Primordial Gravitational Waves Assisted by Cosmological Scalar Perturbations
First author: Yan-Heng Yu
Primordial gravitational waves are one of the most important predictions of inflation theory, and measurements of their imprints on the cosmic microwave background are actively pursued, but not yet succeed until now. Here we point out that measurements of primordial gravitational waves could be conceivable through searching for a signal of second-order tensor perturbations, which were produced due to nonlinear couplings between the linear tensor and scalar perturbations in the early universe. A blue-tilted tensor spectral index is anticipated, and the measurement of the tensor-to-scalar ratio can potentially be performed with high precision with a detector network composed of the ground-based Einstein Telescope and the space-borne LISA project on a decade timescale.