664 research outputs found
Axion cold dark matter in view of BICEP2 results
The properties of axions that constitute 100% of cold dark matter (CDM)
depend on the tensor-to-scalar ratio at the end of inflation. If
as reported by the BICEP2 collaboration, then "half"
of the CDM axion parameter space is ruled out. Namely, the Peccei-Quinn
symmetry must be broken after the end of inflation, and axions do not generate
non-adiabatic primordial fluctuations. The cosmic axion density is then
independent of the tensor-to-scalar ratio , and the axion mass is expected
to be in a narrow range that however depends on the cosmological model before
primordial nucleosynthesis. In the standard CDM cosmology, the CDM
axion mass range is , where is the fractional contribution to the
cosmic axion density from decays of axionic strings and walls.Comment: fixed colors in figure, references adde
Axion cold dark matter in view of BICEP2 results
The properties of axions that constitute 100% of cold dark matter (CDM)
depend on the tensor-to-scalar ratio at the end of inflation. If
as reported by the BICEP2 collaboration, then "half"
of the CDM axion parameter space is ruled out. Namely, the Peccei-Quinn
symmetry must be broken after the end of inflation, and axions do not generate
non-adiabatic primordial fluctuations. The cosmic axion density is then
independent of the tensor-to-scalar ratio , and the axion mass is expected
to be in a narrow range that however depends on the cosmological model before
primordial nucleosynthesis. In the standard CDM cosmology, the CDM
axion mass range is , where is the fractional contribution to the
cosmic axion density from decays of axionic strings and walls.Comment: fixed colors in figure, references adde
Implications of muon anomalous magnetic moment for supersymmetric dark matter
The anomalous magnetic moment of the muon has recently been measured to be in
conflict with the Standard Model prediction with an excess of 2.6 sigma. Taking
the excess at face value as a measurement of the supersymmetric contribution,
we find that at 95% confidence level it imposes an upper bound of 500 GeV on
the neutralino mass and forbids higgsinos as being the bulk of cold dark
matter. Other implications for the astrophysical detection of neutralinos
include: an accessible minimum direct detection rate, lower bounds on the
indirect detection rate of neutrinos from the Sun and the Earth, and a
suppression of the intensity of gamma-ray lines from neutralino annihilations
in the galactic halo.Comment: 4 pages, 2 figures, revised version accepted for publication in
Physical Review Letter
Clumpy Neutralino Dark Matter
We investigate the possibility to detect neutralino dark matter in a scenario
in which the galactic dark halo is clumpy. We find that under customary
assumptions on various astrophysical parameters, the antiproton and continuum
gamma-ray signals from neutralino annihilation in the halo put the strongest
limits on the clumpiness of a neutralino halo. We argue that indirect detection
through neutrinos from the Earth and the Sun should not be much affected by
clumpiness. We identify situations in parameter space where the gamma-ray line,
positron and diffuse neutrino signals from annihilations in the halo may
provide interesting signals in upcoming detectors.Comment: 19 pages, 10 eps-figures (included), LaTeX, uses RevTe
Evidence for "sterile neutrino" dark matter?
I show that it may be possible to explain the present evidence for a gamma-ray emission from the galactic halo as due to halo WIMP annihilations. Not only the intensity and spatial pattern of the halo emission can be matched but also the relic density of the candidate WIMP can be in the cosmologically interesting domain. After a model-independent analysis to learn about the properties of a suitable candidate, I present a working model: a sterile neutrino in a model with an extended Higgs sector. Two examples indicate the existence of an interesting region in the model parameter space where present observational and experimental constraints are satisfied and the gamma-ray emission is reproduced
Model Independent Form Factors for Spin Independent Neutralino-Nucleon Scattering from Elastic Electron Scattering Data
Theoretical calculations of neutralino-nucleon interaction rates with various
nuclei are of great interest to direct dark matter searches such as CDMS,
EDELWEISS, ZEPLIN, and other experiments since they are used to establish upper
bounds on the WIMP-proton cross section. These interaction rates and cross
sections are generally computed with standard, one or two parameter
model-dependent nuclear form factors, which may not exactly mirror the actual
form factor for the particular nucleus in question. As is well known, elastic
electron scattering can allow for very precise determinations of nuclear form
factors and hence nuclear charge densities for spherical or near-spherical
nuclei. We use charge densities derived from elastic electron scattering data
to calculate model independent, analytic form factors for various target nuclei
important in dark matter searches, such as Si, Ge, S, Ca and others. We have
found that for nuclear recoils in the range of 1-100 keV significant
differences in cross sections and rates exist when the model independent form
factors are used: at 30 keV nuclear recoil the form factors squared differ by a
factor of 1.06 for Si, 1.11 for Ca, 1.27 for Ge, and 1.92
for Xe. We show the effect of different form factors on the upper limit
on the WIMP-proton cross section obtained with a hypothetical Ge
detector during a 100 kg-day effective exposure. Helm form factors with various
parameter choices differ at most by 10--20% from the best (Fourier Bessel) form
factor, and can approach it to better than 1% if the parameters are chosen to
mimic the actual nuclear density.Comment: 20 pages, 8 figure
Direct detection of neutralino dark mattter in non-standard cosmologies
We compute the neutralino direct detection rate in non-standard cosmological
scenarios where neutralinos account for the dark matter of the Universe.
Significant differences are found when such rates are compared with those
predicted by the standard cosmological model. For bino-like neutralinos, the
main feature is the presence of additional light (m_\chi\lesssim 40\gev) and
heavy (m_\chi\gtrsim 600\gev) neutralinos with detection rates within the
sensitivity of future dark matter experiments. For higgsino- and wino-like
neutralinos lighter than m_\chi \sim 1\tev, enhancements of more than two
orders of magnitude in the largest detection rates are observed. Thus, if dark
matter is made up of neutralinos, the prospects for their direct detection are
in general more promising than in the standard cosmology.Comment: 10 pages, 5 figure
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