level even at very small angles. The errors increase at larger angles and for lensing halos at lower redshifts: the effect is at a few percent level at the baryonic acoustic oscillation scales for lensing halos of $z\sim 0.2$, and comparable with the effect of primordial non-Gaussianity with $f_{\mathrm{NL}}\sim 10$ at large separations. Our results allow one to readily estimate/correct for the full-sky effect on a high-precision measurement of the average shear profile available from upcoming wide-area lensing surveys.

We investigate the extent to which the uncertainties associated with the propagation of Galactic cosmic rays impact upon estimates for the $\gamma$-ray flux from the mid-latitude region. We consider contributions from both standard astrophysical background (SAB) processes as well as resolved point sources. We have found that the uncertainties in the total $\gamma$-ray flux from the mid-latitude region relating to propagation parameter values consistent with local B/C and ${}^{10}\mathrm{Be}/{}^9\mathrm{Be}$ data dominate by 1–2 orders of magnitude. These uncertainties are reduced to less than an order of magnitude when the normalizations of the SAB spectral components are fitted to the corresponding Fermi LAT data. We have found that for many propagation parameter configurations (PPCs) our fits improve when an extragalactic background (EGB) component is simultaneously fitted to the data. We also investigate the improvement in our fits when a flux contribution from neutralino dark matter (DM), described by the minimal supersymmetric standard model, was simultaneously fitted to the data. We consider three representative cases of neutralino DM for both Burkert and Einasto DM density profiles, in each case simultaneously fitting a boost factor of the DM contribution together with the SAB and EGB components. We have found that for several PPCs there are significant improvements in our fits, yielding both substantial EGB and DM components, where for a few of these PPCs the best-fit EGB component is consistent with recent estimates by the Fermi Collaboration.

We provide a recursive diagrammatic prescription for the exponentiation of gauge theory amplitudes involving products of Wilson lines and loops. This construction generalizes the concept of webs, originally developed for eikonal form factors and cross sections with two eikonal lines, to general soft functions in QCD and related gauge theories. Our coordinate space arguments apply to arbitrary paths for the lines.

We evaluate interhadron interactions in two-color lattice QCD from Bethe-Salpeter amplitudes on the Euclidean lattice. The simulations are performed in quenched SU(2) QCD with the plaquette gauge action at $\beta =2.45$ and the Wilson quark action. We concentrate on $S$-wave scattering states of two scalar diquarks. Evaluating different flavor combinations with various quark masses, we try to find out the ingredients in hadronic interactions. Between two scalar diquarks ($uC{\gamma }_{5}d$, the lightest baryon in SU(2) system), we observe repulsion in short-range region, even though present quark masses are not very light. We define and evaluate the quark-exchange part in the interaction, which is induced by adding quark-exchange diagrams, or equivalently, by introducing Pauli-blocking among some of quarks. The repulsive force in short-distance region arises only from the quark-exchange part and disappears when quark-exchange diagrams are omitted. We find that the strength of repulsion grows in light quark-mass regime, and its quark-mass dependence is similar to or slightly stronger than that of the color-magnetic interaction by one-gluon-exchange (OGE) processes. It is qualitatively consistent with the constituent-quark-model picture that a color-magnetic interaction among quarks is the origin of repulsion. We also find a universal long-range attractive force, which enters in any flavor channels of two scalar diquarks and whose interaction range and strength are quark-mass independent. The weak quark-mass dependence of interaction ranges in each component implies that meson-exchange contributions are small and subdominant, and the other contributions, e.g., flavor-exchange processes, color-Coulomb, or color-magnetic interactions, are considered to be predominant, in the quark-mass range we evaluated.

We investigate some aspects of the self-consistency in the Dyson-Schwinger approach to both the QED and the self-interacting scalar field theories. We prove that the set of the Dyson-Schwinger equations, together with the Green-Ward-Takahashi identity, is equivalent to the analogous set of integral equations studied in condensed matter, namely, many-body perturbation theory, where it is solved self-consistently and iteratively. In this framework, we compute the nonperturbative solution of the gap equation for the self-interacting scalar field theory.

