A Review of Gravitational Waves from Cosmic Domain Walls

Abstract

Abstract:In this contribution, we discuss the cosmological scenario where unstable domain walls are formed in the early universe and their late-time annihilation produces a significant amount of gravitational waves. After describing cosmological constraints on long-lived domain walls, we estimate the typical amplitude and frequency of gravitational waves observed today. We also review possible extensions of the standard model of particle physics that predict the formation of unstable domain walls and can be probed by observation of relic gravitational waves. It is shown that recent results of pulser timing arrays and direct detection experiments partially exclude the relevant parameter space, and that a much wider parameter space can be covered by the next generation of gravitational wave observatories.

Piercing of domain walls: new mechanism of gravitational radiation

“…But from our results it is clear that this mechanism may be relevant in the lower-frequency spectrum of the relic gravitons. Mention that the graviton spectrum from collapsing unstable domain walls is not divergent in the infrared but has maximum at some finite frequency [15]. Also, our mechanism is universal and applicable to stable DWs as well.…”

“…Physically, PGR may be relevant for cosmic DWs, providing additional low-frequency contributions to the standard spectrum of gravitons from collapsing walls, which is typically dies off in the infrared [15]. Detailed study of such applications, however, remains beyond the scope of the present paper which is mostly restricted to theoretical aspects of the problem.…”

“…Indeed, the position of the maximum O(1/γ) for the ultrarelativistic particle goes to zero, while the height γ 2 blows up to infinity. Directly taking the limits of (5.5), (5.8) and (5.9) one gets 15) with no dependence on the Lorentz factor. Here E stands for the photon frequency.…”

“…Collapsing unstable DWs generate gravitational waves, whose spectrum, sensible to particular underlying models, can be an important source of information about the early universe. In view of the forthcoming experimental studies of relict gravitational waves, this subject attracted attention recently [8][9][10][11][12][13][14], for a review see [15]. Particular models considered include the hybrid inflation [9], the standard model extended to the very early universe [14], the Higgs model [11], the next-to-minimal supersymmetric standard model [12] and some other.…”

“…Since the integrand is beamed inside the cone 0 < ψ 1/γ, the final result depends upon the relation between 1/γ and ψ min . Namely, expressing the radiation efficiency (6.13) in terms of inverse minimal emission angle, it estimates as 15) or ln γ * /γ * in terms of effective Lorentz factor γ * ≡ ψ −1 min . Since the function ln x/x does not exceed 1 for x > 1, there is no efficiency catastrophe in our model.…”