We report on a remarkable class of exact solutions to force-free electrodynamics that has four-current along the light cones of an arbitrary timelike worldline in flat spacetime. No symmetry is assumed, and the solutions are given in terms of a free function of three variables. The field configuration should describe the outer magnetosphere of a pulsar moving on the worldline. The power radiated is the sum of an acceleration (Larmor-type) term and a pulsar-type term.

We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency $50\le f_0/\mathrm{Hz}\le 2000$ and decay timescale $0.0001\lesssim \tau /\mathrm{s}\lesssim 0.1$ characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass $50\le M/{\mathrm{M}}_{\odot }\le 450$ and component mass ratios of either 1:1 or 4:1. For systems with total mass $100\le M/{\mathrm{M}}_{\odot }\le 150$, we report a 90% confidence upper limit on the rate of binary IMBH mergers with nonspinning and equal mass components of $6.9\times {10}^{-8}{\mathrm{Mpc}}^{-3}{\mathrm{yr}}^{-1}$. We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, $\ell =m=2$, oscillation mode, that is nearly three orders of magnitude more stringent than previous results.

Precessing black hole-neutron star (BH-NS) binaries produce a rich gravitational wave signal, encoding the binary’s nature and inspiral kinematics. Using the lalinference_mcmc Markov chain Monte Carlo parameter estimation code, we use two fiducial examples to illustrate how the geometry and kinematics are encoded into the modulated gravitational wave signal, using coordinates well adapted to precession. Extending previous work, we demonstrate that the performance of detailed parameter estimation studies can often be estimated by “effective” studies: comparisons of a prototype signal with its nearest neighbors, adopting a fixed sky location and idealized two-detector network. Using a concrete example, we show that higher harmonics provide nonzero but small local improvement when estimating the parameters of precessing BH-NS binaries. We also show that higher harmonics can improve parameter estimation accuracy for precessing binaries by breaking leading-order discrete symmetries and thus ruling out approximately degenerate source orientations. Our work illustrates quantities gravitational wave measurements can provide, such as the orientation of a precessing short gamma ray burst progenitor relative to the line of sight. More broadly, “effective” estimates may provide a simple way to estimate trends in the performance of parameter estimation for generic precessing BH-NS binaries in next-generation detectors. For example, our results suggest that the orbital chirp rate, precession rate, and precession geometry are roughly independent observables, defining natural variables to organize correlations in the high-dimensional BH-NS binary parameter space.

We discuss neutrino masses and mixing in the context of seesaw type I models with three right-handed Majorana neutrinos and an approximately diagonal Dirac sector. This ansatz is motivated by the idea that the flavor structure in the right-handed Majorana masses is responsible for the large mixing angles, whereas the small mixing angle ${\theta }_{13}$ originates from the Dirac Yukawa couplings in analogy to the quark sector. To obtain ${\theta }_{13}\approx 0.15$ we study a possible $SU(5)$ grand unified theory realization with a $U(1)\times {\mathbb{Z}}_2^{\prime }\times {\mathbb{Z}}_2^{\prime \prime }\times {\mathbb{Z}}_2^{\prime \prime \prime }$ flavor symmetry and include a complex perturbation parameter in the Dirac mass matrix. The consequences for $CP$ violating phases and effects on leptogenesis are investigated.

This paper investigates the collider phenomenology of a minimal nonthermal dark matter model with a 1-GeV dark matter candidate, which naturally explains baryogenesis. Since the light dark matter is not parity protected, it can be singly produced at the LHC. This leads to large missing energy associated with an energetic jet whose transverse momentum distribution is featured by a Jacobian-like shape. The monojet, dijet, paired dijet, and two jets + missing energy channels are studied. Currently existing data at the Tevatron and LHC offer significant bounds on our model.

We investigate resonant di-Higgs production as a means of probing extended scalar sectors that include a 125 GeV Standard Model-like Higgs boson. For concreteness, we consider a gauge singlet Higgs portal scenario leading to two mixed doublet-singlet states, $h_{1,2}$. For $m_{h_2}>2m_{h_1}$, the resonant di-Higgs production process $pp\to h_2\to h_1{h}_1$ will lead to final states associated with the decaying pair of Standard Model-like Higgs scalars. We focus on $h_2$ production via gluon fusion and on the $b\overline{b}{\tau }^{+}{\tau }^{-}$ final state. We find that discovery of the $h_2$ at the LHC may be achieved with $\lesssim 100{\mathrm{fb}}^{-1}$ of integrated luminosity for benchmark parameter choices relevant to cosmology. Our analysis directly maps onto the decoupling limit of the next-to-minimal supersymmetric Standard Model and more generically onto extensions of the Standard Model Higgs sector in which a heavy scalar produced through gluon-fusion decays to a pair of Standard Model-like Higgs bosons.

