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Gravitational waves from self-ordering scalar fields

AuthorsFenu, Elisa; García Figueroa, Daniel ; Durrer, Ruth; García-Bellido, Juan
KeywordsCosmological phase transitions
Gravitational waves / sources
Issue Date7-Oct-2009
PublisherInstitute of Physics Publishing
CitationJournal of Cosmology and Astroparticle Physics (JCAP) 10(2009)005
AbstractGravitational waves were copiously produced in the early Universe whenever the processes taking place were sufficiently violent. The spectra of several of these gravitational wave backgrounds on subhorizon scales have been extensively studied in the literature. In this paper we analyze the shape and amplitude of the gravitational wave spectrum on scales which are superhorizon at the time of production. Such gravitational waves are expected from the self ordering of randomly oriented scalar fields which can be present during a thermal phase transition or during preheating after hybrid inflation. We find that, if the gravitational wave source acts only during a small fraction of the Hubble time, the gravitational wave spectrum at frequencies lower than the expansion rate at the time of production behaves as Ω(GW)(f) α f^3 with an amplitude much too small to be observable by gravitational wave observatories like LIGO, LISA or BBO. On the other hand, if the source is active for a much longer time, until a given mode which is initially superhorizon (kη* << 1), enters the horizon, for kη >~ 1, we find that the gravitational wave energy density is frequency independent, i.e. scale invariant. Moreover, its amplitude for a GUT scale scenario turns out to be within the range and sensitivity of BBO and marginally detectable by LIGO and LISA. This new gravitational wave background can compete with the one generated during inflation, and distinguishing both may require extra information.
Description21 pages, 2 figures.-- Full-text version available Open Access at the journal site.
Publisher version (URL)http://dx.doi.org/10.1088/1475-7516/2009/10/005
Appears in Collections:(IFT) Artículos
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