Various approaches aim to describe the recent analysis by the OPERA experiment, which indicates that neutrinos travel faster than the speed of light. We demonstrate that any such theoretical or experimental explanation must not destroy the complicated (nonlinear) structure of the proton waveform recovered in the neutrino signal. As one example, consider that only a fraction of the neutrinos travels faster than the speed of light, such as sterile neutrinos. We fit the OPERA data including this fraction as a free variable, assuming that the OPERA result is correct. In our analysis, the best-fit values are 50% of the neutrinos being superluminal and $(v-c)/c=4.5·{10}^{-5}$, where the neutrino velocity increases as the fraction of superluminal neutrinos decreases. The minimal fraction of superluminal neutrinos is found to be 17% ($3\sigma$), which is constrained by the nonlinearity of the proton waveform. This minimal fraction challenges the hypothesis that only sterile neutrinos travel faster than the speed of light. In addition, we demonstrate that an experimental effect introducing a smearing between the proton waveform and neutrino signal, as expected for some systematical errors, is also limited by the shape of the waveform. Finally, we illustrate that even stronger constraints may be obtained from the recent analysis with a short-bunch beam, in spite of the low statistics.

A proposal by Lüscher enables us to extract the elastic scattering phases from two-particle energy spectrum in a cubic box using lattice simulations. Rummukainen and Gottlieb further extend it to the moving frame, which is devoted to the system of two identical particles. In this work, we generalize Rummukainen-Gottlieb’s formula to the generic two-particle states where two particles are explicitly distinguishable, namely, the masses of the two particles are different. Their relations with the elastic scattering phases of two-particle energy spectrum in the continuum are obtained for both $C_{4v}$ and $C_{2v}$ symmetries. Our analytical results will be very helpful for the study of some resonances, such as kappa, vector kaon, and so on.

We investigate the contribution of inelastic and elastic processes to single inclusive hadron production in proton-proton and proton (deuteron)-nucleus collisions at RHIC and the LHC. Using the hybrid formulation which includes both elastic and inelastic contributions, supplemented with the running-coupling Balitsky-Kovchegov equation, we get a good description of RHIC data. It is shown that inclusion of the inelastic terms makes the transverse momentum dependence of the production cross section steeper in the midrapidity region but does not affect the cross section in the very forward region. The inelastic processes also lead to a sharper increase of the nuclear modification factor $R_{pA}$ with increasing $p_T$. We also make predictions for the nuclear modification factor in proton-nucleus collisions at the LHC ($\sqrt{s}=4.4$ and 8.8 TeV) at various rapidities using the color glass condensate framework.

The standard wave function approach for the treatment of neutrino oscillations fails in situations where quantum ensembles at a finite temperature with or without an interacting background plasma are encountered. As a first step to treat such phenomena in a novel way, we propose a unified approach to both adiabatic and nonadiabatic two-flavor oscillations in neutrino ensembles with finite temperature and generic (e.g., matter) potentials. Neglecting effects of ensemble decoherence for now, we study the evolution of a neutrino ensemble governed by the associated quantum kinetic equations, which apply to systems with finite temperature. The quantum kinetic equations are solved formally using the Magnus expansion and it is shown that a convenient choice of the quantum mechanical picture (e.g., the interaction picture) reveals suitable parameters to characterize the physics of the underlying system (e.g., an effective oscillation length). It is understood that this method also provides a promising starting point for the treatment of the more general case in which decoherence is taken into account.

We consider the family of static, axially symmetric, exact solutions of the vacuum Einstein equations, presented in a recent article by G. A. González, et al. (Phys. Rev. D 79, 124048 (2009)) (I). These solutions are singular on an infinite disk with a central inner edge. This singularity was interpreted in (I) as corresponding to the presence of dust with positive energy density everywhere on the disk. It was further asserted in (I) that the Riemann tensor is regular everywhere. Unfortunately, as we show in this Comment, neither the physical interpretation of the source nor the assertions about the Riemann tensor are correct. We provide an extended analysis of the geometric properties of the solutions that indicates that the Riemann tensor is, in fact, singular on the edge of the disk, and that the disk itself contains a singularity on this edge that acts as an infinite source of negative mass. We further comment on the appropriate use of the Komar formula for the mass of the system to make it consistent with the fact that these solutions have vanishing Arnowitt-Desser-Misner mass.

