Gluino Coannihilation Revisited

Some variants of the MSSM feature a strip in parameter space where the lightest neutralino is identified as the lightest supersymmetric particle (LSP), the gluino is the next-to-lightest supersymmetric particle (NLSP) and is nearly degenerate with the LSP, and the relic cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the gluino NLSP. We calculate the relic density along this gluino coannihilation strip in the MSSM, including the effects of gluino-gluino bound states and initial-state Sommerfeld enhancement, and taking into account the decoupling of the gluino and LSP densities that occurs for large values of the squark mass. We find that bound-state effects can increase the maximum LSP mass for which the relic cold dark matter density lies within the range favoured by astrophysics and cosmology by as much as ~ 50% if the squark to gluino mass ratio is 1.1, and that the LSP may weigh up to ~ 8 TeV for a wide range of the squark to gluino mass ratio \lesssim 100.Comment: 36 pages, 9 figures, matches version to appear in JHE

The MSSM Parameter Space with Non-Universal Higgs Masses

Without assuming that Higgs masses have the same values as other scalar masses at the input GUT scale, we combine constraints on the minimal supersymmetric extension of the Standard Model (MSSM) coming from the cold dark matter density with the limits from direct searches at accelerators such as LEP, indirect measurements such as b to s gamma decay and the anomalous magnetic moment of the muon. The requirement that Higgs masses-squared be positive at the GUT scale imposes important restrictions on the MSSM parameter space, as does the requirement that the LSP be neutral. We analyze the interplay of these constraints in the (mu, m_A), (mu, m_{1/2}), (m_{1/2}, m_0) and (m_A, tan beta) planes. These exhibit new features not seen in the corresponding planes in the constrained MSSM in which universality is extended to Higgs masses.Comment: 18 pages, latex, 10 eps figure

More on Electric Dipole Moment Constraints on Phases in the Constrained MSSM

We reconsider constraints on \cp-violating phases in the Constrained Minimal Supersymmetric Standard Model. We include the recent calculations of Ibrahim and Nath on the chromoelectric and purely gluonic contributions to the quark electric dipole moment and combine cosmological limits on gaugino masses with experimental bounds on the neutron (and electron) electric dipole moments. The constraint on the phase of the Higgs mixing mass $\mu$, |\thm|, is dependent on the value of the trilinear mass parameter, $A$, in the model and on $\tan \beta$. For values of |A| < 300 \gev at the GUT scale, we find |\thm|/\pi \la 0.05, while for |A| < 1500 \gev, |\thm|/\pi \la 0.3. Thus, we find that in principle, large CP violating phases are compatible with the bounds on the electric dipole moments of the neutron and electron, as well as remaining compatible with the cosmological upper bound on the relic density of neutralinos. The other \cp-violating phase \tha is essentially unconstrained.Comment: 11 pages in LaTeX + 4 postscript figures, uses epsf.sty. Added two references, clarified figures. Accepted to Physics Letter

Supersymmetric Dark Matter Candidates

After reviewing the theoretical, phenomenological and experimental motivations for supersymmetric extensions of the Standard Model, we recall that supersymmetric relics from the Big Bang are expected in models that conserve R parity. We then discuss possible supersymmetric dark matter candidates, focusing on the lightest neutralino and the gravitino. In the latter case, the next-to-lightest supersymmetric particle is expected to be long-lived, and possible candidates include spartners of the tau lepton, top quark and neutrino. We then discuss the roles of the renormalization-group equations and electroweak symmetry breaking in delimiting the supersymmetric parameter space. We discuss in particular the constrained minimal extension of the Standard Model (CMSSM), in which the supersymmetry-breaking parameters are assumed to be universal at the grand unification scale, presenting predictions from a frequentist analysis of its parameter space. We also discuss astrophysical and cosmological constraints on gravitino dark matter models, as well as the parameter space of minimal supergravity (mSUGRA) models in which there are extra relations between the trilinear and bilinear supersymmetry-breaking parameters, and between the gravitino and scalar masses. Finally, we discuss models with non-universal supersymmetry-breaking contributions to Higgs masses, and models in which the supersymmetry-breaking parameters are universal at some scale below that of grand unification. http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684Comment: 38 pages, 10 figure

