Axion dark matter has the unique property of having extremely high quantum occupancy. This may lead to thin k that axion dark matter can be described in terms of a classical field.

\n\nThe usual equations for the linear growth of density perturbations in the cold dark matter fluid can be obtained from the classical descripti on of a self-gravitating scalar field in the non-relativistic regime\, wit h differences appearing only on scales smaller than a critical length.

\n\nHowever\, axion dark matter is expected to thermalize through gravita tional self-interactions and to form a Bose-Einstein condensate. I will ar gue that the classical field approximation is in general not valid for the rmalizing quantum fields\, even in the large occupancy regime\, and discus s the different evolution of a homogeneous condensate in classical and qua ntum field theory.

\n DTSTART:20171004T193000Z LOCATION:Physics Building\, Room 204 SUMMARY:Is axion dark matter described by a classical scalar field? END:VEVENT END:VCALENDAR