Subodh Patil

Subodh Patil (University of Geneva)

Title: "Gravitational waves from extra dimensions"

Abstract: We have recently entered the era of gravitational wave astronomy. Although directly interfacing with primordial physics may seem a way off, we remind the audience of a curious aspect of extra dimensions that could offer the upcoming eLISA mission a chance to directly detect primordial gravitational waves. In warped compactifications, Kaluza-Klein (KK) gravitons have the feature that they can couple to localized 4D sources with strength $M_* << M_{pl}$. This in principle allows for KK gravitons to contribute observably to the stochastic background of primordial tensor modes during inflation in spite of their super-horizon decay with a very blue spectrum ($n_T = 3$). We show that in the context of single field inflation, one can obtain large contributions in warped compactifications from decaying massive KK gravitons consistent with Gaussian, adiabatic curvature perturbations (and present day collider constraints) that can fall within eLISA's sensitivity range. The corollaries of this are that it is a) possible to generate an observably large background of tensor perturbations in models of small field inflation and b) plausibly constrain extra dimensional scenarios in a manner complementary to collider searches.