Notes on Unoriented D-Brane Instantons

Abstract

In the first lecture, we discuss basic aspects of worldsheet and penta-brane instantons as well as (unoriented) D-brane instantons, which is our main focus here, and threshold corrections to BPS-saturated couplings. The second lecture is devoted to non-perturbative superpotentials generated by 'gauge' and 'exotic' instantons living on D3-branes at orientifold singularities. In the third lecture we discuss the interplay between worldsheet and D-string instantons on T 4 /Z 2 . We focus on a 4-fermi amplitude, give Heterotic and perturbative Type I descriptions, and offer a multi D-string instanton interpretation. We conclude with possible interesting developments.

Non-perturbative vacuum destabilization and D-brane dynamics

“…Recently, there was a revival of activity concerning phenomenological applications in D-brane models (for reviews, see e.g. [3,4]). These include neutrino masses [5,6], µ-terms in the MSSM [7], moduli stabilization [8], supersymmetry breaking ( [9][10][11][12]; for subtleties related to moduli stabilization in such a setup, see [13]) or fermion masses [14][15][16][17].…”

“…These are due to Euclidean branes with precisely two fermionic neutral zero modes, only charged under the gauge group of the instanton (for reviews, see e.g. [3,4]). In terms of the 4d effective supergravity, these are identified with the fermionic coordinates of the N = 1 superspace.…”

“…Additional fermionic neutral zero modes would render the contribution to the superpotential trivial, as they lead to vanishing Grassman integrals over the instanton moduli space. 4 Notice however that in some cases these extra zero modes can be removed by interactions between instanton zero modes [47,51,52] or/and additional fluxes [47,49,53,54].…”

“…Gauge invariance generically requires these operators to contain also insertions of matter fields, Φ q , localized at the intersections between stacks of Dp-branes (for reviews, see e.g. [3,4]). After integrating over the moduli space of the instanton, a non-perturbative superpotential coupling for the matter fields Φ q is induced.…”

“…From the point of view of the 4d effective theory, these are related to one-loop determinants of fluctuations around the instanton background (for reviews, see e.g. [3,4]). …”