We investigate two-flavor and two-color QCD at finite temperature and chemical potential in comparison with a corresponding Nambu and Jona-Lasinio model. By minimizing the thermodynamic potential of the system, we confirm that a second-order phase transition occurs at a value of the chemical potential equal to half the mass of the chiral Goldstone mode. For chemical potentials beyond this value the scalar diquarks undergo Bose condensation and the diquark condensate is nonzero. We evaluate the behavior of the chiral condensate, the diquark condensate, the baryon charge density and the masses of scalar diquark, antidiquark and pion, as functions of the chemical potential. Very good agreement is found with lattice QCD ($N_c=2$) results. We also compare with a model based on leading-order chiral effective field theory.

We obtain a $3+2$ neutrino spectrum within a left-right symmetric framework by invoking a singular double seesaw mechanism. Higgs doublets are employed to break $S{U}_R(2)$ and three additional fermions, singlets under the left-right symmetric gauge group, are included. The introduction of a singularity into the singlet fermion Majorana mass matrix results in a light neutrino sector of three neutrinos containing predominantly ${\nu }_{\alpha L}$, $\alpha =e,\mu ,\tau$, separated from two neutrinos containing a small ${\nu }_{\alpha L}$ component. The resulting active-sterile mixing in the $5\times 5$ mixing matrix is specified once the mass eigenvalues and the $3\times 3$ submatrix corresponding to the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix are known.

We introduce an approximation scheme to perform an analytic study of the oscillation phenomena in a pedagogical and comprehensive way. By using Gaussian wave packets, we show that the oscillation is bounded by a time-dependent vanishing function which characterizes the slippage between the mass-eigenstate wave packets. We also demonstrate that the wave packet spreading represents a secondary effect which plays a significant role only in the nonrelativistic limit. In our analysis, we note the presence of a new time-dependent phase and calculate how this additional term modifies the oscillating character of the flavor conversion formula. Finally, by considering box and sine wave packets we study how the choice of different functions to describe the particle localization changes the oscillation probability.

We present a new class of models which produce zero ${\theta }_{\mathrm{Q}\mathrm{C}\mathrm{D}}$ angle at the tree and one-loop level due to Hermiticity of sub-blocks in the extended quark mass matrices. The structure can be maintained typically by nonAbelian generation symmetry. Two examples are given for this class of solutions.

The results for the Debye and Meissner screening masses of the gluons and the photon in the case of neutral and $\beta$-equilibrated dense two-flavor quark matter are presented. In the limits of the normal phase and the ideal two-flavor color superconducting phase, the screening masses coincide with the known results. Most interestingly, we find that the Meissner screening masses squared can be negative, indicating a plasma-type chromomagnetic instability in dense quark matter.

We review the notion of the Higgs effect in the context of string theory. We find that by including this effect in time dependent backgrounds, one is led to a natural mechanism for stabilizing moduli at points of enhanced gauge symmetry. We consider this mechanism for the case of the radion (size of the extra dimensions) and find that as decompactification of the large spatial dimensions takes place the radion will remain stabilized at the self-dual radius. We discuss how this mechanism can be incorporated into models of string cosmology and brane inflation to resolve some outstanding problems. We also address some issues regarding which string states should be included when constructing low energy actions in string cosmology.

We consider the Lorentz contraction of a fermion-antifermion bound state in $1+1$ dimensional QED. In $1+1$ dimensions the absence of physical, propagating photons allows us to explicitly solve the weak coupling limit $\alpha \ll m^2$ of the Bethe-Salpeter bound state equation in any Lorentz frame. In a time-ordered formalism it is seen that all pair production is suppressed in this limit. The wave function is shown to contract while the mass spectrum is invariant under boosts.

