A density wave in quark matter is discussed at finite temperature, which occurs along with the chiral condensation, and is described by a dual standing wave in scalar and pseudoscalar condensates on the chiral circle. The mechanism is quite similar to that for the spin density wave suggested by Overhauser and entirely reflects many-body effects. It is found within a mean-field approximation for the Nambu–Jona-Lasinio model that the chiral-condensed phase with the density wave develops at a high-density region just outside the usual chiral-transition line in phase diagram. A magnetic property of the density wave is also elucidated.

We analyze the dissociation of a photon in diffractive deep inelastic scattering in the kinematic regime where the diffractive mass is much bigger than the photon virtuality. We consider the dominant $q\overline{q}g$ component keeping track of the transverse momentum of the gluon which can be measured as a final-state jet. We show that the diffractive gluon-jet production cross-section is strongly sensitive to unitarity constraints. In particular, in a model with parton saturation, this cross-section is sensitive to the scale at which unitarity effects become important, the saturation scale. We argue that the measurement of diffractive jets at HERA in the limit of high diffractive mass can provide useful information on the saturation regime of QCD.

Entropy bounds applied to a system of $\mathcal{N}$ species of light quantum fields in thermal equilibrium at temperature $T$ are saturated in four dimensions at a maximal temperature $T_{\max }=M_{\mathrm{Planck}}/\sqrt{\mathcal{N}}$. We show that the correct setup for understanding the reason for the saturation is a cosmological one, and that a possible explanation is the copious production of black holes at this maximal temperature which prevents any further rise in temperature. The proposed explanation implies, if correct, that $\mathcal{N}$ light fields cannot be in thermal equilibrium in an ideal gas phase at temperatures $T$ above $T_{\max }$. However, we have been unable to identify a concrete mechanism that is efficient and quick enough to prevent the universe from exceeding this limiting temperature. The same issues can be studied in the framework of AdS/CFT by using a brane moving in a five dimensional AdS-Schwarzschild space to model a radiation dominated universe. In this case we show that $T_{\max }$ is the temperature at which the brane just reaches the horizon of the black hole, and that entropy bounds and the generalized second law of thermodynamics seem to be violated when the brane continues to fall into the black hole. We find, again, that the known physical mechanisms, including black hole production, are not efficient enough to prevent the brane from falling into the black hole. We propose several possible explanations for the apparent violation of entropy bounds, but none is a conclusive one.

In this work we construct charged thin-shell Lorentzian wormholes in dilaton gravity. The exotic matter required for the construction is localized in the shell and the energy conditions are satisfied outside the shell. The total amount of exotic matter is calculated and its dependence with the parameters of the model is analyzed.

We construct hypergravity theory in three-dimensions with the gravitino $\psi _{\mu m_1\cdots m_n}{}^A$ with an arbitrary half-integral spin $n+3/2$, carrying also the index $A$ for certain real representations of any gauge group $G$. The possible real representations are restricted by the condition that the matrix representation of all the generators are antisymmetric: $(T^I{)}^{AB}=-(T^I{)}^{BA}$. Since such a real representation can be arbitrarily large, this implies ${\aleph }_0$ hypergravity with infinitely many (${\aleph }_0$) extended local hypersymmetries.

Motivated by the structure of one-loop vacuum polarization effects in curved space-time we discuss a nonminimal extension of the Einstein-Maxwell equations. This formalism is applied to Bianchi I models with magnetic field. We obtain several exact solutions of the nonminimal system including those which describe an isotropization process. We show that there are inflationary solutions in which the cosmological constant is determined by the nonminimal coupling parameters. Furthermore, we find an isotropic de Sitter solution characterized by a “screening” of the magnetic field as a consequence of the nonminimal coupling.

While inflation gives an appealing explanation of observed cosmological data, there are a wide range of different inflation models, providing differing predictions for the initial perturbations. Typically models are motivated either by fundamental physics considerations or by simplicity. An alternative is to generate large numbers of models via a random generation process, such as the flow equations approach. The flow equations approach is known to predict a definite structure to the observational predictions. In this paper, we first demonstrate a more efficient implementation of the flow equations exploiting an analytic solution found by Liddle (2003). We then consider alternative stochastic methods of generating large numbers of inflation models, with the aim of testing whether the structures generated by the flow equations are robust. We find that while typically there remains some concentration of points in the observable plane under the different methods, there is significant variation in the predictions amongst the methods considered.

