Stairway to Axions: the cross-correlation of birefringence and galaxies from NPIPE and Quaia

Abstract

We present the first measurement of the cross-correlation between anisotropic birefringence and galaxy number counts, utilizing polarization data from Planck NPIPE and the Quaia quasar catalog. By employing a QML/pseudo-$C_{\ell }$ combined estimator, we compute the angular power spectrum up to $\ell =191$ from birefringence and clustering maps at $N_{\mathrm{side}}=64$. Our analysis indicates that the observed spectrum is well consistent with the null-hypothesis, with a probability to exceed of 37% and an estimated scale-invariant amplitude of $A^{{\mathcal{D}}_{\ell }}=(2.22\pm 2.09)\times 10^{-4}\text{deg}$, at the 68% confidence level. Finally, we derive constraints on the axion-parameters within an early dark energy model of birefringence. Our findings reveal an unprecedented upper bound on the axion-photon coupling down to $g_{\varphi \gamma }=10^{-15}{\text{GeV}}^{-1}$ for masses around $10^{-32}\text{eV}$ and high initial misalignment angles. This result opens a previously unexplored window in parameter space, providing the first constraint in this ultra-light mass regime.

Comments: 15 + 3 pages + references, 13 figures