MG11 
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Abstract

The gravitational wave background from scalar perturbations

We investigate a new contribution to the primordial stochastic background of tensor modes from inflation using second order perturbation theory. We study tensor modes generated by the non-linear evolution of primordial scalar perturbations during the radiation-dominated era. The power spectrum of tensor modes generated by the scalar perturbations is investigated. Additionally, deviations from power-law spectra at small scales are studied, and we calculate the bounds placed by current and future gravitational wave detectors.

Second order cosmological perturbation theory

We present the Einstein Field Equations for cosmological perturbations up to second order of a Robertson-Walker background solution of arbitrary curvature. We consider the energy momentum tensor for a variety of sources including a perfect fluid, a system of scalar fields minimally coupled to gravity and electro-magnetic fields. We also present the second order gauge transformation equations. In addition we consider the scalar, vector, tensor decomposition of the second order equations, which unlike the decomposition of the linear equations is non-trivial. As an application of the formalism we calculate the tensor modes generated at second order by the non-linear evolution of the scalar perturbations.