An earlier developed model for vector meson photoproduction, based on a dipole Pomeron exchange, is extended to electroproduction. Universality of the nonlinear Pomeron trajectory is tested by fitting the model to ZEUS and H1 data as well as to CDF data on $\overline{p}p$ elastic scattering.

The nature of low-mass baryon-antibaryon enhancements seen in B decays is explored. Three possibilities include (i) states near threshold as found in a model by Nambu and Jona-Lasinio, (ii) isoscalar states with $J^{\mathrm{PC}}{=0\mathrm{}}^{\pm +}$ coupled to a pair of gluons, and (iii) low-mass enhancements favored by the fragmentation process. Ways of distinguishing these mechanisms using angular distributions and flavor symmetry are proposed.

We investigate three Earth density models for the measurement of the CP phase in very long baseline neutrino oscillation experiments to study the effect of the potential error due to Earth density uncertainties. Two of the density models which are commonly used are global models. The third provides a more realistic density profile which takes into account the local density variation along a specific 2100 km baseline. We find significant differences among these density models. The more realistic density model has a smaller intrinsic density fluctuation and hence allows better control of the error caused by the Earth density uncertainty. We also find that the conventional CP violation (CPV) variable, i.e., the CP odd difference, is in general small. Under the running conditions assumed in the present calculation, the differences of this CPV variable among the different density models and even the CPV variable itself can be dominated over by statistical and systematic errors. Therefore, other more suitable CPV variables have to be considered in the extraction of the CP phase.

We present an improved measurement of $\mathrm{CP}$-violating asymmetries in $B^0\to {\pi }^{+}{\pi }^{-}$ decays based on a $78{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We reconstruct one neutral B meson as a $B^0\to {\pi }^{+}{\pi }^{-}$ $\mathrm{CP}$ eigenstate and identify the flavor of the accompanying B meson from inclusive properties of its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the $\mathrm{CP}$-violating asymmetry amplitudes ${\mathcal{A}}_{\pi \pi }=+0.77\mathrm{}\pm 0.27\left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)$ and ${\mathcal{S}}_{\pi \pi }=-1.23\pm 0.41\left(\mathrm{stat}\right){}_{-0.07}^{+0.08\mathrm{}}\left(\mathrm{syst}\right),$ where the statistical uncertainties are determined from the Monte Carlo pseudoexperiments. We obtain confidence intervals for $\mathrm{CP}$-violating asymmetry parameters ${\mathcal{A}}_{\pi \pi }$ and ${\mathcal{S}}_{\pi \pi }$ based on a frequentist approach. We rule out the $\mathrm{CP}$-conserving case, ${\mathcal{A}}_{\pi \pi }={\mathcal{S}}_{\pi \pi }=0,$ at the $99.93\%$ confidence level. We discuss how these results constrain the value of the Cabibbo-Kobayashi-Maskawa (CKM) angle ${\phi }_2.$

The possible decays of four-quark mesons are studied by assigning the newly observed BABAR resonance to a four-quark meson, $F_I^{+}\sim \left[\mathrm{cq}\right]\left[\overline{s}\overline{q}\right]$ with $q=u,d.\mathrm{}$ It is expected that some of them can be observed as narrow resonances. The implication of the existence of four-quark mesons in hadronic weak interactions is also discussed.

We consider the ground state of a supermembrane on the maximally supersymmetric pp-wave background by using the quantum-mechanical procedure of de Wit, Hoppe, and Nicolai. On the pp-wave background the ground state has a nontrivial structure even in the zero-mode Hamiltonian. The supergravity multiplet in flat space comes to split with a certain energy difference. We explicitly derive the supersymmetric ground-state wave function for the zero-mode Hamiltonian, which is obviously normalizable. Moreover, we discuss the nonzero-mode Hamiltonian and construct an example of the ground-state wave function with the truncation of variables, whose $L^2$ norm can be represented by an asymptotic series.

The existence of anomalous symmetry-breaking solutions of the SO(2,1) commutator algebra is explicitly extended beyond the case of scale-invariant contact interactions. In particular, the failure of the conservation laws of the dilation and special conformal charges is displayed for the two-dimensional inverse square potential. As a consequence, this anomaly appears to be a generic feature of conformal quantum mechanics and not merely an artifact of contact interactions. Moreover, a renormalization procedure traces the emergence of this conformal anomaly to the ultraviolet sector of the theory, within which lies the apparent singularity.

