Beatriz de Carlos

de Sitter vacua from uplifting D-terms in effective supergravities from realistic strings

We study the possibility of using the D-term associated to an anomalous U(1) for the uplifting of AdS vacua (to dS or Minkowski vacua) in effective supergravities arising from string theories, particularly in the type IIB context put forward by Kachru, Kallosh, Linde and Trivedi (KKLT). We find a gauge invariant formulation of such a scenario (avoiding previous inconsistencies), where the anomalous D-term cannot be cancelled, thus triggering the uplifting of the vacua. Then, we examine the general conditions for this to happen. Finally, we illustrate the results by presenting different successful examples in the type IIB context.

Moduli Stabilisation In Heterotic String Compactifications

In this paper we analyze the structure of supersymmetric vacua in compactifications of the heterotic string on certain manifolds with SU(3) structure. We first study the effective theories obtained from compactifications on half-flat manifolds and show that solutions which stabilise the moduli at acceptable values are hard to find. We then derive the effective theories associated with compactification on generalized half-flat manifolds. It is shown that these effective theories are consistent with four-dimensional N = 1 supergravity and that the superpotential can be obtained by a Gukov-Vafa-Witten type formula. Within these generalized models, we find consistent supersymmetric (AdS) vacua at weak gauge coupling, provided we allow for general internal gauge bundles. In simple cases we perform a counting of such vacua and find that a fraction of about 1/1000 leads to a gauge coupling consistent with gauge unification.

Ghost conditions for Gauss–Bonnet cosmologies

We investigate the stability against inhomogeneous perturbations and the appearance of ghost modes in Gauss–Bonnet gravitational theories with a non-minimally coupled scalar field, which can be regarded as either the dilaton or a compactification modulus in the context of string theory. Through cosmological linear perturbations we extract four no-ghost and two sub-luminal constraint equations, written in terms of background quantities, which must be satisfied for consistency. We also argue that, for a general action with quadratic Riemann invariants, homogeneous and inhomogeneous perturbations are, in general, inequivalent, and that attractors in the phase space can have ghosts. These results are then generalized to a two-field configuration. Single-field models as candidates for dark energy are explored numerically and severe bounds on the parameter space of initial conditions are placed. A number of cases proposed in the literature are tested and most of them are found to be unstable or observationally unviable.

Non-perturbative vacua for M-theory on G(2) manifolds

We study moduli stabilization in the context of M-theory on compact manifolds with G2 holonomy, using superpotentials from ∞ux and membrane instantons, and recent results for the Kahler potential of such models. The existence of minima with negative cosmological constant, stabilizing all moduli, is established. While most of these minima preserve supersymmetry, we also flnd examples with broken supersymmetry. Supersym- metric vacua with vanishing cosmological constant can also be obtained after a suitable tuning of parameters.

BPS Domain Walls in super Yang-Mills and Landau-Ginzburg models

We study domain walls in two different extensions of super Yang-Mills characterized by the absence of a logarithmic term in their effective superpotential. The models, defined by the usual gaugino condensate and an extra field Y, give different patterns of domain walls despite both leading to the same effective limit for heavy Y, i.e. the Veneziano-Yankielowicz effective lagrangian of super Yang-Mills. We explain the origin of those differences and also give a physical motivation for introducing the field Y.

Selectron pair production in e+e− colliders and the supergravity spectrum

Abstract In Minimal Supergravity, with universality of scalar and gaugino masses and radiative breaking of the electroweak symmetry, the physical spectrum depends only on a few independent parameters. This predictive power implies that a few experimental measurements may be enough to determine these parameters. In these models, selectrons are among the lightest supersymmetric particles. In a scenario where selectrons are light enough to be produced at LEP2, we show that the measurement of their mass, their production cross section, and the mass of their decay product, the lightest neutralino, can be used to determine the value of the fundamental parameters of the model, and with them, the entire supersymmetric and Higgs spectrum can be predicted. In this scenario of light selectrons we find that 65 m h h , the lightest CP even Higgs boson, might be detected at LEP2 if its mass lies in the first half of that range. We also find 45 GeV τ ± 1 e ± R and τ ± 1 might also be detected at LEP2. Light sleptons can be accompanied by lightest neutralinos of a very similar mass, thus they may have escaped detection from LEP1.6. Light Higgs h and light stau have masses which are strongly dependent on tan β , therefore a measurement of m h (if tan β ≳1) or m τ ± 1 (if tan β ≫1) will help to determine this parameter.