We investigate the backreaction equations for an acoustic black hole formed in a Laval nozzle under the assumption that the motion of the fluid is one-dimensional. The solution in the near-horizon region shows that as phonons are (thermally) radiated the sonic horizon shrinks and the temperature decreases. This contrasts with the behavior of Schwarzschild black holes, and is similar to what happens in the evaporation of (near-extremal) Reissner-Nordström black holes (i.e., infinite evaporation time). Finally, by appropriate boundary conditions the solution is extended in both the asymptotic regions of the nozzle.

We study Schwinger pair creation of charged Kaluza-Klein (KK) particles from a static KK electric field. We find that the gravitational backreaction of the electric field on the geometry—which is incorporated via the electric KK-Melvin solution—prevents the electrostatic potential from overcoming the rest mass of the KK particles, thus impeding the tunneling mechanism which is often thought of as responsible for the pair creation. However, we find that pair creation still occurs with a finite rate formally similar to the classic Schwinger result, but via an apparently different mechanism, involving a combination of the Unruh effect and vacuum polarization due to the $E$-field.

The time evolution of a wormhole in a Friedmann universe approaching the big rip is studied. The wormhole is modeled by a thin spherical shell accreting the superquintessence fluid—two different models are presented. Contrary to recent claims that the wormhole overtakes the expansion of the universe and engulfs it before the big rip is reached, it is found that the wormhole becomes asymptotically comoving with the cosmic fluid and the future evolution of the universe is fully causal.

The behavior of a spin-$1/2$ particle in a weak static gravitational field is considered. The Dirac Hamiltonian is diagonalized by the Foldy-Wouthuysen transformation providing also the simple form for the momentum and spin polarization operators. The operator equations of momentum and spin motion are derived for a first time. Their semiclassical limit is analyzed. The dipole spin-gravity coupling in the previously found (another) Hamiltonian does not lead to any observable effects. The general agreement between the quantum and classical approaches is established, contrary to several recent claims. The expression for the gravitational Stern-Gerlach force is derived. The helicity evolution in the gravitational field and corresponding accelerated frame coincides, being the manifestation of the equivalence principle.

We study time-dependent solutions in M and superstring theories with higher-order corrections. We first present general field equations for theories of Lovelock type with stringy corrections in arbitrary dimensions. We then exhaust all exact and asymptotic solutions of exponential and power-law expansions in the theory with Gauss-Bonnet terms relevant to heterotic strings and in the theories with quartic corrections corresponding to the M theory and type II superstrings. We discuss interesting inflationary solutions that can generate enough $e$ foldings in the early universe.

Phantom dark-energy models, with $w<-1$, are characterized by a future singularity and therefore a finite lifetime for the universe. Because the future singularity is triggered by the onset of dark-energy domination, the universe spends a significant fraction of its total lifetime in a state for which the dark-energy and matter densities are roughly comparable. We calculate, as a function of $w$, the fraction of the total lifetime of the universe for which the dark-energy and matter densities differ by less than the ratio $r_0$ in either direction. For $r_0=10$, this fraction varies from $1/3$ to $1/8$ as $w$ varies from $-1.5$ to $-1.1$; the fraction is smaller for smaller values of $r_0$. This result indicates that the coincidence problem is significantly ameliorated in phantom-dominated cosmologies with a future singularity.

In the Penrose limit construction a constant parameter $\Omega$ is introduced by which coordinates as well as the metric are rescaled in a suitable way. It results in a metric which apart from a possible coordinate dependence has an additional dependence on this constant parameter $\Omega$. Here the scaling with $\Omega$ of the components of the Weyl tensor and the energy-momentum tensor is determined in the Penrose limit, i.e. $\Omega \to 0$. In both cases, a type of peeling-off behavior in $\Omega$ is found. Examples of different types of matter are provided. The expansion and shear of the congruence of null geodesics along which the Penrose limit is taken are determined. Finally, the approach to the singularity in the Penrose limit of cosmological space-times is discussed.

Recently an effective action of the SD$p$-brane decaying process in string theory has been proposed. This effective description involves the Tachyon driven matter coupled to bosonic ten-dimensional Type II supergravity. Here the Hamiltonian formulation of this system is given. Exact solutions for the corresponding quantum theory by solving the Wheeler-deWitt equation in the late-time limit of the rolling tachyon are found. The energy spectrum and the probability densities for several values of $p$ are shown and their possible interpretation is discussed. In the process the effects of electromagnetic fields are also incorporated and it is shown that in this case the interpretation of tachyon regarded as “matter clock” is modified.

