121 research outputs found
Double and the Interaction
The - effective interaction, in the channel , in the
nuclear medium is fitted to the available binding energies,
, of double hypernuclei:
He, Be and
B. The mesonic decay of these hypernuclei is also
investigated. Finally, this effective interaction is used to predict the
binding energies and mesonic decays widths of heavier double
hypernuclei.Comment: 4 pages, (latex file, postscript-file and 3 Postscript-figures
included
Lattice-Constrained Parametrizations of Form Factors for Semileptonic and Rare Radiative B Decays
We describe the form factors for semileptonic B to rho l nu and radiative B
to K* gamma decays with just two parameters and the two form factors for
semileptonic B to pi l nu decays with three parameters. The parametrizations
are constrained by lattice results and are consistent with heavy quark
symmetry, kinematic constraints and light cone sum rule scaling relations.Comment: 3 pages, latex, 2 eps files, uses epsf.sty and espcrc2.sty, poster
presented at Lattice 97, Edinburgh, 22-26 July 199
An Investigation of the Soft Pion Relation in Quenched Lattice QCD
A lattice determination of the form factor and decay constants for the
semileptonic decay of heavy pseudoscalar (PS) mesons at zero recoil is
presented from which the soft pion relation is satisfied. Chiral extrapolation
of the form factor is performed at constant . Pole dominance is used to
extrapolate the form factor in heavy quark mass. At the B mass, the form factor
at zero recoil lies somewhat below the ratio of decay constants; the relation
remains satisfied within error.Comment: 3 pages, 2 figure
Standardized Precipitation Index (SPI) evolution over the Iberian Peninsula during the 21st century
Droughts are important natural hazards that occur worldwide and can have severe and long-lasting impacts on humans and ecosystems. These phenomena are usually quantified by means of the so-called drought indices, which are indirect indicators based on climatic information. The Standardized Precipitation Index (SPI) is one of the most widely used indexes and this study attempts to characterize the occurrence and spatial variability of this index in the Iberian Peninsula (IP) over the 21st century. The SPI was calculated at two time scales (3 and 12 months), using simulations from the EURO-CORDEX project under two future scenarios (Representative Concentration Pathway (RCP) 4.5 and RCP 8.5) to analyze meteorological and hydrological droughts. Meteorological droughts (SPI-3) are expected to be less frequent but more intense and durable in the eastern IP, intensifying throughout the century and for the RCP 8.5 scenario. In the first decades of the 21st century, hydrological droughts (SPI-12) are projected to be more common and severe in the northwestern region of the IP for the RCP 4.5, and less frequent but more lasting in the other regions of IP for the RCP 8.5. As the century passes, the drought frequency and intensity experience a decrease in the RCP 4.5 scenario, and a slight increase in the RCP 8.5 scenario.Xunta de Galicia | Ref. ED431C 2021/44Fundação para a CiĂȘncia e a Tecnologia | Ref. SFRH/BD/138755/2018Fundação para a CiĂȘncia e a Tecnologia | Ref. UIDP/50017/2020Fundação para a CiĂȘncia e a Tecnologia | Ref. UIDB/50017/2020Fundação para a CiĂȘncia e a Tecnologia | Ref. LA/P/0094/202
El gĂ©nero Dryopteris Adanson (Dryopteridaceae) en el noroeste de la PenĂnsula IbĂ©rica
Se ha estudiado el nÂș de cromosomas, la cantidad de DNA mediante citometrĂa de flujo, los caracteres esporales
a microscopĂa Ăłptica y de barrido, el indusio, asĂ como la corologĂa de cada uno de los 10 taxones que
viven en el territorio
Heavy quark symmetry constraints on semileptonic form factors and decay widths of doubly heavy baryons
We show how heavy quark symmetry constraints on doubly heavy baryon
semileptonic decay widths can be used to test the validity of different quark
model calculations. The large discrepancies in the results observed between
different quark model approaches can be understood in terms of a severe
violation of heavy quark spin symmetry constraints by some of those models.Comment: 10 LaTex pages, 3 figures, 6 tables. Corrected and enlarged versio
