Impact of string and monopole-type junctions on domain wall dynamics: Implications for dark energy

L Sousa,P.P Avelino

doi:10.1016/j.physletb.2010.04.074

Abstract

We investigate the potential role of string and monopole-type junctions in the frustration of domain wall networks using a velocity-dependent one-scale model for the characteristic velocity, v, and the characteristic length, L, of the network. We show that, except for very special network configurations, v2≲(HL)2≲(ρσ+ρμ)/ρm where H is the Hubble parameter and ρσ, ρμ and ρm are the average density of domain walls, strings and monopole-type junctions. We further show that if domain walls are to provide a significant contribution to the dark energy without generating exceedingly large CMB temperature fluctuations then, at the present time, the network must have a characteristic length L0≲10Ωσ0−2/3 kpc and a characteristic velocity v0≲10−5Ωσ0−2/3 where Ωσ0=ρσ0/ρc0 and ρc is the critical density. In order to satisfy these constraints with Ωσ0∼1, ρm0 would have to be at least 10 orders of magnitude larger than ρσ0, which would be in complete disagreement with observations. This result provides very strong additional support for the conjecture that no natural frustration mechanism, which could lead to a significant contribution of domain walls to the dark energy budget, exists.

Highlights

There is very strong observational evidence that our Universe is currently undergoing a period of accelerated expansion [1, 2]
In the case of global monopoles described by a Lagrangian with a standard kinetic term there is a nearly constant long-range force between monopole and anti-monopole pairs which could be dynamically relevant. Such long-range forces, if they are important, would trigger a very effective annihilation between monopole and anti-monopole pairs. This would constitute an additional obstacle to the frustration of a domain wall network and we shall not consider them in the present paper
We have shown that a successful domain wall scenario for dark energy would reqsturiarteedthtahtaLt 0su

Summary

INTRODUCTION

There is very strong observational evidence that our Universe is currently undergoing a period of accelerated expansion [1, 2]. Strong analytical and numerical evidence was provided that a frustrated domain wall network, accounting for a significant fraction of the energy density of the Universe at the present time, will never emerge from realistic phase transitions. These results appear to rule out a significant contribution of domain walls to the dark energy budget. In order to overcome this potential problem we develop a semi-analytical VOS model which incorporates the contribution of string and monopole-type junctions to the overall dynamics of domain wall networks We use this model to constrain the characteristic length and velocity of domain wall networks and discuss the corresponding cosmological implications, in particular for dark energy

SEMI-ANALITICAL VOS MODEL WITH JUNCTIONS

CONCLUSIONS