224 research outputs found
BIOH2POWER WP1: BIOGASSPECIFICATIONS AND CRITICALANALYSIS OF PRESENT SITUATION ANDFUTURE PERSPECTIVE FOR BIOGASPRODUCTION IN ITALY AND PIEMONTE
The objective of the Work Package 1 on the frame of the BioH2Power project is to define biogas specifications, in terms of quantity and quality, to be used as a reference for desulphurizing/reforming processes, on the basis of the real on-field experience of a major Italian biogas-to-energy enterprise. Asja will carry on its involvement in the research project building upon its 10-years experience in the field of renewable energy generation from biogas. The technological know-how acquired since the beginning of its operation allows Asja to define the major critical factors in the treatment and use of biogas generated from anaerobic digestion of organic matter. Therefore, its role in the research program will be to provide effective knowing of the reality of biogas, on the basis of the plants Asja manages every day all over Italy and abroad. Then an identification of the potential sources of biogas will be provided in collaboration with Politecnico di Torino. DISMIC complements the work covering other biogas sources different from landfill
Axions and high-energy cosmic rays: Can the relic axion density be measured?
In a previous work we investigated the propagation of fast moving charged
particles in a spatially constant but slowly time dependent pseudoscalar
background, such as the one provided by cold relic axions. The background
induces cosmic rays to radiate in the low-energy spectrum. While the energy
loss caused by this mechanism on the primary cosmic rays is negligible, we
investigate the hypothetical detection of the photons radiated and how they
could provide an indirect way of verifying the cosmological relevance of
axions. Assuming that the cosmic ray flux is of the form J(E)~ E^-g we find
that the energy radiated follows a distribution k^-((g-1)/2) for proton
primaries, identical to the Galaxy synchrotron radiation that is the main
background, and k^-(g/2) for electron primaries, which in spite of this sharper
decay provide the dominant contribution in the low-energy spectrum. We discuss
possible ways to detect this small diffuse contribution. Local detection in the
vicinity of powerful cosmic rays emitters might also be possible.Comment: plot improved with background and comments adde
Lattice study of semileptonic form factors with twisted boundary conditions
We apply twisted boundary conditions to lattice QCD simulations of
three-point correlation functions in order to access spatial components of
hadronic momenta different from the integer multiples of 2 pi / L. We calculate
the vector and scalar form factors relevant to the K -> pi semileptonic decay
and consider all the possible ways of twisting one of the quark lines in the
three-point functions. We show that the momentum shift produced by the twisted
boundary conditions does not introduce any additional noise and easily allows
to determine within a few percent statistical accuracy the form factors at
quite small values of the four-momentum transfer, which are not accessible when
periodic boundary conditions are considered. The use of twisted boundary
conditions turns out to be crucial for a precise determination of the form
factor at zero-momentum transfer, when a precise lattice point sufficiently
close to zero-momentum transfer is not accessible with periodic boundary
conditions.Comment: latex 15 pages, 4 figures and 3 tables; modified intro and
discussions of the results; version to appear in PR
Improved estimates of rare K decay matrix-elements from Kl3 decays
The estimation of rare K decay matrix-elements from Kl3 experimental data is
extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at
NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative
corrections are now accounted for. The analysis relies mainly on the cleanness
of two specific ratios of form-factors, for which the theoretical control is
excellent. As a result, the uncertainties on the K+ --> pi+ nu nubar and KL -->
pi0 nu nubar matrix-elements are reduced by a factor of about 7 and 4,
respectively, and similarly for the direct CP-violating contribution to KL -->
pi0 l+ l-. They could be reduced even further with better experimental data for
the Kl3 slopes and the K+l3 branching ratios. As a result, the non-parametric
errors for B(K --> pi nu nubar) and for the direct CP-violating contributions
to B(KL --> pi0 l+ l-) are now completely dominated by those on the
short-distance physics.Comment: 16 pages, 1 figure. Numerical analysis updated to include the recent
Kl3 data. To appear in Phys. Rev.
