Neutralino Relic Abundance Research Articles

Gaugino and higgsino coannihilations I: neutralino-neutralino interactions

We present exact analytic cross sections for all neutralino-neutralino coannihilations into two-body tree level final states. These expressions allow the calculation of important contributions to the neutralino relic abundance over large regions of mSUGRA parameter space and are particularly useful in theories with non-universal gaugino masses.

Neutralino dark matter in non-universal SUSY models

The properties of neutralino dark matter in the context of different supergravity schemes are reviewed. In particular, we discuss the effects induced by the relaxation, at the grand unification scale, of the soft scalar mass universality on the supersymmetric parameter space, on the neutralino relic abundance, and on the event rates for direct and indirect detection of relic neutralinos.

Neutralino dark matter in supersymmetric models with non-universal scalar mass terms

Neutralino dark matter is studied in the context of a supergravity scheme where the soft scalar mass terms are not constrained by universality conditions at the grand unification scale. We analyse in detail the consequences of the relaxation of this universality assumption on the supersymmetric parameter space, on the neutralino relic abundance and on the event rate for the direct detection of relic neutralinos.

On the neutralino as dark matter candidate. I. Relic abundance

The neutralino relic abundance is evaluated for a wide range of the neutralino mass, 20 GeV ≤ m x ≤ 1 TeV, by taking into account the full set of final states in the neutralino-neutralino annihilation. The analysis is performed in the Minimal SuSy Standard Model; it is not restricted by stringent GUT assumptions but only constrained by present experimental bounds. We also discuss phenomenological aspects which are employed in the companion paper (Part II. Direct detection) where the chances for a successful search for dark matter neutralino are investigated.

Simplest, string-derivable, supergravity model and its experimental predictions.

We present the simplest, string-derivable, supergravity model and discuss its experimental consequences. This model is a new string-inspired flipped $SU(5)$ which unifies at the string scale $M_U=10^{18}\GeV$ due to the introduction of an additional pair of \r{10},\rb{10} flipped $SU(5)$ representations which contain new intermediate scale `gap' particles. We study various model-building issues which should be addressed in string-derived incarnations of this model. We focus our study on the no-scale supergravity mechanism and explore thoroughly the three-dimensional parameter space of the model ($m_{\tilde g},m_t,\tan\beta$), thus obtaining several simple relationships among the particle masses, such as: $m_{\tilde q}\approx m_{\tilde g}$, $m_{\tilde e_L}\approx m_{\tilde\nu}\approx0.30 m_{\tilde g}$, $m_{\tilde e_R}\approx0.18m_{\tilde g}$, and $m_{\chi^0_2}\approx2m_{\chi^0_1}\approx m_{\chi^\pm_1}$. In a strict interpretation of the no-scale supergravity scenario we solve for $\tan\beta$ as a function of $m_t$ and $m_{\tilde g}$, and show that $m_t$ determines not only the sign of the Higgs mixing parameter $\mu$ but also whether the lightest Higgs boson mass is above or below $100\GeV$. We also find that throughout the parameter space the neutralino relic abundance is within observational bounds ($\Omega_\chi h^2_0\lsim0.25$) and may account for a significant portion of the dark matter in the Universe.

LEP and radiative electroweak breaking close to the light gluino window

Wer show that the LEP lower bound on the chargino mass, in conjunction with the well motivated theoretical requirement of radiative electroweak symmetry breaking, imply an upper bound on the lightest Higgs boson mass (mh ⪅ 62 GeV) in a supersymmetry breaking scenario where the gluino mass is a few GeV. Moreover, Higgs searches at LEP in the context of this model require mh ⪆ 61 GeV. The remaining experimentally allowed region in the five-dimensional parameter space of this light gluino model is severely fine-tuned (with tan β = 1.88−1.89 and mt = 114.0–114.3 GeV) and cosmologically troublesome (with a neutralino relic abundance over five-hundred time larger than allowed). Modest improvements in sensitivity in LEP Higgs searches and Tevatron top-quark searches should soon exclude this theoretically disfavored model completely.

Implications for minimal supersymmetry from grand unification and the neutralino relic abundance

We examine various predictions of the minimal supersymmetric standard model coupled to minimal supergravity. The previously considered predictions of the model are now extended to include the bottom quark mass and the neutralino relic density which in turn provide stringent bounds on the scale parameters. We find a remarkable consistency among several different constraints only in the region of low-energy supersymmetry, thus avoiding the use of the fine tuning criterion. We find all supersymmetric particle masses preferably within the reach of future supercolliders (LHC and SSC). The requirement that the neutralino be the dominant component of (dark) matter in the flat Universe provides a lower bound on the spectrum of supersymmetric particles beyond the reach of LEP, and most likely also the Tevatron and LEP 200.

New constraints on neutralino dark matter in the supersymmetric standard model.

