We introduce a new version of nonlinear electrodynamics which is produced by a spontaneous symmetry breaking of Lorentz invariance induced by the nonzero vacuum expectation value of the gauge invariant electromagnetic field strength. The symmetry breaking potential is argued to effectively arise from the integration of massive gauge bosons and fermions in an underlying fundamental theory. All possible choices of the vacuum lead only to the remaining invariant subgroups $T(2)$ and HOM(2). We explore in detail the plane wave solutions of the linearized sector of the model for an arbitrary vacuum. They present two types of dispersion relations. One corresponds to the case of the usual Maxwell electrodynamics with the standard polarization properties of the fields. The other dispersion relation involves anisotropies determined by the structure of the vacuum. The corresponding fields reflect these anisotropies. The model is stable in the small Lorentz invariance violation (LIV) approximation. We have also embedded our model in the photon sector of the standard model extension, in order to translate the many bounds obtained in the latter into corresponding limits for our parameters. The one-way anisotropic speed of light is calculated for a general vacuum, and its isotropic component is strongly bounded by $\tilde{\delta }c/c<2\times {10}^{-32}$. The anisotropic violation contribution is estimated by introducing an alternative definition for the difference of the two-way speed of light in perpendicular directions, $\Delta c$, that is relevant to Michelson-Morley type of experiments and which turns out to be also strongly bounded by $\Delta c/c<{10}^{-32}$. Finally, we speculate on the relation of the vacuum energy of the model with the cosmological constant and propose a connection between the vacuum fields and the intergalactic magnetic fields.

We perform three-dimensional relativistic hydrodynamical simulations of the coalescence of strange stars and explore the possibility to decide on the strange matter hypothesis by means of gravitational-wave measurements. Self-binding of strange quark matter and the generally more compact stars yield features that clearly distinguish strange star from neutron star mergers, e.g. hampering tidal disruption during the plunge of quark stars. Furthermore, instead of forming dilute halo structures around the remnant as in the case of neutron star mergers, the coalescence of strange stars results in a differentially rotating hypermassive object with a sharp surface layer surrounded by a geometrically thin, clumpy high-density strange quark matter disk. We also investigate the importance of including nonzero temperature equations of state in neutron star and strange star merger simulations. In both cases we find a crucial sensitivity of the dynamics and outcome of the coalescence to thermal effects, e.g. the outer remnant structure and the delay time of the dense remnant core to black hole collapse depend on the inclusion of nonzero temperature effects. For comparing and classifying the gravitational-wave signals, we use a number of characteristic quantities like the maximum frequency during inspiral or the dominant frequency of oscillations of the postmerger remnant. In general, these frequencies are higher for strange star mergers. Only for particular choices of the equation of state the frequencies of neutron star and strange star mergers are similar. In such cases additional features of the gravitational-wave luminosity spectrum like the ratio of energy emitted during the inspiral phase to the energy radiated away in the postmerger stage may help to discriminate coalescence events of the different types. If such characteristic quantities could be extracted from gravitational-wave signals, for instance with the upcoming gravitational-wave detectors, a decision on the strange matter hypothesis and the existence of strange stars should be possible.

We investigate the properties of the event horizon and static limit for a charged rotating black hole solution of minimal supergravity theory in ($1+4$) dimension. Unlike the four-dimensional case, there are in general two rotations, and they couple to both mass and charge. This gives rise to much richer structure to ergosphere leading to energy extraction even for axial fall. Another interesting feature is that the metric in this case is sensitive to the sign of the Maxwell charge.

We consider a Lemaitre-Tolman-Bondi type space-time in Einstein gravity with the Gauss-Bonnet combination of quadratic curvature terms, and present an exact solution in closed form. It turns out that the presence of the coupling constant of the Gauss-Bonnet terms $\alpha >0$ completely changes the causal structure of the singularities from the analogous general relativistic case. The gravitational collapse of inhomogeneous dust in the five-dimensional Gauss-Bonnet extended Einstein equations leads to formation of a massive, but weak, timelike singularity which is forbidden in general relativity. Interestingly, this is a counterexample to three conjectures, viz., cosmic censorship conjecture, hoop conjecture, and Seifert’s conjecture.

