H0 tension, swampland conjectures, and the epoch of fading dark matter

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 conjectures (c) over tilde is expected to be an O(1) number. Interestingly, when we include the local measurement of H-0, our model prefers a nonzero value of the coupling (c) over tilde with a significance of 2.8 sigma and a best fit at (c) over tilde similar to 0.3. Modifying the recent evolution of the Universe in this way improves the fit to the data at the 2 sigma level compared to A cold dark matter. This string-inspired model automatically reduces cosmological tensions in the H-0 measurement as well as sigma(8).

Automated summary

This article introduces a string-inspired model that incorporates a rolling scalar field as the source of dark energy, connecting it to the swampland de Sitter conjecture and distance conjecture. By modifying the recent evolution of the Universe in this way, the model effectively reduces cosmological tensions in measurements such as H-0 and sigma(8).