A new source for light dark matter isocurvature in low scale inflation

Axion like particles are a compelling dark matter candidate with a vast running experimental program to discover them. Previous studies have shown that axion dark matter can generate sizable isocurvature perturbations, potentially challenging high scale inflationary models in case of dark matter discovery. In particular, dark matter existence and cosmic microwave background measurements could impose an upper bound on the inflationary scale. In this talk I will point out that the presence of ALP dark matter can generate important isocurvature perturbations also in scenarios of low-scale inflation. In this case, the dark matter mass determines a lower bound on the Hubble parameter during inflation. With current cosmological data, this lower bound is of the same order of the bound from relic abundance, and a precise comparison is highly model dependent. Nevertheless, future surveys can improve it and, together with axion experiments like DMRadio-$\rm m^3$, shed light on the scale of inflation.