The rare decays of the ${\Lambda }_b$ baryon governed by the quark level transitions $b\to s$ are investigated in the fourth quark generation model popularly known as SM4. Recently it has been shown that SM4, which is a very simple extension of the standard model, can successfully explain several anomalies observed in the $CP$ violation parameters of $B$ and $B_s$ mesons. We find that in this model due to the additional contributions coming from the heavy $t^{\prime }$ quark in the loop, the branching ratios and other observables in rare ${\Lambda }_b$ decays deviate significantly from their standard model values. Some of these modes are within the reach of the LHCb experiment and search for such channels is strongly argued.

In high-energy processes near the endpoint, there emerge new contributions associated with spectator interactions. Away from the endpoint region, these new contributions are suppressed compared to the leading contribution, but the leading contribution becomes suppressed as we approach the endpoint and the new contributions become comparable. We present how the new contributions scale as we reach the endpoint and show that they are comparable to the suppressed leading contributions in deep inelastic scattering by employing a power-counting analysis. The hadronic tensor in deep inelastic scattering is shown to factorize including the spectator interactions, and it can be expressed in terms of the light cone distribution amplitudes of initial hadrons. We also consider the contribution of the spectator contributions in Drell-Yan processes. Here the spectator interactions are suppressed compared to double parton annihilation according to the power counting.

We study the thermodynamics and the phase structures of Reissner-Nordström and Born-Infeld black holes in AdS space by constructing “off-shell” free energies using thermodynamic quantities derived directly from the action. We then use these results to propose “off-shell” effective potentials for the respective boundary gauge theories. The saddle points of the potentials describe all the equilibrium phases of the gauge theories.

We investigate the structure of quantum correlations in an expanding Bose-Einstein condensate (BEC) through the analogue gravity framework. We consider both a $3+1$ isotropically expanding BEC as well as the experimentally relevant case of an elongated, effectively $1+1$ dimensional, expanding condensate. In this case we include the effects of inhomogeneities in the condensate, a feature rarely included in the analogue gravity literature. In both cases we link the BEC expansion to a simple model for an expanding spacetime and then study the correlation structure numerically and analytically (in suitable approximations). We also discuss the expected strength of such correlation patterns and experimentally feasible BEC systems in which these effects might be detected in the near future.

The structure of the phase diagram for strong interactions becomes richer in the presence of a magnetic background, which enters as a new control parameter for the thermodynamics. Motivated by the relevance of this physical setting for current and future high-energy heavy-ion collision experiments and for the cosmological QCD transitions, we use the linear sigma model coupled to quarks and to Polyakov loops as an effective theory to investigate how the chiral and the deconfining transitions are affected, and present a general picture for the temperature–magnetic field phase diagram. We compute and discuss each contribution to the effective potential for the approximate order parameters, and uncover new phenomena such as the paramagnetically induced breaking of global ${\mathbb{Z}}_3$ symmetry, and possible splitting of deconfinement and chiral transitions in a strong magnetic field.

The nucleon-nucleon scattering in a large magnetic background is considered to find its potential to change the neutrino emissivity of the neutron stars. For this purpose, we consider the one-pion-exchange approximation to find the nucleon-nucleon (NN) cross section in a background field as large as ${10}^{15}–{10}^{18}\mathtt{G}$. We show that the NN cross section in neutron stars with temperatures in the range 0.1–5 MeV can be changed up to the 1 order of magnitude with respect to the one in the absence of the magnetic field. In the limit of the soft neutrino emission, the neutrino emissivity can be written in terms of the NN-scattering amplitude; therefore, the large magnetic fields can dramatically change the neutrino emissivity of the neutron stars as well.

