Searching for axionlike time-dependent cosmic birefringence with data from SPT-3G

Ultralight axionlike particles (ALPs) are compelling dark matter candidates because of their potential to resolve small-scale discrepancies between $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ predictions and cosmological observations. Axion-photon coupling induces a polarization rotation in linearly polarized photons traveling through an ALP field; thus, as the local ALP dark matter field oscillates in time, distant static polarized sources will appear to oscillate with a frequency proportional to the ALP mass. We use observations of the cosmic microwave background from SPT-3G, the current receiver on the South Pole Telescope, to set upper limits on the value of the axion-photon coupling constant ${g}_{\ensuremath{\phi}\ensuremath{\gamma}}$ over the approximate mass range ${10}^{\ensuremath{-}22}--{10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{eV}$, corresponding to oscillation periods from 12 hours to 100 days. For periods between 1 and 100 days ($4.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}\ensuremath{\le}{m}_{\ensuremath{\phi}}\ensuremath{\le}4.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\text{ }\text{ }\mathrm{eV}$), where the limit is approximately constant, we set a median 95% C.L. upper limit on the amplitude of on-sky polarization rotation of 0.071 deg. Assuming that dark matter comprises a single ALP species with a local dark matter density of $0.3\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$, this corresponds to ${g}_{\ensuremath{\phi}\ensuremath{\gamma}}<1.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}\ifmmode\times\else\texttimes\fi{}(\frac{{m}_{\ensuremath{\phi}}}{1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\text{ }\text{ }\mathrm{eV}})$. These new limits represent an improvement over the previous strongest limits set using the same effect by a factor of $\ensuremath{\sim}3.8$.