The accretion process onto spinning objects in Kerr spacetimes is studied with numerical simulations. Our results show that accretion onto compact objects with Kerr parameter (characterizing the spin) $|a|<M$ and $|a|>M$ is very different. In the superspinning case, for $|a|$ moderately larger than $M$, the accretion onto the central object is extremely suppressed due to a repulsive force at short distance. The accreting matter cannot reach the central object, but instead is accumulated around it, forming a high density cloud that continues to grow. The radiation emitted in the accretion process will be harder and more intense than the one coming from standard black holes; e.g. $\gamma$-rays could be produced as seen in some observations. Gravitational collapse of this cloud might even give rise to violent bursts. As $|a|$ increases, a larger amount of accreting matter reaches the central object and the growth of the cloud becomes less efficient. Our simulations find that a quasisteady state of the accretion process exists for $|a|/M\gtrsim 1.4$, independently of the mass accretion rate at large radii. For such high values of the Kerr parameter, the accreting matter forms a thin disk at very small radii. We provide some analytical arguments to strengthen the numerical results; in particular, we estimate the radius where the gravitational force changes from attractive to repulsive and the critical value $|a|/M\approx 1.4$ separating the two qualitatively different regimes of accretion. We briefly discuss the observational signatures which could be used to look for such exotic objects in the Galaxy and/or in the Universe.

A spherically symmetric, static model of the cosmological voids is constructed in the framework of the Tolman-Oppenheimer-Volkov equation with the cosmological constant. Extension of the Tooper result (dimensionless form of the TOV equation) is provided for nonzero $\Lambda$. Then, the equation is simplified in $\alpha \to 0$, $\lambda \to 0$, and $\lambda /\alpha =\mathrm{const}$ regime, suitable for largest structures in $\Lambda$-dominated universe. Voids are treated as underdensity regions in the static Einstein universe. Both overdensity and underdensity (relative to static universe) solutions exist. They are identified with standard astrophysical spherical objects and voids, respectively. The model is tested against observed properties (the radius—the central density relation) and density profiles of voids. Analytical formulas for radial density contrast profile and radii of the voids are derived. Some consequences for cosmological N-body simulations are suggested. Hints on the dark matter/dark energy EOS filling the voids are provided.

Presented in this paper is a technique that we propose for extracting the physical parameters of a rotating stellar core collapse from the observation of the associated gravitational wave signal from the collapse and core bounce. Data from interferometric gravitational wave detectors can be used to provide information on the mass of the progenitor model, precollapse rotation, and the nuclear equation of state. We use waveform libraries provided by the latest numerical simulations of rotating stellar core collapse models in general relativity, and from them create an orthogonal set of eigenvectors using principal component analysis. Bayesian inference techniques are then used to reconstruct the associated gravitational wave signal that is assumed to be detected by an interferometric detector. Posterior probability distribution functions are derived for the amplitudes of the principal component analysis eigenvectors, and the pulse arrival time. We show how the reconstructed signal and the principal component analysis eigenvector amplitude estimates may provide information on the physical parameters associated with the core collapse event.

Past and recent data analyses gave some hints of steps in dark energy. Considering dark energy as a dynamical scalar field, we investigate several models with various steps: a step in the scalar potential, a step in the kinetic term, a step in the energy density, and a step in the equation-of-state parameter $w$. These toy models provide a workable mechanism to generate steps and features of dark energy. Remarkably, a single real scalar can cross $w=-1$ dynamically with a step in the kinetic term.

Observing charge-parity ($CP$) or time-reversal ($T$) violations in the leptonic sector will give useful information to elucidate the nature of neutrinos. $CP$-violating couplings in charged leptonic currents carry out the weak phases necessary to break these symmetries. Here we study the interference of $W^{\pm }$ and $H^{\pm }$ boson mediated amplitudes as the origin of possible $CP$ and $T$ violation in semileptonic decays of $K^{\pm }$ mesons and ${\tau }^{\pm }$ leptons. We use the experimental bound on the $T$-odd transverse polarization asymmetry in $K_{\mu 3}^{+}$ decays to predict an upper limit on the $CP$ violating effects in $\tau \to K\pi \nu$ decays. In the framework of this model with scalar-mediated interactions, we find that current limits on the former process indicate that the $CP$ violating effects in the latter are much smaller than the limits reported so far.

