Explanation for why the Early Universe was Stable and Dominated by the Standard Model

TL;DR

This paper explains why the early universe was dominated by the Standard Model and stable, proposing that a special coupling between the inflaton and the Higgs leads to rapid decay into the SM, resolving potential instabilities.

Contribution

It introduces a natural mechanism involving a super-renormalizable inflaton-Higgs coupling that stabilizes the Higgs potential and explains the SM's dominance in the early universe.

Findings

The Higgs potential instability is resolved during and after inflation.

The SM's dominance is naturally explained by the inflaton-Higgs coupling.

Dark matter can form in hidden sectors through subsequent dynamics.

Abstract

The Standard Model (SM) possesses an instability at high scales that would be catastrophic during or just after inflation, and yet no new physics has been seen to alter this. Furthermore, modern developments in quantum gravity suggest that the SM degrees of freedom are not unique; that a typical low energy effective theory should include a large assortment of hidden sector degrees of freedom. It is therefore puzzling that cosmological constraints from BBN and CMB reveal that the early universe was almost entirely dominated by the SM, when the inflaton $\phi$ could have decayed into many sectors. In this work we propose the following explanation for all of this: we allow the lowest dimension operators with natural coefficients between the inflaton and both the Higgs and hidden sectors. Such hidden sectors are assumed to be entirely natural; this means all unprotected masses are pushed up to high scales and project out of the spectrum, while only massless (or protected) degrees of freedom remain, and so the inflaton can only reheat these sectors through higher dimension (and suppressed) operators. On the other hand, the SM possesses a special feature: it includes a light Higgs $H$, presumably for life to exist, and hence it allows a super-renormalizable coupling to the inflaton $\phi H^\dagger H$, which allows rapid decay into the SM. We show that this naturally (i) removes the instability in the Higgs potential both during and after inflation due to a tree-level effect that increases the value of the Higgs self-coupling from the IR to the UV when one passes the inflaton mass, (ii) explains why the SM is dominant in the early universe, (iii) allows dark matter to form in hidden sector/s through subsequent dynamics (or axions, etc), (iv) allows for high reheating and baryogenesis, and (v) accounts for why there so far has been no direct detection of dark matter or new physics beyond the SM.