We investigate new contributions to the neutron electric dipole moment induced by colored scalars. As an example, we evaluate contributions coming from the color octet, weak doublet scalar, accommodated within a modified minimal flavor-violating framework. These flavor nondiagonal couplings of the color octet scalar might account for the measured asymmetry $a_{CP}(D^0\to K^{-}{K}^{+})-a_{CP}(D^0\to {\pi }^{+}{\pi }^{-})$ at tree level. The same couplings constrained by this asymmetry also induce two-loop contributions to the neutron electric dipole moment. We find that the direct CP-violating asymmetry in neutral $D$-meson decays is more constraining on the allowed parameter space than the current experimental bound on the neutron electric dipole moment. We comment also on contributions of higher-dimensional operators to the neutron electric dipole moment within this framework.

In the generic domain wall fermion formulation of chiral fermions on the lattice, the zero modes of the four-dimensional Wilson fermion operator with the negative mass parameter $-M_5$ introduce unphysical massive modes propagating in the four-dimensional spacetime. In the free fermion case, the pole mass of this kind of unphysical modes is given by $\tilde{E}=\ln (1-M_5)$, which acquires an imaginary part, $i\pi$, when $M_5>1$ and results in an oscillatory behavior of the domain wall fermion propagator in time. The existence of the unphysical modes in the presence of gauge fields is investigated in the mean field approximation, and their physical consequences are discussed. In addition, we also give a semiquantitative criterion for tuning $M_5$ in the realistic numerical study.

We consider the transverse momentum dependent (TMD) quark densities of the proton which are very important ingredients for unpolarized Drell-Yan lepton pair production in proton-proton collisions at the LHC energies. We investigate the case where the gluon-to-quark splitting occurs at the last evolution step and calculate the TMD sea quark density as a convolution of the Catani-Ciafaloni-Fiorani-Marchesini-evolved gluon distribution and the TMD gluon-to-quark splitting function. This splitting function contains all single logarithmic small-$x$ corrections to the sea quark evolution for any order of perturbation theory. Based on the $\mathcal{O}(\alpha )$ production amplitude $q^{*}+{\overline{q}}^{*}\to Z/{\gamma }^{*}\to l^{+}+l^{-}$, calculated by taking into account the effective $q^{*}{\overline{q}}^{*}Z/{\gamma }^{*}$ vertex, we analyze the distributions on the dilepton invariant mass, transverse momentum and rapidity and specific angular correlations between the produced leptons as measured by the CMS, ATLAS and LHCb collaborations. We show that our predictions are sensitive to the TMD quark distributions of the proton.

We investigate the effect of a strong magnetic field on dynamical chiral symmetry breaking in quenched and unquenched QCD. To this end we apply the Ritus formalism to the coupled set of (truncated) Dyson-Schwinger equations for the quark and gluon propagator under the presence of an external constant Abelian magnetic field. We work with an approximation that is trustworthy for large fields $eH>{\mathrm{\Lambda }}_{\text{QCD}}^2$ but is not restricted to the lowest Landau level. We confirm the linear rise of the quark condensate with a large external field previously found in other studies and observe the transition to the asymptotic power law at extremely large fields. We furthermore quantify the validity of the lowest Landau level approximation and find substantial quantitative differences to the full calculation even at very large fields. We discuss unquenching effects in the strong field propagators, condensate and the magnetic polarization of the vacuum. We find a significant weakening of magnetic catalysis caused by the backreaction of quarks on the Yang-Mills sector. Our results support explanations of the inverse magnetic catalysis found in recent lattice studies due to unquenching effects.

A measurement of the parity-violating decay asymmetry parameter, ${\alpha }_b$, and the helicity amplitudes for the decay ${\mathrm{\Lambda }}_b^0\to J/\psi ({\mu }^{+}{\mu }^{-}){\mathrm{\Lambda }}^0(p{\pi }^{-})$ is reported. The analysis is based on 1400 ${\mathrm{\Lambda }}_b^0$ and ${\overline{\mathrm{\Lambda }}}_b^0$ baryons selected in $4.6{\mathrm{fb}}^{-1}$ of proton–proton collision data with a center-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the ${\mathrm{\Lambda }}_b^0$ and ${\overline{\mathrm{\Lambda }}}_b^0$ samples under the assumption of $CP$ conservation, the value of ${\alpha }_b$ is measured to be $0.30\pm 0.16(\text{stat})\pm 0.06(\text{syst})$. This measurement provides a test of theoretical models based on perturbative QCD or heavy-quark effective theory.

