Double Λ\Lambda and the Λ−Λ\Lambda-\Lambda Interaction

The $\Lambda$-$\Lambda$ effective interaction, in the channel $L=S=0$, in the nuclear medium is fitted to the available binding energies, $B_{\Lambda\Lambda}$, of double $\Lambda$ hypernuclei: $^{6}_{\Lambda\Lambda}$He, $^{10}_{\Lambda\Lambda}$Be and $^{13}_{\Lambda\Lambda}$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 $\Lambda$ 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 $q^2$. 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 Ciência e a Tecnologia | Ref. SFRH/BD/138755/2018Fundação para a Ciência e a Tecnologia | Ref. UIDP/50017/2020Fundação para a Ciência e a Tecnologia | Ref. UIDB/50017/2020Fundação para a Ciência e a Tecnologia | Ref. LA/P/0094/202

El género Dryopteris Adanson (Dryopteridaceae) en el noroeste de la Península Ibérica

Se ha estudiado el nº de cromosomas, la cantidad de DNA mediante citometría de flujo, los caracteres esporales a microscopía óptica y de barrido, el indusio, así como la corología 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 $G_{\mathrm{F}}^{2}$.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 M⊙, and includes 7 very massive stars with masses over 100 M⊙. 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 γ ≈ 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 log L/L⊙ = 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 M⊙ 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 (∼1.8). The ionising (log Q0 [ph/s] = 51.4) and mechanical (log LSW [erg/s] = 39.1) output of R136 is dominated by the most massive stars (>100 M⊙). 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