Superpotential de-sequestering in string models

TL;DR

The paper investigates non-perturbative cross-couplings between visible-sector matter and Kähler moduli in Type IIB string theory, focusing on superpotential de-sequestering and its potential to induce flavour violation. It employs computable toroidal orbifold toy models with visible matter on D3-branes and distant non-perturbative effects on D7-branes to compute a threshold correction to the D7 gauge coupling and to evaluate corrections to Yukawa couplings. The key finding is that non-perturbative Yukawa operators generally have a flavour structure that does not align with tree-level Yukawas; two-scalar hidden corrections tend to preserve the tree flavour, while three-scalar insertions can generate non-tree flavour couplings, signaling possible FCNCs. The results suggest that de-sequestering is a robust feature in these string constructions with important phenomenological implications for flavour in KKLT/LVS scenarios and motivate extensions to more realistic Calabi-Yau compactifications and a closed-string formulation.

Abstract

Non-perturbative superpotential cross-couplings between visible sector matter and Kähler moduli can lead to significant flavour-changing neutral currents in compactifications of type IIB string theory. Here, we compute corrections to Yukawa couplings in orbifold models with chiral matter localised on D3-branes and non-perturbative effects on distant D7-branes. By evaluating a threshold correction to the D7-brane gauge coupling, we determine conditions under which the non-perturbative corrections to the Yukawa couplings appear. The flavour structure of the induced Yukawa coupling generically fails to be aligned with the tree-flavour structure. We check our results by also evaluating a correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling. Finally, by calculating a string amplitude between n hidden scalars and visible matter we show how non-vanishing vacuum expectation values of distant D7-brane scalars, if present, may correct visible Yukawa couplings with a flavour structure that differs from the tree-level flavour structure.

Figures (8)

• Figure 1: Calabi-Yau compactification with D3-branes at a singularity and D7-branes wrapping a small cycle. The singularity and the D7-branes share a homologous 2-cycle. This setup appears in LVS constructions.
• Figure 2: Calabi-Yau compactification with D3-branes at a singularity and D7-branes wrapping a small cycle. The singularity and the small cycle are geometrically separated in the bulk. This setup appears in LVS constructions.
• Figure 3: Calabi-Yau compactification with D3-branes at a singularity and D7-branes wrapping a bulk cycle. This setup appears in KKLT constructions.
• Figure 4: Brane configurations for the $\mathbb{T}^6/\mathbb{Z}_6'$ orbifold with $\theta=\frac{1}{6}(1,-3,2)$, for the two alternatives #3 and #4 of table \ref{['table1']}. (This is the AaA lattice, in the classification of Gmeiner:2007zz.) Dots indicate orbifold singularities. Stacks of D3-branes supporting visible matter are denoted by a blue circle at the origin. The branes responsible for nonperturbative effects are indicated by a red box, except that the bulk D7-branes wrap the first two tori of the compact space and are pointlike on the third torus.
• Figure 5: Tadpoles as a problem for generic planar diagrams.