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