Mboyo Esole

D-brane Deconstructions in IIB Orientifolds

With model building applications in mind, we collect and develop basic techniques to analyze the landscape of D7-branes in type IIB compact Calabi-Yau orientifolds, in three different pictures: F-theory, the D7 worldvolume theory and D9-anti-D9 tachyon condensation. A significant complication is that consistent D7-branes in the presence of O7− planes are generically singular, with singularities locally modeled by the Whitney Umbrella. This invalidates the standard formulae for charges, moduli space and flux lattice dimensions. We infer the correct formulae by comparison to F-theory and derive them independently and more generally from the tachyon picture, and relate these numbers to the closed string massless spectrum of the orientifold compactification in an interesting way. We furthermore give concrete recipes to explicitly and systematically construct nontrivial D-brane worldvolume flux vacua in arbitrary Calabi-Yau orientifolds, illustrate how to read off D-brane flux content, enhanced gauge groups and charged matter spectra from tachyon matrices, and demonstrate how brane recombination in general leads to flux creation, as required by charge conservation and by equivalence of geometric and gauge theory moduli spaces.

Stability of warped AdS3 vacua of topologically massive gravity

AdS3 vacua of topologically massive gravity (TMG) have been shown to be perturbatively unstable for all values of the coupling constant except the chiral point μl = 1. We study the possibility that the warped vacua of TMG, which exist for all values of μ, are stable under linearized perturbations. In this paper, we show that spacelike warped AdS3 vacua with Compere-Detournay boundary conditions are indeed stable in the range μl>3. This is precisely the range in which black hole solutions arise as discrete identifications of the warped AdS3 vacuum. The situation somewhat resembles chiral gravity: although negative energy modes do exist, they are all excluded by the boundary conditions, and the perturbative spectrum solely consists of boundary (pure large gauge) gravitons.

New orientifold weak coupling limits in F-theory

We present new explicit constructions of weak coupling limits of F-theory generalizing Sen’s construction to elliptic fibrations which are not necessary given in a Weierstrass form. These new constructions allow for an elegant derivation of several brane configurations that do not occur within the original framework of Sen’s limit, or which would require complicated geometric tuning or break supersymmetry. Our approach is streamlined by first deriving a simple geometric interpretation of Sen’s weak coupling limit. This leads to a natural way of organizing all such limits in terms of transitions from semistable to unstable singular fibers. These constructions provide a new playground for model builders as they enlarge the number of supersymmetric configurations that can be constructed in F-theory. We present several explicit examples for E8, E7 and E6 elliptic fibrations.

A Note on the uniqueness of D = 4, N=1 supergravity

We investigate in four spacetime dimensions, all the consistent deformations of the Lagrangian 2 + 3/2 , which is the sum of the Pauli–Fierz Lagrangian 2 for a free massless spin-2 field and the Rarita–Schwinger Lagrangian 3/2 for a free massless spin-3/2 field. Using BRST-cohomogical techniques, we show, under the assumptions of locality, Poincare invariance, conservation of the number of gauge symmetries and the number of derivatives on each fields, that N = 1, D = 4 supergravity is the only consistent interaction between a massless spin-2 and a massless spin-3/2 field. We do not assume general covariance. This follows automatically, as does supersymmetry invariance. Various cohomologies related to conservation laws are also given.

D-term cosmic strings from N = 2 supergravity

We describe new half-BPS cosmic string solutions in N = 2, d = 4 supergravity coupled to one vector multiplet and one hypermultiplet. They are closely related to D-term strings in N = 1 supergravity. Fields of the N = 2 theory that are frozen in the solution contribute to the triplet moment map of the quaternionic isometries and leave their trace in N = 1 as a constant Fayet-Iliopoulos term. The choice of U(1) gauging and of special geometry are crucial. The construction gives rise to a non-minimal Kahler potential and can be generalized to higher dimensional quaternionic-Kahler manifolds.

Tate Form and Weak Coupling Limits in F-theory

A bstractWe consider the weak coupling limit of F-theory in the presence of non-Abelian gauge groups implemented using the traditional ansatz coming from Tate’s algorithm. We classify the types of singularities that could appear in the weak coupling limit and explain their resolution. In particular, the weak coupling limit of SU(n) gauge groups leads to an orientifold theory which suffers from conifold singulaties that do not admit a crepant resolution compatible with the orientifold involution. We present a simple resolution to this problem by introducing a new weak coupling regime that admits singularities compatible with both a crepant resolution and an orientifold symmetry. We also comment on possible applications of the new limit to model building. We finally discuss other unexpected phenomena as for example the existence of several non-equivalent directions to flow from strong to weak coupling leading to different gauge groups.

The Unphysical nature of the SL(2,R) symmetry and its associated condensates in Yang-Mills theories

BRST cohomology methods are used to explain the origin of the SL(2,R) symmetry in Yang-Mills theories. Clear evidence is provided for the unphysical nature of this symmetry. This is obtained from the analysis of a local functional of mass dimension two and constitutes a no-go statement for giving a physical meaning to condensates associated with the symmetry breaking of SL(2,R).

Renormalisability of gauge invariant extensions of the squared gauge potential

Abstract We show that gauge invariant extensions of the local functional O = 1 2 ∫d 4 x A 2 have long range non-localities which can only be “renormalised” with reference to a specific gauge. Consequently, there is no gauge independent way of claiming the perturbative renormalisability of these extensions. In particular, they are not renormalisable in the modern sense of Weinberg and Gomis. Critically, our study does not support the view that ghost fields play an indispensable role in the extension of a local operator into a non-local one as claimed recently in the literature.

Half-BPS cosmic string in Script N = 2 supergravity in the presence of a dilaton

We construct new half-BPS cosmic string solutions in D = 4 = 2 supergravity compatible with a consistent truncation to = 1 supergravity where they describe D-term cosmic strings. The constant Fayet-Iliopoulos term in the = 1 D-term is not put in by hand but is geometrically engineered by a gauging in the mother = 2 supergravity theory. The coupling of the = 2 vector multiplets is characterized by a cubic prepotential admitting an axion-dilaton field, a common property of many compactifications of string theory. The axion-dilaton field survives the truncation to = 1 supergravity. On the string configuration the BPS equations constrain the dilaton to be an arbitrary constant. All the cosmic string solutions with different values of the dilaton have the same energy per unit length but different lenght scales.