In the Horava-Lifshitz theory of quantum gravity, two conditions—detailed balance and projectability—are usually assumed. The breaking of projectability simplifies the theory, but it leads to serious problems with the theory. The breaking of detailed balance leads to a more complicated form of the theory, but it appears to resolve some of the problems. Sotiriou, Visser and Weinfurtner formulated the most general theory of Horava-Lifshitz type without detailed balance. We compute the linear scalar perturbations of the FRW model in this form of HL theory. We show that the higher-order curvature terms in the action lead to a gravitational effective anisotropic stress on small scales. Specializing to a Minkowski background, we study the spin-0 scalar mode of the graviton, using a gauge-invariant analysis, and find that it is stable in both the infrared and ultraviolet regimes for $0\le \xi \le 2/3$. However, in this parameter range the scalar mode is a ghost.

We analyze the nonequatorial charged particle dynamics around a rotating black hole in the presence of an external magnetic field, the latter being given by Wald’s exact analytical solution to the Maxwell’s equations in the Kerr background. At variance with the corresponding Schwarzschild case, the behavior of the particle becomes here markedly charge-sign dependent, and the more so the more the Kerr parameter increases. The interplay between the rotating black hole and the magnetic field is shown to provide a mechanism both for selective charge ejection in axially collimated jetlike trajectories, and for selective charge confinement into nonequatorial bound orbits around the hole; the possibility of such a confinement allows the fate of an accreting particle to not necessarily be doomed: infall into the hole can be prevented, and the neutrality of the Kerr source could therefore be preserved, while the charge is safely parked into bound cross-equatorial orbits all around it.

We investigate bouncing solutions in the framework of the nonsingular gravity model of Brandenberger, Mukhanov and Sornborger. We show that a spatially flat universe filled with ordinary matter undergoing a phase of contraction reaches a stage of minimal expansion factor before bouncing in a regular way to reach the expanding phase. The expansion can be connected to the usual radiation- and matter-dominated epochs before reaching a final expanding de Sitter phase. In general relativity (GR), a bounce can only take place provided that the spatial sections are positively curved, a fact that has been shown to translate into a constraint on the characteristic duration of the bounce. In our model, on the other hand, a bounce can occur also in the absence of spatial curvature, which means that the time scale for the bounce can be made arbitrarily short or long. The implication is that constraints on the bounce characteristic time obtained in GR rely heavily on the assumed theory of gravity. Although the model we investigate is fourth order in the derivatives of the metric (and therefore unstable vis-à-vis the perturbations), this generic bounce dynamics should extend to string-motivated nonsingular models which can accommodate a spatially flat bounce.

We numerically study the interaction of inflation-produced magnetic fields with gravitational waves, both of which originate from quantum fluctuations during inflation. The resonance between the magnetic field perturbations and the gravitational waves has been suggested as a possible mechanism for magnetic field amplification. However, some analytical studies suggest that the effect of the inflationary gravitational waves is too small to provide significant amplification. Our numerical study shows more clearly how the interaction affects the magnetic fields and confirms the weakness of the influence of the gravitational waves. We present an investigation based on the magnetohydrodynamic approximation and take into account the differences of the Alfven speed.

It has been suggested that the excesses of high-energy cosmic ray electrons and positrons seen by PAMELA and the Fermi Gamma Ray Space Telescope are evidence of dark matter annihilation or decay in the Galactic halo. To accommodate these signals however, the final states must be predominantly muons or taus. These leptonic final states will produce neutrinos, which are potentially detectable with the IceCube neutrino observatory. We find that with five years of data, IceCube (supplemented by DeepCore) can significantly constrain the relevant parameter space for both annihilating or decaying dark matter, and may be capable of discovering leptophilic dark matter in the halo of the Milky Way.

We study Landau-gauge gluon and ghost propagators in Yang-Mills theories at lattice parameter $\beta =0$, considering relatively large lattice volumes for the case of the SU(2) gauge group in three and four space-time dimensions. We compare the lattice data to the so-called massive and conformal-scaling solutions, examining the requirements for a good description of the propagators over various ranges of momenta and discussing possible systematic errors. Our analysis strongly supports the massive solution, i.e. a finite gluon propagator and an essentially free ghost propagator in the infrared limit, in disagreement with A. Sternbeck and L. von Smekal, arXiv:0811.4300.. Moreover, we argue that discretization effects play no role in the analysis of these propagators.