We present viable $F$-term realizations of the hybrid inflationary scenario in the context of supergravity addressing at the same time the well-known problems of the initial conditions and of the adequate suppression of the inflaton mass. An essential role in our construction is played by decoupled superheavy fields without superpotential acquiring large vacuum expectation values due to $D$ terms associated with anomalous $U(1)$ gauge symmetries. The naturalness of the initial conditions is achieved through a chaotic inflation starting at energies close to the Planck scale and driven by the anomalous $D$ terms. We discuss two distinct mechanisms leading to such an early chaotic $D$-term inflation which depend on the choice of the Kähler potential involving the superheavy fields. The one relies on a choice of the Kähler potential of the $SU(1,1)/U(1)$ Kähler manifold of the type encountered in no-scale supergravity whereas the other employs a more conventional choice for the Kähler potential of the $SU(1,1)/U(1)$ or $SU(2)/U(1)$ Kähler manifold but invokes rather specific values of the Fayet-Iliopoulos $\xi$ term. For such specific values of the $\xi$ term we exploit the existence of special classical nonoscillatory solutions describing inflationary expansion at both large and small inflaton field values. In the scenarios considered the superpotential is linear in the inflaton field associated with the observable inflation on account of a $R$ symmetry and the suppression of the inflaton mass is a result of a cancellation between the always positive contribution of the decoupled superheavy fields and a negative contribution originating from the part of the Kähler potential involving the inflaton.

The behavior of the quintessence field is studied during inflation. In order to have a satisfactory model of dark energy, the quintessence field value today should be as insensible to the initial conditions as possible. Usually, only the dependence on the initial conditions specified at the end of inflation or, equivalently, at the beginning of the radiation dominated era, is considered. Provided the quintessence field is initially within a large but, crucially, finite interval, its present value becomes independent of the initial value it started from. The question as to whether inflation naturally drives the quintessence field to the above-mentioned interval is addressed. Since the quantum effects turn out to be important, the formalism of stochastic inflation is used in order to calculate the evolution of the quintessence field. Moreover, the quantum effects originating from the inflaton field are also taken into account and are proved to be subdominant in most cases. Finally, the requirement that the quintessence field is on tracks today is shown to imply quite tight constraints on the initial values of the quintessence and inflaton fields at the beginning of inflation. In particular, the initial value of the inflaton field cannot be too large which indicates that the quintessential scenario seems to be compatible with inflation only if the total number of e-folds is quite small.

We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the Universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.

Searches for known waveforms in gravitational wave detector data are often done using matched filtering. When used on real instrumental data, matched filtering often does not perform as well as might be expected, because nonstationary and non-Gaussian detector noise produces large spurious filter outputs (events). This paper describes a ${\chi }^2$ time-frequency test which is one way to discriminate such spurious events from the events that would be produced by genuine signals. The method works well only for broadband signals. The case where the filter-template does not exactly match the signal waveform is also considered, and upper bounds are found for the expected value of ${\chi }^2$.

We compute the one loop corrected effective Lagrangian for the quark-squark-chargino and quark-squark-neutralino interactions. The effective Lagrangian takes into account the loop corrections arising from the exchange of the gluinos, charginos, neutralinos, W, Z, the charged Higgs, and the neutral Higgs. We further analyze the squark decays into charginos and neutralinos and discuss the effect of the loop corrections on them. The analysis takes into account CP phases in the soft parameters. It is found that the loop corrections to the stop decay widths into chargino and neutralinos can be as much as 30% or even larger. Further, the stop decay widths show a strong dependence on the CP phases. These results are of relevance in the precision predictions of squark decays in the context of specific models of soft breaking in supergravity and string based models.

The possibility is examined that the masses of the light quarks $u$ and $d$ have varied over the course of the universe’s evolution. Such a variation would have an effect on axion cosmology and can be the basis of a solution of the so-called axion energy problem. If this is the case, a scalar force somewhat weaker than gravity could exist that has a range of order 1 km.

Recent developments in string compactifications in the presence of antisymmetric field backgrounds suggest a new simple and predictive structure for soft terms in the MSSM depending only on two parameters. They give rise to a positive definite scalar potential, a solution to the $\mu$-problem, flavor universality and absence of a SUSY-CP problem.

We present an unquenched calculation of the quark propagator in Landau gauge with $2\text{}+\text{}1$ flavors of dynamical quarks. We use configurations generated with an improved staggered (“Asqtad”) action by the MILC Collaboration. This quark action has been seen to have excellent rotational symmetry and scaling properties in the quenched quark propagator. Quenched and dynamical calculations are performed on a ${20}^3\times 64$ lattice with a nominal lattice spacing of $a=0.125\mathrm{fm}$. The matched quenched and dynamical lattices allow us to investigate the relatively subtle sea-quark effects, and even in the quenched case the physical volume of these lattices gives access to lower momenta than our previous study. We calculate the quark mass function and renormalization function for a variety of valence and sea-quark masses.

