On tadpoles and vacuum redefinitions in String Theory

TL;DR

This paper investigates the role of tadpoles and vacuum redefinitions in String Theory, proposing perturbative approaches to understand supersymmetry breaking and demonstrating cases where tadpoles do not affect low-energy physics.

Contribution

It introduces a perturbative framework for analyzing vacuum redefinitions in String Theory and provides examples linking different orientifold models with implications for supersymmetry breaking.

Findings

Perturbative analysis reveals special vacua where tadpole resummations terminate.

Certain string models with broken supersymmetry have UV finite one-loop threshold corrections.

Evidence of a link between IIB and 0B orientifolds through vacuum redefinitions.

Abstract

Tadpoles accompany, in one form or another, all attempts to realize supersymmetry breaking in String Theory, making the present constructions at best incomplete. Whereas these tadpoles are typically large, a closer look at the problem from a perturbative viewpoint has the potential of illuminating at least some of its qualitative features in String Theory. A possible scheme to this effect was proposed long ago by Fischler and Susskind, but incorporating background redefinitions in string amplitudes in a systematic fashion has long proved very difficult. In the first part of this paper, drawing from field theory examples, we thus begin to explore what one can learn by working perturbatively in a ``wrong'' vacuum. While unnatural in Field Theory, this procedure presents evident advantages in String Theory, whose definition in curved backgrounds is mostly beyond reach at the present time. At the field theory level, we also identify and characterize some special choices of vacua where tadpole resummations terminate after a few contributions. In the second part we present a notable example where vacuum redefinitions can be dealt with to some extent at the full string level, providing some evidence for a new link between IIB and 0B orientifolds. We finally show that NS-NS tadpoles do not manifest themselves to lowest order in certain classes of string constructions with broken supersymmetry and parallel branes, including brane-antibrane pairs and brane supersymmetry breaking models, that therefore have UV finite threshold corrections at one loop.