English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The relic density of dark matter in the $\Lambda$CDM model restricts theparameter space for a cosmological axion field, constraining the axion decayconstant, the initial amplitude of the axion field and the axion mass. It isshown via lattice simulations how the relic density of axion-like particleswith masses close to the one of the QCD axion is affected by axion-gauge fieldinteractions and by initial axion inhomogeneities. For pre-inflationary axions,once the Hubble parameter becomes smaller than the axion mass, the latterstarts to oscillate, and part of its energy density is spent producing gaugefields via parametric resonance. If the gauge fields are dark photons andStandard Model photons, the energy density of dark photons becomes higher thanthe one of the axion, while the high conductivity of the primordial plasmadamps the oscillations of the photon field. Such a scenario allows for theproduction of small-scale, primordial magnetic fields, and it is found that therelic density of axions with a low decay constant are within the bounds set bythe $\Lambda$CDM model, while GUT-scale axions are far too abundant. It is alsoshown that initial inhomogeneities of the axion field can change substantiallythe gauge field production, boosting or suppressing (depending on the axionparameters and couplings) the magnetogenesis mechanism with respect to anhomogeneous axion field. It is found that when the axion mass is far lighterthan the QCD axion model and the initial axion field is inhomogeneous, weak butcosmologically relevant magnetic field seeds can be generated on scales of theorder of $0.1$ kpc.

Axions and Primordial Magnetogenesis: the Role of Initial Axion Inhomogeneities