Decompactifications and Massless D-Branes in Hybrid Models

TL;DR

This paper introduces a method to analyze the mass spectrum of BPS D-branes in gauged linear sigma models, revealing conditions for decompactification and the emergence of massless D-branes in hybrid models.

Contribution

It develops a new approach using monodromy rings and K-theory to determine D-brane spectra across different phases of hybrid models.

Findings

Hybrid limits can be at finite or infinite distance in moduli space.

Some hybrid limits lead to decompactification, others to massless D-branes.

An example suggests a novel supergravity theory with SU(2) gauge symmetry.

Abstract

A method of determining the mass spectrum of BPS D-branes in any phase limit of a gauged linear sigma model is introduced. A ring associated to monodromy is defined and one considers K-theory to be a module over this ring. A simple but interesting class of hybrid models with Landau-Ginzburg fibres over CPn are analyzed using special Kaehler geometry and D-brane probes. In some cases the hybrid limit is an infinite distance in moduli space and corresponds to a decompactification. In other cases the hybrid limit is at a finite distance and acquires massless D-branes. An example studied appears to correspond to a novel theory of supergravity with an SU(2) gauge symmetry where the gauge and gravitational couplings are necessarily tied to each other.