Stringy instanton effects in models with rigid magnetised D-branes

Abstract

We compute instantonic effects in globally consistent T 6 /Z 2 × Z 2 orientifold models with discrete torsion and magnetised D-branes. We consider fractional branes and instantons wrapping the same rigid cycles. We clarify and analyse in detail the lowenergy effective action on D-branes in these models. We provide explicit examples where instantons induce linear terms in the charged fields, or non-perturbative mass terms are generated. We also find examples where the gauge theory on fractional branes has conformal symmetry at one-loop, broken by instantonic mass terms at a hierarchically small energy scale.

Non-perturbative vacuum destabilization and D-brane dynamics

“…The requirement of having rigid cycles in models with magnetized branes implies the existence of a Z 2 × Z 2 subgroup within the orbifold action which has discrete torsion [24][25][26][27]. One of our main results is the explicit expression for superpotential (1.1) in these models, provided the three conditions stated above are simultaneously satisfied.…”

“…After integration of eq. (3.1) over the instanton charged zero modes, the following non-perturbative contribution to the effective superpotential results [27],…”

“…Section 5 is devoted to the model presented in refs. [25,27] where stringy instantons induce mass terms for some of the antisymmetrics. By using these techniques we explicitly compute the mass terms, determining whether they vanish or not.…”

“…For toroidal orbifold models with magnetized branes this can only be the case if the orbifold group Γ contains a Z 2 × Z 2 subgroup with discrete torsion [24][25][26][27]. We denote the elements of this subgroup as g, f and h, where each generator reverses the coordinates of two 2-tori within the T 6 ,…”

Non-perturbative transitions among intersecting-brane vacua

“…Explicitly, they are given by 49) where the σ i are the Pauli matrices, and the σ µν are related to the 't Hooft symbols. In complex formulation, the fields can be written in the form 50) with σ ± = σ 1 ± iσ 2 , as usual. In a non-compact space, the F and D flatness conditions imply that the gauge configuration be anti-self-dual since, when written in terms of the field strength they become…”