Semileptonic Hyperon Decays and CKM Unitarity

Using a technique that is not subject to first-order SU(3) symmetry breaking effects, we determine the $V_{us}$ element of the CKM matrix from data on semileptonic hyperon decays. We obtain $V_{us}$ =0.2250(27). This value is of similar precision to the one derived from $K_{l3}$, but higher and in better agreement with the unitarity requirement, $|V_{ud}|^2+|V_{us}|^2+|V_{ub}|^2=1$.Comment: 3 pages, 1 tabl

Deconfinement in Yang-Mills: a conjecture for a general gauge Lie group G

Svetitsky and Yaffe have argued that -- if the deconfinement phase transition of a (d+1)-dimensional Yang-Mills theory with gauge group G is second order -- it should be in the universality class of a d-dimensional scalar model symmetric under the center C(G) of G. These arguments have been investigated numerically only considering Yang-Mills theory with gauge symmetry in the G=SU(N) branch, where C(G)=Z(N). The symplectic groups Sp(N) provide another extension of SU(2)=Sp(1) to general N and they all have the same center Z(2). Hence, in contrast to the SU(N) case, Sp(N) Yang-Mills theory allows to study the relevance of the group size on the order of the deconfinement phase transition keeping the available universality class fixed. Using lattice simulations, we present numerical results for the deconfinement phase transition in Sp(2) and Sp(3) Yang-Mills theories both in (2+1)d and (3+1)d. We then make a conjecture on the order of the deconfinement phase transition in Yang-Mills theories with general Lie groups SU(N), SO(N), Sp(N) and with exceptional groups G(2), F(4), E(6), E(7), E(8). Numerical results for G(2) Yang-Mills theory at finite temperature in (3+1)d are also presented.Comment: Invited talk at the International Workshop "QCD DOWN UNDER", Adelaide, Australia, 10-19 Mar 2004. 6 pages, 6 figure

The electromagnetic effects in Ke4K_{e4} decay

The final state interaction of pions in $K_{e4}$ decay allows one to obtain the value of the isospin and angular momentum zero $\pi\pi$ scattering length $a_0^0$.We take into account the electromagnetic interaction of pions and isospin symmetry breaking effects caused by different masses of neutral and charged pions and estimate the impact of these effects on the procedure of scattering length extraction from $K_{e4}$ decay.Comment: 8 pages,1 figur

The Dynamical Dipole Mode in Dissipative Heavy Ion Collisions

We study the effect of a direct Giant Dipole Resonance ($GDR$) excitation in intermediate dinuclear systems with exotic shape and charge distributions formed in charge asymmetric fusion entrance channels. A related enhancement of the $GDR$ gamma yield in the evaporation cascade of the fused nucleus is expected. The dynamical origin of such $GDR$ extra strength will show up in a characteristic anisotropy of the dipole gamma-emission. A fully microscopic analysis of the fusion dynamics is performed with quantitative predictions of the $GDR$ photon yield based on a dynamics- statistics coupling model. In particular we focus our attention on the energy and mass dependence of the effect. We suggest a series of new experiments, in particular some optimal entrance channel conditions. We stress the importance of using the new available radioactive beams.Comment: 20 pages (Latex), 14 Postscript figure

Light meson decay constants beyond the quenched approximation

We calculate the effects of including dynamical fermion loops in the lattice QCD estimates of meson decay constants, by extrapolating the results from negative flavour numbers after a suitable matching of the pion and rho mass. For moderately light quarks, the values of the decay constants not corrected for the renormalization constants increase with respect to their quenched values.Comment: 9 pages, uuencoded PS file, 2 figures include

Adiabatic heating and role of the intermetallic phase on the ECAP-induced strengthening in an Al-Cu alloy

In the present work, the strengthening effect of the Fe-rich intermetallic phases in a 2219 aluminum alloy subjectedto equal-channel angular pressing (ECAP) has been studied. Three different deformation conditions, correspondingto the as-extruded, ECAP/A-1 pass and ECAP/A-2 passes were considered. Mechanical and morphologicalcharacterizations have been performed by microhardness tests, light microscopy, transmission electron microscopyand scanning electron microscopy observations. All the contributions to the strengthening due to solid solution,dislocation boundary and secondary phase have been discussed. The electron microscopy study focused on theevaluation of the strengthening effect generated by the (Fe,Mn,Cr)3Si2Al15 intermetallic. This strengthening effect,generated by coarse precipitates such are the Fe-rich intermetallics, has also been correlated to the morphologicalparticle aspect. The ECAP-induced adiabatic heating strengthening contribution was also determined. Astrengthening combination model of all the microstructure terms was proposed and applied to this case to meet thealloy yield stress at the two different ECAP straining levels corresponding to the first and the second pass via route A

zno nanowires grown on bulk zno coatings: mechanical response to deep cryogenic treatment

ZnO nanowires are currently used in many application fi elds, such emission displays, dye-sensitized solar cells,gas sensors, nanomachines, to cite but few. Thermal stability is often a concern in terms of the mechanicalresponse and, in particular, for the elasticity of the nanowires. Literature works focused to a certain degree, onthe heating response of nanowires. Anyhow, no experimental data are nowadays available in literature on the lowandvery low-temperature exposures. In the present study, deep-cryogenic treatment was performed on verticallyaligned ZnO nanowires produced by metal organic chemical vapor deposition. The mechanical response of thenanowires was detected by nanoindentation tests. It was found that the Young’s modulus, the critical bucklingstress and strain of individual nanowires is not signifi cantly infl uenced by the cryogenic exposure. Yet, the bulkbase ZnO from which the nanowires are grown halved after the deep-cryogenic treatment

Semileptonic Hyperon Decays on the Lattice: an Exploratory Study

We present preliminary results of an exploratory lattice study of the vector form factor $f_1(q^2 = 0)$ relevant for the semileptonic hyperon decay $\Sigma^{-} --> n l \nu$. This study is based on the same method used for the extraction of $f^+(0)$ for the decay $K^0 --> \pi^{-} l \nu$. The main purpose of this study is to test the method for hyperon form factors in order to estimate the precision that can be reached and the importance of SU(3)-breaking effects.Comment: 3 pages, 5 figures, talk presented at Lattice2004(weak), Fermilab, Batavia, Illinois, 21-26 June 200

Preon Prophecies by the Standard Model

The Standard Model of quarks and leptons is, at first sight, nothing but a set of {\it ad hoc} rules, with no connections, and no clues to their true background. At a closer look, however, there are many inherent prophecies that point in the same direction: {\it Compositeness} in terms of three stable preons.Comment: 13 pages, 8 eps-figures, invited talk at Beyond the Desert '03, Schloss Ringberg, Bavaria, June 2003; to be published in the Proceeding

Precise Determination of |V{us}| from Lattice Calculations of Pseudoscalar Decay Constants

Combining the ratio of experimental kaon and pion decay widths, Gamma(K to mu antineutrino{mu} (gamma)) / Gamma(pi to mu \antineutrino (gamma)), with a recent lattice gauge theory calculation of f{K}/f{pi} provides a precise value for the CKM quark mixing matrix element |V{us}|=0.2236(30) or if 3 generation unitarity is assumed |V{us}|=0.2238(30). Comparison with other determinations of that fundamental parameter, implications, and an outlook for future improvements are given