Lower Limits on Soft Supersymmetry-Breaking Scalar Masses

Working in the context of the CMSSM, we argue that phenomenological constraints now require the universal soft supersymmetry-breaking scalar mass m_0 be non-zero at the input GUT scale. This conclusion is primarily imposed by the LEP lower limit on the Higgs mass and the requirement that the lightest supersymmetric particle not be charged. We find that m_0 > 0 for all tan beta if mu 0 only when tan beta sim 8 and one allows an uncertainty of 3+ GeV in the theoretical calculation of the Higgs mass. Upper limits on flavour-changing neutral interactions in the MSSM squark sector allow substantial violations of non-universality in the m_0 values, even if their magnitudes are comparable to the lower limit we find in the CMSSM. Also, we show that our lower limit on m_0 at the GUT scale in the CMSSM is compatible with the no-scale boundary condition m_0 = 0 at the Planck scale.Comment: 11 pages, latex, 6 eps figure

Maximal Sfermion Flavor Violation in Super-GUTs

We consider supersymmetric grand unified theories with soft supersymmetry-breaking scalar masses $m_0$ specified above the GUT scale (super-GUTs) and patterns of Yukawa couplings motivated by upper limits on flavour-changing interactions beyond the Standard Model. If the scalar masses are smaller than the gaugino masses $m_{1/2}$, as is expected in no-scale models, the dominant effects of renormalization between the input scale and the GUT scale are generally expected to be those due to the gauge couplings, which are proportional to $m_{1/2}$ and generation-independent. In this case, the input scalar masses $m_0$ may violate flavour maximally, a scenario we call MaxSFV, and there is no supersymmetric flavour problem. We illustrate this possibility within various specific super-GUT scenarios that are deformations of no-scale gravity.Comment: 38 pp, 16 figures. Change of title to describe better the scope of the work, minor comments added, one reference added, matches published versio

Re-Evaluation of the Elastic Scattering of Supersymmetric Dark Matter

We examine the cross sections for the elastic scattering of neutralinos $\chi$ on nucleons $p,n$, as functions of $m_\chi$ in the constrained minimal supersymmetric standard model. We find narrow bands of possible values of the cross section, that are considerably lower than some previous estimates. The constrained model is based on the minimal supergravity-inspired framework for the MSSM, with universal scalar and gaugino masses $m_0, m_{1/2}$, and $\mu$ and the MSSM Higgs masses treated as dependent parameters. We explore systematically the region of the $(m_{1/2}, m_0)$ plane where LEP and other accelerator constraints are respected, and the relic neutralino density lies in the range $0.1 \le \Omega_{\chi} h^2 \le 0.3$ preferred by cosmology. We update previous discussions of both the spin-independent and -dependent scattering matrix elements on protons and neutrons, using recent analyses of low-energy hadron experiments.Comment: 16 pages, latex, 14 eps figure

On the Feasibility of a Stop NLSP in Gravitino Dark Matter Scenarios

We analyze the possibility that the lighter stop {\tilde t_1} could be the next-to-lightest supersymmetric particle (NLSP) in models where the gravitino is the lightest supersymmetric particle (LSP). We do not find any possibility for a stop NLSP in the constrained MSSM with universal input soft supersymmetry-breaking masses at the GUT scale (CMSSM), but do find small allowed regions in models with non-universal Higgs masses (NUHM). We discuss the cosmological evolution of stop hadrons. Most {\tilde t_1}qq `sbaryons' and the corresponding `antisbaryons' annihilate with conventional antibaryons and baryons into {\tilde t_1}{\bar q} `mesinos' and the corresponding `antimesinos', respectively, shortly after the quark-hadron transition in the early Universe, and most mesinos and antimesinos subsequently annihilate. As a result, insufficient metastable charged stop hadrons survive to alter Big Bang nucleosynthesis.Comment: 31 pages, 14 figure

Charginos and Neutralinos in the Light of Radiative Corrections: Sealing the Fate of Higgsino Dark Matter

We analyze the LEP constraints from searches for charginos $\chi^{\pm}$ and neutralinos $\chi_i$, taking into account radiative corrections to the relations between their masses and the underlying Higgs-mixing and gaugino-mass parameters $\mu, m_{1/2}$ and the trilinear mass parameter $A_t$. Whilst radiative corrections do not alter the excluded domain in $m_{\chi^{\pm}}$ as a function of $m_{\chi^{\pm}} - m_{\chi}$, its mapping into the $\mu, m_{1/2}$ plane is altered. We update our previous lower limits on the mass of gaugino dark matter and on tan$\beta$, the ratio of Higgs vacuum expectation values, in the light of the latest LEP data and these radiative corrections. We also discuss the viability of Higgsino dark matter, incorporating co-annihilation effects into the calculation of the Higgsino relic abundance. We find that Higgsino dark matter is viable for only a very limited range of $\mu$ and $m_{1/2}$, which will be explored completely by upcoming LEP runs.Comment: Version to appear in Phys. Rev. D., 21 pages in LateX, including 10 encapsulated postscript figures; uses epsf.sty.; Figures modified (one deleted), conclusions unchange