271 research outputs found
Lepton Flavour Violation in charged leptons within SUSY-seesaw
In this paper we review our main results for Lepton Flavour Violating (LFV)
semileptonic tau decays and muon-electron conversion in nuclei within the
context of two Constrained SUSY-Seesaw Models, the CMSSM and the NUHM. The
relevant spectrum is that of the Minimal Supersymmetric Standard Model extended
by three right handed neutrinos, and their corresponding SUSY
partners, , (). We use the seesaw mechanism for
neutrino mass generation and choose a parameterisation of this mechanism that
allows us to incorporate the neutrino data in our analysis of LFV processes. In
addition to the full one-loop results for the rates of these processes, we will
also review the set of simple formulas, valid at large , which are
very useful to compare with present experimental bounds. The sensitivity to
SUSY and Higgs sectors in these processes will also be discussed. This is a
very short summary of the works in Refs. \cite{Arganda:2008jj} and
\cite{Arganda:2007jw} to which we refer the reader for more details.Comment: 6 pages, 6 figures. To be published in the proceedings of the Tau08
Conference, Novosibirsk, Russia, 22-25 September 200
Hadron structure in tau -> KKpi nu_tau decays
We analyse the hadronization structure of both vector and axial-vector
currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc
expansion, and considering only the contribution of the lightest resonances, we
work out, within the framework of the resonance chiral Lagrangian, the
structure of the local vertices involved in those processes. The couplings in
the resonance theory are constrained by imposing the asymptotic behaviour of
vector and axial-vector spectral functions ruled by QCD. In this way we predict
the hadron spectra and conclude that, contrarily to previous assertions, the
vector contribution dominates by far over the axial-vector one in all KKpi
charge channels.Comment: 32 pages, 7 figure
On the massless contributions to the vacuum polarization of heavy quarks
Recently Groote and Pivovarov have given notice of a possible fault in the
use of sum rules involving two-point correlation functions to extract
information on heavy quark parameters, due to the presence of massless
contributions that invalidate the construction of moments of the spectral
densities. Here we show how to circumvent this problem through a new definition
of the moments, providing an infrared safe and consistent procedure.Comment: 1+9 pages, 3 figures. Discussion on QCD sum rules applications added.
Conclusions unchanged. Version to be published in Journal of Physics
Phenomenology of the <VVP> Green's function within the Resonance Chiral Theory
We analyse the odd-intrinsic-parity effective Lagrangian of QCD valid for
processes involving one pseudoscalar with two vector mesons described in terms
of antisymmetric tensor fields. Substantial information on the
odd-intrinsic-parity couplings is obtained by constructing the
vector-vector-pseudoscalar Green's three-point function, at leading order in
1/N_C, and demanding that its short-distance behaviour matches the
corresponding OPE result. The QCD constraints thus enforced allow us to predict
the decay amplitude omega -> pi gamma, the O(p^6) corrections to pi -> gamma
gamma and the slope parameter in pi -> gamma gamma^*.Comment: 4 pages, 1 figure. Talk given at QCD 03: High-Energy Physics
International Conference in Quantum Chromodynamics, Montpellier, France, 2-8
Jul 200
Vector form factor of the pion : A model-independent approach
We study a model-independent parameterization of the vector pion form factor
that arises from the constraints of analyticity and unitarity. Our description
should be suitable up to s^(1/2) ~ 1.2 GeV and allows a model-independent
determination of the mass of the rho(770) resonance. We analyse the
experimental data on tau^- -> pion^- pion^0 nu_tau and e^+ e^- -> pion^+ pion^-
in this framework, and its consequences on the low-energy observables worked
out by chiral perturbation theory. An evaluation of the two pion contribution
to the anomalous magnetic moment of the muon, a_{mu}, and to the fine structure
constant, alpha(M_Z^2), is also performed.Comment: 5 pages, 2 figures. To appear in the proceedings of the High-Energy
Physics International Conference on Quantum Chromodynamics QCD02, Montpellier
(France), 2-9 July (2002
Form Factors in the radiative pion decay
We perform an analysis of the form factors that rule the structure-dependent
amplitude in the radiative pion decay. The resonance contributions to pion -> e
nu_e gamma decays are computed through the proper construction of the vector
and axial-vector form factors by setting the QCD driven asymptotic properties
of the three-point Green functions VVP and VAP, and by demanding the smoothing
of the form factors at high transfer of momentum. A comparison between
theoretical and experimental determinations of the form factors is also carried
out. We also consider and evaluate the role played by a non-standard tensor
form factor. We conclude that, at present and due to the hadronic incertitudes,
the search for New Physics in this process is not feasible.Comment: 14 pages, no figures. Typos corrected. Accepted for publication in
The European Physical Journal
The <SPP> Green function and SU(3) breaking in Kl3 decays
Using the 1=/N-C expansion scheme and truncating the hadronic spectrum to the lowest-lying resonances, we match a meromorphic approximation to the Green function onto QCD by imposing the correct large-momentum falloff, both off- shell and on the relevant hadron mass shells. In this way we determine a number of chiral low-energy constants of O(p(6)), in particular the ones governing SU(3) breaking in the K-l3 vector form factor at zero momentum transfer. The main result of our matching procedure is that the known loop contributions largely dominate the corrections of O(p(6)) to f(+)(0). We discuss the implications of our final value f(+)(K0 pi-) (0) = 0.984 +/- 0.012 for the extraction of V-us from K-l3 decays
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