90 research outputs found
Inelastic Dark Matter at DAMA, CDMS and Future Experiments
The DAMA annual modulation signature, interpreted as evidence for a
spin-independent WIMP coupling, seems in conflict with null results from CDMS.
However, in models of ``inelastic dark matter'', the experiments are
compatible. Inelastic dark matter can arise in supersymmetric theories as the
real component of a sneutrino mixed with a singlet scalar. In contrast with
ordinary sneutrino dark matter, such particles can satisfy all experimental
constraints while giving the appropriate relic abundance. We discuss the
modifications to the signal seen at DAMA, in particular noting the strong
suppression of low energy events in both modulated and unmodulated components.
We discuss future experiments, with emphasis on distinguishing inelastic dark
matter from ordinary dark matter, and stressing the significance of experiments
with heavy target nuclei, such as xenon and tungsten.Comment: 4 pages; to appear in the proceedings of 5th International UCLA
Symposium on Sources and Detection of Dark Matter and Dark Energy in the
Universe (DM 2002), Marina del Rey, California, 20-22 Feb 200
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Log cabin construction techniques in western Siskiyou County, 1850-1935 : their function and ethnic origins
Under the sponsorship of the Klamath National Forest, 25 log cabins
which were built in western Siskiyou County between 1850 and 1937 were located
and studied. First, 11 exterior dimensions of these cabins were selected,
measured and recorded. Then 26 building elements were identified for the
purpose of finding whether there was a relationship between the exterior
attributes of these structures and the occupation of their builders. Four
major builder occupations were identified: (1) placer mining, (2) hardrock
mining, (3) homesteading, and (4) ranching. It was hypothesized that there is
a correlation between these builder occupations and the exterior attributes of
the cabins.
A forward stepwise discriminant analysis was performed on the parametric
variables. None of the 11 variables met the default criteria to enter (i.e.,
F=.15). Hence the null hypothesis that there is a relationship between the
occupation of the builder and the exterior variables of the log cabins was
confirmed. The 26 categorical variables which were used to classify the cabins were
crosstabulated against the occupation of the builders. The results indicated
that only four nominal variables discriminated between the builder occupation
groups. A predictive model for classifying cabins on the basis of these four
variables is presented.
A second hypothesis was proposed to examine the relationship between log
cabin construction elements and the builder's ethnic background. Data
collected on building variables was compared with those ethnic traits
described by other log cabin researchers. From this comparison an index of
ethnic trait compatibility was produced which demonstrated the strength of
relationship between builder's background and cabin construction variables
Expected Performance of CryoArray
WIMP-nucleon cross sections below 10^(-9) pb may be probed by ton-scale
experiments with low thresholds and background rates ~20 events per year. An
array of cryogenic detectors ("CryoArray") could perform well enough to reach
this goal. Sufficient discrimination and background suppression of photons has
already been demonstrated. Reduction of neutron backgrounds may be achieved by
siting the experiment deep enough. Removal of the surface-electron backgrounds
alone has not yet been demonstrated, but the reductions required even for this
troublesome background are quite modest and appear achieveable.Comment: 4 pages, 2 figures. Talk at DM2002 Conference, Marina del Rey, CA,
Feb 20-22, 200
Triaxial Haloes and Particle Dark Matter Detection
This paper presents the properties of a family of scale-free triaxial haloes.
