2,650 research outputs found
Masses and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model
We evaluate masses and semileptonic decay widths for the ground state of
doubly heavy and baryons in the framework of a nonrelativistic
quark model. We solve the three-body problem by means of a variational ansatz
made possible by heavy-quark spin symmetry constraints. Our masses are
comparable to the ones obtained in relativistic calculations and we get one of
the best agreements with lattice data. Our simple wave functions are used to
evaluate semileptonic decays of doubly heavy and baryons. Our results for the decay widths are in reasonable
agreement with calculations done in a relativistic calculation in the
quark-diquark approximation. We also check that our wave functions comply with
what it is expected in the infinite heavy quark mass limit.Comment: 3 latex pages, two tables. To appear in the INPC07 proceeding
Masses and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model
We evaluate masses and semileptonic decay widths for the ground state of
doubly heavy and baryons in the framework of a nonrelativistic
quark model. We solve the three-body problem by means of a variational ansatz
made possible by heavy-quark spin symmetry constraints. Our masses are
comparable to the ones obtained in relativistic calculations and we get one of
the best agreements with lattice data. Our simple wave functions are used to
evaluate semileptonic decays of doubly heavy and baryons. Our results for the decay widths are in reasonable
agreement with calculations done in a relativistic calculation in the
quark-diquark approximation. We also check that our wave functions comply with
what it is expected in the infinite heavy quark mass limit.Comment: 3 latex pages, two tables. To appear in the INPC07 proceeding
Strong one-pion decay of , and
Working in the framework of a nonrelativistic quark model we evaluate the
widths for the strong one-pion decays ,
and . We take advantage of
the constraints imposed by heavy quark symmetry to solve the three-body problem
by means of a simple variational ansatz. We use partial conservation of the
axial current hypothesis to get the strong vertices from weak axial current
matrix elements. Our results are in good agreement with experimental data.Comment: 3 latex pages. Contribution to the Proceedings of the Quark
Confinement and the Hadron Spectrum VII Conference (QCHS7) Ponta Delgada (PT)
Sept 2-7, 200
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
Quark model study of the semileptonic B -> pi decay
The semileptonic decay B->pi is studied starting from a simple quark model
and taking into account the effect of the B* resonance. A novel, multiply
subtracted, Omn\`es dispersion relation has been implemented to extend the
predictions of the quark model to all physical q^2 values. We find
|V_{ub}|=0.0034 +/- 0.0003(exp.)+/- 0.0007(theory), in good agreement with
experiment.Comment: Three pages, two figures. To appear in the proceedings of Quark
Confinament and Hadron Spectrum VII. Azores, September 200
Assessment and validation of wildfire susceptibility and hazard in Portugal
A comprehensive methodology to assess forest fire susceptibility, that uses variables of strong spatial correlation, is presented and applied for the Portuguese mainland. Our study is based on a thirty-year chronological series of burnt areas. The first twenty years (1975–1994) are used for statistical modelling, and the last ten (1995–2004) are used for the independent validation of results. The wildfire affected areas are crossed with a set of independent layers that are assumed to be relevant wildfire conditioning factors: elevation, slope, land cover, rainfall and temperature. Moreover, the wildfire recurring pattern is also considered, as a proxy variable expressing the influence of human action in wildfire occurrence. A sensitivity analysis is performed to evaluate the weight of each individual theme within the susceptibility model. Validation of the wildfire susceptibility models is made through the computation of success rate and prediction rate curves. The results show that it is possible to have a good compromise between the number of variables within the model and the model predictive power. Additionally, it is shown that integration of climatic variables does not produce any relevant increase in the prediction capacity of wildfire susceptibility models. Finally, the prediction rate curves produced by the independent cross validation are used to assess the probabilistic wildfire hazard at a scenario basis, for the complete mainland Portuguese territory
Simulação da Produção de Cupuaçu (Theobroma grandiflorum) e Pupunha (Bactris gasipaes) em Sistemas Agroflorestais Utilizando Modelos de Dinâmica de Sistemas.
bitstream/item/64869/1/cot32-2009-safs-marcelo.pd
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