We compactify four-dimensional $\mathcal{N}=1$ gauged supergravity theories on a circle including fluxes for shift-symmetric scalars. Four-dimensional Taub-NUT gravitational instantons universally correct the three-dimensional superpotential in the absence of fluxes. In the presence of fluxes these Taub-NUT instanton contributions are no longer gauge-invariant. Invariance can be restored by gauge-instantons on top of Taub-NUT instantons. We establish the embedding of this scenario into M-theory. Circle fluxes and gaugings arise from a restricted class of M-theory four-form fluxes on a resolved Calabi-Yau fourfold. The M5-brane on the base of the elliptic fourfold dualizes into the universal Taub-NUT instanton. In the presence of fluxes this M5-brane is anomalous. We argue that anomaly-free contributions arise from involved M5-brane geometries dual to gauge-instantons on top of Taub-NUT instantons. Adding a four-dimensional superpotential to the gravitational instanton corrections leads to three-dimensional Anti-de Sitter vacua at stabilized compactification radius. We comment on the possibility to uplift these M-theory vacua, and to tunnel to four-dimensional F-theory vacua.

We present the complete integrands of five-point superamplitudes in $\mathcal{N}=4$ super-Yang-Mills theory and $\mathcal{N}=8$ supergravity, at one and two loops, for four-dimensional external states and $D$-dimensional internal kinematics. For $\mathcal{N}=4$ super-Yang-Mills theory we give the amplitudes for general gauge group—including all nonplanar contributions. The results are constructed using integral diagrams that manifestly satisfy the conjectured duality between color and kinematics, providing additional nontrivial evidence in favor of the duality for multipoint and multiloop amplitudes. We determine the ultraviolet poles by integrating the amplitudes in the dimensions where logarithmic divergences first occur. We introduce new kinematic prefactors which offer a convenient decomposition of the external state structure of the nonplanar five-point amplitudes in the maximally supersymmetric theories to all loop orders.

The formulation of the Lisfshitz formula in terms of real frequencies is reconsidered for half-spaces described by the plasma model. It is shown that besides the surface modes (for the TM polarization), and the photonic modes, also waveguide modes must be considered.

Recently it was found that the superposition of a strong and slow electric field with a weaker and faster pulse can significantly enhance the probability for nonperturbative electron-positron pair creation out of the vacuum—the dynamically assisted Sauter-Schwinger effect. Via the WKB method, we estimate the momentum dependence of the pair creation probability and compare it to existing numerical results. Besides the theoretical interest, a better understanding of this pair creation mechanism should be helpful for the planned experiments aiming at its detection.

We present the Hamiltonian analysis of the theory of gravity based on a Lagrangian density containing the Hilbert-Palatini term along with three topological densities, Nieh-Yan, Pontryagin and Euler. The addition of these topological terms modifies the symplectic structure nontrivially. The resulting canonical theory develops a dependence on three parameters which are coefficients of these terms. In the time gauge, we obtain a real $SU(2)$ gauge theoretic description with a set of seven first-class constraints corresponding to three $SU(2)$ rotations, three spatial diffeomorphisms and one to evolution in a timelike direction. The inverse of the coefficient of the Nieh-Yan term, identified as the Barbero-Immirzi parameter, acts as the coupling constant of the gauge theory.

We study the homogeneous sector of the Rousso-Susskind-Thorlacius model describing the gravitational dynamics, including backreaction, of radiating 2D black holes. We find the exact solutions both in conformal gauge and in time-parametrized form, isolate the black hole sector of the classical phase space, and quantize the near-singularity dynamics in conformal gauge. We show that different choices of measure and different self-adjoint extensions can lead to inequivalent quantum theories, all of which resolve the singularity. For a specific range of extension parameters, the Hamiltonian spectrum admits bound states that correspond physically to stable remnants. Finally, we argue that our work provides a good starting point for Dirac and reduced quantization of the homogeneous theory in the full spacetime.

We construct the asymptotically flat charged thin-shell wormholes of Lovelock gravity in seven dimensions by a cut-and-paste technique and apply the generalized junction conditions in order to calculate the energy-momentum tensor of these wormholes on the shell. We find that for negative second-order and positive third-order Lovelock coefficients, there are thin-shell wormholes that respect the weak energy condition. In this case, the amount of normal matter decreases as the third-order Lovelock coefficient increases. For positive second- and third-order Lovelock coefficients, the weak energy condition is violated and the amount of exotic matter decreases as the charge increases. Finally, we perform a linear stability analysis against a symmetry-preserving perturbation and find that the wormholes are stable, provided the derivative of surface pressure density with respect to surface energy density is negative and the throat radius is chosen suitably.

A generic second-order scalar-tensor theory contains a nonlinear derivative self-interaction of the scalar degree of freedom $\varphi$ à la Galileon models, which allows for the Vainshtein screening mechanism. We investigate this effect on subhorizon scales in a cosmological background, based on the most general second-order scalar-tensor theory. Our analysis takes into account all the relevant nonlinear terms and the effect of metric perturbations consistently. We derive an explicit form of Newton’s constant, which in general is time-dependent and hence is constrained from observations, as suggested earlier. It is argued that in the most general case the inverse-square law cannot be reproduced on the smallest scales. Some applications of our results are also presented.

