The Physical Content of Long Tensor Modes in Cosmology

TL;DR

This paper demonstrates that long-wavelength tensor modes in cosmology have physical significance and cannot be gauged away, impacting the interpretation of inflationary models and the potential for future observational tests.

Contribution

It clarifies the physical content of long tensor modes in the squeezed bispectrum and discusses implications for the Maldacena consistency relation and inflationary model discrimination.

Findings

Long tensor modes are physically meaningful and not gauge artifacts.

The Maldacena consistency relation holds only in the exact infinite wavelength limit.

Future experiments could observe squeezed mixed correlators to probe early Universe physics.

Abstract

We analyze the physical content of squeezed bispectra involving long-wavelength tensor perturbations, showing that these modes cannot be gauged away, except for the exact (unphysical) limit of infinite wavelength, $k = 0$. This result has a direct implication on the validity of the Maldacena consistency relation, respected by a subclass of inflationary models. Consequently, in the squeezed limit, as in the case of the scalar-scalar-scalar bispectrum, squeezed mixed correlators could be observed by future experiments, remaining a key channel to study Early Universe physics and discriminate among different models of inflation.