Speaker
Description
If dark matter is ultralight, the number density of dark matter is very high and the techniques of zero-temperature field theory are no longer valid. The dark matter number density modifies the vacuum giving it a non-negligible particle occupation number. For fermionic dark matter, this occupation number can be no larger than one. However, in the case of bosons the occupation number is unbounded. If there is a large occupation number, the Bose enhancement needs to be taken into consideration for any process involving particles which interact with the dark matter. Because the occupation number scales inversely with the dark matter mass, this effect is most prominent for ultralight dark matter. In fact, the Bose enhancement effect from the background is so significant for ultralight dark matter that, the correction to the anomalous magnetic moment is larger than experimental uncertainties for an effective coupling of of order 10−17 for a mass of order $10^{−20}$ eV if the dark matter is a dark photon or axion like particle. Furthermore, the constraint scales linearly with the dark matter mass and so new significant constraints can be placed on the dark matter mass all the way up to about $10^{−14}$ eV. Future experiments measuring $g-2$ will probe even smaller effective couplings.
