Exact Cross Sections for the Neutralino-Slepton Coannihilation

Coannihilation processes provide an important additional mechanism for reducing the density of stable relics in the Universe. In the case of the stable lightest neutralino of the MSSM, and in particular the Constrained MSSM (CMSSM), the coannihilation with sleptons plays a major role in opening up otherwise cosmologically excluded ranges of supersymmetric parameters. In this paper, we derive a full set of exact, analytic expressions for the coannihilation of the lightest neutralino with the sleptons into all two--body tree--level final states in the framework of minimal supersymmetry. We make no simplifying assumptions about the neutralino nor about sfermion masses and mixings other than the absence of explicit CP--violating terms and inter--family mixings. The expressions should be particularly useful in computing the neutralino WIMP relic abundance without the approximation of partial wave expansion. We illustrate the effect of our analytic results with numerical examples and demonstrate a sizeable difference with approximate expressions available in the literature.Comment: LaTeX, 46 pages, 8 eps figure

A Simple Way of Calculating Cosmological Relic Density

A simple procedure is presented which leads to a dramatic simplification in the calculation of the relic density of stable particles in the Universe.Comment: 7 pages in LaTex, no figures; University of Michigan preprint UM-TH-94-02 (February 1994). Changes: a coefficient in $b^0$ (Eq. 16) corrected; added Acknowledgements and revised Note Added; plain LaTex only (no need to use RevTex

Upper and Lower Limits on Neutralino WIMP Mass and Spin--Independent Scattering Cross Section, and Impact of New (g-2)_{mu} Measurement

We derive the allowed ranges of the spin--independent interaction cross section \sigsip for the elastic scattering of neutralinos on proton for wide ranges of parameters of the general Minimal Supersymmetric Standard Model. We investigate the effects of the lower limits on Higgs and superpartner masses from colliders, as well as the impact of constraints from \bsgamma and the new measurement of \gmtwo on the upper and lower limits on \sigsip. We further explore the impact of the neutralino relic density, including coannihilation, and of theoretical assumptions about the largest allowed values of the supersymmetric parameters. For $\mu>0$, requiring the latter to lie below 1\tev leads to \sigsip\gsim 10^{-11}\pb at \mchi\sim100\gev and \sigsip\gsim 10^{-8}\pb at \mchi\sim1\tev. When the supersymmetric parameters are allowed above 1\tev, for 440\gev \lsim \mchi\lsim 1020 \gev we derive a {\em parameter--independent lower limit} of \sigsip \gsim 2\times 10^{-12}\pb. (No similar lower limits can be set for $\mu<0$ nor for 1020\gev\lsim\mchi\lsim2.6\tev.) Requiring \abundchi<0.3 implies a {\em parameter--independent upper limit} \mchi\lsim2.6\tev. The new \epem--based measurement of $(g-2)_{\mu}$ restricts \mchi\lsim 350\gev at $1 \sigma$ CL and \mchi\lsim515\gev at $2 \sigma$ CL, and implies $\mu>0$. The largest allowed values of \sigsip have already become accessible to recent experimental searches.Comment: LaTeX, 17 pages, 9 eps figures. Version to appear in JHE

High Efficiency RNA Extraction From Sperm Cells Using Guanidinium Thiocyanate Supplemented With Tris(2-Carboxyethyl)Phosphine

The extraction of high-quality ribonucleic acid (RNA) from tissues and cells is a key step in many biological assays. Guanidinium thiocyanate-phenol-chloroform (AGPC) is a widely used and efficient method to obtain pure RNA from most tissues and cells. However, it is not efficient with some cells like sperm cells because they are resistant to chaotropic lysis solutions containing guanidinium thiocyanate such as Buffer RLT+ and Trizol. Here, we show that disulfide bonds are responsible for the chemical resistance of sperm cells to RNA extraction reagents. We show that while β-mercaptoethanol (βME) can increase sperm lysis in Buffer RLT+, it has no effect in Trizol and leaves sperm cells intact. We measured the reduction of disulfide bonds in 2,2′-dithiodipyridine (DTDP) and observed that βME has a pH-dependent activity in chaotropic solutions, suggesting that pH is a limiting factor. We identified tris(2-carboxyethyl)phosphine (TCEP) as an efficient lysis enhancer of AGPC solutions that can retain reducing activity even at acidic pH. Trizol supplemented with TCEP allows the complete and rapid lysis of sperm cells, increasing RNA yield by 100-fold and resulting in RNA with optimal quality for reverse transcription and polymerase chain reaction. Our findings highlight the importance of efficient cell lysis and extraction of various macromolecules for bulk and single-cell assays, and can be applied to other lysis-resistant cells and vesicles, thereby optimizing the amount of required starting material and animals

The impact of priors and observables on parameter inferences in the Constrained MSSM

