Cosmic D-Strings and Vortons in Supergravity

TL;DR

This paper investigates the constraints on cosmic D-strings, especially those with higher winding numbers, based on relic vorton density bounds, and explores their relation to supersymmetry breaking mechanisms in supergravity models.

Contribution

It provides new constraints on D-string tensions from vorton bounds and analyzes the compatibility of supersymmetry breaking with cosmic D-strings in supergravity.

Findings

D-strings with n>1 are more constrained than standard cosmic strings.

D-strings with n=1 evade vorton bounds due to lack of currents.

An incompatibility exists between supersymmetry breaking and cosmic D-strings with a single U(1).

Abstract

Recent developments in string inspired models of inflation suggest that D-strings are formed at the end of inflation. Within the supergravity model of D-strings there are 2(n-1) chiral fermion zero modes for a D-string of winding n. Using the bounds on the relic vorton density, we show that D-strings with winding number n>1 are more strongly constrained than cosmic strings arising in cosmological phase transitions. The D-string tension of such vortons, if they survive until the present, has to satisfy 8\pi G_N \mu \lesssim p 10^{-26} where p is the intercommutation probability. Similarly, D-strings coupled with spectator fermions carry currents and also need to respect the above bound. D-strings with n=1 do not carry currents and evade the bound. We discuss the coupling of D-strings to supersymmetry breaking. When a single U(1) gauge group is present, we show that there is an incompatibility between spontaneous supersymmetry breaking and cosmic D-strings. We propose an alternative mechanism for supersymmetry breaking, which includes an additional U(1), and might alleviate the problem. We conjecture what effect this would have on the fermion zero modes.