Vassilis C. Spanos

Update on the Direct Detection of Supersymmetric Dark Matter

We compare updated predictions for the elastic scattering of supersymmetric neutralino dark matter with the improved experimental upper limit recently published by Cryogenic Dark Matter Search (CDMS) II. We take into account the possibility that the {pi}-nucleon {sigma} term may be somewhat larger than was previously considered plausible, as may be supported by the masses of exotic baryons reported recently. We also incorporate the new central value of m{sub t}, which affects indirectly constraints on the supersymmetric parameter space, for example, via calculations of the relic density. Even if a large value of {sigma} is assumed, the CDMS II data currently exclude only small parts of the parameter space in the constrained minimal standard model (CMSSM) with universal soft supersymmetry-breaking Higgs, squark, and slepton masses. None of the previously proposed CMSSM benchmark scenarios is excluded for any value of {sigma}, and the CDMS II data do not impinge on the domains of the CMSSM parameter space favored at the 90% confidence level in a recent likelihood analysis. However, some models with nonuniversal Higgs, squark, and slepton masses and neutralino masses < or approx. 700 GeV are excluded by the CDMS II data.

Gravitino dark matter in the CMSSM

We consider the possibility that the gravitino might be the lightest supersymmetric particle (LSP) in the constrained minimal extension of the Standard Model (CMSSM). In this case, the next-to-lightest supersymmetric particle (NSP) would be unstable, with an abundance constrained by the concordance between the observed light-element abundances and those calculated on the basis of the baryon-to-entropy ratio determined using CMB data. We modify and extend previous CMSSM relic neutralino calculations to evaluate the NSP density, also in the case that the NSP is the lighter stau, and show that the constraint from late NSP decays is respected only in a limited region of the CMSSM parameter space. In this region, gravitinos might constitute the dark matter.

Likelihood analysis of the constrained minimal supersymmetric standard model parameter space

We present a likelihood analysis of the parameter space of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the input scalar masses m0 and fermion masses m1/2 are each assumed to be universal. We include the full experimental likelihood function from the LEP Higgs search as well as the likelihood from a global precision electroweak fit. We also include the likelihoods for b → sγ decay and (optionally) gμ−2. For each of these inputs, both the experimental and theoretical errors are treated. We include the systematic errors stemming from the uncertainties in mt and mb, which are important for delineating the allowed CMSSM parameter space as well as calculating the relic density of supersymmetric particles. We assume that these dominate the cold dark matter density, with a density in the range favoured by WMAP. We display the global likelihood function along cuts in the (m1/2, m0) planes for tan β = 10 and both signs of μ, tanβ = 35, μ < 0 and tanβ = 50, μ > 0, which illustrate the relevance of gμ − 2 and the uncertainty in mt. We also display likelihood contours in the (m1/2, m0) planes for these values of tanβ. The likelihood function is generally larger for μ > 0 than for μ < 0, and smaller in the focus-point region than in the bulk and coannihilation regions, but none of these possibilities can yet be excluded. CERN–TH/2003-262 October 2003

Nucleosynthesis constraints on a massive gravitino in neutralino dark matter scenarios

The decays of massive gravitinos into neutralino dark matter particles and Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may alter the primordial light-element abundances. We present here details of a new suite of codes for evaluating such effects, including a new treatment based on PYTHIA of the evolution of showers induced by hadronic decays of massive, unstable particles such as a gravitino. We present several sets of results obtained using these codes, including general constraints on the possible lifetime and abundance of an unstable particle decaying into neutralino dark matter under various hypotheses for its decay mechanism. We also develop an analytical treatment of non-thermal hadron propagation in the early universe, and use this to derive analytical estimates for light-element production and in turn on decaying particle lifetimes and abundances, which confirm our numerical results and illuminate the underlying physics. We then consider specifically the case of an unstable massive gravitino within the constrained minimal supersymmetric extension of the Standard Model (CMSSM). We present upper limits on its possible primordial abundance before decay for different possible gravitino masses, with CMSSM parameters along strips where the lightest neutralino provides all the astrophysical cold dark matter density. We do not find any CMSSM solution to the cosmological 7Li problem for small m3/2. Discounting this, for m1/2 ~ 500 GeV and tan β = 10 the other light-element abundances impose an upper limit m3/2n3/2/nγ 3 × 10−12 GeV to 2 × 10−13 GeV for m3/2 = 250 GeV to 1 TeV, which is similar in both the coannihilation and focus-point strips and somewhat weaker for tan β = 50, particularly for larger m1/2. The constraints also weaken in general for larger m3/2, and for m3/2 > 3 TeV we find a narrow range of m3/2n3/2/nγ, at values which increase with m3/2, where the 7Li abundance is marginally compatible with the other light-element abundances.

