We study reflection and transmission of light at the interface between different phases of a $U\left(1\right)\mathrm{}\otimes U\left(1\right)\mathrm{}$ gauge theory. On each side of the interface, one can choose a basis so that one generator is free (allowing propagation of light), and the orthogonal one may be free, have a Higgs phase, or be confined. However, the basis on one side will in general be rotated relative to the basis on the other by some angle $\alpha .$ We calculate reflection and transmission coefficients for both polarizations of light and all 8 types of boundary, for arbitrary $\alpha .$ We find that an observer measuring the behavior of light beams at the boundary would be able to distinguish 4 different types of boundary, and we show how the remaining ambiguity arises from the principle of complementarity (indistinguishability of confined and Higgs phases) which leaves observables invariant under a global electric/magnetic duality transformation. We also explain the seemingly paradoxical behavior of Higgs/Higgs and confined/confined boundaries, and clarify some previous arguments that confinement must involve magnetic monopole condensation.

An analysis of the sensitivity of supersymmetric dark matter to variations in the b quark mass is given. Specifically we study the effects on the neutralino relic abundance from supersymmetric loop corrections to the mass of the b quark. It is known that these loop corrections can become significant for large $\tan \beta .$ The analysis is carried out in the framework of MSUGRA and we focus on the region where the relic density constraints are satisfied by resonant annihilation through the s-channel Higgs poles. We extend the analysis to include CP phases taking into account the mixing of the CP-even and CP-odd Higgs boson states which play an important role in determining the relic density. Implications of the analysis for the neutralino relic density consistent with the recent WMAP relic density constraints are discussed.

We investigate the QED Compton process in longitudinally polarized lepton-proton scattering both in the elastic and inelastic channels and show that the cross section can be expressed in terms of the polarized equivalent photon distribution of the proton. We provide the necessary kinematical constraints to extract the polarized photon content of the proton using this process at HERMES, COMPASS, and eRHIC. We also discuss the suppression of the major background process coming from virtual Compton scattering. We point out that such an experiment can give valuable information on $g_1{(x}_B{,Q}^2)$ in the small $x_B,$ broad $Q^2$ region at the future polarized collider eRHIC and especially in the lower $Q^2,$ medium $x_B$ region in fixed target experiments.

We investigate the general features of renormalization group flows near superconformal fixed points of four dimensional $\mathcal{N}=1\mathrm{}$ gauge theories with gravity duals. The gauge theories we study arise as the world-volume theory on a set of D-branes at a Calabi-Yau singularity where a del Pezzo surface shrinks to zero size. Based mainly on field theory analysis, we find evidence that such flows are often chaotic and contain exotic features such as duality walls. For a gauge theory where the del Pezzo is the Hirzebruch zero surface, the dependence of the duality wall height on the couplings at some point in the cascade has a self-similar fractal structure. For a gauge theory dual to $P^2$ blown up at a point, we find periodic and quasiperiodic behavior for the gauge theory couplings that does not violate the a conjecture. Finally, we construct supergravity duals for these del Pezzos that match our field theory beta functions.

We consider late-time cosmology in a (phantom) scalar-tensor theory with an exponential potential, as a dark-energy model with equation of state parameter close to $-1$ (a bit above or below this value). Scalar (and also other kinds of) matter can be easily taken into account. An exact spatially flat FRW cosmology is constructed for such theory, which admits (eternal or transient) acceleration phases for the current universe, in correspondence with observational results. Some remarks on the possible origin of the phantom, starting from a more fundamental theory, are also made. It is shown that quantum gravity effects may prevent (or, at least, delay or soften) the cosmic doomsday catastrophe associated with the phantom, i.e., the otherwise unavoidable finite-time future singularity (Big Rip). A dark-energy model (higher-derivative scalar-tensor theory) is introduced, and it is shown to admit an effective phantom and/or quintessence description with a transient acceleration phase. In this case, gravity favors that an initially insignificant portion of dark energy becomes dominant over the standard matter and radiation components in the evolution process.

