Abstract
Starting from a peculiar orientifold projection proposed long ago by Angelantonj and Cardella, we elaborate on a novel perturbative scenario that involves only D-branes, together with the two types of orientifold planes O± and anti-orientifold planes {overline{mathrm{O}}}_{pm } . We elucidate the microscopic ingredients of such models, connecting them to a novel realization of brane supersymmetry breaking. Depending on the position of the D-branes in the internal space, supersymmetry can be broken at the string scale on branes, or alternatively only at the massive level. The main novelty of this construction is that it features no NS-NS disk tadpoles, while avoiding open-string instabilities. The one-loop potential, which depends on the positions of the D-branes, is minimized for maximally broken, non-linearly realized supersymmetry. The orientifold projection and the effective field theory description reveal a soft breaking of supersymmetry in the closed-string sector. In such models it is possible to decouple the gravitino mass from the value of the scalar potential, while avoiding brane instabilities.
Highlights
In practice to obtain at the effective field-theory level, adding extra ingredients like fluxes or nonperturbative effects
Let us mention that the coexistence of massless gravitinos and broken supersymmetry in the open sector in Brane Supersymmetry Breaking” (BSB) models is shared by compactifications with internal magnetic fields that break supersymmetry [61,62,63,64]
Depending on where the background D-branes sit in the internal space, their massless spectrum can be supersymmetric or non-supersymmetric
Summary
Let us start by describing alternative viewpoints for deriving the supersymmetric and nonsupersymmetric torus amplitudes to be combined later on with orientifold amplitudes. The starting point is a freely-acting orbifold of type IIB with B89 = 0 and generator g = δw8δp, where δw stands for a winding shift along direction X8 while δp denotes a momentum shift along direction X9 The action of this generator on the lattice states is g|m, n = (−1)n8+m9|m, n. From the freely-acting orbifold perspective, it is easy to build a non-supersymmetric deformation of the type IIB model in a Scherk-Schwarz spirit It is obtained by replacing g with the generator g = (−1)F δw8δp, where F denotes the spacetime fermion number. This transformation amounts to exchanging the lattice sums of the two directions and switching X8 ↔ X9, leading to the new amplitude The latter can be obtained by a free action generated by g = (−1)F δp8δw, followed by the rescaling R8 → 2R8. Supersymmetry is restored in the limits R8 → ∞ and/or R9 → 0
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