Question AXION GLUON MATTER AS DARK MATTER

[Harry Costas]

Properties of Axion matter hold the keys to how the universe functions.

[Submitted on 3 Apr 2025]

No Dark Matter Axion During Minimal Higgs Inflation​

Claire Rigouzzo, Sebastian Zell

We study minimal versions of Higgs inflation in the presence of a massless QCD axion. While the inflationary energy scale of the metric variant is too high to accommodate isocurvature bounds, it was argued that Palatini Higgs inflation could evade these constraints. We show, however, that an energy-dependent decay constant enhances isocurvature perturbations, implying that axions can at most constitute a tiny fraction <10−5 of dark matter. This conclusion can be avoided in Einstein-Cartan gravity by an additional coupling of the axion to torsion, albeit for a very specific choice of parameters. Analogous constraints as well as the possibility to alleviate them are relevant for all inflationary models with a non-minimal coupling to gravity.

 

[Harry Costas]

These are the days. that scientists are becoming aware of the properties of axion and Neutrino matter.

[Submitted on 8 Apr 2025]

Generalised Symmetries in Particle Physics​

Joe Davighi

In this talk I review various notions of generalised global symmetry: higher-form, higher-group, and non-invertible symmetry. All these notions have had profound impact on quantum field theory research in the last decade. I highlight various applications of these new symmetries in particle physics, focussing on theories beyond the Standard Model. Areas touched upon include axions, gauge unification, dark matter, neutrino masses, and flavour hierarchies.

 

[Harry Costas]

This is one more step forward to understanding the full potential of Axion Matter.

[Larger PBH abundances can be generated by axion-like particles. Alternatively, in scenarios where isocurvature constraints can be relaxed, we find that the totality of the DM can be produced by the QCD axion misalignment mechanism, accompanied by a O(10−3) DM fraction in PBHs of masses (105−106) M⊙. These can act as seeds for the formation of massive black holes at large redshifts, as suggested by recent JWST observations.]

[Submitted on 10 Apr 25]

Stupendously Large Primordial Black Holes from the QCD axion​

Miguel Faria, Ricardo Z. Ferreira, Fabrizio Rompineve

The inflationary diffusion of (pseudo-)scalar fields with discrete symmetries can seed the formation of a gas of closed domain walls after inflation, when the distance between degenerate minima in field space is not too far from the inflationary Hubble scale. Primordial black holes (PBHs) can then be formed once sufficiently heavy domain walls re-enter the Hubble sphere. In this scenario, inflation determines a distinctive PBH mass distribution that is rather flat and can thus lead to a sizable total abundance of PBHs, while avoiding some of the downsides of PBH formation from critical collapse. We show that generic QCD axion models, with decay constant close to the inflationary Hubble scale, can yield up to 1% of the dark matter (DM) today in the form of PBHs, while being compatible with isocurvature constraints from Cosmic Microwave Background observations. This occurs for values of axion decay constants around fa≃108 GeV, that is the region targeted by axion helioscopes and partially constrained by astrophysical observations. The resulting PBHs have \textit{stupendously} large masses, above 1011M⊙, and their existence can be probed by Large Scale Structure observations. Larger PBH abundances can be generated by axion-like particles. Alternatively, in scenarios where isocurvature constraints can be relaxed, we find that the totality of the DM can be produced by the QCD axion misalignment mechanism, accompanied by a O(10−3) DM fraction in PBHs of masses (105−106) M⊙. These can act as seeds for the formation of massive black holes at large redshifts, as suggested by recent JWST observations.