General analysis of dark radiation in sequestered string models

Abstract

Abstract:We perform a general analysis of axionic dark radiation produced from the decay of the lightest modulus in the sequestered LARGE Volume Scenario. We discuss several cases depending on the form of the Kähler metric for visible sector matter fields and the mechanism responsible for achieving a de Sitter vacuum. The leading decay channels which determine dark radiation predictions are to hidden sector axions, visible sector Higgses and SUSY scalars depending on their mass. We show that in most of the parameter space of split SUSY-like models squarks and sleptons are heavier than the lightest modulus. Hence dark radiation predictions previously obtained for MSSM-like cases hold more generally also for split SUSY-like cases since the decay channel to SUSY scalars is kinematically forbidden. However the inclusion of string loop corrections to the Kähler potential gives rise to a parameter space region where the decay channel to SUSY scalars opens up, leading to a significant reduction of dark radiation production. In this case, the simplest model with a shift-symmetric Higgs sector can suppress the excess of dark radiation ∆N eff to values as small as 0.14, in perfect agreement with current experimental bounds. Depending on the exact mass of the SUSY scalars all values in the range 0.14 ∆N eff 1.6 are allowed. Interestingly dark radiation overproduction can be avoided also in the absence of a Giudice-Masiero coupling.

Global embedding of fibre inflation models

“…where (for 27) for natural values C W ∼ W 0 ∼ O(1), g s ∼ O(0.1) and |λ| ∼ O(10 −3 ) [39]. The term proportional to U is therefore suppressed by both |U | 1 and τ f 1, and so it can be…”

“…This is crucial to have full control over the inflationary dynamics since it determines the properties of all directions orthogonal to the inflaton and fixes all the mass and energy scales in the model. On top of moduli stabilisation, other important issues to trust inflationary models building are the study of the post-inflationary cosmological history starting with reheating [9][10][11][12][13] and the interplay between inflation and other phenomenological implications of the same model like the supersymmetry breaking scale [14][15][16][17][18], the nature of dark matter [19][20][21][22][23] and dark radiation [24][25][26][27] or the origin of the matter-antimatter asymmetry [28,29].…”

Moduli stars

“…A b = 1, g s = 0.1 and 10 −1 a b 1) and therefore θ b is a good candidate to be ULDM, although lighter and less constrained 6 The volume axion has a rih phenomenology, as it can act as dark radiation [81][82][83]. 7 Notice that even though it is relatively easy to get axion masses in the ULA range from non-perturbative effects in string theory, as discussed for instance in [63], generically, the closed string moduli τ will receive a mass of the same order as the corresponding axion (since the superpotential is holomorphic) which would violate fifth force bounds.…”

Light higgsino dark matter from non-thermal cosmology

“…The mechanism responsible to make the moduli massive fixes also all the main energy scales of a string compactification like the string scale, the Kaluza-Klein scale, the inflationary scale and the SUSY-breaking scale. The presence of such scalar fields has also a very important impact on cosmology since they can both drive inflaton in the very early universe, and affect the post-inflationary evolution of our universe [61][62][63][64][65][66][67][68].…”