We derive general expressions at the one-loop level for the coefficients of the covariant structure of the neutrino self-energy in the presence of a constant magnetic field. The neutrino energy spectrum and index of refraction are obtained for neutral and charged media in the strong-field limit ${(M}_W\gg \sqrt{B}\gg m_e,T,\mu ,|\mathbf{p}|)$ using the lowest Landau level approximation. The results found within the lowest Landau level approximation are numerically validated, summing in all Landau levels, for strong $B\gg T^2$ and weakly strong $B\gtrsim T^2$ fields. The neutrino energy in leading order of the Fermi coupling constant is expressed as the sum of three terms: a kinetic-energy term, a term of interaction between the magnetic field and an induced neutrino magnetic moment, and a rest-energy term. The leading radiative correction to the kinetic-energy term depends linearly on the magnetic field strength and is independent of the chemical potential. The other two terms are only present in a charged medium. For strong and weakly strong fields, it is found that the field-dependent correction to the neutrino energy in a neutral medium is much larger than the thermal one. Possible applications to cosmology and astrophysics are considered.

Primordial inhomogeneous magnetic fields of the right strength can leave a signature on the cosmic microwave background (CMB) temperature anisotropy and polarization. Potentially observable contributions to polarization B modes are generated by vorticity and gravitational waves sourced by the magnetic anisotropic stress. We compute the corresponding CMB transfer functions in detail, including the effect of neutrinos. The shear rapidly causes the neutrino anisotropic stress to cancel the stress from the magnetic field, suppressing the production of gravitational waves and vorticity on superhorizon scales after neutrino decoupling. A significant large scale signal from tensor modes can only be produced before neutrino decoupling, and the actual amplitude is somewhat uncertain. Plausible values suggest primordial nearly scale invariant fields with $B_{\lambda }\sim {10}^{-10}\mathrm{G}$ today may be observable from their large scale tensor anisotropy. They can be distinguished from primordial gravitational waves by their non-Gaussianity. Vector mode vorticity sources B-mode power on much smaller scales with a power spectrum somewhat similar to that expected from weak lensing, suggesting amplitudes $B_{\lambda }\sim {10}^{-9}\mathrm{G}$ may be observable on small scales for a spectral index $n\sim -\mathrm{2.9.}$ In the Appendix we review the covariant equations for computing the vector and tensor CMB power spectra that we implement numerically.

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.6 solar masses, no matter the model chosen for describing the pure quark phase.

We discuss how to extract renormalized loops from bare Polyakov loops in $\mathrm{SU}\left(N\right)\mathrm{}$ lattice gauge theories at nonzero temperature. Single loops in an irreducible representation are multiplicatively renormalized, without mixing, through mass renormalization. The values of renormalized loops in the four lowest representations of $\mathrm{SU}\left(3\right)\mathrm{}$ were measured numerically on small, coarse lattices. We find that in magnitude, condensates for the sextet and octet loops are approximately the square of the triplet loop. This agrees with a large N expansion, where factorization implies that the expectation values of loops in adjoint and higher representations are powers of fundamental and antifundamental loops. The corrections to the large N relations at three colors are greatest for the sextet loop, $\sim 1/N,$ and are found to be $<~25\%.$ The values of the renormalized triplet loop can be described by a matrix model, with an effective action dominated by the triplet loop: the deconfining phase transition for $N=3\mathrm{}$ is close to the Gross-Witten point at $N=\infty .$

We show that spontaneous breaking of global $B-L$ symmetry responsible for small neutrino masses via the seesaw mechanism provides a unified picture of hybrid inflation and dark matter if the scale of $B-L$ breaking is close to the GUT scale. The Majoron, which acquires a small mass due to Planck scale breaking of $B-L,$ is the dark matter candidate. The coupling of the Majoron field to the neutrino induces a small violation of CPT and Lorentz invariance at the present epoch. We discuss some of the phenomenological and cosmological implications of the model.

