Dark Matter in the Standard Model?

TL;DR

This paper critically examines two Standard Model-based dark matter candidates: a stable uuddss exa-quark and primordial black holes from Higgs potential instability, analyzing their viability and constraints.

Contribution

It provides a detailed analysis of the potential for a stable exa-quark and the conditions for primordial black hole formation from Higgs instability within the Standard Model.

Findings

Exa-quark mass of 1.2 GeV could reproduce dark matter abundance but is excluded by nuclear stability.

Higgs non-minimal coupling must be very small, and universe must survive many regions to avoid vacuum decay.

Primordial black hole formation requires fine-tuned conditions in Higgs potential.

Abstract

We critically reexamine two possible Dark Matter candidate within the Standard Model. First, we consider the $uuddss$ exa-quark. Its QCD binding energy could be large enough to make it (quasi) stable. We show that the cosmological Dark Matter abundance is reproduced thermally if its mass is 1.2 GeV. However, we also find that such mass is excluded by the stability of Oxygen nuclei. Second, we consider the possibility that the instability in the Higgs potential leads to the formation of primordial black holes while avoiding vacuum decay during inflation. We show that the non-minimal Higgs coupling to gravity must be as small as allowed by quantum corrections, $|\xi_H| < 0.01$. Even so, one must assume that the Universe survived in $e^{120}$ independent regions to fluctuations that lead to vacuum decay with probability 1/2 each.