Quantum corrections to the primordial tensor spectrum: open EFTs & Markovian decoupling of UV modes

Abstract

Perturbative quantum corrections to primordial power spectra are important for testing the robustness and the regime of validity of inflation as an effective field theory. Although this has been done extensively for the density power spectrum (and, to some extent, for the tensor spectrum) using loop corrections, we do so in an open quantum system approach to the problem. Specifically, we calculate the first-order corrections to the primordial gravitational wave spectrum due to (cubic) tensor interactions alone. We show that our results match expectations from standard loop corrections only in the strict Markovian limit, and therefore, establish a systematic way to relax this approximation in the future, as is generally necessary for gravitational systems.

Universal signature of quantum entanglement across cosmological distances

“…Moreover, it is straightforward to extend our computation to primordial gravitational waves, the leading order interaction term for which is independent of slow-roll parameters and therefore, the expected correction to the tensor power spectrum due to entanglement may be larger than the scalar one (in relative magnitude to the tree-level value). We have already shown the emergence of non-Markovian behaviour for the tensor modes [57] and the non-perturbative resummation for these will be pursued in the future and this work forms the foundation of exploring such hitherto undiscovered quantum effects in cosmology.…”

“…Clearly, this is part of a larger discussion which is beyond the scope of this paper, and it would be interesting to compute the effects of the quartic interaction using open quantum system techniques. Alternatively, one could look at other observables with manifestly gauge invariant interactions, such as the tensor spectrum [57], which has the additional advantage of allowing to compare the Wilsonian and Open EFT approaches without these concerns. Moreover, this also puts into light the potential importance of open EFTs to study topics such as the IR divergences of dS spacetimes or the decoupling of UV modes.…”

Looking inside the Swampland from Warm Inflation: Dissipative Effects in De Sitter Expansion

“…The role of IR modes during inflation can also raise some obstructions in a very long-lasting quasi-dS phase of expansion. Put differently, there have been some recent studies which show that away from the spurious limit of k → 0, long wavelength modes can have a non-negligible effect through their backreaction on the background dynamics [85][86][87][88]. The role of IR modes in inflation has been a matter of some debate for some time (see, e.g., [89,90], and contrast with [2,91]).…”

Entanglement in cosmology

“…A very interesting example of such a quantity is the entanglement entropy. In the simplest approach, one may consider the momentum-space entanglement between high and lowmomentum modes, such as between modes with physical momenta below and above the Hubble scale H [10][11][12][13]. However, this would vanish for a free field, as long as the initial state can be written as a tensor product of states, one for each momentum mode, as in the Minkowski vacuum.…”