1,161 research outputs found
A WIMP Detector with Two-Phase Liquid Xenon
We describe the liquid-xenon dark-matter detector program of the UCLA-Torino
team. A two-phase detector, ZEPLIN II, for the Boulby Mine is a good match for
the current search for WIMP dark matter.Comment: 3 pages with 4 figures; for Proceedings, Sixth Int'l Wksp. On Topics
in Astroparticle and Underground Physics, TAUP99 (College de France, Paris,
Sept. 6-10, 1999), to be published in Nucl. Phys. B(PS
Quantitative Perspectives on Fifty Years of the Journal of the History of Biology
Journal of the History of Biology provides a fifty-year long record for
examining the evolution of the history of biology as a scholarly discipline. In
this paper, we present a new dataset and preliminary quantitative analysis of
the thematic content of JHB from the perspectives of geography, organisms, and
thematic fields. The geographic diversity of authors whose work appears in JHB
has increased steadily since 1968, but the geographic coverage of the content
of JHB articles remains strongly lopsided toward the United States, United
Kingdom, and western Europe and has diversified much less dramatically over
time. The taxonomic diversity of organisms discussed in JHB increased steadily
between 1968 and the late 1990s but declined in later years, mirroring broader
patterns of diversification previously reported in the biomedical research
literature. Finally, we used a combination of topic modeling and nonlinear
dimensionality reduction techniques to develop a model of multi-article fields
within JHB. We found evidence for directional changes in the representation of
fields on multiple scales. The diversity of JHB with regard to the
representation of thematic fields has increased overall, with most of that
diversification occurring in recent years. Drawing on the dataset generated in
the course of this analysis, as well as web services in the emerging digital
history and philosophy of science ecosystem, we have developed an interactive
web platform for exploring the content of JHB, and we provide a brief overview
of the platform in this article. As a whole, the data and analyses presented
here provide a starting-place for further critical reflection on the evolution
of the history of biology over the past half-century.Comment: 45 pages, 14 figures, 4 table
Light Relic Neutralinos
The relic abundance and the scalar cross{section o nucleon for light neutralinos (of mass m below about 45 GeV) are evaluated in an e ective MSSM model with R-parity conservation and without GUT{inspired relations among gaugino masses. It is shown that these neutralinos may provide a sizeable contribution to the matter density in the Universe CDM. By requiring that its relic abundance does not exceed the upper bound on CDM based on the new WMAP data, a lower bound on the neutralino mass m > 6 GeV is derived. These light neutralinos can also produce measurable e ects in WIMP direct detection experiments, and in particular could explain the modulation result recently con rmed by DAMA. Uncertainties in direct detection calculations due to the modeling of the WIMP velocity distribution function are also discussed
Extending the DAMA annual-modulation region by inclusion of the uncertainties in the astrophysical velocities
The original annual-modulation region, singled out by the DAMA/NaI experiment
for direct detection of WIMPs, is extended by taking into account the
uncertainties in the galactic astrophysical velocities. Also the effect due to
a possible bulk rotation for the dark matter halo is considered. We find that
the range for the WIMP mass becomes 30 GeV < m_chi < 130 GeV at 1-sigma C.L.
with a further extension in the upper bound, when a possible bulk rotation of
the dark matter halo is taken into account. We show that the DAMA results, when
interpreted in the framework of the Minimal Supersymmetric extension of the
Standard Model, are consistent with a relic neutralino as a dominant component
of cold dark matter (on the average in our universe and in our galactic halo).
It is also discussed the discovery potential for the relevant supersymmetric
configurations at accelerators of present generation.Comment: ReVTeX, 12 pages, 1 table, 7 figure
Does Solar Physics Provide Constraints to Weakly Interacting Massive Particles?
We investigate whether present data on helioseismology and solar neutrino
fluxes may constrain WIMP--matter interactions in the range of WIMP parameters
under current exploration in WIMP searches. We find that, for a WIMP mass of 30
GeV, once the effect of the presence of WIMPs in the Sun's interior is
maximized, the squared isothermal sound speed is modified, with respect to the
standard solar model, by at most 0.4% at the Sun's center. The maximal effect
on the Boron-8 solar neutrino flux is a reduction of 4.5%. Larger masses lead
to smaller effects. These results imply that present sensitivities in the
measurements of solar properties, though greatly improved in recent years, do
not provide information or constraints on WIMP properties of relevance for dark
matter. Furthermore, we show that, when current bounds from direct WIMP
searches are taken into account, the effect induced by WIMPs with dominant
coherent interactions are drastically reduced as compared to the values quoted
above. The case of neutralinos in the minimal supersymmetric standard model is
also discussed.Comment: 31 pages, 2 tables and 9 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/helio.ps.gz or
through http://www.to.infn.it/astropart/index.htm
Nonlinear interplay of Alfven instabilities and energetic particles in tokamaks
The confinement of energetic particles (EP) is crucial for an efficient
heating of tokamak plasmas. Plasma instabilities such as Alfven Eigenmodes (AE)
can redistribute the EP population making the plasma heating less effective,
and leading to additional loads on the walls. The nonlinear dynamics of
toroidicity induced AE (TAE) is investigated by means of the global gyrokinetic
particle-in-cell code ORB5, within the NEMORB project. The nonperturbative
nonlinear interplay of TAEs and EP due to the wave-particle nonlinearity is
studied. In particular, we focus on the nonlinear modification of the
frequency, growth rate and radial structure of the TAE, depending on the
evolution of the EP distribution in phase space. For the ITPA benchmark case,
we find that the frequency increases when the growth rate decreases, and the
mode shrinks radially. This nonlinear evolution is found to be correctly
reproduced by means of a quasilinear model, namely a model where the linear
effects of the nonlinearly modified EP distribution function are retained.Comment: Submitted to Plasma Phys. Control. Fusio
Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
adde
Further investigation of a relic neutralino as a possible origin of an annual-modulation effect in WIMP direct search
We analyze the annual-modulation effect, measured by the DAMA Collaboration
with the new implementation of a further two-years running, in the context of a
possible interpretation in terms of relic neutralinos. We impose over the set
of supersymmetric configurations, selected by the annual-modulation data, the
constraints derived from WIMP indirect measurements, and discuss the features
of the ensuing relic neutralinos. We critically discuss the sources of the main
theoretical uncertainties in the analysis of event rates for direct and
indirect WIMP searches.Comment: 29 pages, 12 figures, typeset with ReVTeX. In order to reduce size,
the version on the archive has low resolution figures. A full version of the
paper can be found at http://www.to.infn.it/~fornengo/papers
Neutralino Proton Cross Sections In Supergravity Models
The neutralino-proton cross section is examined for supergravity models with
R-parity invariance with universal and non-universal soft breaking. The region
of parameter space that dark matter detectors are currently (or will be
shortly) sensitive i.e. pb, is examined. For universal
soft breaking (mSUGRA), detectors with sensitivity
pb will be able to
sample parts of the parameter space for .
Current relic density bounds restrict GeV
for the maximum cross sections, which is below where astronomical uncertainties
about the Milky Way are relevant. Nonuniversal soft breaking models can allow
much larger cross sections and can sample the parameter space for . In such models, can be quite large reducing the
tension between proton decay bounds and dark matter analysis. We note the
existance of two new domains where coannihilation effects can enter, i.e. for
mSUGRA at large , and for nonuniversal models with small .Comment: 22 pages, latex, 18 figure
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