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Abstract: We investigate the generation of gravitational waves due to the gravitationalinstability of primordial density perturbations in an early matter-dominatedera which could be detectable by experiments such as LIGO and LISA. We userelativistic perturbation theory to give analytic estimates of the tensorperturbations generated at second order by linear density perturbations. Wefind that large enhancement factors with respect to the naive second-orderestimate are possible due to the growth of density perturbations on sub-Hubblescales. However very large enhancement factors coincide with a breakdown oflinear theory for density perturbations on small scales. To produce aprimordial gravitational wave background that would be detectable with LIGO orLISA from density perturbations in the linear regime requires primordialcomoving curvature perturbations on small scales of order 0.02 for AdvancedLIGO or 0.005 for LISA, otherwise numerical calculations of the non-linearevolution on sub-Hubble scales are required.



Author: Hooshyar Assadullahi, David Wands ICG, Portsmouth

Source: https://arxiv.org/







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