The decay $B\to f_0(980)K$ is studied within the framework of QCD factorization and the two-quark scenario for $f_0(980)$. There are two distinct penguin contributions and their interference depends on the unknown mixing angle $\theta$ of strange and nonstrange quark contents of $f_0(980)$: destructive for $0<\theta <\pi /2$ and constructive for $\pi /2<\theta <\pi$. The QCD sum-rule method is applied to evaluate the leading-twist light-cone distribution amplitudes and the scalar decay constant of $f_0$. We conclude that the short-distance approach is not adequate to explain the observed large rates of $f_0{K}^{-}$ and $f_0{\overline{K}}^0$. Among many possible subleading corrections, we study and estimate the contributions from the three-parton Fock states of the $f_0$ and from the intrinsic gluon inside the $B$ meson. It is found that the spectator gluon of the $B$ meson may play an eminent role for the enhancement of $f_0(980)K$. We point out that if $f_0(980)$ is a four-quark state as widely perceived, there will exist extra diagrams contributing to $B\to f_0(980)K$. However, in practice it is difficult to make quantitative predictions based on the four-quark picture for $f_0(980)$ as it involves additional nonfactorizable contributions that are difficult to estimate and the calculations of the decay constant and form factors of $f_0(980)$ are beyond the conventional quark model.

We apply a model for the study of quark-hadron duality in inclusive electron scattering to the calculation of spin observables. The model is based on solving the Dirac equation numerically for a scalar confining linear potential and a vector color Coulomb potential. We qualitatively reproduce the features of quark-hadron duality for all potentials considered, and discuss the onset of scaling and duality for the responses, spin structure functions, and polarization asymmetries. Duality may be applied to gain access to kinematic regions which are hard to access in deep inelastic scattering, namely, for $x_{\mathrm{Bj}}\to 1$, and we discuss which observables are most suitable for this application of duality.

Power corrections for virtual Compton scattering at leading twist are determined at operator level. From the complete off-cone representation of the twist-2 Compton operator integral representations for the trace, antisymmetric and symmetric part of that operator are derived. The operator valued invariant functions are written in terms of iterated operators and may lead to interrelations. For matrix elements they go over into relations for generalized parton distributions. Reducing to the $s$-channel relevant part one gets operator preforms of the Wandzura-Wilczek and the (target mass corrected) Callan-Gross relations whose structure is exactly the same as known from the case of deep inelastic scattering; taking nonforward matrix elements one reproduces earlier results [B. Geyer, D. Robaschik and J. Eilers, Nucl. Phys. B704, 279 (2005).] for the absorptive part of the virtual Compton amplitude. All these relations, obtained without any approximation or using equations of motion, are determined solely by the twist-2 structure of the underlying operator and, therefore, are purely of geometric origin.

Using 180 $\mathrm{p}{\mathrm{b}}^{-1}$ of data collected with the CDF II detector at the Tevatron, we measure the first two moments of the hadronic invariant mass-squared distribution in charmed semileptonic $B$ decays. From these we determine the nonperturbative Heavy Quark Effective Theory parameters $\Lambda$ and ${\lambda }_1$ used to relate the $B$ meson semileptonic branching ratio to the CKM matrix element $|V_{cb}|$. For a minimum lepton momentum of 0.7 GeV/$c$ in the $B$ rest frame we measure the first two moments of the $D^{**}\to D^{(*)}\pi$ component to be $⟨m_{D^{**}}^2⟩=(5.83\pm {0.16}_{\mathrm{stat}}\pm {0.08}_{\mathrm{syst}}){\mathrm{GeV}}^2/c^4$ and $⟨(m_{D^{**}}^2-⟨m_{D^{**}}^2⟩{)}^2⟩=(1.30\pm {0.69}_{\mathrm{stat}}\pm {0.22}_{\mathrm{syst}})\mathrm{Ge}{\mathrm{V}}^4/c^8$. Combining these with the discrete mass terms from the $D$ and $D^{*}$ mesons, we find the total moments to be $⟨M_{X_c}^2⟩-{\overline{m}}_D^2=(0.467\pm {0.038}_{\mathrm{stat}}\pm {0.068}_{\mathrm{syst}})\mathrm{Ge}{\mathrm{V}}^2/c^4$ and $⟨(M_{X_c}^2-⟨M_{X_c}^2⟩{)}^2⟩=(1.05\pm {0.26}_{\mathrm{stat}}\pm {0.13}_{\mathrm{syst}})\mathrm{Ge}{\mathrm{V}}^4/c^8$, where ${\overline{m}}_D$ is the spin-averaged $D$ mass. The systematic error is dominated by the uncertainties in the world-average branching ratios used to combine the $D$, $D^{*}$, and $D^{**}$ contributions. The analysis makes no assumptions about the shape or resonant structure of the $D^{**}\to D^{(*)}\pi$ invariant mass distribution.