$H_0$ tension and the String Swampland
Abstract
We realize the AgrawalObiedVafa swampland proposal of fading dark matter for solving the $H_0$ tension by the model of SalamSezgin and its string realization of CveticGibbonsPope. The model describes a compactification of sixdimensional supergravity with a monopole background on a 2sphere. In four dimensions, there are two scalar fields, $X$ and $Y $, and the effective potential in the Einstein frame is an exponential with respect to $Y$ times a quadratic polynomial in the field $e^{X}$. When making the volume of the 2sphere large, namely for large values of $Y$, there appears a tower of states, which according to the infinite distance swampland conjecture becomes exponentially massless. We confront the model with recent cosmological observations. We show that this set up is well equipped to explain the overall data even when considering local measurements of $H_0$, and that it can potentially ameliorate the tension between lowredshift observations and measurements of the cosmic microwave background. Indeed, the tower of string states that emerges from the rolling of $Y$ constitutes a portion of the dark matter, and the way in which the $X$ particle and its KK excitations evolve over time (refer to as fading dark matter) is responsible for reducing the $H_0$ tension.
 Publication:

arXiv eprints
 Pub Date:
 November 2019
 arXiv:
 arXiv:1912.00242
 Bibcode:
 2019arXiv191200242A
 Keywords:

 High Energy Physics  Theory;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Phenomenology