A study of the $J/\psi \pi \pi$ and $J/\psi K\overline{K}$ systems, treating them as coupled channels, has been made by solving the Faddeev equations, with the purpose of investigating the possibility of generation of the $J^{\mathrm{PC}}=1^{--}$, $Y(4260)$ resonance due to the interaction between these three mesons. In order to do this, we start by solving the Bethe-Salpeter equation for the two pseudoscalar and for the vector-pseudocalar meson systems using the amplitudes obtained from the lowest order chiral Lagrangians as potentials. With the $t$- matrices generated from these potentials, which contain the poles of the $\sigma$, $f_0(980)$, and $a_0(980)$ resonances for the pseudoscalar-pseudoscalar system and the pole of the $X(3872)$, along with other new charmed resonant states, for the vector-pseudoscalar system, we solve the Faddeev equations. As a result, we get a peak around 4150 MeV with a width $\sim 90\mathrm{MeV}$ when the invariant mass of the two pseudoscalars is close to that of the $f_0(980)$.

We study gauge threshold corrections for local grand unified theory models in IIB/F-theory. Consistency with holomorphy requirements of supergravity and the Kaplunovsky-Louis formula implies that the unification scale is enhanced by the bulk radius $R$ from the string scale to $M_X=R{M}_S$. We argue that the stringy interpretation of this is via a locally uncanceled tadpole sourced by the hypercharge flux. This sources closed string modes propagating into the bulk—equivalently open string gauge coupling running up to the winding scale $M_X$. The enhancement to $R{M}_s$ is tied to grand unified theory breaking by a globally trivial hypercharge flux and will occur in all models realizing this mechanism.

In light of recent discussions of the string landscape, it is essential to understand the degree to which string theory is predictive. We argue that it is unlikely that the landscape as a whole will exhibit unique correlations amongst low-energy observables, but rather that different regions of the landscape will exhibit different overlapping sets of correlations. We then provide a statistical method for quantifying this degree of predictivity, and for extracting statistical information concerning the relative sizes and overlaps of the regions corresponding to these different correlation classes. Our method is robust and requires no prior knowledge of landscape properties, and can be applied to the landscape as a whole as well as to any relevant subset.

We calculate triangle anomalies for fermions with noncanonical scaling dimensions. The most well-known example of such fermions (aka unfermions) occurs in Seiberg duality where the matching of anomalies (including mesinos with scaling dimensions between $3/2$ and $5/2$) is a crucial test of duality. By weakly gauging the nonlocal action for an unfermion, we calculate the one-loop three-current amplitude. Despite the fact that there are more graphs with more complicated propagators and vertices, we find that the calculation can be completed in a way that nearly parallels the usual case. We show that the anomaly factor for fermionic unparticles is independent of the scaling dimension and identical to that for ordinary fermions. This can be viewed as a confirmation that unparticle actions correctly capture the physics of conformal fixed point theories like Banks-Zaks or supersymmetric QCD.

The gluon condensate is very sensitive to the QCD deconfinement transition since its value changes drastically with the deconfinement transition. We calculate the gluon condensate dependence of the heavy quark potential in AdS/CFT to study how the property of the heavy quarkonium is affected by a relic of the deconfinement transition. We observe that the heavy quark potential becomes deeper as the value of the gluon condensate decreases. We interpret this as a dropping of the heavy quarkonium mass just above the deconfinement transition. We finally argue that dropping of the gluon condensate and the pure thermal effect are competing with each other in the physics of heavy quarkonium at high temperature.

In this paper, we explore the relation between crossing symmetry and modular invariance in conformal field theory and $S$ duality in gauge theory. It is shown that partition functions of different $S$ dual theories of $N=2$ $SU(2)$ gauge theory with four fundamentals can be derived from the crossing symmetry of the Liouville four-point function. We also show that the partition function of $N=4$ $SU(2)$ gauge theory can be derived from the Liouville partition function on torus.

