Final Report Summary - STRING MODELS (Realistic Local Models in Moduli Stabilised String Compactifications)
The goal of the project was to explore the phenomenology in the setting of II B flux compactification. There was progress achieved in both the area of of moduli stabilisation and construction of realistic models. in the area of module stabilisation a new scenario to obtaining de Sitter vacua was proposed.
We consider a novel scenario for modulus stabilisation in IIB string compactifications in which the Kahler moduli are stabilised by a general set-up with two kinds of non-perturbative effects: (i) standard Kahler moduli-dependent non-perturbative effects from gauging condensation on D7-branes or E3-instantons wrapping four-cycles in the geometric regime; (ii) dilation-dependent non-perturbative effects from gauging condensation on space-time filling D3-branes or E (-1)-instantons at singularities. For the LARGE Volume Scenario (LVS), the new dilaton-dependent non-perturbative effects provide a positive definite contribution to the scalar potential that can be arbitrarily tuned from fluxes to give rise to de Sitter vacua. Contrary to anti D3-branes at warped throats, this term arises from a manifestly supersymmetric effective action. In this new scenario the "uplifting" term comes from F-terms of blow-up modes resolving the singularity of the non-perturbative quiver. We discuss phenomenological and cosmological implications of this mechanism. This set-up also allows a realisation of the LVS for manifolds with zero or positive Euler number.
In the area of constructing the Standard model sector, radioactive generation of Yukawa couplings was studied
In the context of D-brane model building, we present a realistic framework for generating fermions masses that are forbidden by global symmetries. We show that the string theoretical Large volume scenario circumvents the standard lore that fermions masses generated by loop effects are too small in generic gravity mediated scenarios. We argue that the fact that in toric singularity models, the up quark masses have always a zero eigenvalue, corresponding to the lightest generation, is due to the presence of approximate global symmetries that we explicitly identify in del Pezzo singularities. These symmetries are broken by global effects and therefore proportional to inverse powers of the volume. We estimate the generic size of radioactive corrections to fermions masses in different phenomenological manifestations of the Large volume scenario. Concrete realisations in terms of flavour violating soft-terms are estimated and contrasted with current bounds on flavour changing neutral currents. Contributions from generic extra Higgs-like fields set bounds on their masses close to the GUT scale to produce realistic fermions masses.
A systematic method to study compactification effects in string constructions was proposed
We study symmetry breaking effects in local D-brane models that arise as a result of compactification, taking models constructed on C^3/Z_3 as prototype. Zero-modes of the Lichnerowicz operator in cone-like geometries have a power law behaviour; thus the leading symmetry breaking effects are captured by the modes with the lowest scaling dimension which transform non-trivially under the isometric group. Combining this with the fact that global symmetries in local models are gauged upon compactification we determine the strength and form of the leading operators responsible for the symmetry breaking. We find a hierarchical separation in the size of symmetry breaking parameters.
We consider a novel scenario for modulus stabilisation in IIB string compactifications in which the Kahler moduli are stabilised by a general set-up with two kinds of non-perturbative effects: (i) standard Kahler moduli-dependent non-perturbative effects from gauging condensation on D7-branes or E3-instantons wrapping four-cycles in the geometric regime; (ii) dilation-dependent non-perturbative effects from gauging condensation on space-time filling D3-branes or E (-1)-instantons at singularities. For the LARGE Volume Scenario (LVS), the new dilaton-dependent non-perturbative effects provide a positive definite contribution to the scalar potential that can be arbitrarily tuned from fluxes to give rise to de Sitter vacua. Contrary to anti D3-branes at warped throats, this term arises from a manifestly supersymmetric effective action. In this new scenario the "uplifting" term comes from F-terms of blow-up modes resolving the singularity of the non-perturbative quiver. We discuss phenomenological and cosmological implications of this mechanism. This set-up also allows a realisation of the LVS for manifolds with zero or positive Euler number.
In the area of constructing the Standard model sector, radioactive generation of Yukawa couplings was studied
In the context of D-brane model building, we present a realistic framework for generating fermions masses that are forbidden by global symmetries. We show that the string theoretical Large volume scenario circumvents the standard lore that fermions masses generated by loop effects are too small in generic gravity mediated scenarios. We argue that the fact that in toric singularity models, the up quark masses have always a zero eigenvalue, corresponding to the lightest generation, is due to the presence of approximate global symmetries that we explicitly identify in del Pezzo singularities. These symmetries are broken by global effects and therefore proportional to inverse powers of the volume. We estimate the generic size of radioactive corrections to fermions masses in different phenomenological manifestations of the Large volume scenario. Concrete realisations in terms of flavour violating soft-terms are estimated and contrasted with current bounds on flavour changing neutral currents. Contributions from generic extra Higgs-like fields set bounds on their masses close to the GUT scale to produce realistic fermions masses.
A systematic method to study compactification effects in string constructions was proposed
We study symmetry breaking effects in local D-brane models that arise as a result of compactification, taking models constructed on C^3/Z_3 as prototype. Zero-modes of the Lichnerowicz operator in cone-like geometries have a power law behaviour; thus the leading symmetry breaking effects are captured by the modes with the lowest scaling dimension which transform non-trivially under the isometric group. Combining this with the fact that global symmetries in local models are gauged upon compactification we determine the strength and form of the leading operators responsible for the symmetry breaking. We find a hierarchical separation in the size of symmetry breaking parameters.