# Deformations, Moduli Stabilisation and Gauge Couplings at One-Loop

## TL;DR

This paper studies how geometric deformations in a specific string theory compactification affect gauge couplings and moduli stabilization, with implications for phenomenology and string scale determination.

## Contribution

It develops methods to analyze deformation effects on D-brane models on orbifolds, extending previous formalism to more complex orbifold groups and assessing their impact on gauge couplings.

## Key findings

- Deformation parameters for U(N) branes are constrained by D-term supersymmetry.
- Number of stabilized moduli varies with different global models.
- One-loop gauge threshold corrections are compared with tree-level couplings under deformations.

## Abstract

We investigate deformations of $\mathbb{Z}_2$ orbifold singularities on the toroidal orbifold $T^6/(\mathbb{Z}_2\times\mathbb{Z}_6)$ with discrete torsion in the framework of Type IIA orientifold model building with intersecting D6-branes wrapping special Lagrangian cycles. To this aim, we employ the hypersurface formalism developed previously for the orbifold $T^6/(\mathbb{Z}_2\times\mathbb{Z}_2)$ with discrete torsion and adapt it to the $\mathbb{Z}_2\times\mathbb{Z}_6\times\Omega\mathcal{R}$ point group by modding out the remaining $\mathbb{Z}_3$ subsymmetry and the orientifold projection $\Omega\mathcal{R}$. We first study the local behaviour of the $\mathbb{Z}_3\times\Omega\mathcal{R}$ invariant deformation orbits under non-zero deformation and then develop methods to assess the deformation effects on the fractional three-cycle volumes globally. We confirm that D6-branes supporting USp(2N) or SO(2N) gauge groups do not constrain any deformation, while deformation parameters associated to cycles wrapped by D6-branes with U(N) gauge groups are constrained by D-term supersymmetry breaking. These features are exposed in global prototype MSSM, Left-Right symmetric and Pati-Salam models first constructed in arXiv:1509.00048 and arXiv:1409.1236, for which we here count the number of stabilised moduli and study flat directions changing the values of some gauge couplings. Finally, we confront the behaviour of tree-level gauge couplings under non-vanishing deformations along flat directions with the one-loop gauge threshold corrections at the orbifold point and discuss phenomenological implications, in particular on possible LARGE volume scenarios and the corresponding value of the string scale $M_{\text{string}}$, for the same global D6-brane models.