102 research outputs found
Bounds on Broken R-Parity from Leptonic Meson Decays
Investigating leptonic decays of pi^-, K^-, B^-, pi^0, K_L^0, B_s^0 we
present new bounds on some products of two R-parity violating coupling
constants. For mesons of a similar structure but so far poor experimental data
we give the corresponding formulae, to be used in the future.Comment: Latex, 15 pages, 1 figure; final version which appeared in Phys.Rev.
Relations between the K_{l3} and tau --> K pi nu_tau decays
We investigate the relations between the K_{l3} and tau --> K pi nu_tau
decays using the meson dominance approach. First, the experimental branching
fractions (BF) for K^-_{e3} and K^0_{e3} are used to fix two normalization
constants (isospin invariance is not assumed). Then, the BF of tau^- -->
K^*(892)^- nu_tau is calculated in agreement with experiment. We further argue
that the nonzero value of the slope parameter lambda_0 of the K^-_{mu3} and
K^0_{mu3} form factors f_0(t) implies the existence of the tau^- -->
K_0^*(1430)^- nu_tau decay. We calculate its BF, together with BF's of the
K^-_{mu3}, K^0_{mu3}, tau- --> K^- pi^0 nu_tau, and tau- --> antiK^0 pi^0
nu_tau decays, as a function of the lambda_0 parameter. At some value of
lambda_0, different for charged and neutral kaons, calculated BF's seem to
match existing data and a prediction is obtained for the tau^- --> K pi nu
decays going through the K_0^*(1430)^- resonance.Comment: 14 pages, RevTeX, epsf.sty, 3 embedded figure
Reparameterization Invariance Revisited
Reparameterization invariance, a symmetry of heavy quark effective theory,
appears in different forms in the literature. The most commonly cited forms of
the reparameterization transformation are shown to induce the same constraints
on operators that do not vanish under the equation of motion to order ,
and to be related by a redefinition of the heavy quark field. We give a new,
very straightforward proof that that the reparameterization invariance
constraints apply to all orders in under matching to full QCD and
renormalization-group running, at least up to and including .Comment: 20 pages, no figures, Latex. Revised version: Discussion of
reparameterization invariance constraints on class-II operators adde
Vector vibrations and the Ioffe-Regel crossover in disordered lattices
The spectral density for vector vibrations in the f.c.c. lattice with
force-constant disorder is analysed within the coherent potential
approximation. The phase diagram showing the weak- and strong-scattering
regimes is presented and compared with that for electrons. The weak-scattering
regime for external long-wavelength vibrational plane waves is shown to be due
to sum-rule correlations in the dynamical matrix. A secondary peak below the
Brillouin peak for sufficiently large wavevectors is found for the lattice
models. The results obtained are supported by precise numerical solutions.Comment: 21 pages, 13 figure
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
Heavy-baryon chiral perturbation theory and reparametrization invariance
We examine the constraints imposed by reparametrization invariance on
heavy-baryon chiral perturbation theory (HBChPT). We study the case of 3
flavors and consider both the strong and weak () interaction
sector. Some of the parameters in the HBChPT Lagrangian are fixed as a
consequence of reparametrization invariance. We discuss the consequences for
the calculation of hyperon weak radiative decays in HBChPT.Comment: 8 pages, Latex, no figure
Simultaneous Extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation
Several recent studies performed on constraints of a fourth generation of
quarks and leptons suffer from the ad-hoc assumption that 3 x 3 unitarity holds
for the first three generations in the neutrino sector. Only under this
assumption one is able to determine the Fermi constant G_F from the muon
lifetime measurement with the claimed precision of G_F = 1.16637 (1) x 10^-5
GeV^-2. We study how well G_F can be extracted within the framework of four
generations from leptonic and radiative mu and tau decays, as well as from K_l3
decays and leptonic decays of charged pions, and we discuss the role of lepton
universality tests in this context. We emphasize that constraints on a fourth
generation from quark and lepton flavour observables and from electroweak
precision observables can only be obtained in a consistent way if these three
sectors are considered simultaneously. In the combined fit to leptonic and
radiative mu and tau decays, K_l3 decays and leptonic decays of charged pions
we find a p-value of 2.6% for the fourth generation matrix element |U_{e 4}|=0
of the neutrino mixing matrix.Comment: 19 pages, 3 figures with 16 subfigures, references and text added
refering to earlier related work, figures and text in discussion section
added, results and conclusions unchange
Study of 3-prong Hadronic Decays with Charged Kaons
Using a sample of 4.7/fb integrated luminosity accumulated with the CLEO-II
detector at the Cornell Electron Storage Ring (CESR), we have measured the
branching fractions of the tau lepton into and relative to and relative to . The relative branching fractions are: (5.16+-0.20+-0.50)*,
(1.52+-0.14+-0.29)*, (2.54+-0.44+-0.39)* and at 95%
C.L., respectively. Coupled with additional experimental information, we use
our results to extract information on the structure of three-prong tau decays
to charged kaons.Comment: 16 pages postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Effective CP-violating operators of the tau lepton and some of their phenomenologies
The dimension-six CP-violating SU_L(2)\times U_Y(1) invariant operators
involving the tau lepton are studied. The constraints from the available
experimental data on tau dipole moments are derived. Under the current
constraints, the induced CP-violating effects could possibly be observed in tau
-> 3\pi \nu_{\tau} at the future tau-charm factory.Comment: comments added, refs corrected, version to appear in PR
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