The previous thermodynamic treatment for models with density and/or temperature dependent quark masses is shown to be inconsistent with the requirement of fundamental thermodynamics. We therefore study a fully self-consistent one according to the fundamental differential equation of thermodynamics. After obtaining a new quark mass scaling with the inclusion of both confinement and leading-order perturbative interactions, we investigate properties of strange quark matter in the fully consistent thermodynamic treatment. It is found that the equation of state become stiffer, and accordingly, the maximum mass of strange stars is as large as about 2 times the solar mass, if strange quark matter is absolutely or metastable.

The closed-time-path (CTP) formalism is applied, in the framework of open quantum systems, to study the time evolution of the expectation value of the energy-momentum tensor of a scalar field in the presence of real materials. We analyze quantum (Casimir) fluctuations in a fully nonequilibrium scenario, when the scalar field is interacting with the polarization degrees of freedom of matter, described as quantum Brownian particles (harmonic oscillators coupled to a bath) at each point of space. A generalized analysis is done for two types of couplings between the field and the polarization degrees of freedom. On the one hand, we consider a bilinear coupling between the field and the polarization degrees of freedom, and on the other hand, a (more realistic) current-type coupling as in the case of the electromagnetic field interacting with matter. We successfully compute the CTP generating functional for the field through calculating the corresponding influence functionals. We consider the high-temperature limit for the field, keeping arbitrary temperatures for each part of the material’s volume elements. We obtain a closed form for the Hadamard propagator, which allows us to study the dynamical evolution of the expectations values of the energy-momentum tensor components from the initial time when the interactions are turned on. We show that two contributions always take place in the transient evolution: one is associated with the material, and the other is only associated with the field. Transient features are studied and the long-time limit is derived in several cases. We prove that in the steady situation of a field in $n+1$ dimensions, the material always contributes unless it is nondissipative. Conversely, the proper field contribution vanishes unless the material is nondissipative or—at least for the $1+1$ case—if there are regions without material. We finally conclude that any steady quantization scheme in $1+1$ dimensions must consider both contributions and, on the other hand, we argue why these results are physically expected from a dynamical point of view, and also could be valid for higher dimensions based on the expected continuity between the nondissipative and real-material cases.

We show how the neutrino can sacrifice itself to quantum gravity and save the axion solution to the strong-$CP$ problem. This mechanism puts an upper bound on the lightest neutrino mass.

We study the quantum entanglement of the quasiparticle pairs emitted by analog black holes. We use a phenomenological description of the spectra in dispersive media to study the domains in parameter space where the final state is nonseparable. In stationary flows, three modes are involved in each sector of fixed frequency, and not two as in homogeneous situations. The third spectator mode acts as an environment for the pairs, and the strength of the coupling significantly reduces the quantum coherence. The nonseparability of the pairs emitted by white holes is also considered and compared with that of black holes.

We perform a set of 38 fully nonlinear numerical simulations of equal-mass black hole binaries in a configuration where the two black hole spins in the binary are equal in both magnitude and direction, to study precession effects. We vary the initial direction of the total spin $\overrightarrow{S}$ with respect to the orbital angular momentum $\overrightarrow{L}$, covering the two-dimensional space of orientation angles with 38 configurations consisting of 36 configurations distributed in the azimuthal angle $\varphi$ and polar angle $\mu =\cos \theta$, and two configurations on the poles. In all cases, we set the initial dimensionless black hole spins to 0.8. We observe that during the late-inspiral stage, the total angular momentum of the system $\overrightarrow{J}$ remains within 5° of its original direction, with the largest changes in direction occurring when the spins are nearly (but not exactly) counteraligned with the orbital angular momentum. We also observe that the angle between $\overrightarrow{S}$ and $\overrightarrow{L}$ is nearly conserved during the inspiral phase. These two dynamical properties allow us to propose a new phenomenological formula for the final mass and spin of merged black holes in terms of the individual masses and spins of the progenitor binary at far separations. We determine coefficients of this formula (in the equal-mass limit) using a least-squared fit to the results of this new set of 38 runs, an additional set of five new configurations with spins aligned or counteraligned with the orbital angular momentum, and more than a hundred recent simulations. We find that our formulas reproduce the remnant mass and spin of these simulations to within a relative error of 2.5%. We discuss the region of validity of this dynamical picture for precessing unequal-mass binaries. Finally, we perform a statistical study to see the consequence of this new formula for distributions of spin magnitudes and remnant masses with applications to black hole spin distributions and gravitational radiation in cosmological scenarios involving several mergers.