First Lattice Study of the Form Factors A_0 and A_3 in the Decay Bbar^0 to rho^+ l^- nubar_l
We report on a lattice calculation of the form factors A_0 and A_3 for the
pseudoscalar to vector meson semileptonic decay Bbar^0 to rho^+ l^- nubar_l. We
find that resonant (or pole-type) contributions alone are unable to describe
these two form factors simultaneously. For the quantity A_0(q^2=0), which is
important phenomenologically for the determination of |Vub|, we extract a range
of values, A_0(q^2=0) = (0.16--0.35) +0.09-0.06, where the range is due to
systematic uncertainty and the quoted error is statistical. We have also
determined A_2(q^2=0) = 0.28 +0.09-0.06 +0.04-0.05.Comment: 14 pages LaTeX209 with 5 figures from 11 encapsulated PostScript
files, using epsf.sty. Also available from
http://wwwhep.phys.soton.ac.uk/hepwww/papers/shep9601
Plasma wave instabilities induced by neutrinos
Quantum field theory is applied to study the interaction of an electron
plasma with an intense neutrino flux. A connection is established between the
field theory results and classical kinetic theory. The dispersion relation and
damping rate of the plasma longitudinal waves are derived in the presence of
neutrinos. It is shown that Supernova neutrinos are never collimated enough to
cause non-linear effects associated with a neutrino resonance. They only induce
neutrino Landau damping, linearly proportional to the neutrino flux and
.Comment: 18 pages, 3 figures, title and references correcte
Test of the heavy quark-light diquark approximation for baryons with a heavy quark
We check a commonly used approximation in which a baryon with a heavy quark
is described as a heavy quark-light diquark system. The heavy quark influences
the diquark internal motion reducing the average distance between the two light
quarks. Besides, we show how the average distance between the heavy quark and
any of the light quarks, and that between the heavy quark and the center of
mass of the light diquark, are smaller than the distance between the two light
quarks, which seems to contradict the heavy quark-light diquark picture. This
latter result is in agreement with expectations from QCD sum rules and lattice
QCD calculations. Our results also show that the diquark approximations
produces larger masses than the ones obtained in a full calculation.Comment: 9 latex pages, 5 figures, 6 table
The R136 star cluster dissected with Hubble Space Telescope/STIS. II. Physical properties of the most massive stars in R136
We present an optical analysis of 55 members of R136, the central cluster in the Tarantula Nebula of the Large Magellanic Cloud. Our sample was observed with STIS aboard the Hubble Space Telescope, is complete down to about 40 Mâ, and includes 7 very massive stars with masses over 100 Mâ. We performed a spectroscopic analysis to derive their physical properties. Using evolutionary models we find that the initial mass function (IMF) of massive stars in R136 is suggestive of being top-heavy with a power-law exponent Îł â 2 ± 0.3, but steeper exponents cannot be excluded. The age of R136 lies between 1 and 2 Myr with a median age of around 1.6 Myr. Stars more luminous than logâL/Lâ = 6.3 are helium enriched and their evolution is dominated by mass loss, but rotational mixing or some other form of mixing could be still required to explain the helium composition at the surface. Stars more massive than 40 Mâ have larger spectroscopic than evolutionary masses. The slope of the wind-luminosity relation assuming unclumped stellar winds is 2.41 ± 0.13 which is steeper than usually obtained (âŒ1.8). The ionising (logâQ0â[ph/s] = 51.4) and mechanical (logâLSWâ[erg/s] = 39.1) output of R136 is dominated by the most massive stars (>100âMâ). R136 contributes around a quarter of the ionising flux and around a fifth of the mechanical feedback to the overall budget of the Tarantula Nebula. For a census of massive stars of the Tarantula Nebula region we combined our results with the VLT-FLAMES Tarantula Survey plus other spectroscopic studies. We observe a lack of evolved Wolf-Rayet stars and luminous blue and red supergiants
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