We study brane cosmology as 4D (four-dimensional) domain-wall dynamics in 5D bulk spacetime. For a generic 5D bulk with 3D maximal symmetry, we derive the equation of motion of a domain wall and find that it depends on mass function of the bulk spacetime, and the energy-momentum conservation in a domain wall is affected by a lapse function in the bulk. Especially, for a bulk spacetime with nontrivial lapse function, energy of matter field on the domain wall goes out or comes in from the bulk spacetime. Applying our result to the case with SU(2) gauge bulk field, we obtain a singularity-free universe in brane world scenario, that is, not only a big bang initial singularity of the brane is avoided but also a singularity in a 5D bulk does not exist.

The idea of relating the infrared and ultraviolet cutoffs is applied to the Brans-Dicke theory of gravitation. We find that the Hubble scale or the particle horizon as the infrared cutoff will not give accelerating expansion. The dynamical cosmological constant with the event horizon as the infrared cutoff is a viable dark energy model.

We provide a method for analytically constructing high-accuracy templates for the gravitational-wave signals emitted by compact binaries moving in inspiralling eccentric orbits. In contrast to the simpler problem of modeling the gravitational-wave signals emitted by inspiralling circular orbits, which contain only two different time scales, namely, those associated with the orbital motion and the radiation reaction, the case of inspiralling eccentric orbits involves three different time scales: orbital period, periastron precession, and radiation-reaction time scales. By using an improved “method of variation of constants,” we show how to combine these three time scales, without making the usual approximation of treating the radiative time scale as an adiabatic process. We explicitly implement our method at the 2.5PN post-Newtonian accuracy. Our final results can be viewed as computing new “postadiabatic” short-period contributions to the orbital phasing or, equivalently, new short-period contributions to the gravitational-wave polarizations, $h_{+,\times }$, that should be explicitly added to the “post-Newtonian” expansion for $h_{+,\times }$, if one treats radiative effects on the orbital phasing of the latter in the usual adiabatic approximation. Our results should be of importance both for the LIGO/VIRGO/GEO network of ground based interferometric gravitational-wave detectors (especially if Kozai oscillations turn out to be significant in globular cluster triplets) and for the future space-based interferometer LISA.

Using relativistic kinetic theory, we study spherically symmetric, static equilibrium configurations of a collisionless Maxwell-Boltzmann gas with nonstandard self-interactions, modeled by an effective one-particle force. The resulting set of equilibrium conditions represents a generalization of the classical Tolman-Oppenheimer-Volkov equations. We specify these conditions for two types of Lorentz-like forces: one coupled to the 4-acceleration and the 4-velocity and the other one coupled to the Riemann tensor. We investigate the weak field limits in each case and show that they lead to various Newtonian type configurations that are different from the usual isothermal sphere characterizing the conventional Newtonian Maxwell-Boltzmann gas. These configurations could provide a plausible phenomenological and theoretical description of galactic dark matter halo structures. We show how the self-interaction may act phenomenologically as an effective cosmological constant and discuss possible connections with Modified Newtonian Dynamics (MOND).

Positively curved oscillatory universes are studied within the context of loop quantum cosmology subject to a consistent semiclassical treatment. The semiclassical effects are reformulated in terms of an effective phantom fluid with a variable equation of state. In cosmologies sourced by a massless scalar field, these effects lead to a universe that undergoes ever-repeating cycles of expansion and contraction. The presence of a self-interaction potential for the field breaks the symmetry of the cycles and can enable the oscillations to establish the initial conditions for successful slow-roll inflation, even when the field is initially at the minimum of its potential with a small kinetic energy. The displacement of the field from its minimum is enhanced for lower and more natural values of the parameter that sets the effective quantum gravity scale. For sufficiently small values of this parameter, the universe can enter a stage of eternal self-reproduction.

In this paper we study the inflation model driven by the phantom field. We propose a possible exit from phantom inflation to our observational cosmology by introducing an additional normal scalar field, similar to hybrid inflation model. Then we discuss the primordial perturbation spectra from various phantom inflation models and give an interesting comparison with those of normal scalar field inflation models.

