Title: Some properties of Gravitational Waves in Modified Theories of Gravity

Abstract: In this talk, at first, I'll briefly discuss polarisation modes of Gravitational Waves (GWs) in modified theories of gravity mainly focusing on f(R) gravity metric formalism and Palatini formalism. After that I'll discuss quasinormal modes of black holes or ring-down GWs in some selected modified theories of gravity. These two properties may be helpful in the near future to constrain different modified theories of gravity.

Title: Gravitational Waves from Stochastic Scalar Fluctuations

Abstract: In this talk, we will present a novel mechanism for gravitational wave generation in the early Universe. Light spectator scalar fields during inflation can acquire a blue-tilted power spectrum due to stochastic effects. We show that this effect can lead to large curvature perturbations at small scales (induced by the spectator field fluctuations) while maintaining the observed, slightly red-tilted curvature perturbations at large cosmological scales (induced by inflaton fluctuations). Along with other observational signatures, such as enhanced dark matter substructure, large curvature perturbations can induce a stochastic gravitational wave background (SGWB). We will discuss this mechanism in detail and present several benchmark scenarios that result in gravitational wave strengths visible to near-future detectors.