Particle theory

Abstract:

Gauge theory-gravity duality predicts that the shear viscosity of N = 4 supersymmetric SU(Nc) Yang-Mills plasma at temperature T in the limit of large N c and large 't Hooft coupling gYM2Nc is independent of the coupling and equals to πNc2T3 /8. In this paper, we compute the leading correction to the shear viscosity in inverse powers of 't Hooft coupling using the α′-corrected low-energy effective action of type IIB string theory. We also find the correction to the ratio of shear viscosity to the volume entropy density (equal to 1/4π in the limit of infinite coupling). The correction to 1/4π scales as (gYM2Nc) -3/2 with a positive coefficient. © 2004 Elsevier B.V. All rights reserved.

Abstract:

We study the large volume limit of the scalar potential in Calabi-Yau flux compactifications of type IIB string theory. Under general circumstances there exists a limit in which the potential approaches zero from below, with an associated non-supersymmetric AdS minimum at exponentially large volume. Both this and its de Sitter uplift are tachyon-free, thereby fixing all Kahler and complex structure moduli, which has been difficult to achieve in the KKLT scenario. Also, for the class of vacua described in this paper, the gravitino mass is independent of the flux discretuum, whereas the ratio of the string scale to the 4d Planck scale is hierarchically small but flux dependent. The inclusion of alpha' corrections plays a crucial role in the structure of the potential. We illustrate these ideas through explicit computations for a particular Calabi-Yau manifold.

Abstract:

Compact manifolds of G2 holonomy may be constructed by dividing a seven-torus by some discrete symmetry group and then blowing up the singularities of the resulting orbifold. We classify possible group elements that may be used in this construction and use this classification to find a set of possible orbifold groups. We then derive the moduli Kähler potential for M-theory on the resulting class of G2 manifolds with blown-up codimension four singularities. © 2005 The American Physical Society.

Abstract:

M theory is considered in its low-energy limit on a G2 manifold with nonvanishing flux. Using the Killing spinor equations for linear flux, an explicit set of first-order bosonic equations for supersymmetric solutions is found. These solutions describe a warped product of a domain wall in four-dimensional space-time and a deformed G2 manifold. It is shown how these domain walls arise from the perspective of the associated four-dimensional N = 1 effective supergravity theories. We also discuss the inclusion of membrane and M5-brane sources. © 2005 The American Physical Society.