The average transverse momentum transfer per unit path length to a fast parton scattering elastically in a perturbative quark-gluon plasma is related to the radiative energy loss of the parton. We first calculate the momentum transfer coefficient $\widehat{q}$ in terms of a classical Langevin problem and then define it quantum mechanically through a scattering matrix element. After treating the well-known case of a quark-gluon plasma in equilibrium, we consider an off-equilibrium unstable plasma. As a specific example, we treat the two-stream plasma with unstable modes of longitudinal chromoelectric field. In the presence of the instabilities, $\widehat{q}$ is shown to exponentially grow in time.

Binary black-hole systems with spins aligned or anti-aligned to the orbital angular momentum, and which therefore do not exhibit precession effects, provide the natural ground to start detailed studies of the influence of strong-field spin effects on gravitational-wave observations of coalescing binaries. Furthermore, such systems may be the preferred end state of the inspiral of generic supermassive binary black-hole systems. In view of this, we have computed the inspiral and merger of a large set of binary systems of equal-mass black holes with spins parallel to the orbital angular momentum but otherwise arbitrary. Our attention is particularly focused on the gravitational-wave emission so as to quantify how much spin effects contribute to the signal-to-noise ratio, to the horizon distances, and to the relative event rates for the representative ranges in masses and detectors. As expected, the signal-to-noise ratio increases with the projection of the total black-hole spin in the direction of the orbital momentum. We find that equal-spin binaries with maximum spin aligned with the orbital angular momentum are more than “3 times as loud” as the corresponding binaries with anti-aligned spins, thus corresponding to event rates up to 30 times larger. We also consider the waveform mismatch between the different spinning configurations and find that, within our numerical accuracy, binaries with opposite spins ${\mathit{S}}_1=-{\mathit{S}}_2$ cannot be distinguished, whereas binaries with spin ${\mathit{S}}_1={\mathit{S}}_2$ have clearly distinct gravitational-wave emissions. Finally, we derive a simple expression for the energy radiated in gravitational waves and find that the binaries always have efficiencies $E_{\mathrm{rad}}/M\gtrsim 3.6\%$, which can become as large as $E_{\mathrm{rad}}/M\simeq 10\%$ for maximally spinning binaries with spins aligned with the orbital angular momentum. These binaries are therefore among the most efficient sources of energy in the Universe.

We give general sufficient conditions for the existence of trapped surfaces due to concentration of matter in spherically symmetric initial data sets satisfying the dominant energy condition. These results are novel in that they apply and are meaningful for arbitrary spacelike slices, that is, they do not require any auxiliary assumptions such as maximality, time symmetry, or special extrinsic foliations, and most importantly they can easily be generalized to the nonspherical case once an existence theory for a modified version of the Jang equation is developed. Moreover, our methods also yield positivity and monotonicity properties of the Misner-Sharp energy.

If dark energy (DE) couples to neutrinos, then there may be apparent violations of $\mathrm{\text{Lorentz}}/CPT$ invariance in neutrino oscillations. The DE-induced $\mathrm{\text{Lorentz}}/CPT$ violation takes a specific form that introduces neutrino oscillations that are energy independent, differ for particles and antiparticles, and can lead to novel effects for neutrinos propagating through matter. We show that ultra-high-energy neutrinos may provide one avenue to seek this type of $\mathrm{\text{Lorentz}}/CPT$ violation in ${\nu }_{\mu }\mathrm{\text{−}}{\nu }_{\tau }$ oscillations, improving the current sensitivity to such effects by 7 orders of magnitude. $\mathrm{\text{Lorentz}}/CPT$ violation in electron-neutrino oscillations may be probed with the zenith-angle dependence for high-energy atmospheric neutrinos. More compelling evidence for a DE-neutrino coupling would be provided by a dependence of neutrino oscillations on the direction of the neutrino momentum relative to our peculiar velocity with respect to the cosmic microwave background rest frame. While the amplitude of this directional dependence is expected to be small, it may nevertheless be worth seeking in current data and may be a target for future neutrino experiments.

The dynamics of a cosmological model of dark matter and dark energy represented by a scalar field endowed with a cosh-like potential plus a cosmological constant is investigated in detail. By studying the appropriate phase space of the equations of motion, it is shown that a standard evolution of the Universe is recovered for appropriate values of the free parameters, and that the only late-time attractor is always the de  Sitter solution. We also discuss the appearance of scalar field oscillations corresponding to dark matter behavior.

