$H_0$ tension and the String Swampland. (arXiv:1912.00242v1 [hep-th])
<a href="http://arxiv.org/find/hep-th/1/au:+Anchordoqui_L/0/1/0/all/0/1">Luis A. Anchordoqui</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Antoniadis_I/0/1/0/all/0/1">Ignatios Antoniadis</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Lust_D/0/1/0/all/0/1">Dieter Lust</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Soriano_J/0/1/0/all/0/1">Jorge F. Soriano</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Taylor_T/0/1/0/all/0/1">Tomasz R. Taylor</a>
We realize the Agrawal-Obied-Vafa swampland proposal of fading dark matter
for solving the $H_0$ tension by the model of Salam-Sezgin and its string
realization of Cvetic-Gibbons-Pope. The model describes a compactification of
six-dimensional supergravity with a monopole background on a 2-sphere. 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
2-sphere 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 low-redshift 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.
We realize the Agrawal-Obied-Vafa swampland proposal of fading dark matter
for solving the $H_0$ tension by the model of Salam-Sezgin and its string
realization of Cvetic-Gibbons-Pope. The model describes a compactification of
six-dimensional supergravity with a monopole background on a 2-sphere. 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
2-sphere 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 low-redshift 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.
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