We investigate the prospects for neutralino dark matter within the supersymmetric standard model (SSM) including the constraints from universal soft supersymmetry breaking and radiative breaking of the electroweak symmetry. The latter is enforced by using the one-loop Higgs effective potential which automatically gives the one-loop-corrected Higgs-boson masses. The radiative breaking constraint imposes novel correlations between the traditional relic density variables and makes the Higgs-boson masses variable and generally heavy throughout the allowed parameter space. We perform an exhaustive search of this five-dimensional space and find that the neutralino relic abundance ${\ensuremath{\Omega}}_{\ensuremath{\chi}}{h}_{0}^{2}$ depends most strongly on the ratio ${\ensuremath{\xi}}_{0}=\frac{{m}_{0}}{{m}_{\frac{1}{2}}}$. For ${\ensuremath{\xi}}_{0}\ensuremath{\gg}1$ the relic abundance is almost always much too large, wheras for ${\ensuremath{\xi}}_{0}\ensuremath{\ll}1$ the opposite occurs. For ${\ensuremath{\xi}}_{0}\ensuremath{\sim}1$ there are wide ranges of the remaining parameters for which ${\ensuremath{\Omega}}_{\ensuremath{\chi}}\ensuremath{\sim}1$. We also determine that ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{l}}\ensuremath{\gtrsim}100$ GeV is necessary in order to possibly achieve ${\ensuremath{\Omega}}_{\ensuremath{\chi}}\ensuremath{\sim}1$. Moreover, for ${m}_{{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{t}}_{1}}\ensuremath{\gtrsim}45(100)$ GeV ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}}\ensuremath{\gtrsim}170(250)$ GeV is also required.

A new investigation on neutralino dark matter: relic density and detection rates

The main properties of the neutralino dark matter are revisited in the light of the new theoretical developments in Susy theories and of the recent constraints from accelerators and underground experiments. The neutralino relic abundance and the detection rates relevant for direct and indirect searches are evaluated in the minimal supersymmetric standard model (MSSM) with the full inclusion of the (one-loop) radiative corrections, both to the Higgs masses and to the trilinear Higgs self-coupling. The relevance of these corrections for the neutralino-neutralino annihilation cross-section, and thus for the relic density, is discussed in detail. Large regions of the parameter space are considered, including those where the neutralino only provides a fraction of the local dark matter density; in these domains the standard value for the local density is appropriately scaled down. Some general properties of the detection rates as functions of the MSSM parameters are also elucidated; in particular it is shown that in the regions of the parameter space where scaling of the local density occurs, the rates are largely independent of two of the model free parameters. The relevance of the Kamiokande upper bounds to the upgoing muon fluxes is discussed in connection with the possible neutrino outputs from the Earth and from the Sun due to neutralino accumulation and annihilation in these macroscopic bodies. Finally, the complementarity between the search for neutralino dark matter and the discovery potential of future accelerators is discussed.

Relic abundance of the neutralino in the grand unified theories coupled to N=1 supergravity.

The relic abundance of the lightest neutralino is calculated in the scheme of grand unified theories (GUT's) coupled to $N=1$ supergravity. We take ${m}_{\frac{3}{2}}$, ${M}_{\mathrm{gX}}$, and ${m}_{\mathrm{sX}}$ as free parameters, where ${m}_{\frac{3}{2}}$ is the gravitino mass, ${M}_{\mathrm{gX}}$ the universal gaugino mass at the GUT scale, and ${m}_{\mathrm{sX}}$ the supersymmetric Higgs-boson mass at that scale. Even after we impose the experimental and cosmological constraints, it is found that there remains some supersymmetric parameter region and the lightest neutralino with a mass below about 500 GeV can be the dark matter of the Universe. In particular, the abundance of the neutralino can amount to the critical density of the Universe and is consistent with the inflationary universe scenario which naturally solves the "gravitino problem" is supergravity theories.

DIRECT VERSUS INDIRECT SEARCHES FOR NEUTRALINO DARK MATTER

Direct search for neutralino dark matter is analyzed in the framework of the minimal supersymmetric extension of the standard model, using a realistic evaluation of the neutralino relic abundance which also includes radiative corrections to the Higgs masses. Relevance of the present (Ge detectors) experimental data to set constraints on the parameters of the model is discussed and expectations for future experiments which involve neutralino-nucleus coherent processes are investigated. These results are compared to those obtained in a previous paper from indirect search data. In the present analysis particular attention is paid to the theoretical uncertainties due to the different estimates of the Higgs-nucleon coupling strength.

Neutralino dark matter after LEP 200

I discuss some possible implications from LEP 200 on the lightest neutralino of the minimal supersymmetry, especially as a candidate for the dark matter in the Universe. I show that a non-discovery of a chargino would essentially rule out higgsino-like neutralinos below m w , which are already strongly disfavored by naturalness, and place a rather mild lower bound of about 40 GeV on the mass of gaugino-like neutralinos. Even one charged sfermion with mass below about 80 GeV, if discovered at LEP 200, would imply a deficit of the neutralino relic abundance in the flat Universe in the natural regions of the parameter space. Thus, the cosmologically favored range of sfermion masses lies beyond the reach of LEP 200.