Cosmic string current stability

Abstract

The stability of fermionic charge carriers on cosmic strings is considered. We show that neutral fermion currents in cosmic strings are always chiral or timelike, in contrast with the case of bosonic currents. The spectrum of bound states on an Abelian SO͑10͒ string is determined both before and after the electroweak phase transition. We determine the mass acquired by the zero mode at this transition. A range of charge carrier scattering processes are considered and corresponding decay rates calculated. Couplings between the carriers and the electroweak sector generate scattering from the plasma which can thermalize some currents. If the zero mode is isolated from the electroweak sector, then it survives. Current-current scattering is considered, but found to be unimportant in realistic settings where the string density is low.PACS number͑s͒: 98.80.Cq

Equation of state of cosmic strings with fermionic current carriers

“…Such massive bound states depend therefore of the particular values of the model parameters. Recently, it was shown numerically [25] that the Abelian Higgs model with one Weyl fermion admits always at least two massive bound states, as a result, the present toy model also may have such states. However, in order to simplify the quantization, we will only consider the generic zero modes, and consequently, the following results will be relevant for cosmic string only when the occupancy of the massive bound states can be neglected compared to the occupancy of the zero mode states.…”

“…However, in order to simplify the quantization, we will only consider the generic zero modes, and consequently, the following results will be relevant for cosmic string only when the occupancy of the massive bound states can be neglected compared to the occupancy of the zero mode states. Such physical situations are likely to occur far below the energy scale where the string was formed, since the massive states are generally expected to decay much more rapidly than the massless ones [25].…”

“…Yet it will also have to be addressed in the more general context that will be discussed below. In the meantime it was believed that a quantum treatment was necessary in order to decide on the quantum stability: as one wants to compare the characteristic life-time of a vorton with the age of the Universe, quantum effects can turn out to be relevant; hence the following work in which the simplest of all fermionic Witten models is detailed [2] that can give rise to both spacelike as well as timelike charge currents, generalizing the usual point of view [25].…”

The Fate of Cosmic String Zero Modes

“…The decay rates of both massive and massless modes have been calculated at tree level 13 . The main difference between scattering in the string background and that in a trivial background is the lack of translation invariance transverse to the string.…”

“…On the other hand if the decay rate is too low the Universe could become vorton dominated. We address this issue and show that these processes can remove current carriers close to the phase transition, but not otherwise 13 . We then consider vorton constraints in chiral theories, showing this leads to stringent constraints on the underlying particle physics theory.…”