We propose the Gauss-Bonnet dark energy model inspired by string/M-theory where standard gravity with scalar contains additional scalar-dependent coupling with a Gauss-Bonnet invariant. It is demonstrated that the effective phantom (or quintessence) phase of the late universe may occur in the presence of such a term when the scalar is phantom or for nonzero potential (for canonical scalar). However, with the increase of the curvature, the Gauss-Bonnet term may become dominant so that the phantom phase is transient and the $w=-1$ barrier may be passed. Hence, the current acceleration of the universe may be caused by a mixture of scalar phantom and/or potential or stringy effects. It is remarkable that scalar-Gauss-Bonnet coupling acts against the big rip occurrence also in phantom cosmology.

Several conserved and/or gauge-invariant quantities described as the second-order curvature perturbation have been given in the literature. We revisit various scenarios for the generation of second-order non-Gaussianity in the primordial curvature perturbation $\zeta$, employing for the first time a unified notation and focusing on the normalization $f_{\mathrm{NL}}$ of the bispectrum. When $\zeta$ first appears a few Hubble times after horizon exit, $|f_{\mathrm{NL}}|$ is much less than 1 and is, therefore, negligible. Thereafter $\zeta$ (and hence $f_{\mathrm{NL}}$) is conserved as long as the pressure is a unique function of energy density (adiabatic pressure). Nonadiabatic pressure comes presumably only from the effect of fields, other than the one pointing along the inflationary trajectory, which are light during inflation (“light noninflaton fields”). During single-component inflation $f_{\mathrm{NL}}$ is constant, but multicomponent inflation might generate $|f_{\mathrm{NL}}|\sim 1$ or bigger. Preheating can affect $f_{\mathrm{NL}}$ only in atypical scenarios where it involves light noninflaton fields. The simplest curvaton scenario typically gives $f_{\mathrm{NL}}\ll -1$ or $f_{\mathrm{NL}}=+5/4$. The inhomogeneous reheating scenario can give a wide range of values for $f_{\mathrm{NL}}$. Unless there is a detection, observation can eventually provide a limit $|f_{\mathrm{NL}}|\lesssim 1$, at which level it will be crucial to calculate the precise observational limit using second-order theory.

We study QCD with two flavors of nonperturbatively improved Wilson fermions at finite temperature on the ${16}^{3}8$ lattice. We determine the transition temperature at lattice spacing as small as $a\sim 0.12$ fm, and study string breaking below the finite temperature transition. We find that the static potential can be fitted by a two-state ansatz, including a string state and a two-meson state. We investigate the role of Abelian monopoles at finite temperature.

We calculate numerically the eigenvalue distribution of the overlap Dirac operator in the quenched Schwinger model on a lattice. The distribution does not fit any of the three universality classes of spontaneous chiral-symmetry breaking, and its strong volume dependence indicates that the chiral condensate in the quenched theory is an ill-defined and divergent quantity. When we reweight configurations with the Dirac determinant to study the theory with $N_f=1$, we obtain a distribution of eigenvalues that is well-behaved and consistent with the theory of explicit symmetry breaking due to the anomaly.

In theories with a low quantum gravity scale, global symmetries are expected to be violated, inducing excessive proton decay or large Majorana neutrino masses. The simplest cure is to impose discrete gauge symmetries, which in turn make neutrinos massless. We construct models that employ these gauge symmetries while naturally generating small neutrino masses. Majorana (Dirac) neutrino masses are generated through the breaking of a discrete (continuous) gauge symmetry at low energies, e.g., $2\mathrm{keV}-1\mathrm{GeV}$. The Majorana case predicts $\Delta N_{\nu }\simeq 1$ at BBN, neutrinoless double beta decay with scalar emission, and modifications to the CMB anisotropies from domain walls in the Universe as well as providing a possible Dark Energy candidate. For the Dirac case, despite the presence of a new light gauge boson, all laboratory, astrophysical, and cosmological constraints can be avoided.

