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26 May, SFB1258 Colloquy with Subir Sakar (U Oxford)

Welcome to our second SFB1258 Colloquy of the summer term 2025, held at the MPP main auditorium.

Timetable
9:30 Welcome coffee

10:00 Subir Sarkar (U Oxford): Rethinking axion dark matter
Abstract: We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry (e.g. DFSZ). 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 naturally 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 rather low (<5.4x10^8 GeV) – thus ruling out an axion mass below 11 meV, where most experimental searches are in fact focused. This motivated our new light-shining-through-walls experiment targeted at heavier axions at the Hamburg X-ray Free Electron Lightsource; I will describe the first results. [SciPost Physics 15:003, 2023; PRL (in press) 2025].

10:45 Coffee break

11:15 N.N.: tba

26 May, SFB1258 Colloquy with Subir Sakar (U Oxford)

Welcome to our second SFB1258 Colloquy of the summer term 2025, held at the MPP main auditorium.

Timetable
9:30 Welcome coffee

10:00 Subir Sarkar (U Oxford): Rethinking axion dark matter
Abstract: We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry (e.g. DFSZ). 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 naturally 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 rather low (<5.4x10^8 GeV) – thus ruling out an axion mass below 11 meV, where most experimental searches are in fact focused. This motivated our new light-shining-through-walls experiment targeted at heavier axions at the Hamburg X-ray Free Electron Lightsource; I will describe the first results. [SciPost Physics 15:003, 2023; PRL (in press) 2025].

10:45 Coffee break

11:15 N.N.: tba

26 May, SFB1258 Colloquy with Subir Sakar (U Oxford)

Welcome to our second SFB1258 Colloquy of the summer term 2025, held at the MPP main auditorium.

Timetable
9:30 Welcome coffee

10:00 Subir Sarkar (U Oxford): Rethinking axion dark matter
Abstract: We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry (e.g. DFSZ). 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 naturally 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 rather low (<5.4x10^8 GeV) – thus ruling out an axion mass below 11 meV, where most experimental searches are in fact focused. This motivated our new light-shining-through-walls experiment targeted at heavier axions at the Hamburg X-ray Free Electron Lightsource; I will describe the first results. [SciPost Physics 15:003, 2023; PRL (in press) 2025].

10:45 Coffee break

11:15 N.N.: tba

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