SU(3)-breaking effects in kaon and hyperon semileptonic decays from lattice QCD
We discuss the result of a recent quenched lattice calculation of the K -> pi
vector form factor at zero-momentum transfer, relevant for the determination of
|V_us| from K-> pi l nu decays. Using suitable double ratios of three-point
correlation functions, we show that it is possible to calculate this quantity
at the percent-level precision. The leading quenched effects are corrected for
by means of quenched chiral perturbation theory. The final result, f+(0) =
0.960 +- 0.005_stat +- 0.007_syst, turns out to be in good agreement with the
old quark model estimate made by Leutwyler and Roos. In this paper, we discuss
the phenomenological impact of the lattice result for the extraction of |V_us|,
by updating the analysis of K -> pi l nu decays with the most recent
experimental data. We also present a preliminary lattice study of hyperon Sigma
-> n l nu decays, based on a similar strategy.Comment: 17 pages, 8 figures. Based on talks given at: DAFNE 2004: Physics at
meson factories, Laboratori Nazionali di Frascati (Italy), June 7-11, 2004;
VIII International Conference on "Electron-Nucleus Scattering", Marciana
Marina (Italy), June 21-25, 2004; Lattice 2004, Fermi National Accelerator
Laboratory, Batavia, Illinois (USA), June 21-26, 2004; ICHEP 2004, Beijing
(China), August 16-22, 200
Light hadron spectroscopy on the lattice with the non-perturbatively improved Wilson action
We present results for the light meson masses and decay constants as obtained
from calculations with the non-perturbatively improved (`Alpha') action and
operators on a 24^3 \times 64 lattice at beta = 6.2, in the quenched
approximation. The analysis was performed in a way consistent with O(a)
improvement. We obtained: reasonable agreement with experiment for the
hyperfine splitting; f_K=156(17) MeV, f_pi =139(22) MeV, f_K/f_pi = 1.13(4) ;
f_{K*}=219(7) MeV, f_rho =199(15) MeV, f_phi =235(4) MeV; f_{K*}^{T}(2 GeV) =
178(10) MeV, f_rho^{T}(2 GeV) =165(11) MeV, where f_V^{T} is the coupling of
the tensor current to the vector mesons; the chiral condensate
^\bar{MS} (2 GeV)= - (253 +/- 25 MeV)^3. Our results are compared to
those obtained with the unimproved Wilson action. We also verified that the
free-boson lattice dispersion relation describes our results very accurately
for a large range of momenta.Comment: 29 pages (LaTeX), 14 Postscript figure
Decays of Heavy Mesons
We present preliminary results for heavy to light transitions of pseudoscalar
mesons, induced by the vector and tensor operators. This lattice study is
performed in quenched approximation, by using the nonperturbatively improved
Wilson action and operators. We also update the values of the heavy-light meson
decay constants.Comment: LATT99(Heavy Quarks), 3 pages, 2 figure
New results from APE with non-perturbatively improved Wilson fermions
We present the results for light hadron spectrum, decay constants and the
quark masses obtained with non-perturbatively improved Wilson fermions. We also
give our preliminary results for the heavy-light decay constants.Comment: 3 pages, 2 figures, corrected some typos and one reference added,
LATTICE98(spectrum
Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks
We compute non-perturbatively the B-parameters of the complete basis of
four-fermion operators needed to study the Kaon oscillations in the SM and in
its supersymmetric extension. We perform numerical simulations with two
dynamical maximally twisted sea quarks at three values of the lattice spacing
on configurations generated by the ETMC. Unwanted operator mixings and O(a)
discretization effects are removed by discretizing the valence quarks with a
suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are
renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result
for BK(RGI) is 0.73(3)(3).Comment: 7 pages, 3 figures, 1 table, proceedings of the XXVII Int'l Symposyum
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
Unitarity and causality constraints in composite Higgs models
We study the scattering of longitudinally polarized W bosons in extensions of the Standard Model where anomalous Higgs couplings to gauge sector and higher-order O(p4) operators are considered. These new couplings with respect to the Standard Model should be thought of as the low-energy remnants of some new dynamics involving the electroweak symmetry breaking sector. By imposing unitarity and causality constraints on the WW scattering amplitudes, we find relevant restrictions on the possible values of the new couplings and the presence of new dynamical resonances above 300 GeV. We investigate the properties of these new resonances and their experimental detectability. Custodial symmetry is assumed to be exact throughout, and the calculation avoids using the equivalence theorem as much as possible
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