We explore potential of current and next-generation $\gamma$-ray telescopes for the detection of weak magnetic fields in the intergalactic medium. We demonstrate that using two complementary techniques, observation of extended emission around point sources and observation of time delays in $\gamma$-ray flares, one would be able to probe most of the cosmologically and astrophysically interesting part of the “magnetic field strength” vs “correlation length” parameter space. This implies that $\gamma$-ray observations with Fermi and ground-based Cherenkov telescopes will allow to (a) strongly constrain theories of the origin of magnetic fields in galaxies and galaxy clusters and (b) discover, constrain or rule out the existence of weak primordial magnetic field generated at different stages of evolution of the Early Universe.

The theoretical description of compact structures that share some features with mass varying particles allows for a simple analysis of the equilibrium and stability for massive stellar bodies. We investigate static, spherically symmetric solutions of Einstein equations for a system composed by nonbaryonic matter (neutrinos or dark matter) which forms stable structures through attractive forces mediated by a background scalar field (dark energy). Assuming that the dark matter, or massive neutrinos, consists of a gas of weakly interacting particles, the coupling with the scalar field is translated into an effective dependence of the mass of the compounding particle on the radial coordinate of the curved spacetime. The stability analysis reveals that these static solutions become dynamically unstable for different Buchdahl limits of the ratio between the total mass energy and the stellar radius, $M/R$. We also find regular solutions that for an external observer resemble Schwarzschild black holes. Our analysis leaves unanswered the question whether such solutions, which are both regular and stable, do exist.

We examine supersymmetric theories with approximately conformal sectors. Without an IR cutoff the theory has a continuum of modes, which are often referred to as “unparticles.” Making use of the AdS/CFT correspondence we find that in the presence of a soft-wall, a gap in the spectrum can arise, separating the zero-modes from the continuum modes. In some cases there are also discrete massive levels in the gap. We also show that when supersymmetry is broken the superpartner of a quark or lepton may simply be a bosonic continuum above a gap. Such extensions of the standard model have novel signatures at the LHC.

We present a search for the radiative leptonic decay $B^{+}\to {\ell }^{+}{\nu }_{\ell }\gamma$, where $\ell =e$, $\mu$, using a data sample of $465\times {10}^6$ $B\overline{B}$ pairs collected by the BABAR experiment. In this analysis, we fully reconstruct the hadronic decay of one of the $B$ mesons in ${\rm Y}(4S)\to B^{+}{B}^{-}$ decays, then search for evidence of $B^{+}\to {\ell }^{+}{\nu }_{\ell }\gamma$ in the rest of the event. We observe no significant evidence of signal decays and report model-independent branching fraction upper limits of $\mathcal{B}(B^{+}\to e^{+}{\nu }_e\gamma )<17\times {10}^{-6}$, $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu }\gamma )<24\times {10}^{-6}$, and $\mathcal{B}(B^{+}\to {\ell }^{+}{\nu }_{\ell }\gamma )<15.6\times {10}^{-6}$ ($\ell =e$ or $\mu$), all at the 90% confidence level.

Infinite statistics in which all representations of the symmetric group can occur is known as a special case of quon theory. However, the validity of relativistic quon theories is still in doubt. In this paper we prove that there exists a relativistic quantum field theory which allows interactions involving infinite statistics particles. We also give some consistency analysis of this theory, such as conservation of statistics and Feynman rules.

We construct charged and rotating asymptotically Schrödinger black hole solutions of type IIB supergravity. We begin by obtaining a closed-form expression for the null Melvin twist of a broad class of type IIB backgrounds, including solutions of minimal five-dimensional gauged supergravity, and identify the resulting five-dimensional effective action. We use these results to demonstrate that the near-horizon physics and thermodynamics of asymptotically Schrödinger black holes obtained in this way are essentially inherited from their anti–de Sitter (AdS) progenitors, and verify that they admit zero-temperature extremal limits with ${\mathrm{AdS}}_2$ near-horizon geometries. Notably, the ${\mathrm{AdS}}_2$ radius is parametrically larger than that of the asymptotic Schrödinger space.

The minimal supersymmetric standard model has several flat directions, which can naturally be excited during inflation. If they have a slow (perturbative) decay, they may affect the thermalization of the inflaton decay products. In the present paper, we consider the system of $udd$ and $QLd$ flat directions, which breaks the $U(1)\times SU(2)\times SU(3)$ symmetry completely. In the unitary gauge and assuming a general soft breaking mass configuration, we show that for a range of parameters, the background condensate of flat directions can undergo a fast nonperturbative decay, due to nonadiabatic evolution of the eigenstates. We find that both the background evolution and part of the decay can be described accurately by previously studied gauged toy models of flat direction decay.