We use a newly released version of the SuperBayeS code to analyze the impact of the choice of priors and the influence of various constraints on the statistical conclusions for the preferred values of the parameters of the Constrained MSSM. We assess the effect in a Bayesian framework and compare it with an alternative likelihood-based measure of a profile likelihood. We employ a new scanning algorithm (MultiNest) which increases the computational efficiency by a factor ~200 with respect to previously used techniques. We demonstrate that the currently available data are not yet sufficiently constraining to allow one to determine the preferred values of CMSSM parameters in a way that is completely independent of the choice of priors and statistical measures. While b->s gamma generally favors large m_0, this is in some contrast with the preference for low values of m_0 and m_1/2 that is almost entirely a consequence of a combination of prior effects and a single constraint coming from the anomalous magnetic moment of the muon, which remains somewhat controversial. Using an information-theoretical measure, we find that the cosmological dark matter abundance determination provides at least 80% of the total constraining power of all available observables. Despite the remaining uncertainties, prospects for direct detection in the CMSSM remain excellent, with the spin-independent neutralino-proton cross section almost guaranteed above sigma_SI ~ 10^{-10} pb, independently of the choice of priors or statistics. Likewise, gluino and lightest Higgs discovery at the LHC remain highly encouraging. While in this work we have used the CMSSM as particle physics model, our formalism and scanning technique can be readily applied to a wider class of models with several free parameters.Comment: Minor changes, extended discussion of profile likelihood. Matches JHEP accepted version. SuperBayeS code with MultiNest algorithm available at http://www.superbayes.or

Embedding spherical spacelike slices in a Schwarzschild solution

Given a spherical spacelike three-geometry, there exists a very simple algebraic condition which tells us whether, and in which, Schwarzschild solution this geometry can be smoothly embedded. One can use this result to show that any given Schwarzschild solution covers a significant subset of spherical superspace and these subsets form a sequence of nested domains as the Schwarzschild mass increases. This also demonstrates that spherical data offer an immediate counter example to the thick sandwich `theorem'

Non-zero trilinear parameter in the mSUGRA model - dark matter and collider signals at Tevatron and LHC

Phenomenologically viable and interesting regions of parameter space in the minimal super-gravity (mSUGRA) model with small $m_0$ and small $m_{1/2}$ consistent with the WMAP data on dark matter relic density and the bound on the mass of the lightest Higgs scalar $m_h>$ 114 GeV from LEP2 open up if the rather adhoc assumption $A_0$=0, where $A_0$ is the common trilinear soft breaking parameter, employed in most of the existing analyses is relaxed. Since this region corresponds to relatively light squarks and gluinos which are likely to be probed extensively in the very early stages of the LHC experiments, the consequences of moderate or large negative values of $A_0$ are examined in detail. We find that in this region several processes including lightest supersymmetric particle (LSP) pair annihilation, LSP - lighter tau slepton (${\tilde \tau}_1$) coannihilation and LSP - lighter top squark (${\tilde t}_1$) coannihilation contribute to the observed dark matter relic density. %\sout{The possibility that a relic density producing ${\tilde t}_1$ can be %observed at the current experiments at the Tevatron is wide open.} The possibility that a ${\tilde t}_1$ that can participate in coannihilation with the lightest neutralino to satisfy the WMAP bound on relic density and at the same time be observed at the current experiments at the Tevatron is wide open. At the LHC a large number of squark - gluino events lead to a very distinctive semi-inclusive signature $\tau^\pm$+X$_\tau$ (anything without a tau lepton) with a characteristic size much larger than $e^\pm$+X$_e$ or $\mu^\pm$+X$_\mu$ events.Comment: Some minor changes made in the text. To appear in Phys Rev

Particle Dark Matter - A Theorist's Perspective

Dark matter is presumably made of some new, exotic particle that appears in extensions of the Standard Model. After giving a brief overview of some popular candidates, I discuss in more detail the most appealing case of the supersymmetric neutralino.Comment: Invited talk at PASCOS--03, Mumbai, Indi

Challenges of Profile Likelihood Evaluation in Multi-Dimensional SUSY Scans

Statistical inference of the fundamental parameters of supersymmetric theories is a challenging and active endeavor. Several sophisticated algorithms have been employed to this end. While Markov-Chain Monte Carlo (MCMC) and nested sampling techniques are geared towards Bayesian inference, they have also been used to estimate frequentist confidence intervals based on the profile likelihood ratio. We investigate the performance and appropriate configuration of MultiNest, a nested sampling based algorithm, when used for profile likelihood-based analyses both on toy models and on the parameter space of the Constrained MSSM. We find that while the standard configuration is appropriate for an accurate reconstruction of the Bayesian posterior, the profile likelihood is poorly approximated. We identify a more appropriate MultiNest configuration for profile likelihood analyses, which gives an excellent exploration of the profile likelihood (albeit at a larger computational cost), including the identification of the global maximum likelihood value. We conclude that with the appropriate configuration MultiNest is a suitable tool for profile likelihood studies, indicating previous claims to the contrary are not well founded.Comment: 21 pages, 9 figures, 1 table; minor changes following referee report. Matches version accepted by JHE