The symmetry properties of a proposal to go beyond relativistic quantum field theory based on a modification of the commutation relations of fields are identified. Poincaré invariance in an auxiliary spacetime is found in the Lagrangian version of the path integral formulation. This invariance is contrasted with the idea of doubly (or deformed) special relativity. This analysis is then used to go from the free theory of a complex field to an interacting field theory.

We consider the Einstein-Maxwell system as a Cauchy initial value problem taking the electric and magnetic fields as independent variables. Maxwell’s equations in curved spacetimes are derived in detail using a $3+1$ formalism and their hyperbolic properties are analyzed, showing that the resulting system is symmetric hyperbolic. We also focus on the problem of finding initial data for multiple charged black holes assuming time-symmetric initial data and using a puncturelike method to solve the Hamiltonian and the Gauss constraints. We study the behavior of the resulting initial data families, and show that previous results in this direction can be obtained as particular cases of our approach.

We study the stability of static black holes in Lovelock theory, which is a natural higher dimensional generalization of Einstein theory. We derive a master equation for tensor perturbations in general Lovelock theory. It turns out that the resultant equation is characterized by one functional which determines the background black hole solutions. Thus, the stability issue of static black holes under tensor perturbations in general dimensions is reduced to an algebraic problem. We show that small Lovelock black holes in even-dimensions are unstable.

The Wheeler-DeWitt (WDW) equation for the Kantowski-Sachs model can also be understood as the WDW equation corresponding to the Schwarzschild black hole due to the well known diffeomorphism between these two metrics. The WDW equation and its solutions are ignorant of the coordinate patch one is using, only by imposing coordinate conditions we can differentiate between cosmological and black hole models. At that point, the foliation parameter $t$ or $r$ will appear in the solution of interest. In this work we supersymmetrize this WDW equation obtaining an extra term in the potential with two possible signs. The WKB method is then applied, giving rise to two classical equations. It is shown that the event horizon can never be reached because very near to it, the extra term in the potential, for each one of the equations, is more relevant than the one that corresponds to Schwarzschild. One can then study the asymptotic cases in which one of the two terms in the Hamiltonian dominates the behavior. One of them corresponds to the usual Schwarzschild black hole. We will study here the other two asymptotic regions; they provide three solutions. All of them have a singularity in $r=0$ and depending on an integration constant $C$ they can also present a singularity in $r=C^2$. Neither of these solutions have a Newtonian limit. The black hole solution we study is analyzed between the singularity $r=C^2$ and a maximum radius $r_m$. We find an associated mass, considering the related cosmological solution inside $r=C^2$, and based on the holographic principle an entropy can be assigned to this asymptotic solution.

We calculate the ratio of shear viscosity to entropy density for charged black branes in third order Lovelock theory. For chargeless black branes, the result turns out to be consistent with the prediction made by Brustein and Medved [Phys. Rev. D 79, 021901 (2009)].. We find that the third order Lovelock gravity term does not contribute to causality violation unlike the Gauss-Bonnet term. The stability of the black brane again requires the value of the Lovelock coupling constant to be bounded by $1/4$ in the infinite dimensionality limit.

The coupled dark energy models, in which the quintessence scalar field nontrivially couples to the cold dark matter, have been proposed to explain the coincidence problem. In this paper we study the perturbations of coupled dark energy models and the effects of this interaction on the current observations. Here, we pay particular attention to its imprint on the late-time integrated Sachs-Wolfe effect. We perform a global analysis of the constraints on this interaction from the current observational data. Considering the typical exponential form as the interaction form, we obtain that the strength of interaction between dark sectors is constrained as $\beta <0.085$ at 95% confidence level. Furthermore, we find that future measurements with smaller error bars could improve the constraint on the strength of coupling by a factor of 2, when compared to the present constraints.

