H0 tension and the string swampland

Abstract

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 Cvetič-Gibbons-Pope. The model describes a compactification of six-dimensional 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 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.

The shadow of dark matter as a shadow of string theory: string origin of the dipole term

“…This motivates the assignments of indices to the components of the 2D Dirac spinor in the Weyl basis: (ψ √ + ) 2 and (ψ √ − ) 2 transform like the components of a tangent vector in the lightcone basis.…”

“…It can be imposed on C μν using the KR gauge symmetry (2) while preserving Lorentz gauge for B μ , see Appendix B. 2 There is also another possibility. In multi-scale string theories with different kinds of strings with different tensions T s , T s , the Kalb-Ramond picture might correspond to an effective intermediate energy theory for energies T s E T s , such that for the high scale string modes an effective field theory description applies, whereas for the lowscale strings the world sheet description is still needed.…”

“…Comparison with the operator (54) in Coulomb gauge shows that the single transverse physical polarization in Lorentz gauge is (1) μ (k) (2) ν (k) −…”

“…It is an intriguing possibility that dark matter might provide a window into low energy string phenomenology, e.g. through the swampland conjecture leading to fading dark matter within a tower of light string states [1,2], or through models where a low string scale [3,4] implies phenomenologically acceptable dark axions or dark gauge bosons [5][6][7][8]. It has been pointed out recently [9] that electroweak dipole dark matter [10,11] may open a window into low energy string phenomenology through the Kalb-Ramond field.…”

“…The string equations of motion which follow from (1) are invariant under the KR gauge symmetry (2) and under the U (1) gauge transformation B μ → B μ + ∂ μ f , and these gauge symmetries are preserved through addition of a field theory action for the gauge fields,…”