Cosmic D-strings and vortons in supergravity

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 π G N μ ≲ 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.