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

Understand

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.