491 research outputs found
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
Scalar form-factor of the proton with light-cone QCD sum rules
In this article, we calculate the scalar form-factor of the proton in the
framework of the light-cone QCD sum rules approach with the three valence quark
light-cone distribution amplitudes up to twist-6, and observe the scalar
form-factor at intermediate and large momentum transfers has significant contributions from the end-point (or soft) terms. The
numerical values for the are compatible with the calculations
from the chiral quark model and lattice QCD at the region .Comment: 18 pages, 7 figures, revised versio
The Contribution of the Light Quark Condensate to the Pion-Nucleon Sigma Term
There has been a discrepancy between values of the pion-nucleon sigma term
extracted by two different methods for many years. Analysis of recent high
precision pion-nucleon data has widened the gap between the two determinations.
It is argued that the two extractions correspond to different quantities and
that the difference between them can be understood and calculated.Comment: Modern Physics Letters A (in press
Neutrino Fluxes from CMSSM LSP Annihilations in the Sun
We evaluate the neutrino fluxes to be expected from neutralino LSP
annihilations inside the Sun, within the minimal supersymmetric extension of
the Standard Model with supersymmetry-breaking scalar and gaugino masses
constrained to be universal at the GUT scale (the CMSSM). We find that there
are large regions of typical CMSSM planes where the LSP
density inside the Sun is not in equilibrium, so that the annihilation rate may
be far below the capture rate. We show that neutrino fluxes are dependent on
the solar model at the 20% level, and adopt the AGSS09 model of Serenelli et
al. for our detailed studies. We find that there are large regions of the CMSSM
planes where the capture rate is not dominated by
spin-dependent LSP-proton scattering, e.g., at large along the CMSSM
coannihilation strip. We calculate neutrino fluxes above various threshold
energies for points along the coannihilation/rapid-annihilation and focus-point
strips where the CMSSM yields the correct cosmological relic density for
tan(beta) = 10 and 55 for > 0, exploring their sensitivities to
uncertainties in the spin-dependent and -independent scattering matrix
elements. We also present detailed neutrino spectra for four benchmark models
that illustrate generic possibilities within the CMSSM. Scanning the
cosmologically-favored parts of the parameter space of the CMSSM, we find that
the IceCube/DeepCore detector can probe at best only parts of this parameter
space, notably the focus-point region and possibly also at the low-mass tip of
the coannihilation strip.Comment: 32 pages, 13 figures. v2: updated/expanded discussion of
IceCube/DeepCor
On the estimate of the sigma^(I = 1)_(KN)(0)-term value from the energy level shift of kaonic hydrogen in the ground state
Using the experimental data on the energy level shift of kaonic hydrogen in
the ground state (the DEAR Collaboration, Phys. Rev. Lett. 94, 212302 (2005))
and the theoretical value of the energy level shift, calculated within the
phenomenological quantum field theoretic approach to the description of strong
low-energy anti-K N and anti-K NN interactions developed at Stefan Meyer
Institut fuer subatomare Physik in Vienna, we estimate the value of the
sigma^(I = 1)_(KN)(0)-term of low-energy anti-K N scattering. We get sigma^(I =
1)_(KN)(0) = (433 +/- 85) MeV. This testifies the absence of strange quarks in
the proton structure.Comment: 7 pages, no figure
Gyromagnetic Factors and Atomic Clock Constraints on the Variation of Fundamental Constants
We consider the effect of the coupled variations of fundamental constants on
the nucleon magnetic moment. The nucleon g-factor enters into the
interpretation of the measurements of variations in the fine-structure
constant, alpha, in both the laboratory (through atomic clock measurements) and
in astrophysical systems (e.g. through measurements of the 21 cm transitions).
A null result can be translated into a limit on the variation of a set of
fundamental constants, that is usually reduced to alpha. However, in specific
models, particularly unification models, changes in alpha are always
accompanied by corresponding changes in other fundamental quantities such as
the QCD scale, Lambda_QCD. This work tracks the changes in the nucleon
g-factors induced from changes in Lambda_QCD and the light quark masses. In
principle, these coupled variations can improve the bounds on the variation of
alpha by an order of magnitude from existing atomic clock and astrophysical
measurements. Unfortunately, the calculation of the dependence of g-factors on
fundamental parameters is notoriously model-dependent.Comment: 35 pages, 3 figures. Discussions of the effects of the polarization
of the non-valence nucleons, spin-spin interaction and nuclear radius on the
nuclear g-factor are added. References added. Matches published versio
The in-medium isovector pi N amplitude from low energy pion scattering
Differential cross sections for elastic scattering of 21.5 MeV positive and
negative pions by Si, Ca, Ni and Zr have been measured as part of a study of
the pion-nucleus potential across threshold. The `anomalous' repulsion in the
s-wave term was observed, as is the case with pionic atoms. The extra repulsion
can be accounted for by a chiral-motivated model where the pion decay constant
is modified in the medium. Unlike in pionic atoms, the anomaly cannot be
removed by merely introducing an empirical on-shell energy dependence.Comment: 9 pages, 2 figures. Minor changes, to appear in PR
Hadronic Uncertainties in the Elastic Scattering of Supersymmetric Dark Matter
We review the uncertainties in the spin-independent and -dependent elastic
scattering cross sections of supersymmetric dark matter particles on protons
and neutrons. We propagate the uncertainties in quark masses and hadronic
matrix elements that are related to the -nucleon term and the
spin content of the nucleon. By far the largest single uncertainty is that in
spin-independent scattering induced by our ignorance of the matrix elements linked to the -nucleon term, which affects
the ratio of cross sections on proton and neutron targets as well as their
absolute values. This uncertainty is already impacting the interpretations of
experimental searches for cold dark matter. {\it We plead for an experimental
campaign to determine better the -nucleon term.} Uncertainties in
the spin content of the proton affect significantly, but less strongly, the
calculation of rates used in indirect searches.Comment: 25 pages, 10 figures. v2: added references. To appear in PR
Heritability of Bullying and Victimization in Children and Adolescents: Moderation by the KiVa Antibullying Program
Objective: Bullying affects approximately a quarter of schoolchildren and is associated with numerous adverse outcomes. Although distinct risk factors for bullying and victimization have been identified, few studies have investigated the genetic and environmental underpinnings of bullying and victimization. The aims of this study were twofold: first, to examine the contributions of genetic and environmental factors to bullying and victimization, and second, to analyze whether the KiVa antibullying program moderated the magnitude of these contributions by comparing estimates derived from the KiVa versus control groups.Method: The sample comprised students from schools that participated in the evaluation of the KiVa antibullying program in Finland during 2007-2009. Bullying and victimization were measured using peer nominations by classmates. The sample for the twin analyses comprised of 447 twins (107 monozygotic and 340 dizygotic twins) aged 7-15.Results: Genetic contributions accounted for 62% and 77% of the variance in bullying and in victimization at pre-intervention, respectively. There was a post-intervention difference in the overall role of genetic and environmental contributions between the intervention and the control group for bullying and victimization, with non-shared environmental effects playing a lesser role (and genes a larger role) in the intervention than in the control group context.Conclusions: This study replicates previous findings on the genetic underpinnings of both bullying and victimization, and indicates that a school-based antibullying program reduces the role of non-shared environmental factors in bullying and victimization. The results indicate that prevention and intervention efforts need to target both environmental and (heritable) individual level factors to maximize effectiveness
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