We take as a starting point the planar model arising from the dimensional reduction of Maxwell electrodynamics with the (Lorentz-violating) Carroll-Field-Jackiw term. We then write and study the extended Maxwell equations and the corresponding wave equations for the potentials. The solution to these equations shows some interesting deviations from the usual MCS electrodynamics, with background-dependent correction terms. In the case of a timelike background, the correction terms dominate over the MCS sector in the region far from the origin, and establish the behavior of a massless electrodynamics (in the electric sector). In the spacelike case, the solutions indicate the clear manifestation of spatial anisotropy, which is consistent with the existence of a privileged direction in space.

We show how the linear delta expansion, as applied to the slow-roll transition in quantum mechanics, can be recast in the closed time-path formalism. This results in simpler, explicit expressions than were obtained in the Schrödinger formulation and allows for a straightforward generalization to higher dimensions. Motivated by the success of the method in the quantum-mechanical problem, where it has been shown to give more accurate results for longer than existing alternatives, we apply the linear delta expansion to four-dimensional field theory. At small times all methods agree. At later times, the first-order linear delta expansion is consistently higher than the Hartree-Fock approximation, but does not show any sign of a turnover. A turnover emerges in second-order of the method, but the value of $〈{\hat{\Phi }}^2\mathrm{}\left(t\right)\mathrm{}〉$ at the turnover is larger than that given by the Hartree-Fock approximation. Based on this calculation, and our experience in the corresponding quantum-mechanical problem, we believe that the Hartree-Fock approximation does indeed underestimate the value of $〈{\hat{\Phi }}^2\mathrm{}\left(t\right)\mathrm{}〉$ at the turnover. In subsequent applications of the method we hope to implement the calculation in the context of an expanding universe, following the line of earlier calculations by Boyanovsky et al., who used the Hartree-Fock and large-$N$ methods. It seems clear, however, that the method will become unreliable as the system enters the reheating stage.

We argue that two-dimensional (0,2) gauged linear sigma models are not destabilized by instanton generated world-sheet superpotentials. We construct several examples where we show this to be true. The general proof is based on the Konishi anomaly for (0,2) theories.

Gravity on noncommutative analogues of compact spaces can give a finite mode truncation of ordinary commutative gravity. We obtain the actions for gravity on the noncommutative two-sphere and on the noncommutative ${\mathbf{CP}}^2$ in terms of finite dimensional $(N\times N)$ matrices. The commutative large N limit is also discussed.

The one-loop energy density of an infinitely thin static magnetic vortex in $\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ Yang-Mills theory is evaluated using the Schrödinger picture. Both the gluonic fluctuations as well as the quarks in the vortex background are included. The energy density of the magnetic vortex is discussed as a function of the magnetic flux. The center vortices correspond to local minima in the effective potential. These minima are degenerated with the perturbative vacuum if the fermions are ignored. Inclusion of fermions lifts this degeneracy, raising the vortex energy above the energy of the perturbative vacuum.

We study neutron stars in a varying speed of light (VSL) theory of gravity in which the local speed of light depends upon the value of a scalar field $\phi .$ We find that the masses and radii of the stars are strongly dependent on the strength of the coupling between $\phi$ and the matter field and that for certain choices of coupling parameters, the maximum neutron star mass can be arbitrarily small. We also discuss the phenomenon of cosmological evolution of VSL stars (analogous to the gravitational evolution in scalar-tensor theories) and we derive a relation showing how the fractional change in the energy of a star is related to the change in the cosmological value of the scalar field.

Although slow light (electromagnetically induced transparency) would seem an ideal medium in which to institute a “dumb hole” (black hole analogue), it suffers from a number of problems. We show that the high phase velocity in the slow light regime ensures that the system cannot be used as an analogue displaying Hawking radiation. Even though an appropriately designed slow-light setup may simulate classical features of black holes—such as horizon, mode mixing, “Bogoliubov” coefficients, etc.—it does not reproduce the related quantum effects.

In the Randall-Sundrum scenario we investigate the dynamics of a spherically symmetric 3-brane world when matter fields are present in the bulk. To analyze the 5-dimensional Einstein equations we employ a global conformal transformation whose factor characterizes the $Z_2$ symmetric warp. We find a new set of exact dynamical collapse solutions which localize gravity in the vicinity of the brane for a stress-energy tensor of conformal weight -4 and a warp factor that depends only on the coordinate of the fifth dimension. Geometries which describe the dynamics of inhomogeneous dust and generalized dark radiation on the brane are shown to belong to this set. The conditions for singular or globally regular behavior and the static marginally bound limits are discussed for these examples. Also explicitly demonstrated is complete consistency with the effective point of view of a 4-dimensional observer who is confined to the brane and makes the same assumptions about the bulk degrees of freedom.