We propose that the different angular distributions in two-photon collisions observed at low and high center-of-mass energies $W_{\gamma \gamma }$ indicate the transition from nonperturbative to perturbative QCD. We calculate the differential cross sections of $\gamma \gamma \to \pi \pi ,KK$ in the angle $\theta$ of one of the final-state mesons using QCD sum rules and the perturbative QCD approach based on $k_T$ factorization theorem. Our predictions from sum rules (perturbative QCD) decrease (increase) with $|\cos \theta |$, consistent with the Belle data of $\gamma \gamma \to K^{+}{K}^{-}$ for $W_{\gamma \gamma }\approx 1.5-1.7(2.2-2.4)\mathrm{G}\mathrm{e}\mathrm{V}$.

We study nuclear ${\mu }^{-}-e^{-}$ conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation ($\mathrm{L̸}{}_f$). We examine the impact of a specific hadronization prescription on the analysis of new physics in nuclear ${\mu }^{-}-e^{-}$ conversion and stress the importance of vector meson exchange between lepton and nucleon currents. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the $\varphi$ meson. This allows us to extract new limits on the $\mathrm{L̸}{}_f$ lepton-quark effective couplings from the existing experimental data.

The probabilistic model of parton distributions, previously developed by one of the authors, is generalized to include the transversity distribution. When interference effects are attributed to quark level only, the intrinsic quark motion produces the transversity, which is about twice as large as the usual polarized distribution. The applicability of such a picture is considered and possible corrections, accounting for interference effects at the parton-hadron transition stage are discussed.

The concept of Lorentz scalar quark confinement has a long history and is still widely used despite its well-known theoretical faults. We point out here that the predictions of scalar confinement also conflict directly with experiment. We investigate the dependence of heavy-light meson mass differences on the mass of the light quark. In particular, we examine the strange and nonstrange $D$ mesons. We find that the predictions of scalar confinement are in considerable conflict with measured values.

In this work we present an accurate parameterization of the antineutrino flux produced by the isotopes ${}^{235}\mathrm{U}$, ${}^{239}\mathrm{P}\mathrm{u}$, and ${}^{241}\mathrm{P}\mathrm{u}$ in nuclear reactors. We determine the coefficients of this parameterization, as well as their covariance matrix, by performing a fit to spectra inferred from experimentally measured beta spectra. Subsequently we show that flux shape uncertainties play only a minor role in the KamLAND experiment, however, we find that future reactor-neutrino experiments to measure the mixing angle ${\theta }_{13}$ are sensitive to the fine details of the reactor-neutrino spectra. Finally, we investigate the possibility to determine the isotopic composition in nuclear reactors through an antineutrino measurement. We find that with a three month exposure of a 1 ton detector the isotope fractions and the thermal reactor power can be determined at a few percent accuracy, which may open the possibility of an application for safeguard or nonproliferation objectives.

The Born-Infeld Lagrangian for non-Abelian gauge theory is adapted to the case of the generalized gauge fields arising in noncommutative matrix geometry. Basic properties of static and time-dependent solutions of the scalar sector of this model are investigated.

We have considered the most general gauge invariant five-dimensional action of a second rank antisymmetric Kalb-Ramond tensor gauge theory, including a topological term of the form ${ϵ}^{ABLMN}{B}_{AB}{H}_{LMN}$ in a Randall-Sundrum scenario. Such a tensor field $B_{AB}$ (whose rank-3 field strength tensor is $H_{LMN}$), which appears in the massless sector of a heterotic string theory, is assumed to coexist with the gravity in the bulk. The third rank field strength corresponding to the Kalb-Ramond field has a well-known geometric interpretation as the space-time torsion. The only nontrivial classical solutions corresponding to the effective four-dimensional action are found to be self-dual or anti-self-dual Kalb-Ramond fields. This ensures that the four-dimensional effective action on the brane is parity-conserving. The massive modes for both cases, lying in the TeV range, are related to the fundamental parameters of the theory. These modes can be within the kinematic reach of forthcoming TeV-scale experiments. However, the couplings of the massless as well as massive Kalb-Ramond modes with matter on the visible brane are found to be suppressed vis-a-vis that of the graviton by the warp factor, whence the conclusion is that both the massless and the massive torsion modes appear much weaker than curvature to an observer on the visible brane.