We report an analysis of the impressive new lattice simulation results for octet baryon masses in $2+1$-flavor QCD. The analysis is based on a low-order expansion about the chiral SU(3) limit in which the symmetry breaking arises from terms linear in the quark masses plus the variation of the Goldstone boson masses in the leading chiral loops. The baryon masses evaluated at the physical light-quark masses are in remarkable agreement with the experimental values, with a model dependence considerably smaller than the rather small statistical uncertainty. From the mass formulas one can evaluate the sigma commutators for all octet baryons. This yields an accurate value for the pion-nucleon sigma commutator. It also yields the first determination of the strangeness sigma term based on $2+1$-flavor lattice QCD and, in general, the sigma commutators provide a resolution to the difficult issue of fine-tuning the strange-quark mass.

Thermal Hilbert moment QCD sum rules are used to obtain the temperature dependence of the hadronic parameters of charmonium in the vector channel, i.e. the $J/\psi$ resonance mass, coupling (leptonic decay constant), total width, and continuum threshold. The continuum threshold $s_0$, which signals the end of the resonance region and the onset of perturbative QCD, behaves as in all other hadronic channels, i.e. it decreases with increasing temperature until it reaches the perturbative QCD threshold $s_0=4m_Q^2$, with $m_Q$ the charm quark mass, at $T\simeq 1.22T_c$. The rest of the hadronic parameters behave very differently from those of light-light and heavy-light quark systems. The $J/\psi$ mass is essentially constant in a wide range of temperatures, while the total width grows with temperature up to $T\simeq 1.04T_c$ beyond which it decreases sharply with increasing $T$. The resonance coupling is also initially constant and then begins to increase monotonically around $T\simeq T_c$. This behavior of the total width and of the leptonic decay constant provides a strong indication that the $J/\psi$ resonance might survive beyond the critical temperature for deconfinement.

We discuss the problem of initial states for a system of coupled scalar fields out of equilibrium in the one-loop approximation. The fields consist of classical background fields, taken constant in space, and quantum fluctuations. If the initial state is the adiabatic vacuum, i.e., the ground state of a Fock space of particle excitations that diagonalize the mass matrix, the energy-momentum tensor is infinite at $t=0$, its most singular part behaves as $1/t$. When the system is coupled to gravity this presents a problem that we solve by a Bogoliubov transformation of the naive initial state. As a side result we also discuss the canonical formalism and the adiabatic particle number for such a system. Most of the formalism is presented for Minkowksi space. Embedding the system and its dynamics into a flat Friedmann-Robertson-Walker universe is straightforward and we briefly address the essential modifications.

The ${\Lambda }_c(2940{)}^{+}$ baryon with possible quantum numbers $J^P={\frac{1}{2}}^{+}$ and ${\frac{1}{2}}^{-}$ is studied as a molecular state composed of a nucleon and $D^{*}$ meson. We give predictions for the strong two-body decay channels ${\Lambda }_c(2940{)}^{+}\to p{D}^0$, ${\Sigma }_c^{++}{\pi }^{-}$ and ${\Sigma }_c^0{\pi }^{+}$, where the sum of partial widths is consistent with current data for the case of $J^P={\frac{1}{2}}^{+}$. The case of $J^P={\frac{1}{2}}^{-}$ is shown to be ruled out.

We show that a TeV scale inverse seesaw model for neutrino masses can be realized within the framework of a supersymmetric $SO(10)$ model consistent with gauge coupling unification and observed neutrino masses and mixing. We present our expectations for nonunitarity effects in the leptonic mixing matrix, some of which are observable at future neutrino factories as well as the next generation searches for lepton flavor violating processes such as $\mu \to e+\gamma$. The model has TeV scale $W_R$ and $Z^{\prime }$ bosons which are accessible at the Large Hadron Collider.

We consider the grand unified theory (GUT)-compatible formulation of noncommutative QED, as well as noncommutative $\mathrm{SU}(N)$ GUTs, for $N>2$, with no scalars but with fermionic matter in an arbitrary, anomaly-free representation, in the enveloping-algebra approach. We compute, to first order in the noncommutativity parameters ${\theta }^{\mu \nu }$, the UV divergent part of the one-loop background-field effective action involving at most two fermion fields and an arbitrary number of gauge fields. It turns out that, for special choices of the ambiguous trace over the gauge degrees of freedom, for which the $O(\theta )$ triple gauge-field interactions vanish, the divergences can be absorbed by means of multiplicative renormalizations and the inclusion of $\theta$-dependent counterterms that vanish on shell and are thus unphysical. For this to happen in the $\mathrm{SU}(N)$, $N>2$ case, the representations of the matter fields must have a common second Casimir; anomaly cancellation then requires the ordinary (commutative) matter content to be nonchiral. Together with the vanishing of the divergences of fermionic four point functions, this shows that GUT-inspired theories with U(1) and $\mathrm{SU}(N)$, $N>2$ gauge groups and ordinary vector matter content not only have a renormalizable matter sector, but are on-shell one-loop multiplicatively renormalizable at order one in $\theta$.

