1,426 research outputs found
High-Energy Constraints on the Direct Detection of MSSM Neutralinos
The requirement that the MSSM remain an acceptable effective field theory up
to energies beyond the weak scale constrains the sparticle spectrum, and hence
the permissible ranges of cold dark matter neutralino-proton cross sections.
Specifically, squarks are generally much heavier than sleptons if no tachyons
are to appear before the GUT scale ~10^16 GeV, or even before 10 TeV. We
display explicitly the allowed ranges of effective squark and slepton masses at
the weak scale, and the cross-section ranges allowed if the MSSM is to remain
valid without tachyons up to 10 TeV or the GUT scale. The allowed areas in the
cross section-mass plane for both spin-independent and spin-dependent
scattering are significantly smaller than would be allowed if the MSSM were
required to be valid only around the weak scale. In addition to a reduction in
the maximum cross section, the upper limit on the neutralino mass is greatly
reduced when tachyons are avoided, particularly for smaller values of the
squark masses.Comment: 22 pages, 22 figure
Kinetics and Inhibition Studies of the L205R Mutant of cAMP-Dependent Protein Kinase Involved in Cushingâs Syndrome
Overproduction of cortisol by the hypothalamusâpituitaryâadrenal hormone system results in the clinical disorder known as Cushing\u27s syndrome. Genomics studies have identified a key mutation (L205R) in the αâisoform of the catalytic subunit of cAMPâdependent protein kinase (PKACα) in adrenal adenomas of patients with adrenocorticotropic hormoneâindependent Cushing\u27s syndrome. Here, we conducted kinetics and inhibition studies on the L205RâPKACα mutant. We have found that the L205R mutation affects the kinetics of both Kemptide and ATP as substrates, decreasing the catalytic efficiency (kcat/KM) for each substrate by 12âfold and 4.5âfold, respectively. We have also determined the IC50 and Ki for the peptide substrateâcompetitive inhibitor PKI(5â24) and the ATPâcompetitive inhibitor H89. The L205R mutation had no effect on the potency of H89, but causes a \u3e 250âfold loss in potency for PKI(5â24). Collectively, these data provide insights for the development of L205RâPKACα inhibitors as potential therapeutics
Metastable Charged Sparticles and the Cosmological Li7 Problem
We consider the effects of metastable charged sparticles on Big-Bang
Nucleosynthesis (BBN), including bound-state reaction rates and chemical
effects. We make a new analysis of the bound states of negatively-charged
massive particles with the light nuclei most prominent in BBN, and present a
new code to track their abundances, paying particular attention to that of Li7.
Assuming, as an example, that the gravitino is the lightest supersymmetric
particle (LSP), and that the lighter stau slepton, stau_1, is the metastable
next-to-lightest sparticle within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM), we analyze the possible effects on the
standard BBN abundances of stau_1 bound states and decays for representative
values of the gravitino mass. Taking into account the constraint on the CMSSM
parameter space imposed by the discovery of the Higgs boson at the LHC, we
delineate regions in which the fit to the measured light-element abundances is
as good as in standard BBN. We also identify regions of the CMSSM parameter
space in which the bound state properties, chemistry and decays of metastable
charged sparticles can solve the cosmological Li7 problem.Comment: 49 pages, 29 eps figure
Nuclear Reaction Uncertainties, Massive Gravitino Decays and the Cosmological Lithium Problem
We consider the effects of uncertainties in nuclear reaction rates on the
cosmological constraints on the decays of unstable particles during or after
Big-Bang nucleosynthesis (BBN). We identify the nuclear reactions due to
non-thermal hadrons that are the most important in perturbing standard BBN,
then quantify the uncertainties in these reactions and in the resulting
light-element abundances. These results also indicate the key nuclear processes
for which improved cross section data would allow different light-element
abundances to be determined more accurately, thereby making possible more
precise probes of BBN and evaluations of the cosmological constraints on
unstable particles. Applying this analysis to models with unstable gravitinos
decaying into neutralinos, we calculate the likelihood function for the
light-element abundances measured currently, taking into account the current
experimental errors in the determinations of the relevant nuclear reaction
rates. We find a region of the gravitino mass and abundance in which the
abundances of deuterium, He4 and Li7 may be fit with chi^2 = 5.5, compared with
chi^2 = 31.7 if the effects of gravitino decays are unimportant. The best-fit