We adduce arguments to suggest that the velocity ellipsoids of such models are
aligned in conical coordinates. We provide an algorithm to find the set of
conically aligned velocity second moments that support a given density against
the gravity field of the halo. The case of the logarithmic ellipsoidal model --
the simplest triaxial generalisation of the familiar isothermal sphere -- is
examined in detail. The velocity dispersions required to hold up the
self-consistent model are analytic. The velocity distribution of the dark
matter can be approximated as a triaxial Gaussian with semiaxes equal to the
velocity dispersions. There are roughly twenty experiments worldwide that are
searching for evidence of scarce interactions between weakly-interacting
massive-particle dark matter (WIMPs) and detector nuclei. The annual modulation
signal, caused by the Earth's rotation around the Sun, is a crucial
discriminant between WIMP events and the background. The greatest rate is in
June, the least in December. We compute the differential detection rate for
energy deposited by the rare WIMP-nucleus interactions in our logarithmic
ellipsoidal halo models. Triaxiality and velocity anisotropy change the total
rate by up to 40 %, and have a substantial effect on the amplitude of the
annual modulation signal. The overall rate is greatest, but the amplitude of
the modulation is weakest, in our radially anisotropic halo models. Even the
sign of the signal can be changed. Restricting attention to low energy events,
the models predict that the maximum rate occurs in December, and not in June.Comment: In press, Monthly Notice
Detectability of a subdominant density component of cold dark matter
Here we examine the detectability of collisionless dark matter candidates
that may constitute not all but only a subdominant component of galactic cold
dark matter. We show that current axion searches are not suited for a
subdominant component, while direct WIMP searches would not be severely
affected by the reduced density. In fact, the direct detection rates of
neutralinos stay almost constant even if neutralinos constitute 1% of the halo
dark matter. Only for lower densities do the rates decrease with density. Even
neutralinos accounting for only of the local dark halo density are
within proposed future discovery limits. We comment also on indirect WIMP
searches.Comment: 11 pages, 3 figures (references added, minor rewriting
GENIUS-TF: a test facility for the GENIUS project
GENIUS is a proposal for a large scale detector of rare events. As a first
step of the experiment, a small test version, the GENIUS test facility, will be
build up at the Laboratorio Nazionale del Gran Sasso (LNGS). With about 40 kg
of natural Ge detectors operated in liquid nitrogen, GENIUS-TF could exclude
(or directly confirm) the DAMA annual modulation signature within about two
years of measurement.Comment: 14 pages, latex, 5 figures, 3 tables; submitted to Astroparticle
Physic
Measurement of T\u3csub\u3ec\u3c/sub\u3e suppression in tungsten using magnetic impurities
We have measured the effects of dilute magnetic-atom doping on the superconducting transition temperature of tungsten thin films. Our âTc tuningâ technique is accurate, precise, and simple. Experiments were performed using dc-magnetron-sputtered tungsten films with undoped values of Tc in the range of 70â150 mK. The magnetic-atom doping was achieved using ion implantation. Specific Tc suppressions of between 5% and 65% were targeted and observed in this study. The transition width of each undoped sample was â1 mK and the transition widths remained sharp after implantation with 56Fe+ ions. Our data are in good agreement with predictions of a linear dependence of Tc suppression with increasing magnetic-atom concentration, in the small concentration limit. At higher concentrations, antiferromagnetic coupling between the magnetic dopant atoms becomes important and the Tc-suppression effect is diminished. We use our Tc data to calculate the AbrikosovâGorâkov (AG) and RudermanâKittelâKasuyaâYosida (RKKY) spinâflip relaxation parameters ÏAG and ÏRKKY. We conclude with a brief discussion of applications of the Tc-tuning technique, and present our plans for future studies in this area
Search for Supersymmetric Dark Matter with Superfluid He3 (MACHe3)
MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for
direct Dark Matter search, using superfluid He3 as a sensitive medium. This
paper presents a phenomenological study done with the DarkSUSY code, in order
to investigate the discovery potential of this project of detector, as well as
its complementarity with existing and planned devices.Comment: 15 pages, 5 figures, submitted to Phys. Letters B, minor changes in
the tex
Nucleon scattering with higgsino and wino cold dark matter
Neutralinos that are mostly wino or higgsino are shown to be compatible with
the recent DAMA annual modulation signal. The nucleon scattering rates for
these dark matter candidates are typically an order of magnitude above the
oft-considered bino. Although thermal evolution of higgsino and wino number
densities in the early universe implies that they are not viable dark matter
candidates, non-thermal sources, such as from gravitino or moduli decay in
anomaly mediated supersymmetry breaking, suggest that they can be the dominant
source of cold dark matter. Their stealthiness at high energy colliders gives
even more impetus to analyze nucleon scattering detection methods. We also
present calculations for their predicted scattering rate with Germanium
detectors, which have yet to see evidence of WIMP scattering.Comment: 16 pages, LaTex, 4 figures, uses feynMF, minor changes made for PRD
publicatio
Generalized Analysis of Weakly-Interacting Massive Particle Searches
We perform a generalized analysis of data from WIMP search experiments for
point-like WIMPs of arbitrary spin and general Lorenz-invariant WIMP-nucleus
interaction. We show that in the non-relativistic limit only spin-independent
(SI) and spin-dependent (SD) WIMP-nucleon interactions survive, which can be
parameterized by only five independent parameters. We explore this
five-dimensional parameter space to determine whether the annual modulation
observed in the DAMA experiment can be consistent with all other experiments.
The pure SI interaction is ruled out except for very small region of parameter
space with the WIMP mass close to 50 GeV and the ratio of the WIMP-neutron to
WIMP-proton SI couplings . For the predominantly SD
interaction, we find an upper limit to the WIMP mass of about 18 GeV, which can
only be weakened if the constraint stemming from null searches for energetic
neutrinos from WIMP annihilation the Sun is evaded. None of the regions of the
parameter space that can reconcile all WIMP search results can be easily
accommodated in the minimal supersymmetric extension of the standard model.Comment: 27 pages, 3 figure
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