We propose a model where a sterile Majorana fermion with mass in the range of 10 GeV–1 TeV can account for the whole amount of dark matter in the Universe. The model involves a right-handed singlet Majorana fermion as a weakly interacting massive particle, a charged and a neutral scalar, and all singlets by the standard model symmetry and makes use of a discrete symmetry in order to guarantee the singlet fermion stability. Also, motivated by the recent results reported by CoGeNT and CDMS-II experiments concerning excess events of the expected background, and the intriguing annual modulation observed by DAMA, we look for a possible explanation to some of these experiments. Our results show that there is a lot of room in the parameter space to make this sterile Majorana fermion a viable dark matter candidate, and, if it is realized in nature, it is also capable of explaining DAMA annual modulation signal and/or CoGeNT excess events or CDMS-II excess event candidates. Besides, a light Higgs boson is preferred in this scenario.

In this paper we complete the program of the noncomutative geometry inspired black holes, providing the richest possible solution, endowed with mass, charge and angular momentum. After providing a prescription for employing the Newman-Janis algorithm in the case of nonvanishing stress tensors, we find regular axisymmetric charged black holes in the presence of a minimal length. We study also the new thermodynamics and we determine the corresponding higher-dimensional solutions. As a conclusion we make some consideration about possible applications.

We find exact static stringy solutions of Hořava-Lifshitz gravity with the projectability condition but imposing the detailed balance condition near the UV fixed point, and propose a method on constraining the possible pattern of flows in Hořava-Lifshitz gravity by using the obtained classical solutions. In the obtained vacuum solutions, the parameters related to the speed of the graviton and the coefficients of quartic spatial derivative terms lead to intriguing effects: the change of graviton speed yields a surplus angle and the quartic derivatives make the square of effective electric charge negative. The result of a few tests based on the geometries of a cone, an excess cone, a black string, and a charged (black) string seems suggestive. For example, the flow of constant graviton speed and variable Newton’s coupling can be favored in the vicinity of an IR fixed point, but the conclusion is indistinct and far from definite yet. Together with the numerous classical solutions, static or time dependent, which have already been found, the accumulated data from various future tests will give some hints in constraining the flow patterns more deterministic.

We examine numerically the process of momentum extraction by gravitational waves in the merger of two colliding black holes, in the realm of Robinson-Trautman spacetimes. The initial data have already a common horizon so that the evolution covers the post-merger phase up to the final configuration of the remnant black hole. The analysis of the momentum flux carried out by gravitational waves indicates that two distinct regimes are present in the post-merger phase: (i) an initial accelerated regime, followed by (ii) a deceleration regime in which the deceleration increases rapidly towards a maximum and then decreases to zero, when the gravitational wave emission ceases. The analysis is based on the Bondi-Sachs conservation law for the total momentum of the system. We obtain the total kick velocity $V_k$ imparted on the merged black hole during the accelerated regime (i) and the total antikick velocity $V_{\mathrm{ak}}$ during the decelerated regime (ii), by evaluating the impulse of the gravitational wave flux during both regimes. The distributions of both $V_k$ and $V_{\mathrm{ak}}$ as a function of the symmetric mass ratio $\eta$ satisfy a simple $\eta$-scaling law motivated by post-Newtonian analytical estimates. In the $\eta$-scaling formula the Newtonian factor is dominant in the decelerated regime, that generates $V_{\mathrm{ak}}$, contrary to the behavior in the initial accelerated regime. For an initial infalling velocity $v/c\simeq 0.462$ of each individual black hole we obtain a maximum kick $V_k\simeq 6.4\mathrm{km}/\mathrm{s}$ at $\eta \simeq 0.209$, and a maximum antikick $V_{\mathrm{ak}}\simeq 109\mathrm{km}/\mathrm{s}$ at $\eta \simeq 0.205$. The net antikick velocity ($V_{\mathrm{ak}}-V_k$) also satisfies a similar $\eta$-scaling law with a maximum approximately $102\mathrm{km}/\mathrm{s}$ also at $\eta \simeq 0.205$, qualitatively consistent with results from numerical relativity simulations, and post-Newtonian evaluations of binary black hole inspirals. For larger values of the initial data parameter $v/c$ substantial larger values of the net antikick velocity are obtained. Based on the several velocity variables obtained, we discuss a possible definition of the center-of-mass motion of the merged system.