Anna Tokareva: Background-induced complex mass states of graviton: quantization and tensor power spectrum

I start from the assumption that the theory of gravity can be formulated in terms of 4-dimensional action, and there are only 2 graviton polarization states, as in general relativity. It can be a non-perturbative effective action discussed in the asymptotic safety program or the result of some other UV modification of the general relativity making it a complete theory. From these general grounds, I will discuss the properties of the graviton two-point function on top of cosmological de-Sitter space. I find that the no-ghost requirement formulated for the flat background does not necessarily hold for the de-Sitter space where the graviton two-point function can have an infinite number of complex-conjugate poles. We show that under certain stability conditions, their appearance doesn’t contradict any fundamental principle. I will present their observational consequences for the tensor power spectrum from inflation and for the stochastic gravitational wave background.