Abstract
In anomaly-mediated supersymmetry breaking, superpartners in a hidden sector have masses that are proportional to couplings squared and so naturally freeze out with the desired dark matter relic density for a large range of masses. We present an extremely simple realization of this possibility, with WIMPless dark matter arising from a hidden sector that is supersymmetric QED with ${N}_{F}$ flavors. Dark matter is multicomponent, composed of hidden leptons and sleptons with masses anywhere from 10 GeV to 10 TeV, and hidden photons provide the thermal bath. The dark matter self-interacts through hidden sector Coulomb scatterings that are potentially observable. In addition, the hidden photon contribution to the number of relativistic degrees of freedom is in the range $\ensuremath{\Delta}{N}_{\mathrm{eff}}\ensuremath{\sim}0--2$, and, if the hidden and visible sectors were initially in thermal contact, the model predicts $\ensuremath{\Delta}{N}_{\mathrm{eff}}\ensuremath{\sim}0.2--0.4$. Data already taken by Planck may provide evidence of such deviations.
Highlights
The thermal relic density of a particle X has the parametric dependence ΩX ∝ 1 σanv ∼ m2X gX4 (1)where σanv is the thermally-averaged product of the annihilation cross section and relative velocity, and mX and gX are the characteristic mass scale and coupling determining this cross section
As in the case of WIMPs, the thermal relic density of these particles is directly related to the mechanism of electroweak symmetry breaking and is naturally of the right order of magnitude to be dark matter
In contrast to WIMPs, the dark matter has a mass that may be anywhere from ∼ 10 GeV to 10 TeV, and it has interesting astrophysical implications that are absent for WIMPs
Summary
Where σanv is the thermally-averaged product of the annihilation cross section and relative velocity, and mX and gX are the characteristic mass scale and coupling determining this cross section. To realize the WIMPless scenario fully, the dark matter candidate must (1) be stable on cosmological time scales and (2) annihilate to light particles, i.e., the thermal bath, with cross section σan ∼ gX4 /m2X. The model must satisfy basic constraints, such as vacuum stability and perturbativity, and the dark matter’s properties must be consistent with all experimental and observational constraints These are not trivial constraints in the context of AMSB models, in which all superpartner masses are determined by a small number of low-energy parameters. This property makes the scenarios more predictive, a highly laudable feature given the usual standards of hidden sector scenarios. For all values of μ, irrespective of how it is generated, we see that this scenario cannot provide a viable WIMPless dark matter model
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