We consider astrophysical objects such as main-sequence stars, white- dwarfs, and neutron stars in a noncommutative context. Noncommutativity is implemented via a deformed dispersion relation $E^2=p^2{c}^2(1+\lambda E{)}^2+m^2{c}^4$ from which we obtain noncommutative corrections to the pressure, particle number, and energy densities for radiation and for a degenerate fermion gas. The main implications of noncommutativity for the considered astrophysical objects are examined and discussed.

We present a supersymmetric $SU(5)$ grand unified theory model with a discrete non-Abelian flavor symmetry that is broken by Wilson lines. The model is formulated in $4+3$ dimensions compactified on a manifold $S^3/Z_n$. Symmetry breaking by Wilson lines is topological and allows to realize the necessary flavor symmetry breaking without a vacuum alignment mechanism. The model predicts the hierarchical pattern of charged fermion masses and quark mixing angles. Small normal hierarchical neutrino masses are generated by the type-I seesaw mechanism. The non-Abelian flavor symmetry predicts to leading order exact maximal atmospheric mixing while the solar angle emerges from a variant of quark-lepton complementarity. As a consequence, the resulting leptonic mixing matrix is in excellent agreement with current data and could be tested in future neutrino oscillation experiments.

Inspiralling compact binaries are expected to circularize before their gravitational-wave signals reach the sensitive frequency band of ground-based detectors. Current searches for gravitational waves from compact binaries using the LIGO and Virgo detectors therefore use circular templates to construct matched filters. Binary formation models have been proposed which suggest that some systems detectable by the LIGO-Virgo network may have non-negligible eccentricity. We investigate the ability of the restricted 3.5 post-Newtonian order TaylorF2 template bank, used by LIGO and Virgo to search for gravitational waves from compact binaries with masses $M\le 35M_{\odot }$, to detect binaries with nonzero eccentricity. We model the gravitational waves from eccentric binaries using the $x$-model post-Newtonian formalism proposed by Hinder et al. [I. Hinder, F. Hermann, P. Laguna, and D. Shoemaker, arXiv:0806.1037v1]. We find that small residual eccentricities ($e_0\lesssim 0.05$ at 40 Hz) do not significantly affect the ability of current LIGO searches to detect gravitational waves from coalescing compact binaries with total mass $2M_{\odot }<M<15M_{\odot }$. For eccentricities $e_0\gtrsim 0.1$, the loss in matched filter signal-to-noise ratio due to eccentricity can be significant and so templates which include eccentric effects will be required to perform optimal searches for such systems.

Inspired by the Randall-Sundrum framework we consider a number of phenomenologically relevant model-building questions on a slice of compactified ${\mathrm{AdS}}_d$ for $d>5$. Such spaces are interesting as they enable one to realize the weak scale via warping. We perform the Kaluza-Klein (KK) reduction for gravitons and bulk vectors in these spaces, and for the case of ${\mathrm{AdS}}_6$ consider the KK spectrum of gauge scalars. We further obtain the KK towers for bulk fermions on a slice of ${\mathrm{AdS}}_7$ and ${\mathrm{AdS}}_9$ and show that the Randall-Sundrum approach to flavor generalizes to these spaces with the localization of chiral zero-mode fermions controlled by their bulk Dirac mass parameters. However, for the phenomenologically interesting case where the transverse radius is $R^{-1}\sim \mathrm{TeV}$, we show that bulk standard model fields are not viable due to a resulting volume suppression of the gauge-coupling constants. A similar suppression occurs for the case of UV localization. Thus it seems that the standard model fields should be confined to the infrared brane in such spaces. Sterile fields and extended gauge sectors may propagate in the bulk, with the gauge-coupling volume suppression experienced by the latter motivating a weak coupling to standard model fields. We also discuss some issues regarding the effective 4D theory description in these spaces.