This article provides a general study of the Hamiltonian stability and the hyperbolicity of vector field models involving both a general function of the Faraday tensor and its dual, $f(F^2,F\tilde{F})$, as well as a Proca potential for the vector field, $V(A^2)$. In particular it is demonstrated that theories involving only $f(F^2)$ do not satisfy the hyperbolicity conditions. It is then shown that in this class of models, the cosmological dynamics always dilutes the vector field. In the case of a nonminimal coupling to gravity, it is established that theories involving $Rf(A^2)$ or $Rf(F^2)$ are generically pathologic. To finish, we exhibit a model where the vector field is not diluted during the cosmological evolution, because of a nonminimal vector field-curvature coupling which maintains second-order field equations. The relevance of such models for cosmology is discussed.

We consider a spacetime with empty Schwarzschild-de Sitter exterior and Schwarzschild-de Sitter interior metric for a spherical fluid with constant density. The fluid interior may be taken to represent a galaxy supercluster, for which the proper distance from the center of the supercluster to the cosmological horizon has the same order of magnitude as the Hubble radius derived from Friedmann-Robertson-Walker cosmologies. The fluid interior and surrounding vacuum may also be considered as a model of the Local Group of galaxies in the far future. Particle motion is subject both to the attractive gravity exerted by the fluid and the repelling cosmological constant. Using global Fermi coordinates for the central observer within the fluid, the Fermi velocity, the astrometric velocity, the kinematic velocity, and the spectroscopic velocity, relative to the central (Fermi) observer, of a radially receding test particle are calculated and compared. We find that the Fermi relative velocity can exceed the speed of light in this model, but the presence of a positive cosmological constant causes recessional speeds of distant high energy particles to decrease rather than increase. We derive a version of Hubble’s law for this spacetime which might be applicable for the analysis of a receding mass within a great void adjacent to a supercluster, relatively isolated from gravitational sources other than the supercluster. We also compare some of our results to related behavior in Friedmann-Robertson-Walker cosmologies and consider implications to arguments regarding the expansion of space.

We present a detailed study of the collapse of a spherical perturbation in Dvali-Gabadadze-Porrati (DGP) braneworld gravity for the purpose of modeling simulation results for the halo mass function, bias, and matter power spectrum. The presence of evolving modifications to the gravitational force in the form of the scalar brane-bending mode leads to qualitative differences to the collapse in ordinary gravity. In particular, differences in the energetics of the collapse necessitate a new, generalized method for defining the virial radius which does not rely on strict energy conservation. These differences and techniques apply to smooth dark energy models with $w\ne -1$ as well. We also discuss the impact of the exterior of the perturbation on collapse quantities due to the lack of a Birkhoff theorem in DGP. The resulting predictions for the mass function, halo bias, and power spectrum are in good overall agreement with DGP $N$-body simulations on both the self-accelerating and normal branch. In particular, the impact of the Vainshtein mechanism as measured in the full simulations is matched well. The model and techniques introduced here can serve as practical tools for placing consistent constraints on braneworld models using observations of large-scale structure.

Dark energy dynamics in the recent universe is influenced by its evolution through the long, matter-dominated expansion history. A particular dynamical property, the flow variable, remains constant in several classes of scalar field models as long as matter dominates; the dark energy is only free to change this behavior at recent times. This gives natural initial conditions for Monte Carlo studies of dark energy dynamics. We propose a parametrization for the later evolution that covers a wide range of possible behaviors, is tractable in making predictions, and can be constrained by observations. We compare the approach to directly parametrizing the potential, which does not take into account the history of the dark energy dynamics.

A bosonic field impinging on a rotating black hole can be amplified as it scatters off the hole, a phenomenon known as superradiant scattering. If in addition the field has a nonzero rest mass $\mu$, the mass term effectively works as a mirror, reflecting the scattered wave back towards the black hole. In this physical system, known as a black-hole bomb, the wave may bounce back and forth between the black hole and some turning point, amplifying itself each time. Consequently, the field grows exponentially over time and is unstable. In this paper we study analytically for the first time the phenomenon of superradiant instability (the black-hole bomb mechanism) in the regime $M\mu =O(1)$ of greatest instability. We find a maximal instability growth rate of ${\tau }^{-1}=1.7\times {10}^{-3}{M}^{-1}$. This instability is 4 orders of magnitude stronger than has been previously estimated.