We investigate oscillating instanton solutions of a self-gravitating scalar field between degenerate vacua. We show that there exist $O(4)$-symmetric oscillating solutions in a de Sitter background. The geometry of this solution is finite and preserves the $Z_2$ symmetry. The nontrivial solution corresponding to tunneling is possible only if the effect of gravity is taken into account. We present numerical solutions of this instanton, including the phase diagram of solutions in terms of the parameters of the present work and the variation of energy densities. Our solutions can be interpreted as solutions describing an instanton-induced domain wall or braneworld-like object rather than a kink-induced domain wall or braneworld. The oscillating instanton solutions have a thick wall and the solutions can be interpreted as a mechanism providing nucleation of the thick wall for topological inflation. We remark that $Z_2$ invariant solutions also exist in a flat and anti-de Sitter background, though the physical significance is not clear.

Local and nonlocal properties of Hawking radiation in the presence of short distance dispersion are computed using connection formulae. The robustness of the spectrum and that of the two-point function are explained by showing that the leading deviations from the relativistic expressions decrease with the inverse of the spatial extension of the near horizon region. This region corresponds to a portion of de Sitter space with a preferred frame. We show that the phases of the Bogoliubov coefficients are relevant for the two-point function in black and white holes, and also for the black hole laser effect. We also present an unexpected relation between the spectra obtained with sub and with superluminal dispersion and we apply our formalism to massive fields. Our predictions are validated by numerical analysis.

We study the collision of particles in the vicinity of a horizon of a weakly magnetized nonrotating black hole. In the presence of the magnetic field innermost stable circular orbits of charged particles can be located close to the horizon. We demonstrate that for a collision of two particles, one of which is charged and revolving at innermost stable circular orbits and the other is neutral and falling from infinity, the maximal collision energy can be high in the limit of a strong magnetic field. This effect has some similarity with the recently discussed effect of high center-of-mass energy for the collision of particles in extremely rotating black holes. We also demonstrate that for “realistic” astrophysical black holes their ability to play the role of “accelerators” is in fact quite restricted.

We derive field equations of Gauss-Bonnet gravity in four dimensions after dimensional reduction of the action and demonstrate that in this scenario the Vainshtein mechanism operates in the flat spherically symmetric background. We show that inside this Vainshtein sphere the fifth force is negligibly small compared to the gravitational force. We also investigate the stability of the spherically symmetric solution, and clarify the vocabulary used in the literature about the hyperbolicity of the equation and the ghost-Laplacian stability conditions. We find superluminal behavior of the perturbation of the field in the radial direction. However, because of the presence of the nonlinear terms, the structure of the space-time is modified and as a result the field does not propagate in the Minkowski metric but rather in an “aether” composed of the scalar field $\pi (r)$. We thereby demonstrate that the superluminal behavior does not create time paradoxes thanks to the absence of causal closed curves. We also derive the stability conditions for a Friedmann universe in context with scalar and tensor perturbations and we study the cosmology of the model.

We consider possibly observable effects of asymmetric dark matter (ADM) in neutron stars. Since dark matter does not self-annihilate in the ADM scenario, dark matter accumulates in neutron stars, eventually reaching the Chandrasekhar limit and forming a black hole. We focus on the case of scalar ADM, where the constraints from Bose-Einstein condensation and subsequent black hole formation are most severe due to the absence of Fermi degeneracy pressure. We also note that in some portions of this constrained parameter space, nontrivial effects from Hawking radiation can modify our limits. We find that for scalar ADM with mass between 5 MeV and 13 GeV, the constraint from nearby neutron stars on the scattering cross section with neutrons ranges from ${\sigma }_n\lesssim {10}^{-45}{\mathrm{cm}}^2$ to ${10}^{-47}{\mathrm{cm}}^2$.

We study the stability of superconducting strings in a $\mathrm{U}(1{)}_{\mathrm{local}}\times \mathrm{U}(1{)}_{\mathrm{global}}$ model coupled via a gauge field interaction term to U(1) Abelian-Higgs strings. The effect of the interaction on current stability is numerically investigated by varying the relevant parameters within the physical limits of our model. We find that the propagation speed of transverse (resp. longitudinal) perturbations increases (decreases) with increasing binding between the superconducting and Abelian-Higgs string. Moreover, we observe that for small enough width of the flux tube of the superconducting string and/or large enough interaction between the superconducting and the Abelian-Higgs string superconducting strings cannot carry spacelike, i.e. magnetic currents. Our model can be seen as a field theoretical realization of bound states of p F-strings and q superconducting D-strings and has important implications to vorton formation during the evolution of networks of such strings.