We examine current numerical relativity computations of gravitational waves, which typically determine the asymptotic waves at infinity by extrapolation from finite (small) radii. Using simulations of a black hole binary with accurate wave extraction at $r=1000M$, we show that extrapolations from the near zone are self-consistent in approximating measurements at this radius, although with a somewhat reduced accuracy. We verify that ${\psi }_4$ is the dominant asymptotic contribution to the gravitational energy (as required by the peeling theorem) but point out that gauge effects may complicate the interpretation of the other Weyl components.

We investigated the finite temperature ($T$) phase transition for $\mathrm{SU}(N_c)$ gauge theory with $N_c=4$, 6, 8 and 10 at lattice spacing, $a$, of $1/(6T)$ or less. We checked that these theories have first-order transitions at such small $a$. In many cases we were able to find the critical couplings with precision as good as a few parts in ${10}^4$. We also investigated the use of two-loop renormalization group equations in extrapolating the lattice results to the continuum, thus fixing the temperature scale in units of the phase transition temperature, $T_c$. We found that when $a\le 1/(8T_c)$ the two-loop extrapolation was accurate to about 1%–2%. However, we found that trading $T_c$ for the QCD scale, ${\Lambda }_{\overline{\mathrm{MS}}}$, increases uncertainties significantly, to the level of about 5%–10%.

The masses of the low-lying baryons are evaluated using two degenerate flavors of twisted mass sea quarks corresponding to pseudoscalar masses in the range of about 270–500 MeV. The strange valence quark mass is tuned to reproduce the mass of the kaon in the physical limit. The tree-level Symanzik improved gauge action is employed. We use lattices of spatial size 2.1 and 2.7 fm at two values of the lattice spacing with $r_0/a=5.22(2)$ and $r_0/a=6.61(3)$. We check for both finite volume and cutoff effects on the baryon masses. We performed a detailed study of the chiral extrapolation of the octet and decuplet masses using SU(2) $\chi \mathrm{PT}$. The lattice spacings determined using the nucleon mass at the physical point are consistent with the values extracted using the pion decay constant. We examine the issue of isospin symmetry breaking for the octet and decuplet baryons and its dependence on the lattice spacing. We show that in the continuum limit isospin breaking is consistent with zero, as expected. The baryon masses that we find after taking the continuum limit and extrapolating to the physical limit are in good agreement with experiment.

We study the impact of cosmic inhomogeneities on the interpretation of observations. We build an inhomogeneous universe model without dark energy that can confront supernova data and yet is reasonably well compatible with the Copernican principle. Our model combines a relatively small local void, that gives apparent acceleration at low redshifts, with a meatball model that gives sizable lensing (dimming) at high redshifts. Together these two elements, which focus on different effects of voids on the data, allow the model to mimic the concordance model.

In a previous work (arXiv:0902.3750 [hep-th]) we studied the world-sheet conformal invariance for superstrings in the type IIB R-R plane-wave in semi-light-cone gauge. Here we give further justification to the results found in that work through alternative arguments using dynamical supersymmetries. We show that by using the supersymmetry algebra the same quantum definition of the energy-momentum (EM) tensor can be derived. Furthermore, using certain Jacobi identities we indirectly compute the Virasoro anomaly terms by calculating the second-order supersymmetry variation of the EM tensor. Certain integrated forms of all such terms are shown to vanish. In order to deal with various divergences that appear in such computations we take a point-split definition of the same EM tensor. The final results are shown not to suffer from the ordering ambiguity as noticed in the previous work provided the coincidence limit is taken before sending the regularization parameter to zero at the end of the computation.

We study torus/orbifold models with magnetic flux and Wilson line backgrounds. The number of zero modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology.

Invoking the Peccei-Quinn (PQ) solution to the strong $CP$ problem substitutes the puzzle of why ${\theta }_{\mathrm{qcd}}$ is so small with the puzzle of why the PQ symmetry is of such high quality. Cosmological and astrophysical considerations raise further puzzles. This paper explores these issues in several contexts: string theory and field theory, and theories without and with low energy supersymmetry. Among the questions studied are whether requiring axion dark matter can account for the quality of the PQ symmetry, to which the answer is sometimes yes. In nonsupersymmetric theories, we find $f_a={10}^{12}\mathrm{GeV}$ is quite plausible. In gauge mediation, cosmological constraints on pseudomoduli place $f_a$ in this range, and require that the gravitino mass be of order an MeV.

We prove that the light-cone time cutoff on the multiverse defines the same probabilities as a causal patch with initial conditions in the longest-lived metastable vacuum. This establishes the equivalence of two measures of eternal inflation which naively appear very different (though both are motivated by holography). The duality can be traced to an underlying geometric relation which we identify.