Dimension-5 corrections to the gauge kinetic term of grand unified theories may capture effects of quantum gravity or string compactification. Such operators modify the usual gauge coupling unification prediction in a calculable manner. Here we examine $SU(5)$, $SO(10)$, and $E(6)$ grand unified theories in the light of all such permitted operators and calculate the impact on the intermediate scales and the unification program. We show that in many cases at least one intermediate scale can be lowered to even 1–10 TeV, where a neutral $Z^{\prime }$ and possibly other states are expected.

We calculate the QCD equation of state for temperatures corresponding to the transition region with physical mass values for two degenerate light quark flavors and a strange quark using an improved staggered fermion action (p4-action) on lattices with temporal extent $N_{\tau }=8$. We compare our results with previous calculations performed at twice larger values of the light quark masses as well as with results obtained from a resonance gas model calculation. We also discuss the deconfining and chiral aspects of the QCD transition in terms of renormalized Polyakov loop, strangeness fluctuations, and subtracted chiral condensate. We show that compared to the calculations performed at twice larger value of the light quark mass the transition region shifts by about 5 MeV toward smaller temperatures.

The Drell–Yan dilepton production at backward rapidities is studied in proton-nucleus collisions at Relativistic Heavy Ion Collider and LHC energies by comparing two different approaches: the $k_T$ factorization at next-to-leading order with intrinsic transverse momentum and the same process formulated in the target rest frame, i.e., the color dipole approach. Our results are expressed in terms of the ratio between $p(d)-A$ and $p-p$ collisions as a function of transverse momentum and rapidity. Three nuclear parton distribution functions are used: EKS (Eskola, Kolhinen, and Ruuskanen), EPS08, and EPS09 and, in both approaches, dileptons show sensitivity to nuclear effects, specially regarding the intrinsic transverse momentum. Also, there is room to discriminate between formalisms: the color dipole approach lacks soft effects introduced by the intrinsic $k_T$. Geometric scaling GBW (Golec-Biernat and Wusthoff) and BUW (Boer, Utermann, and Wessels) color dipole cross section models and also a DHJ (Dumitru, Hayashigaki, and Jalilian-Marian) model, which breaks geometric scaling, are used. No change in the ratio between collisions is observed, showing that this observable is not changed by the particular shape of the color dipole cross section. Furthermore, our $k_T$ factorization results are compared with color glass condensate results at forward rapidities: the results agree at Relativistic Heavy Ion Collider although disagree at LHC, mainly due to the different behavior of target gluon and quark shadowing.

We define a mapping of the QCD Balitsky-Kovchegov equation in the diffusive approximation with noise and a generalized coupling allowing a common treatment of the fixed and running QCD couplings. It corresponds to the extension of the stochastic Fisher and Kolmogorov-Petrovskii-Piscounov equation to the radial wave propagation in a medium with negative-gradient absorption responsible for anomalous diffusion, noninteger dimension, and damped noise fluctuations. We obtain its analytic traveling-wave solutions with a new scaling curve and for running coupling a new scaling variable allowing to extend the range and validity of the geometric-scaling QCD prediction beyond the previously known domain.

One can determine antiquark polarizations in a proton using the information from deep inelastic scattering, $\beta$ decays of baryons, orbital angular momenta of quarks, as well as their integrated magnetic distributions. The last quantities were determined previously by us performing a fit to magnetic moments of a baryon octet. However, because of the $SU(3)$ symmetry our results depend on two parameters. The quantity ${\Gamma }_V$, measured recently in a COMPASS experiment, gives the relation between these parameters. We can fix the last unknown parameter using the ratio of up and down quark magnetic moments which one can get from the fit to radiative vector meson decays. We calculate antiquark polarizations with the orbital momenta of valence quarks that follow from lattice calculations. The value of the difference of up and down antiquark polarizations obtained in our calculations is consistent with the result obtained in a HERMES experiment.

The cross section for photon production in association with at least one jet containing a $b$ quark has been measured in proton antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The data sample used corresponds to an integrated luminosity of $340{\mathrm{pb}}^{-1}$ collected with the CDF II detector. Both the differential cross section as a function of photon transverse energy $E_T^{\gamma }$ and the total cross section are measured and compared to a next-to-leading order prediction for the process.

