585 research outputs found
Reconfigured Cyanogenic Glucoside Biosynthesis in <i>Eucalyptus cladocalyx</i> Involves a Cytochrome P450 CYP706C55
Dark Matter Direct Detection with Non-Maxwellian Velocity Structure
The velocity distribution function of dark matter particles is expected to
show significant departures from a Maxwell-Boltzmann distribution. This can
have profound effects on the predicted dark matter - nucleon scattering rates
in direct detection experiments, especially for dark matter models in which the
scattering is sensitive to the high velocity tail of the distribution, such as
inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for
experiments that require high energy recoil events, such as many directionally
sensitive experiments. Here we determine the velocity distribution functions
from two of the highest resolution numerical simulations of Galactic dark
matter structure (Via Lactea II and GHALO), and study the effects for these
scenarios. For directional detection, we find that the observed departures from
Maxwell-Boltzmann increase the contrast of the signal and change the typical
direction of incoming DM particles. For iDM, the expected signals at direct
detection experiments are changed dramatically: the annual modulation can be
enhanced by more than a factor two, and the relative rates of DAMA compared to
CDMS can change by an order of magnitude, while those compared to CRESST can
change by a factor of two. The spectrum of the signal can also change
dramatically, with many features arising due to substructure. For LDM the
spectral effects are smaller, but changes do arise that improve the
compatibility with existing experiments. We find that the phase of the
modulation can depend upon energy, which would help discriminate against
background should it be found.Comment: 34 pages, 16 figures, submitted to JCAP. Tables of g(v_min), the
integral of f(v)/v from v_min to infinity, derived from our simulations, are
available for download at http://astro.berkeley.edu/~mqk/dmdd
Dependence of direct detection signals on the WIMP velocity distribution
The signals expected in WIMP direct detection experiments depend on the
ultra-local dark matter distribution. Observations probe the local density,
circular speed and escape speed, while simulations find velocity distributions
that deviate significantly from the standard Maxwellian distribution. We
calculate the energy, time and direction dependence of the event rate for a
range of velocity distributions motivated by recent observations and
simulations, and also investigate the uncertainty in the determination of WIMP
parameters. The dominant uncertainties are the systematic error in the local
circular speed and whether or not the MW has a high density dark disc. In both
cases there are substantial changes in the mean differential event rate and the
annual modulation signal, and hence exclusion limits and determinations of the
WIMP mass. The uncertainty in the shape of the halo velocity distribution is
less important, however it leads to a 5% systematic error in the WIMP mass. The
detailed direction dependence of the event rate is sensitive to the velocity
distribution. However the numbers of events required to detect anisotropy and
confirm the median recoil direction do not change substantially.Comment: 21 pages, 7 figures, v2 version to appear in JCAP, minor change
Light propagation in statistically homogeneous and isotropic universes with general matter content
We derive the relationship of the redshift and the angular diameter distance
to the average expansion rate for universes which are statistically homogeneous
and isotropic and where the distribution evolves slowly, but which have
otherwise arbitrary geometry and matter content. The relevant average expansion
rate is selected by the observable redshift and the assumed symmetry properties
of the spacetime. We show why light deflection and shear remain small. We write
down the evolution equations for the average expansion rate and discuss the
validity of the dust approximation.Comment: 42 pages, no figures. v2: Corrected one detail about the angular
diameter distance and two typos. No change in result
Optimal k-fold colorings of webs and antiwebs
A k-fold x-coloring of a graph is an assignment of (at least) k distinct
colors from the set {1, 2, ..., x} to each vertex such that any two adjacent
vertices are assigned disjoint sets of colors. The smallest number x such that
G admits a k-fold x-coloring is the k-th chromatic number of G, denoted by
\chi_k(G). We determine the exact value of this parameter when G is a web or an
antiweb. Our results generalize the known corresponding results for odd cycles
and imply necessary and sufficient conditions under which \chi_k(G) attains its
lower and upper bounds based on the clique, the fractional chromatic and the
chromatic numbers. Additionally, we extend the concept of \chi-critical graphs
to \chi_k-critical graphs. We identify the webs and antiwebs having this
property, for every integer k <= 1.Comment: A short version of this paper was presented at the Simp\'osio
Brasileiro de Pesquisa Operacional, Brazil, 201
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Search for R-Parity Violating Decays of Scalar Fermions at LEP
A search for pair-produced scalar fermions under the assumption that R-parity
is not conserved has been performed using data collected with the OPAL detector
at LEP. The data samples analysed correspond to an integrated luminosity of
about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An
important consequence of R-parity violation is that the lightest supersymmetric
particle is expected to be unstable. Searches of R-parity violating decays of
charged sleptons, sneutrinos and squarks have been performed under the
assumptions that the lightest supersymmetric particle decays promptly and that
only one of the R-parity violating couplings is dominant for each of the decay
modes considered. Such processes would yield final states consisting of
leptons, jets, or both with or without missing energy. No significant
single-like excess of events has been observed with respect to the Standard
Model expectations. Limits on the production cross- section of scalar fermions
in R-parity violating scenarios are obtained. Constraints on the supersymmetric
particle masses are also presented in an R-parity violating framework analogous
to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.
Measurement of the Strong Coupling alpha s from Four-Jet Observables in e+e- Annihilation
Data from e+e- annihilation into hadrons at centre-of-mass energies between
91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study
the four-jet rate as a function of the Durham algorithm resolution parameter
ycut. The four-jet rate is compared to next-to-leading order calculations that
include the resummation of large logarithms. The strong coupling measured from
the four-jet rate is alphas(Mz0)=
0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass)
in agreement with the world average. Next-to-leading order fits to the
D-parameter and thrust minor event-shape observables are also performed for the
first time. We find consistent results, but with significantly larger
theoretical uncertainties.Comment: 25 pages, 15 figures, Submitted to Euro. Phys. J.
Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2
The hadronic structure function of the photon F_2^gamma is measured as a
function of Bjorken x and of the factorisation scale Q^2 using data taken by
the OPAL detector at LEP. Previous OPAL measurements of the x dependence of
F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of
F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted
by QCD, the data show positive scaling violations in F_2^gamma. Several
parameterisations of F_2^gamma are in agreement with the measurements whereas
the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001,
Ascona, Switzerlan
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
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