Signatures of a High Temperature QCD Transition in the Early Universe

TL;DR

This paper explores how beyond Standard Model QCD modifications at high temperatures could lead to primordial black holes and gravitational wave signals, linking early universe physics with current observational searches.

Contribution

It proposes that high-temperature QCD transitions beyond the Standard Model can produce primordial black holes and gravitational wave signatures detectable today.

Findings

High-temperature QCD transitions can produce PBHs that account for dark matter.

A 7 TeV QCD transition is consistent with Subaru Hyper-Suprime Cam events.

A 70 GeV transition could explain OGLE events and NANOGrav signals.

Abstract

Beyond Standard Model extensions of QCD could result in quark and gluon confinement occurring well above a temperature of $\sim$GeV. These models can also alter the order of the QCD phase transition. The enhanced production of primordial black holes (PBHs) that can accompany the change in relativistic degrees of freedom at the QCD transition therefore could favor the production of PBHs with mass scales smaller than the Standard Model QCD horizon scale. Consequently, and unlike PBHs associated with a standard GeV-scale QCD transition, such PBHs can account for all the dark matter abundance in the unconstrained asteroid-mass window. This links beyond Standard Model modifications of QCD physics over a broad range of unexplored temperature regimes ($\sim 10-10^3$ TeV) with microlensing surveys searching for PBHs. Additionally, we discuss implications of these models for gravitational wave experiments. We show that a first order QCD phase transition at $\sim7$ TeV is consistent with the Subaru Hyper-Suprime Cam candidate event, while a $\sim 70$ GeV transition is consistent with OGLE candidate events, and also could account for the claimed NANOGrav gravitational wave signal.