6 research outputs found
Three Generations in Type I Compactifications
Generalizing the recent work on three-family Type I compactifications, we
classify perturbative Type I vacua obtained via compactifying on the T^6/Z_2 X
Z_2 X Z_3 orbifold with all possible Wilson lines. In particular, we
concentrate on models with gauge groups containing the Standard Model gauge
group SU(3)_c X SU(2)_w X U(1)_Y as a subgroup. All of the vacua we obtain
contain D5-branes and are non-perturbative from the heterotic viewpoint. The
models we discuss have three-chiral families. We study some of their
phenomenological properties, and point out non-trivial problems arising in
these models in the phenomenological context.Comment: 16 pages, revtex, minor misprints correcte
Superstring Theory and CP- Violating Phases: Can They Be Related?
We investigate the possibility of large CP- violating phases in the soft
breaking terms derived in superstring models. The bounds on the electric dipole
moments (EDM's) of the electron and neutron are satisfied through cancellations
occuring because of the structure of the string models. Three general classes
of four-dimensional string models are considered: (i) orbifold
compactifications of perturbative heterotic string theory, (ii) scenarios based
on Ho\v{r}ava-Witten theory, and (iii) Type I string models (Type IIB
orientifolds). Nonuniversal phases of the gaugino mass parameters greatly
facilitate the necessary cancellations among the various contributions to the
EDM's; in the overall modulus limit, the gaugino masses are universal at tree
level in both the perturbative heterotic models and the Ho\v{r}ava-Witten
scenarios, which severely restricts the allowed regions of parameter space.
Nonuniversal gaugino masses do arise at one-loop in the heterotic orbifold
models, providing for corners of parameter space with phases
consistent with the phenomenological bounds. However, there is a possibility of
nonuniversal gaugino masses at tree level in the Type I models, depending on
the details of the embedding of the SM into the D- brane sectors. We find that
in a minimal model with a particular embedding of the Standard Model gauge
group into two D- brane sectors, viable large phase solutions can be obtained
over a wide range of parameter space.Comment: 28 pages, 6 figures; corrected bug in the code and a few typos,
results qualitatively unchange
Finite Temperature Aging Holography
We construct the gravity background which describes the dual field theory
with aging invariance. We choose the decay modes of the bulk scalar field in
the internal spectator direction to obtain the dissipative behavior of the
boundary correlation functions of the dual scalar fields. In particular, the
two-time correlation function at zero temperature has the characteristic
features of the aging system: power law decay, broken time translation and
dynamical scaling. We also construct the black hole backgrounds with asymptotic
aging invariance. We extensively study characteristic behavior of the finite
temperature two-point correlation function via analytic and numerical methods.Comment: 38 pages and 5 figures, expanded discussions on correlator, one
mistake is fixed, modified discussion on shear viscosity, to appear in JHE
Appearance of Keplerian discs orbiting Kerr superspinars
We study optical phenomena related to appearance of Keplerian accretion discs
orbiting Kerr superspinars predicted by the string theory. The superspinar
exterior is described by the standard Kerr naked singularity geometry breaking
the black hole limit on the internal angular momentum (spin). We construct
local photon escape cones for a variety of orbiting sources that enable to
determine the superspinars silhouette in the case of distant observers. We show
that the superspinar silhouette depends strongly on the assumed edge where the
external Kerr spacetime is joined to the internal spacetime governed by the
string theory and significantly differs from the black hole silhouette. The
appearance of the accretion disc is strongly dependent on the value of the
superspinar spin in both their shape and frequency shift profile. Apparent
extension of the disc grows significantly with growing spin, while the
frequency shift grows with descending spin. This behavior differs substantially
from appearance of discs orbiting black holes enabling thus, at least in
principle, to distinguish clearly the Kerr superspinars and black holes. In
vicinity of a Kerr superspinar the non-escaped photons have to be separated to
those captured by the superspinar and those being trapped in its strong
gravitational field leading to self-illumination of the disc that could even
influence its structure and causes self-reflection effect of radiation of the
disc. The amount of trapped photons grows with descending of the superspinar
spin. We thus can expect significant self-illumination effects in the field of
Kerr superspinars with near-extreme spin .Comment: accepted in Classical and Quantum Gravity (September 1st, 2010
Dimers, orientifolds and anomalies
We study 4dN = 1 gauge theories engineered via D-branes at orientifolds of toric singularities, where gauge anomalies are cancelled without the introduction of non-compact flavor branes. Using dimer model techniques, we derive geometric criteria for establishing whether a given singularity can admit anomaly-free D-brane configurations purely based on its toric data and the type of orientifold projection. Our results therefore extend the dictionary between geometric properties of singularities and physical properties of the corresponding gauge theories