We examine the noncommutative cylinder solution to a matrix model with a Minkowski background metric. It can be regarded as the noncommutative analogue of a static circular string. Perturbations about the solution yield a tachyonic scalar field (and an additional tachyonic fermion in the full supersymmetric version of the model) in the commutative limit. The tachyonic mode is attributed to the fact that the circular string is unstable under uniform adiabatic deformations. We obtain a stabilizing term which, when added to the matrix model, removes the tachyonic mass.

We formulate a spherical harmonically decomposed $1+1$ scheme to self-consistently evolve the trajectory of a point particle and its gravitational metric perturbation to a Schwarzschild background spacetime. Following the work of Moncrief, we write down an action for perturbations in spacetime geometry, combine that with the action for a point particle moving through this spacetime, and then obtain Hamiltonian equations of motion for metric perturbations, the particle’s coordinates, as well as its canonical momenta. Hamiltonian equations for the metric perturbation and their conjugate momenta, for even and odd parities, reduce to Zerilli-Moncrief and Regge-Wheeler master equations with source terms, which are gauge invariant, plus auxiliary equations that specify the gauge. Hamiltonian equations for the particle, on the other hand, now include effect of metric perturbations—with these new terms derived from the same interaction Hamiltonian that lead to those well-known source terms. In this way, spacetime geometry and particle motion can be evolved in a self-consistent manner, in principle in any gauge. However, the point-particle nature of our source requires regularization, and we outline how the Detweiler-Whiting approach can be applied. In this approach, a singular field can be obtained analytically using the Hadamard decomposition of the Green’s function and the regular field, which needs to be evolved numerically, is the result of subtracting the singular field from the total metric perturbation. In principle, any gauge that has the singular-regular field decomposition is suitable for our self-consistent scheme. In reality, however, this freedom is only possible if our singular field has a high enough level of smoothness. For a singular field with a minimum quality, one can adopt the Lorenz gauge condition, which we have recast into our formalism: for each $l$ and $m$, we have two wave equations to evolve odd and even parity gauge invariant quantities and eigh first-order differential equations to fix the Lorenz gauge and determine the metric components.

Some strong field effects on test particle motion associated with the propagation of a plane electromagnetic wave in the exact theory of general relativity are investigated. Two different profiles of the associated radiation flux are considered in comparison, corresponding to either constant or oscillating electric and magnetic fields with respect to a natural family of observers. These are the most common situations to be experimentally explored, and have a well known counterpart in the flat spacetime limit. The resulting line elements are determined by a single metric function, which turns out to be expressed in terms of standard trigonometric functions in the case of a constant radiation flux, and in terms of special functions in the case of an oscillating flux, leading to different features of test particle motion. The world line deviation between both uncharged and charged particles on different spacetime trajectories due to the combined effect of gravitational and electromagnetic forces is studied. The interaction of charged particles with the background radiation field is also discussed through a general relativistic description of the inverse Compton effect. Motion as well as deviation effects on particles endowed with spin are studied too. Special situations may occur in which the direction of the spin vector changes during the interaction, leading to observable effects like spin flip.

We demonstrate that ultra-high-energy collisions of particles falling freely from rest at infinity can occur in the field of near-extreme Kehagias-Sfetsos naked singularities related to the Hořava gravity. However, the efficiency of escaping of created ultrarelativistic particles and the energy efficiency of the collisional process relative to distant observers are significantly lowered due to large gravitational redshift, which is substantially lower in comparison to those related to the collisions occurring close to the equatorial plane of near-extreme Kerr naked-singularity spacetimes. In the Kehagias-Sfetsos naked-singularity spacetimes, the energy efficiency relative to distant observers corresponds to the covariant energy of the colliding particles only. Finally, we demonstrate how the ultra-high-energy collisions are modified for charged particles if the Kehagias-Sfetsos naked singularities are immersed in a uniform magnetic field.