Cosmological scaling solutions, which give rise to a scalar-field density proportional to a background fluid density during radiation and matter eras, are attractive to alleviate the energy scale problem of dark energy. In the presence of multiple scalar fields, the scaling solution can exit to the epoch of cosmic acceleration through the so-called assisted inflation mechanism. We study cosmological dynamics of a multifield system in details with a general Lagrangian density $p=\sum _{i=1}^n{X}_{i}g(X_i{e}^{{\lambda }_i{\varphi }_i})$, where $X_i=-(\nabla {\varphi }_i{)}^2/2$ is the kinetic energy of the $i$th field ${\varphi }_i$, ${\lambda }_i$ is a constant, and $g$ is an arbitrary function in terms of $Y_i=X_i{e}^{{\lambda }_i{\varphi }_i}$. This covers most of the scalar-field models of dark energy proposed in literature that possess scaling solutions. Using the bound coming from big-bang nucleosynthesis and the condition under which each field cannot drive inflation as a single component of the universe, we find the following features: (i) a transient or eternal cosmic acceleration can be realized after the scaling matter era, (ii) a thawing property of assisting scalar fields is crucial to determine the evolution of the field equation of state $w_{\varphi }$, and (iii) the field equation of state today can be consistent with the observational bound $w_{\varphi }<-0.8$ in the presence of multiple scalar fields.

We estimate the sensitivity of various experiments detecting ultrahigh-energy cosmic rays to primary photons with energies above ${10}^{19}\mathrm{eV}$. We demonstrate that the energy of a primary photon may be significantly (up to a factor of $\sim 10$) underestimated or overestimated for particular primary energies and arrival directions. We consider distortion of the reconstructed cosmic-ray spectrum for the photonic component. As an example, we use these results to constrain the parameter space of models of superheavy dark matter by means of both the observed spectra and available limits on the photon content. We find that a significant contribution of ultrahigh-energy particles (photons and protons) from decays of superheavy dark matter is allowed by all these constraints.

For the Laser Interferometer Space Antenna (LISA) to reach its design sensitivity, the coupling of the free-running laser frequency noise to the signal readout must be reduced by more than 14 orders of magnitude. One technique employed to reduce the laser frequency noise will be arm locking, where the laser frequency is locked to the LISA arm length. In this paper we detail an implementation of arm locking. We investigate orbital effects (changing arm lengths and Doppler frequencies), the impact of errors in the Doppler knowledge that can cause pulling of the laser frequency, and the noise limit of arm locking. Laser frequency pulling is examined in two regimes: at lock acquisition and in steady state. The noise performance of arm locking is calculated with the inclusion of the dominant expected noise sources: ultrastable oscillator (clock) noise, spacecraft motion, and shot noise. We find that clock noise and spacecraft motion limit the performance of dual arm locking in the LISA science band. Studying these issues reveals that although dual arm locking [A. Sutton and D. A. Shaddock, Phys. Rev. D 78, 082001 (2008)] has advantages over single (or common) arm locking in terms of allowing high gain, it has disadvantages in both laser frequency pulling and noise performance. We address this by proposing a modification to the dual arm-locking sensor, a hybrid of common and dual arm-locking sensors. This modified dual arm-locking sensor has the laser frequency pulling characteristics and low-frequency noise coupling of common arm locking, but retains the control system advantages of dual arm locking. We present a detailed design of an arm-locking controller and perform an analysis of the expected performance when used with and without laser prestabilization. We observe that the sensor phase changes beneficially near unity-gain frequencies of the arm-locking controller, allowing a factor of 10 more gain than previously believed, without degrading stability. With a time-delay error of 3 ns (equivalent of 1 m interspacecraft ranging error), time-delay interferometry (TDI) is capable of suppressing $300\mathrm{Hz}/\sqrt{\mathrm{Hz}}$ of laser frequency noise to the required level. We show that if no interspacecraft laser links fail, arm locking alone surpasses this noise performance for the entire mission. If one interspacecraft laser link fails, arm locking alone will achieve this performance for all but approximately 1 h per year, when the arm length mismatch of the two remaining arms passes through zero. Therefore, the LISA sensitivity can be realized with arm locking and time-delay interferometry only, without any form of prestabilization.