Dark matter neutralinos in the constrained minimal supersymmetric model (CMSSM) may account for the recent cosmic ray electron and positron observations reported by the PAMELA and ATIC experiments either through self annihilation or via decay. However, to achieve this, both scenarios require new physics beyond the 'standard' CMSSM, and a unified explanation of the two experiments suggests a neutralino mass of order 700 GeV - 2 TeV. A relatively light neutralino with mass around 100 GeV (300 GeV) can accomodate the PAMELA but not the ATIC observations based on a model of annihilating (decaying) neutralinos. We study the implications of these scenarios for Higgs and sparticle spectroscopy in the CMSSM and highlight some benchmark points. An estimate of neutrino flux expected from the annihilating and decaying neutralino scenarios is provided.
It is generally accepted that nearly 23% of the universe's energy density resides in the form of non-luminous 'dark' matter [1]. This is a new form of matter which is non-baryonic and manifests itself primarily through its gravitational interactions. The highly successful Standard Model (SM) of strong, weak and electromagnetic interactions does not possess a viable dark matter candidate. Thus, new physics beyond the SM is required to incorporate dark matter, and many potential dark matter candidates have been proposed in the literature [2].
Supersymmetry, more precisely MSSM, (minimal supersymmetric SM), with R-parity conservation, is arguably the most compelling extension of the SM. The MSSM predicts the existence of a stable new elementary particle called the neutralino (lightest supersymmetric particle). With mass of order 100 GeV -TeV, the thermal relic abundance of the lightest neutralino has the right order of magnitude to account for the observed dark matter density.
Many recent investigations of the MSSM have focused on a theoretically well motivated special case called the CMSSM [3] (constrained MSSM, based on supergravity) which is far more predictive than the generic MSSM version. The latter can have more than a hundred free parameters, in contrast to the CMSSM with just 5 or so parameters. In these investigations the stable neutralino is usually found to be relatively light (100-few hundred GeV), and its indirect discovery relies on detecting cosmic ray signals (including positrons, antiprotons, gamma rays, etc.) from neutralino decay or pair annihilation in the galactic halo, galactic center, and the haloes of nearby galaxies.
The PAMELA experiment is currently taking data of high energy anti-proton and positron fluxes, and their most recent publication claims a significant positron ’excess’ [4] with no corresponding anti-proton excess [5]. This result appears to confirm previous results from HEAT [6] and AMS [7] within the error bars. It has been pointed out that pulsars and/or other nearby astrophysical sources may account for the PAMELA results [8,9]. More recently, the ATIC experiment [10] (see also PPB-BETS [11]) has reported an appreciable flux of electrons and positrons at energies around 100 -800 GeV, which appears to be considerably higher than the expected background at these energies. A unified explanation of the PAMELA and ATIC experiments involving neutralino as the dark matter candidate could be based on one of the following two mechanisms:
• The dark matter is a stable neutralino with mass around 700 GeV which primarily annihilates into leptons through new interactions which lie outside the MSSM framework [12]. Depending on the framework chosen, this scenario also invokes some ‘boost’ factor physics such as Sommerfeld enhancement [13].
• The dark matter is not entirely stable [14,15] but extremely long-lived, with a lifetime ∼ 10 26 sec. For neutralino dark matter, one could introduce suitably ’tiny’ R (or ‘matter’) -parity violating couplings which satisfy the lifetime constraint and allow the neutralino to decay primarily into leptons. The tiny (∼ 10 -13 ) Rparity violating couplings can be understood through non-renormalizable couplings with additional discrete symmetries [16]. A simple example of this is provided by the R-parity violating superpotential coupling LLE c , which leads to a three-body decay mode for the neutralino [14]. With a neutralino mass of around 2 TeV, this can simultaneously explain the PAMELA and ATIC data.
If one ignores say the ATIC result, it is possible to explain the PAMELA observations with a decaying neutralino of mass ∼ 300 GeV, which would make supersymmetry, and in particular the sparticles, far more accessible at the LHC. Even lighter (∼ 100 GeV) neutralino mass is feasible in the annihilation scenario.
Motivated by the PAMELA and ATIC observations we have performed an ISAJET [17] based analysis of CMSSM spectrocopy in which particular attention is paid to those regions of the CMSSM parameter space which contain heavy (∼ 300 GeV -2 TeV) neutralinos, with a relic abundance consistent with the WMAP 5 dark matter bounds [1], and which provide a unified explanation of the PAMELA and ATIC observations. The plan of the paper is as follows. We summarize the observations by PAMELA/ATIC experiments in Section II and review their implications in the context of dark matter decays or annihilations in Section III. In Section IV an estimate of neutrino flux expected from the annihilating and decaying neutralino scenarios is provided. Section V discusses how the CMSSM could be supplemented by new physics while preserving the neutralino cold dark matter framework. We outline in Section VI the procedure that we use to scan the CMSSM parameter space and the various experimental bounds that we take into account. In Section VII we present plots displaying the relevant CMSSM parameter space and highlight in Tables I and II a few benchmark points that are co
This content is AI-processed based on open access ArXiv data.