solution is improved to chi^2 ~ 2.0 when the lithium abundance is taken from
globular cluster data. Some such re-evaluation of the observed light-element
abundances and/or nuclear reaction rates would be needed if this region of
gravitino parameters is to provide a complete solution to the cosmological Li7
problem.Comment: 24 pages, 10 figure
Gravitino Decays and the Cosmological Lithium Problem in Light of the LHC Higgs and Supersymmetry Searches
We studied previously the impact on light-element abundances of gravitinos
decaying during or after Big-Bang nucleosynthesis (BBN). We found regions of
the gravitino mass m_{3/2} and abundance zeta_{3/2} plane where its decays
could reconcile the calculated abundance of Li7 with observation without
perturbing the other light-element abundances unacceptably. Here we revisit
this issue in light of LHC measurements of the Higgs mass and constraints on
supersymmetric model parameters, as well as updates in the astrophysical
measurements of light-element abundances. In addition to the constrained
minimal supersymmetric extension of the Standard Model with universal soft
supersymmetry-breaking masses at the GUT scale (the CMSSM) studied previously,
we also study models with universality imposed below the GUT scale and models
with non-universal Higgs masses (NUHM1). We calculate the total likelihood
function for the light-element abundances, taking into account the
observational uncertainties. We find that gravitino decays provide a robust
solution to the cosmological Li7 problem along strips in the (m_{3/2},
zeta_{3/2}) plane along which the abundances of deuterium, He4 and Li7 may be
fit with chi^2_min < 3, compared with chi^2 ~ 34 if the effects of gravitino
decays are unimportant. The minimum of the likelihood function is reduced to
chi^2 < 2 when the uncertainty on D/H is relaxed and < 1 when the lithium
abundance is taken from globular cluster data.Comment: 20 pages, 5 figures; added a new table and a discussion paragraph for
it in Section 4, matches the published versio
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 m_0 and gaugino masses m_{1/2} to be universal at some input scale,
impose relations between the trilinear and bilinear soft supersymmetry breaking
parameters A_0 and B_0. These relations may be linear, as in simple minimal
supergravity models, or nonlinear, as in the Giudice-Masiero mechanism for
generating the Higgs-mixing mu term. We discuss the application of the
electroweak vacuum conditions in VCMSSMs, which may be used to make a
prediction for tan beta as a function of m_0 and m_{1/2} that is usually
unique. We baseline the discussion of the parameter spaces allowed in VCMSSMs
by updating the parameter space allowed in the CMSSM for fixed values of tan
beta with no relation between A_0 and B_0 assumed {\it a priori}, displaying
contours of B_0 for a fixed input value of A_0, incorporating the latest CDF/D0
measurement of m_t and the latest BNL measurement of g_mu - 2. We emphasize
that phenomenological studies of the CMSSM are frequently not applicable to
specific VCMSSMs, notably those based on minimal supergravity, which require
m_0 = m_{3/2} as well as A_0 = B_0 + m_0. We then display (m_{1/2}, m_0) planes
for selected VCMSSMs, treating in a unified way the parameter regions where
either a neutralino or the gravitino is the LSP. In particular, we examine in
detail the allowed parameter space for the Giudice-Masiero model.Comment: 26 pages, 32 eps figure
Prospects for Sparticle Discovery in Variants of the MSSM
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 chi, 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.Comment: 19 pages, 16 eps figures, as accepted in PL
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.Comment: 15 pages, 12 figures, reference adde
Supersymmetric Dark Matter in Light of WMAP
We re-examine the parameter space of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), taking account of the restricted range of \Omega_{CDM} h^2 consistent with the WMAP data. This provides a significantly reduced upper limit on the mass of the lightest supersymmetric particle LSP: m_\chi 0, or \tan \beta < 30 and \mu < 0, thereby improving the prospects for measuring supersymmetry at the LHC, and increasing the likelihood that a 1-TeV linear e^+ e^- collider would be able to measure the properties of some supersymmetric particles
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 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_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
MSSM (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 favoured at the 90 % confidence level in a
recent likelihood analysis. However, some models with non-universal Higgs,
squark and slepton masses and neutralino masses \lappeq 700 GeV are excluded by
the CDMS II data.Comment: 25 pages, 28 eps figure
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