Very constrained minimal supersymmetric standard models

We consider very constrained versions of the minimal supersymmetric extension of the Standard Model (VCMSSMs) which, in addition to constraining the scalar masses m0 and gaugino masses m1/2 to be universal at some input scale, impose relations between the trilinear and bilinear soft supersymmetry breaking parameters A0 and B0. These relations may be linear, as in simple minimal supergravity models, or nonlinear, as in the GiudiceMasiero mechanism for generating the Higgs-mixing µ term. We discuss the application of the electroweak vacuum conditions in VCMSSMs, which may be used to make a prediction � � � = � � � �

Phenomenological constraints on patterns of supersymmetry breaking

Specic models of supersymmetry breaking predict relations between the trilinear and bilinear soft supersymmetry breaking parameters A0 and B0 at the input scale. In such models, the value of tan can be calculated as a function of the scalar masses m0 and the gaugino masses m1=2, which we assume to be universal. The experimental constraints on sparticle and Higgs masses, b ! s decay and the cold dark matter density CDMh 2 can then be used to constrain tan in such specic models of supersymmetry breaking. In the simplest Polonyi model with A0 =( 3 p 3)m0 = B0 + m0, we nd 11 0( 0, and the range 1:25 < A0=m0 < 4:8 for <0. In these models, we nd no solutions in the rapid-annihilation ‘funnels’ or in the ‘focus-point’ region. We also discuss the allowed range of tan in the no-scale model with A0 = B0 =0 . In all these models, most of the allowed regions are in the ~ 1 coannihilation ‘tail’.

Dark matter direct searches and the anomalous magnetic moment of muon

Abstract In the framework of the Constrained Minimal Supersymmetric Standard Model (CMSSM) we discuss the impact of the recent experimental information, especially from E821 Brookhaven experiment on g μ −2 along with the light Higgs boson mass bound from LEP, to the dark matter direct searches. Imposing these experimental bounds, the maximum value of the spin-independent neutralino–nucleon cross section turns out to be of the order of 10 −8 pb for large values of tan β and low M 1/2 , m 0 . The effect of the recent experimental bounds is to decrease the maximum value of the cross section by about an order of magnitude, demanding the analogous sensitivity from the direct dark matter detection experiments.

Prospects for sparticle discovery in variants of the MSSM

Abstract We discuss the prospects for detecting supersymmetric particles in variants of the minimal supersymmetric extension of the Standard Model (MSSM), in light of laboratory and cosmological constraints. We first assume that the lightest supersymmetric particle (LSP) is the lightest neutralino χ, and present scatter plots of the masses of the two lightest visible supersymmetric particles when the input scalar and gaugino masses are constrained to be universal (CMSSM), when the input Higgs scalar masses are non-universal (NUHM), and when the squark and slepton masses are also non-universal and the MSSM is regarded as a low-energy effective field theory valid up to the GUT scale (LEEST) or just up to 10 TeV (LEEST10). We then present similar plots in various scenarios when the LSP is the gravitino. We compare the prospects for detecting supersymmetry at linear colliders (LCs) of various energies, at the LHC, and as astrophysical dark matter. We find that, whilst a LC with a centre-of-mass energy E CM ⩽ 1000 GeV has some chance of discovering the lightest and next-to-lightest visible supersymmetric particles, E CM ⩾ 3000 GeV would be required to ‘guarantee’ finding supersymmetry in the neutralino LSP scenarios studied, and an even higher E CM might be required in certain gravitino dark matter scenarios. Direct dark matter experiments could explore part of the low-mass neutralino LSP region, but would not reveal all the models accessible to a low-energy LC.

On the interpretation of

We discuss the interpretation of present and possible future experimental constraints on B_s to mu^+ mu^- decay in the context of the constrained minimal extension of the Standard Model (CMSSM) with universal scalar masses. We emphasize the importance of including theoretical and other experimental uncertainties in calculating the likelihood function, which can affect significantly the inferred 95% confidence-level limit on the CMSSM parameters. The principal uncertainties are the B_s meson decay constant, m_t and m_b. The latter induce uncertainties in the mass of the charged Higgs boson that dominates the B_s to mu^+ mu^- decay amplitude at large tan beta, reducing the CMSSM region excluded by present and possible future limits from the Fermilab Tevatron collider and the LHC.

B_s \to \mu^{+} \mu^{-}

We show that present experimental constraints on Bs→μ+μ− decay and the CDMS upper limit on the cold dark matter elastic scattering cross section already have significant impact on the parameter space of the minimal supersymmetric extension of the Standard Model (MSSM) with non-universal supersymmetry-breaking scalar masses for the Higgs multiplets (NUHM). The relaxation of scalar universality in the MSSM allows the possibility of a relatively light mass MA for the pseudoscalar Higgs boson. The present upper limit on Bs→μ+μ− already excludes much of the scope for this possibility in the NUHM, in contrast to the constrained MSSM with universal scalar masses (CMSSM), where Bs→μ+μ− decay does not exclude any ranges of parameters not already excluded by b→sγ decay. Cold dark matter scattering is also enhanced for small MA, but the impact of present upper limit on Bs→μ+μ− on the NUHM parameter space is in many cases greater than that of the CDMS scattering limit, particularly at large tan β.