What if ALP dark matter for the XENON1T excess is the inflaton

Abstract: The recent XENON1T excess in the electron recoil data can be explained by anomaly-free axion-like particle (ALP) dark matter with mass $m_\phi = 2.3 \pm 0.2\,$keV and the decay constant $f_\phi/q_e \simeq 2 \times 10^{10} \sqrt{\Omega_\phi/\Omega_{\rm DM}}\,{\rm GeV}$. Intriguingly, the suggested mass and decay constant are consistent with the relation, $f_\phi \sim 10^3 \sqrt{m_\phi M_p}$, predicted in a scenario where the ALP plays the role of the inflaton. This raises a possibility that the ALP dark matter responsible for the XENON1T excess also drove inflation in the very early universe. We study implications of the XENON1T excess for the ALP inflation and thermal history of the universe after inflation.