Axions, Domain Walls, and the Early Universe

Abstract

Axion models have a spontaneously broken Z(N) symmetry. The resulting discretely degenerate vacua and domain-wall solitons are incompatible with the standard cosmology. It is possible, however, to introduce a small Z(N) breaking interaction into axion models without upsetting the Peccei-Quinn mechanism. In that case the domain walls disappear a certain time after their formation in the early universe. Their presence for a limited time period might lead to galaxy formation.PACS numbers: 11.15. Ex, 11.30.Er, 12.10.En, 98.80.Bp When a gauge interaction explicitly breaks a global symmetry, it often happens that a discrete subgroup of the global symmetry remains unbroken. Such is the case in axion models 1 which, as I am about to show, have a spontaneously broken Z(N) symmetry. The result applies to all models which have a Peccei-Quinn symmetry UPQ(1) which is broken only by the QCD gluon anomaly. N is the number of quark flavors that rotate under UPQ(1). TO be specific however, I analyze the Dine-Fischler-Srednicki model 2 in which the axion can be made "invisible." The Yukawa couplings and scalar selfinteractions of that model, N/2

Majorana dark matter through the Higgs portal under the vacuum stability lamppost

“…It is well known that the spontaneous breaking of a global U (1) symmetry have several disconnected and degenerate vacua (the phase of the vacuum expectation value 0|S|0 can be different in different regions of space, and actually we expect it to be different in casually disconnected regions), yielding dangerous domainwall structure in the early universe [43,44]. In the spirit of [43], it may be possible to explicitly break the symmetry introducing (possibly small) terms in V , such that the domain walls disappear before dominating the matter density of the universe, while leaving (pseudo-)Goldstone bosons and the same dark matter phenomenology [26]. 1 For simplicity, we restrict our considerations to the potential in (4), but generalizations are straightforward.…”

The soft supersymmetry-breaking Lagrangian: theory and applications

“…If inflation reheats to a temperature larger than the lower bound of f P Q /N of 4 × 10 9 GeV, gravitinos tend to disrupt the successes of standard cosmology (see Section 6.6). Furthermore, if the reheating temperature is above f P Q , there may be a problem with domain wall formation; this leads to at best a complicated, more model-dependent cosmology [588]. To keep the model dependence down and the physics simple for this review, we will focus on situations where the reheating temperature is lower than the PQ transition.…”

The Peccei-Quinn field as curvaton

“…[35,36]). This would lead [37] to a disastrous domain wall production if the PQ transition occurred after inflation. Avoidance of this disaster would then require extending [38] the model so that such spontaneously broken discrete symmetries do not appear.…”