In this paper we study the possibility of probing for the absolute neutrino mass and its variation with short gamma ray burst (GRB). We have calculated the flight time difference between a massive neutrino and a photon in two different approaches to the mass varying neutrinos. Firstly we parametrize the neutrino mass as a function of the redshift in a model independent way, then we consider two specific models where the neutrino mass varies during the evolution of the quintessence fields. Our calculations show in general the value of the time delay is changed substantially relative to a constant neutrino mass and is also expected to be larger than the duration time of the short GRB.

We have measured the process $B^{\pm }\to (K^{*\pm }\to K^{\pm }{\pi }^0){\pi }^0$ with $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. From a signal yield of $89\pm 26$ events we obtain the branching fraction $\mathcal{B}(B^{\pm }\to K^{*\pm }{\pi }^0)=[6.9\pm 2.0(\mathrm{stat})\pm 1.3(\mathrm{syst})]\times {10}^{-6}$ with a statistical significance of 3.6 standard deviations including systematic uncertainties, and a charge asymmetry of $0.04\pm 0.29(\mathrm{stat})\pm 0.05(\mathrm{syst})$.

We obtain an exact result for the soft-gluon production and its $p_T$ distribution due to a gluon loop in a constant chromoelectric background field $E^a$ with arbitrary color. Unlike Schwinger’s result for $e^{+}{e}^{-}$ pair production in QED which depends only on one gauge invariant quantity, the electric field $E$, we find that the $p_T$ distribution of the gluons depend on two gauge invariant quantities, $E^a{E}^a$ and $[d_{abc}{E}^a{E}^b{E}^c{]}^2$.

Diffeomorphism-induced symmetry transformations and time evolution are distinct operations in generally covariant theories formulated in phase space. Time is not frozen. Diffeomorphism invariants are consequently not necessarily constants of the motion. Time-dependent invariants arise through the choice of an intrinsic time, or equivalently through the imposition of time-dependent gauge fixation conditions. One example of such a time-dependent gauge fixing is the Komar-Bergmann use of Weyl curvature scalars in general relativity. An analogous gauge fixing is also imposed for the relativistic free particle and the resulting complete set time-dependent invariants for this exactly solvable model are displayed. In contrast with the free particle case, we show that gauge invariants that are simultaneously constants of motion cannot exist in general relativity. They vary with intrinsic time.

We investigate the Dirac quasinormal modes (QNMs) of the Schwarzschild-anti-de Sitter and Reissner-Nordstrom-anti-de Sitter (SAdS/RNAdS) black holes using Horowitz-Hubeny approach. For large black holes, the fundamental QNMs are the linear functions of the Hawking temperature, and the slope of the lines decreases as the charge increases. For intermediate and small SAdS black holes, the real part of the fundamental QNMs approximates a temperature curve but the corresponding imaginary part is almost a linear function of the radius of the black hole. The quasinormal frequencies for high overtones become evenly spaced and the spacings are related to the mass and charge of the black hole. We also study the relation between QNMs and angular quantum number and find that the quasinormal frequencies increase as the angular quantum number increases.

I address some recently raised issues regarding the time-parametrization dependence in stochastic descriptions of eternal inflation. To clarify the role of the choice of the time gauge, I show examples of gauge-dependent as well as gauge-independent statements about physical observables in eternally inflating spacetimes. In particular, the relative abundance of thermalized and inflating regions is highly gauge-dependent. The unbounded growth of the 3-volume of the inflating regions is found in certain time gauges, such as the proper-time or the scale-factor gauge. Yet in the same spacetimes there exist time foliations with a finite and monotonically decreasing 3-volume, which I demonstrate by an explicit construction. I also show that there exists no choice of the time gauge that would yield an unbiased stationary probability distribution for observables in thermalized regions.

We consider the evolution of cosmological magnetic fields in Friedmann-Robertson-Walker models and outline a geometrical mechanism for their superadiabatic amplification on large scales. The mechanism operates within standard electromagnetic theory and applies to Friedmann-Robertson-Walker universes with open spatial sections. We discuss the general relativistic nature of the effect and show how it modifies the adiabatic magnetic evolution. Assuming a universe that is only marginally open today, we estimate the main features of the superadiabatically amplified residual field.