In a 5-dimensional spacetime ${(M,g}_{\mathrm{ab}})$ with a Killing vector field ${\xi }^a$ which is either everywhere time like or everywhere space like, the collection of all trajectories of ${\xi }^a$ gives a 4-dimensional space S. The reduction of ${(M,g}_{\mathrm{ab}})$ is studied in the geometric language, which is a generalization of Geroch’s method for the reduction of 4-dimensional spacetime. A 4-dimensional gravity coupled to a vector field and a scalar field on S is obtained by the reduction of vacuum Einstein’s equations on M, which gives also an alternative description of the 5-dimensional Kaluza-Klein theory. In addition to the symmetry-reduced action from the Hilbert action on M, an alternative action of the fields on S is also obtained, the variations of which lead to the same fields equations as those reduced from the vacuum Einstein equation on M.

Overall, brane inflation is compatible with the recent analysis of the Wilkinson microwave anisotropy probe (WMAP) data. Here we explore the constraints of WMAP and the 2dF Galaxy Redshift Survey (2dFGRS) data on the various brane inflationary scenarios. Brane inflation naturally ends with the production of cosmic strings, which may provide a way to distinguish these models observationally. We argue that currently available data cannot exclude a non-negligible contribution from cosmic strings definitively. We perform a partial statistical analysis of mixed models that include a subdominant contribution from cosmic strings. Although the data favor models without cosmic strings, we conclude that they cannot definitively rule out a cosmic-string-induced contribution of $\sim 10\%$ to the observed temperature, polarization and galaxy density fluctuations. These results imply that $G\mu \lesssim 1.3\times {10}^{-6}\sqrt{B\lambda /0.1\mathrm{}},$ where $\lambda <~1$ is a measure of the intercommutation probability of the cosmic string networks and B measures the importance of perturbations induced by cosmic strings. We argue that, conservatively, the data available currently still permit $B\lesssim \mathrm{0.1.}$ Precision measurements sensitive to the B-mode polarization produced by vector density perturbation modes driven by the string network could provide evidence for these models. Accurate determinations of $n_s\mathrm{}\left(k\right),$ the scalar fluctuation index, could also distinguish among various brane inflation models.

General relativistic superfluid neutron stars have a significantly more intricate dynamics than their ordinary fluid counterparts. Superfluidity allows different superfluid (and superconducting) species of particles to have independent fluid flows, a consequence of which is that the fluid equations of motion contain as many fluid element velocities as superfluid species. Whenever the particles of one superfluid interact with those of another, the momentum of each superfluid will be a linear combination of both superfluid velocities. This leads to the so-called entrainment effect whereby the motion of one superfluid will induce a momentum in the other superfluid. We have constructed a fully relativistic model for entrainment between superfluid neutrons and superconducting protons using a relativistic $\sigma -\omega$ mean field model for the nucleons and their interactions. In this context there are two notions of “relativistic”: relativistic motion of the individual nucleons with respect to a local region of the star (i.e. a fluid element containing, say, an Avogadro’s number of particles), and the motion of fluid elements with respect to the rest of the star. While it is the case that the fluid elements will typically maintain average speeds at a fraction of that of light, the supranuclear densities in the core of a neutron star can make the nucleons themselves have quite high average speeds within each fluid element. The formalism is applied to the problem of slowly rotating superfluid neutron star configurations, a distinguishing characteristic being that the neutrons can rotate at a rate different from that of the protons.

We represent the reionization history of the universe as a free function in redshift and study the potential for its extraction from cosmic microwave background (CMB) polarization spectra. From a principal component analysis, we show that the ionization history information is contained in 5 modes, resembling low-order Fourier modes in redshift space. The amplitudes of these modes represent a compact description of reionization observables in the CMB, easily predicted given a model for the ionization fraction. Measurement of these modes can ultimately constrain the total optical depth, or equivalently the initial amplitude of fluctuations to the 1% level regardless of the true model for reionization.

Chiral symmetry restoration at nonzero temperature is studied in the framework of the $O\left(4\right)\mathrm{}$ linear sigma model and the ${U(N}_f{)}_r\times {U(N}_f{)}_{\mathcal{l}}$ linear sigma model with $N_f=2,3$ and 4 quark flavors. We investigate the temperature dependence of the masses of the scalar and pseudoscalar mesons, and the nonstrange, strange, and charm condensates within the Hartree approximation as derived from the Cornwall-Jackiw-Tomboulis formalism. We find that the masses of the nonstrange and strange mesons at nonzero temperature depend sensitively on the particular symmetry of the model and the number of light quark flavors $N_f.$ On the other hand, because of the large charm quark mass, neither do charmed mesons significantly affect the properties of the other mesons, nor do their masses change appreciably in the temperature range around the chiral symmetry restoration temperature. In the chiral limit, the transition temperatures for chiral symmetry restoration are surprisingly close to those found in lattice QCD.