Anomalous quartic couplings between the electroweak gauge bosons may contribute to the $\nu \overline{\nu }\gamma \gamma$ and $q\overline{q}\gamma \gamma$ final states produced in $e^{+}{e}^{-}$ collisions. This analysis uses the LEP2 OPAL data sample at center-of-mass energies up to 209 GeV. Event selections identify $\nu \overline{\nu }\gamma \gamma$ and $q\overline{q}\gamma \gamma$ events in which the two photons are reconstructed within the detector acceptance. The cross section for the process $e^{+}{e}^{-}\to q\overline{q}\gamma \gamma$ is measured. Averaging over all energies, the ratio of the observed $e^{+}{e}^{-}\to q\overline{q}\gamma \gamma$ cross section to the standard model expectation is $\mathrm{R}(\mathrm{data}/\mathrm{SM})=0.92\mathrm{}\pm 0.07\pm 0.04,$ where the errors represent the statistical and systematic uncertainties respectively. The $\nu \overline{\nu }\gamma \gamma$ and $q\overline{q}\gamma \gamma$ data are used to constrain possible anomalous $W^{+}{W}^{-}\gamma \gamma$ and $\mathrm{ZZ}\gamma \gamma$ couplings. Combining with previous OPAL results from the $W^{+}{W}^{-}\gamma$ final state, the 95% confidence level limits on the anomalous coupling parameters $a_0^{\mathrm{Z}},$ $a_{\mathrm{c}}^{\mathrm{Z}},$ $a_0^{\mathrm{W}}$ and $a_{\mathrm{c}}^{\mathrm{W}}$ are found to be $-0.007\hspace{0.5em}{\mathrm{GeV}}^{-2}<a_0^{\mathrm{Z}}/{\Lambda }^2<0.023\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^{-2},$ $-0.029\hspace{0.5em}{\mathrm{GeV}}^{-2}<a_{\mathrm{c}}^{\mathrm{Z}}/{\Lambda }^2<0.029\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^{-2},$ $-0.020\hspace{0.5em}{\mathrm{GeV}}^{-2}<a_0^{\mathrm{W}}/{\Lambda }^2<0.020\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^{-2},$ $-0.052\hspace{0.5em}{\mathrm{GeV}}^{-2}<a_{\mathrm{c}}^{\mathrm{W}}/{\Lambda }^2<0.037\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^{-2},$ where $\Lambda$ is the energy scale of the new physics. Limits found when allowing two or more parameters to vary are also presented.

In the paper of Díaz-Miguel [Phys. Rev. D 69, 027101 (2004)], it is argued that the vertical deflection of a photon in the vicinity of the Earth surface is different from the one in a uniform gravitational field. We show by a detailed analysis that this result is obtained in coordinates which are different from those that should normally be used.

We elaborate on four different types of twisted $\mathcal{N}=(4,4)\mathrm{}$ supermultiplets in the $\mathrm{SU}\left(2\right)\mathrm{}\times \mathrm{SU}\left(2\right),$ 2D harmonic superspace. In the conventional $\mathcal{N}=(4,4),$ 2D superspace they are described by the superfields $q^{\mathrm{ia}},$ $q^{\underset{¯}{i}a},$ $q^{i\underset{¯}{a}},$ $q^{\underset{¯}{i}\underset{¯}{a}}$ subjected to proper differential constraints, $(i,\underset{¯}{i},a,\underset{¯}{a})$ being the doublet indices of four groups $\mathrm{SU}\left(2\right)\mathrm{}$ that form the full R-symmetry group ${\mathrm{SO}\left(4\right)\mathrm{}}_L\times {\mathrm{SO}\left(4\right)\mathrm{}}_R$ of $\mathcal{N}=(4,4)\mathrm{}$ supersymmetry. We construct the torsionful off-shell sigma model actions for each type of these multiplets, as well as the corresponding invariant mass terms in an analytic subspace of the $\mathrm{SU}\left(2\right)\mathrm{}\times \mathrm{SU}\left(2\right)\mathrm{}$ harmonic superspace. As an instructive example, $\mathcal{N}=(4,4)\mathrm{}$ superconformal extension of the $\mathrm{SU}\left(2\right)\mathrm{}\times U\left(1\right)\mathrm{}$ WZNW sigma model action and its massive deformation are presented for the multiplet $q^{i\underset{¯}{a}}.$ We prove that $\mathcal{N}=(4,4)\mathrm{}$ supersymmetry requires the general sigma model action of a pair of different multiplets to split into a sum of sigma model actions of each multiplet. This phenomenon also persists if a larger number of nonequivalent multiplets are simultaneously included. We show that different multiplets may interact with each other only through mixed mass terms, which can be set up for multiplets belonging to “self-dual” pairs $(q^{\mathrm{ia}},q^{\underset{¯}{i}\underset{¯}{a}})$ and $(q^{\underset{¯}{i}a},q^{i\underset{¯}{a}}).\mathrm{}$ The multiplets from different pairs cannot interact at all. For a “self-dual” pair of the twisted multiplets, we give the most general form of the on-shell scalar potential.

