Is a classical description of stable non-BPS D-branes possible?

TL;DR

This paper investigates whether a classical geometric description of stable non-BPS D-branes in K3 compactifications is possible, revealing singularities that challenge simple models and suggesting more complex bound states may be needed.

Contribution

It provides the first classical supergravity analysis of stable non-BPS D-branes in K3, highlighting singularities and proposing the need for bound state configurations.

Findings

Classical solutions exhibit repulson-like singularities.

Simple coincident brane configurations are not physically acceptable.

More complex bound states may resolve singularities.

Abstract

We study the classical geometry produced by a stack of stable (i.e. tachyon free) non-BPS D-branes present in K3 compactifications of type II string theory. This classical representation is derived by solving the equations of motion describing the low-energy dynamics of the supergravity fields which couple to the non-BPS state. Differently from what expected, this configuration displays a singular behaviour: the space-time geometry has a repulson-like singularity. This fact suggests that the simplest setting, namely a set of coinciding non-interacting D-branes, is not acceptable. We finally discuss the possible existence of other acceptable configurations corresponding to more complicated bound states of these non-BPS branes.