We discuss the possibility of searching for the $\Lambda -\overline{\Lambda }$ oscillations for coherent $\Lambda \overline{\Lambda }$ production in the $J/\psi \to \Lambda \overline{\Lambda }$ decay process. The sensitivity of measurement of $\Lambda -\overline{\Lambda }$ oscillation in the external field at BES-III experiment is considered. These considerations indicate an alternative way to probe the $\Delta B=2$ amplitude in addition to neutron oscillation experiments. Both coherent and time-dependent information can be used to extract the $\Lambda -\overline{\Lambda }$ oscillation parameter. With one year’s luminosity at BES-III, we can set an upper limit of $\delta m_{\Lambda \overline{\Lambda }}<{10}^{-15}\mathrm{MeV}$ at 90% confidence level, corresponding to about ${10}^{-6}\mathrm{s}$ of $\Lambda -\overline{\Lambda }$ oscillation time.

We discuss the phase transition of planar black holes in Hořava-Lifshitz gravity by introducing a Maxwell field and a complex scalar field. We calculate the condensate of the charged operators in the dual conformal field theories when the mass square of the complex scalar field is $m^2=-2/L^2$ and $m^2=0$, respectively. We compute the electrical conductivity of the Hořava-Lifshitz superconductor in the probe approximation. In particular, it is found that there exists a spike in the conductivity for the case of the operator with scaling dimension one. These results are quite similar to those in the case of Schwarzschild-AdS black holes, which demonstrates that the holographic superconductivity is a robust phenomenon associated with asymptotic AdS black holes.

As one step towards a systematic modeling of the electromagnetic (EM) emission from an inspiralling black hole binary we consider a simple scenario in which the binary moves in a uniform magnetic field anchored to a distant circumbinary disc. We study this system by solving the Einstein-Maxwell equations in which the EM fields are chosen with strengths consistent with the values expected astrophysically and treated as test fields. Our initial data consists of a series of binaries with spins aligned or antialigned with the orbital angular momentum and we study the dependence of gravitational and EM signals with different spin configurations. Overall we find that the EM radiation in the lowest $\ell =2$, $m=2$ multipole accurately reflects the gravitational one, with identical phase evolutions and amplitudes that differ only by a scaling factor. This is no longer true when considering higher $\ell$ modes, for which the amplitude evolution of the scaled EM emission is slightly larger, while the phase evolutions continue to agree. We also compute the efficiency of the energy emission in EM waves and find that it scales quadratically with the total spin and is given by $E_{\mathrm{EM}}^{\mathrm{rad}}/M\simeq {10}^{-15}(M/{10}^8{M}_{\odot }{)}^2(B/{10}^4\mathrm{G}{)}^2$, hence 13 orders of magnitude smaller than the gravitational energy for realistic magnetic fields. Although large in absolute terms, the corresponding luminosity is much smaller than the accretion luminosity if the system is accreting at near the Eddington rate. Most importantly, this EM emission is at frequencies of $\sim {10}^{-4}({10}^8{M}_{\odot }/M)\mathrm{Hz}$, which are well outside those accessible to astronomical radio observations. As a result, it is unlikely that the EM emission discussed here can be detected directly and simultaneously with the gravitational-wave one. However, indirect processes, driven by changes in the EM fields behavior could yield observable events. In particular we argue that if the accretion rate of the circumbinary disc is small and sufficiently stable over the timescale of the final inspiral, then the EM emission may be observable indirectly as it will alter the accretion rate through the magnetic torques exerted by the distorted magnetic field lines.

We study the geodesic equation in the space-time of a Schwarzschild black hole pierced by an infinitely thin cosmic string and give the complete set of analytical solutions of this equation for massive and massless particles, respectively. The solutions of the geodesic equations can be classified according to the particle’s energy and angular momentum, the ratio between the component of the angular momentum aligned with the axis of the string and the total angular momentum, the deficit angle of the space-time and as well the horizon radius (or mass) of the black hole. For bound orbits of massive test particles we calculate the perihelion shift, we discuss light deflection and comment on the Newtonian limit.

