Mixed axion/neutralino cold dark matter in supersymmetric models

Abstract

We consider supersymmetric (SUSY) models wherein the strong CP problem is solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino supermultiplet. We examine R-parity conserving models where the neutralino is the lightest SUSY particle, so that a mixture of neutralinos and axions serve as cold dark matter (a Z 1 CDM). The mixed a Z 1 CDM scenario can match the measured dark matter abundance for SUSY models which typically give too low a value of the usual thermal neutralino abundance, such as models with wino-like or higgsino-like dark matter. The usual thermal neutralino abundance can be greatly enhanced by the decay of thermally-produced axinos (ã) to neutralinos, followed by neutralino re-annihilation at temperatures much lower than freeze-out. In this case, the relic density is usually neutralino dominated, and goes as ∼ (f a /N )/m 3/2 a . If axino decay occurs before neutralino freeze-out, then instead the neutralino abundance can be augmented by relic axions to match the measured abundance. Entropy production from late-time axino decays can diminish the axion abundance, but ultimately not the neutralino abundance. In a Z 1 CDM models, it may be possible to detect both a WIMP and an axion as dark matter relics. We also discuss possible modifications of our results due to production and decay of saxions. In the appendices, we present expressions for the Hubble expansion rate and the axion and neutralino relic densities in radiation, matter and decaying-particle dominated universes.

Probing light higgsinos in natural SUSY from monojet signals at the LHC

“…This makes the standard thermally produced WIMP dark matter inadequate in the natural MSSM. In order to provide the required relic density, several alternative ways have been proposed [60][61][62][63][64][65], such as choosing the axion-higgsino admixture as the dark matter [66,67]. In this case, the spin-independent neutralino-proton scattering cross section σ SI p must be re-scaled by a factor Ωχ0 1 h 2 /Ω PL h 2 [66,67], where Ω PL h 2 is the relic density measured by Planck satellite [68].…”

Thermal effects on saxion in supersymmetric model with Peccei–Quinn symmetry

“…To see when there may exist such a problem, we calculate the density of the oscillating saxion. The yield variable of the saxion is estimated as 19) where σ R is the saxion amplitude at T = T R , andm σ is the effective mass of saxion which may include the effect of the Hubble-induced mass. In our numerical analysis, we use g * (T R ) = 228.75.…”

Dark radiation constraints on mixed Axion/Neutralino dark matter

“…In Ref. [20], this avenue was pushed much further, where analytic formulae were presented for both neutralino and axion production in either radiation-, matter-or decay-dominated universes. The effect of saxion production and entropy injection from late-time saxion decays was also considered.…”

“…This effect allowed much higher values of f a ∼ 10 13 − 10 15 GeV to be cosmologically allowed, even for θ i as large as ∼ 0.1. While the semi-analytic approach presented in [19,20] and [31] is applicable in many cases, there also exist numerous cases where a fully numeric solution to the coupled Boltzmann equations is required. Such cases include the possibility of bino-like neutralinos where σv is variable with temperature T instead of constant, and where multiple processes of neutralino injection or entropy dilution are possible, such as simultaneously accounting for axino, axion, neutralino and saxion production and possible decays.…”

“…[20,31] and references therein). In the general case both saxions and axinos can dominate the universe and inject entropy at different times, which can lead to quite involved scenarios.…”