Lower bound on the neutralino mass from new data on CMB and implications for relic neutralinos

Abstract

In the frame of an effective MSSM model without gaugino-mass unification at a grand unification scale, we set a lower bound on the neutralino mass based on the new WMAP data on ΩCDM (R-parity conservation is assumed). Our lower bound, mχ > ∼ 6 GeV, leaves much room for relic neutralinos significantly lighter than those commonly considered (mχ > ∼ 50 GeV). We prove that these light neutralinos may produce measurable effects in WIMP direct detection experiments of low energy threshold and large exposure.

Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification

“…In Refs. [1,2] we also showed that direct detection rates for light relic neutralinos make these particles detectable with WIMP direct search experiments with current technologies. A comparison of our predictions with intervening experimental results was presented in Ref.…”

“…The relic abundance Ω χ h 2 of neutralinos lighter than 50 GeV which arise in our class of gaugino non-universal models has a relatively simple structure in terms of dominant diagrams in the annihilation cross section [1,2]. Here we just remind that combining our calculation of the relic abundance of light neutralinos with the value of (Ω CDM h 2 ) max , an absolute lower bound on the neutralino mass of 6 GeV can be set [1,2].…”

“…This range for R implies that the accelerator lower bound on the neutralino mass can be moved down to few GeV for R ∼ 0.01. The ensuing light neutralinos have a dominant bino component; a deviation from a pure bino composition is mainly due to a mixture ofB withH • 1 [1,2,3]. Notice that our range of R includes also the usual model with gaugino-mass universality.…”

“…Here we just remind that combining our calculation of the relic abundance of light neutralinos with the value of (Ω CDM h 2 ) max , an absolute lower bound on the neutralino mass of 6 GeV can be set [1,2]. We note that within our present scanning of the supersymmetric parameter space, the lower limit on the neutralino mass shifts to about 7 GeV, when the upper bound on BR(B s → µ + +µ − ) < 7.5·10 −7 is implemented (this constraint was not included in [1,2]). It is remarkable that a lower limit on m χ is set not by searches at accelerators, but instead by cosmological arguments.…”

“…In Refs. [1,2] we discussed the properties of these light neutralinos as relic particles (R-parity conservation is assumed) and showed that an absolute lower limit of 6 GeV on the neutralino mass m χ can be placed by applying the most recent determinations of the upper bound on the Cold Dark Matter (CDM) content in the Universe, in combination with constraints imposed on the Higgs and supersymmetric parameters by measurements at colliders and other precision experiments, like the muon anomalous magnetic moment and the rare decay b → s + γ. In Refs.…”