The static, apparently cylindrically symmetric vacuum solution of Linet and Tian for the case of a positive cosmological constant $\Lambda$ is shown to have toroidal symmetry and, besides $\Lambda$, to include three arbitrary parameters. It possesses two curvature singularities, of which one can be removed by matching it across a toroidal surface to a corresponding region of the dust-filled Einstein static universe. In four dimensions, this clarifies the geometrical properties, the coordinate ranges, and the meaning of the parameters in this solution. Some other properties and limiting cases of this space-time are described. Its generalization to any higher number of dimensions is also explicitly given.

We investigate the precision with which the parameters describing the characteristics and location of nonspinning black hole binaries can be measured with the Laser Interferometer Space Antenna (LISA). By using complete waveforms including the inspiral, merger, and ringdown portions of the signals, we find that LISA will have far greater precision than previous estimates for nonspinning mergers that ignored the merger and ringdown. Our analysis covers nonspinning waveforms with moderate mass ratios, $q\ge 1/10$, and total masses ${10}^5\lesssim M/M_{\odot }\lesssim {10}^7$. We compare the parameter uncertainties using the Fisher-matrix formalism, and establish the significance of mass asymmetry and higher-order content to the predicted parameter uncertainties resulting from inclusion of the merger. In real-time observations, the later parts of the signal lead to significant improvements in sky-position precision in the last hours and even the final minutes of observation. For comparable-mass systems with total mass $M/M_{\odot }\sim {10}^6$, we find that the increased precision resulting from including the merger is comparable to the increase in signal-to-noise ratio. For the most precise systems under investigation, half can be localized to within $\mathcal{O}(10\mathrm{arcmin})$, and 10% can be localized to within $\mathcal{O}(1\mathrm{arcmin})$.

We consider the evolution of a network of strings in an expanding Universe, allowing for the formation of junctions between strings of different tensions. By explicitly including, in the velocity-dependent evolution equations for the network, kinematic constraints associated with the formation of Y-shaped string junctions, we show how they lead to scaling solutions in regimes where they would not otherwise be found, thereby extending the range of parameters which lead to scaling. By incorporating these constraints we are able to study their general behavior for networks with cosmic superstring interaction rules, and predict the scaling densities expected by these networks.

We determine upper limits on the dark matter (DM) self-annihilation cross section for scenarios in which annihilation leads to the production of electron—positron pairs. In the Galactic center, relativistic electrons and positrons produce a radio flux via synchroton emission, and a gamma-ray flux via bremsstrahlung and inverse Compton scattering. On the basis of archival, interferometric and single-dish radio data, we have determined the radio spectrum of an elliptical region around the Galactic center of extent 3° semimajor axis (along the Galactic plane) and 1° semiminor axis and a second, rectangular region, also centered on the Galactic center, of extent $1.6°\times 0.6°$. The radio spectra of both regions are nonthermal over the range of frequencies for which we have data: 74 MHz–10 GHz. We also consider gamma-ray data covering the same region from the EGRET instrument (about GeV) and from HESS (around TeV). We show how the combination of these data can be used to place robust constraints on DM annihilation scenarios, in a way which is relatively insensitive to assumptions about the magnetic field amplitude in this region. Our results are approximately an order of magnitude more constraining than existing Galactic center radio and gamma-ray limits. For a DM mass of $m_{\chi }=10\mathrm{GeV}$, and an Navarro-Frank-White profile, we find $⟨{\sigma }_{A}v⟩\le \mathrm{\text{few}}\times {10}^{-25}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$.

We present a Bayesian analysis of four different types of backreaction models, which are based on the Buchert equations. In this approach, one considers a solution to the Einstein equations for a general matter distribution and then an average of various observable quantities is taken. Such an approach became of considerable interest when it was shown that it could lead to agreement with observations without resorting to dark energy. In this paper we compare the $\Lambda \mathrm{CDM}$ model and the backreaction models with type Ia supernovae, baryon acoustic oscillations, and cosmic microwave background data, and find that the former is favored. However, the tested models were based on some particular assumptions about the relation between the average spatial curvature and the backreaction, as well as the relation between the curvature and curvature index. In this paper we modified the latter assumption, leaving the former unchanged. We find that, by varying the relation between the curvature and curvature index, we can obtain a better fit. Therefore, some further work is still needed—in particular, the relation between the backreaction and the curvature should be revisited in order to fully determine the feasibility of the backreaction models to mimic dark energy.