We construct, in the framework of the $\mathcal{N}=4\mathrm{}$ SYM theory, a supermultiplet of twist-two conformal operators and study their renormalization properties. The components of the supermultiplet have the same anomalous dimension and enter as building blocks into multiparticle quasipartonic operators. The latter are determined by the condition that their twist equals the number of elementary constituent fields from which they are built. A unique feature of the $\mathcal{N}=4\mathrm{}$ SYM is that all quasipartonic operators with different SU(4) quantum numbers fall into a single supermultiplet. Among them there is a subsector of the operators of maximal helicity, which has been known to be integrable in the multi-color limit in QCD, independent of the presence of supersymmetry. In the $\mathcal{N}=4\mathrm{}$ SYM theory, this symmetry is extended to the whole supermultiplet of quasipartonic operators and the one-loop dilatation operator coincides with a Hamiltonian of integrable $\mathrm{SL}\left(2\mathrm{}|4\right)$ Heisenberg spin chain.

The CPT anomaly of certain chiral gauge theories has been established previously for flat multiply connected spacetime manifolds M of the type $R^3\times S^1,$ where the noncontractible loops have a minimal length. In this article, we show that the CPT anomaly also occurs for manifolds where the noncontractible loops can be arbitrarily small. Our basic calculation is performed for a flat noncompact manifold with a single “puncture,” namely $M=R^2\times \left(R^2\backslash \{0\}\right).\mathrm{}$ A hypothetical spacetime foam might have many such punctures (or other structures with similar effects). Assuming the multiply connected structure of the foam to be time independent, we present a simple model for photon propagation, which generalizes the single-puncture result. This model leads to a modified dispersion law of the photon. Observations of high-energy photons (gamma-rays) from explosive extragalactic events can then be used to place an upper bound on the typical length scale of these punctures.

We discuss the use of BRST symmetry and the resulting Ward identities as consistency checks for orbifold gauge theories in an arbitrary number of dimensions. We demonstrate that both the usual orbifold symmetry breaking and the recently proposed Higgsless symmetry breaking are consistent with the nilpotency of the BRST transformation. The corresponding Ward identities for four-point functions of the theory engender relations among the coupling constants that are equivalent to the sum rules from tree level unitarity. We present the complete set of these sum rules also for inelastic scattering and discuss applications to six-dimensional models and to incomplete matter multiplets on orbifold fixed points.

We develop a Born-Infeld type theory for gravity in any dimension. We show that in four dimensions our formalism allows a self-dual (or anti-self-dual) Born-Infeld gravity description. Moreover, we show that such a self-dual action is reduced to both the Deser-Gibbons and the Jacobson-Smolin-Samuel action of Ashtekar formulation. A supersymmetric generalization of our approach is outlined.

We investigate highly damped quasinormal mode of single-horizon black holes motivated by its relation to the loop quantum gravity. Using the WKB approximation, we show that the real part of the frequency approaches the value $T_{\mathrm{H}}\ln 3$ for dilatonic black hole as conjectured by Medved et al. and Padmanabhan. It is surprising since the area spectrum of the black hole determined by the Bohr’s correspondence principle completely agrees with that of Schwarzschild black hole for any values of the electromagnetic charge or the dilaton coupling. We discuss its generality for single-horizon black holes and the meaning in the loop quantum gravity.

Three new classes (II-IV) of solutions of the vacuum low energy effective string theory in four dimensions are derived. Wormhole solutions are investigated in those solutions including the class I case both in the Einstein and in the Jordan (string) frame. It turns out that, of the eight classes of solutions investigated (four in the Einstein frame and four in the corresponding string frame), massive Lorentzian traversable wormholes exist in five classes. Nontrivial massless limit exists only in class I Einstein frame solution while none at all exists in the string frame. An investigation of test scalar charge motion in the class I solution in the two frames is carried out by using the Plebański-Sawicki theorem. A curious consequence is that the motion around the extremal zero (Keplerian) mass configuration leads, as a result of scalar-scalar interaction, to a new hypothetical “mass” that confines test scalar charges in bound orbits, but does not interact with neutral test particles.