R Symmetries in the Landscape

TL;DR

The paper analyzes how discrete R symmetries populate the string landscape, focusing on IIB orientifolds of Calabi–Yau spaces and Gepner-model realizations. It shows that R-symmetric, W=0 vacua are substantially suppressed after fluxes and orientifold projections, with typically no more than about one-third of fluxes invariant under a given R symmetry. While R-parity (Z2) is relatively common and can persist without requiring W=0, full R-symmetries are seldom compatible with low-energy SUSY. Non-perturbative effects and gravity generally break R symmetries, and the landscape dynamics suggest the intermediate-scale branch is more natural phenomenologically than a low-energy SUSY branch or split SUSY.

Abstract

In the landscape, states with $R$ symmetries at the classical level form a distinct branch, with a potentially interesting phenomenology. Some preliminary analyses suggested that the population of these states would be significantly suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau spaces based on vanishing polynomials in weighted projective spaces, and find that the suppression is quite substantial. On the other hand, we find that a $Z_2$ R-parity is a common feature in the landscape. We discuss whether the cosmological constant and proton decay or cosmology might select the low energy branch. We include also some remarks on split supersymmetry.