CHEP Colloquium – The cosmological axion domain wall problem

Speaker : Prof. Subir Sarkar

University of Oxford, U.K

Title : The cosmological axion domain wall problem

Date : 27th January 2025
Time : 4:00 PM
Venue : Auditorium – New Physical Science Building

Abstract:-

We revisit the domain wall problem for QCD axion models (e.g. DFSZ) with more than one quark charged under the Peccei-Quinn symmetry. If the symmetry breaks after inflation, then axion domain walls form which would cause cosmic catastrophe if they come to dominate the Universe. However the walls are natur ally unstable due to non-renormalisable Planck scale suppressed operators, which generate a ‘tilt’ in the axion potential. Consideration of the axions generated by the collapse of the walls then requires the Peccei-Quinn scale to be quite low (<5.4x108 GeV) – thus ruling out an axion mass below 11 meV, where most experimental searches are in fact focused. This motivated a new light-shining-through-walls experiment at the Hamburg X-ray Free Electron Lightsource, targeted at heavier axions.