<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math> tension, swampland conjectures, and the epoch of fading dark matter
Prateek Agrawal, Georges Obied, Cumrun Vafa
Abstract
Motivated by the swampland de Sitter conjecture, we consider a rolling scalar field as the source of dark energy. Furthermore, the swampland distance conjecture suggests that the rolling field will lead at late times to an exponentially light tower of states. Identifying this tower as residing in the dark sector suggests a natural coupling of the scalar field to the dark matter, leading to a continually reducing dark matter mass as the scalar field rolls in the recent cosmological epoch. The exponent in the distance conjecture $\stackrel{\texttildelow{}}{c}$ is expected to be an $\mathcal{O}(1)$ number. Interestingly, when we include the local measurement of ${H}_{0}$, our model prefers a nonzero value of the coupling $\stackrel{\texttildelow{}}{c}$ with a significance of $2.8\ensuremath{\sigma}$ and a best fit at $\stackrel{\texttildelow{}}{c}\ensuremath{\sim}0.3$. Modifying the recent evolution of the Universe in this way improves the fit to the data at the $2\ensuremath{\sigma}$ level compared to $\mathrm{\ensuremath{\Lambda}}$ cold dark matter. This string-inspired model automatically reduces cosmological tensions in the ${H}_{0}$ measurement as well as ${\ensuremath{\sigma}}_{8}$.