Is the Spectrum of Gravitational Waves the "Holy Grail" of Inflation?

TL;DR

Detecting primordial gravitational waves via B-mode polarization is scientifically valuable, but a positive signal may not confirm inflation and could potentially falsify it, highlighting the need for careful spectrum analysis.

Contribution

This note emphasizes that B-mode polarization signals could originate from sources other than inflation and might even challenge the inflationary paradigm.

Findings

B-mode polarization detection is scientifically important.

A positive signal does not necessarily confirm inflation.

Spectrum analysis could falsify inflationary models.

Abstract

It is often said that detecting a spectrum of primordial gravitational waves via observing B-mode polarization of the Cosmic Microwave Background is the "Holy Grail" of inflation. The purpose of this short note is to point out that it is indeed of immense scientific interest to search for a signal of gravitational waves in B-mode polarization. However, rather than proving that inflation is the right paradigm of early universe cosmology, a positive signal of direct primordial B-mode polarization might well be due to other sources than inflation. In fact, a careful characterization of the spectrum of B-mode polarization might even falsify the inflationary paradigm.