3,180 research outputs found
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
Physics Beyond the Standard Model: Focusing on the Muon Anomaly
We present a model based on the implication of an exceptional E_{6}-GUT
symmetry for the anomalous magnetic moment of the muon. We follow a particular
chain of breakings with Higgses in the 78 and 351 representations. We analyse
the radiative correction contributions to the muon mass and the effects of the
breaking of the so-called Weinberg symmetry. We also estimate the range of
values of the parameters of our model.Comment: 14 RevTeX pages, 5 figure
Baryon chiral perturbation theory with virtual photons and leptons
We construct the general pion-nucleon SU(2) Lagrangian including both virtual
photons and leptons for relativistic baryon chiral perturbation theory up to
fourth order. We include the light leptons as explicit dynamical degrees of
freedom by introducing new building blocks which represent these leptons.Comment: 11 page
Performance of Geant4 in simulating semiconductor particle detector response in the energy range below 1 MeV
Geant4 simulations play a crucial role in the analysis and interpretation of
experiments providing low energy precision tests of the Standard Model. This
paper focuses on the accuracy of the description of the electron processes in
the energy range between 100 and 1000 keV. The effect of the different
simulation parameters and multiple scattering models on the backscattering
coefficients is investigated. Simulations of the response of HPGe and
passivated implanted planar Si detectors to \beta{} particles are compared to
experimental results. An overall good agreement is found between Geant4
simulations and experimental data
Orbital-selective Mott transitions in the anisotropic two-band Hubbard model at finite temperatures
The anisotropic degenerate two-orbital Hubbard model is studied within
dynamical mean-field theory at low temperatures. High-precision calculations on
the basis of a refined quantum Monte Carlo (QMC) method reveal that two
distinct orbital-selective Mott transitions occur for a bandwidth ratio of 2
even in the absence of spin-flip contributions to the Hund exchange. The second
transition -- not seen in earlier studies using QMC, iterative perturbation
theory, and exact diagonalization -- is clearly exposed in a low-frequency
analysis of the self-energy and in local spectra.Comment: 4 pages, 5 figure
Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory
We compute the hadronic light-by-light scattering contributions to the muon
anomalous magnetic moment, \amulbl, in chiral perturbation theory that are
enhanced by large logarithms and a factor of . They depend on a low-energy
constant entering pseudoscalar meson decay into a charged lepton pair. The
uncertainty introduced by this constant is , which is
comparable in magnitude to the present uncertainty entering the leading-order
vacuum polarization contributions to the anomalous moment. It may be reduced to
some extent through an improved measurement of the branching
ratio. However, the dependence of \amulbl on non-logarithmically enhanced
effects cannot be constrained except through the measurement of the anomalous
moment itself. The extraction of information on new physics would require a
future experimental value for the anomalous moment differing significantly from
the 2001 result reported by the E821 collaboration.Comment: 7 pages, 2 figure
- …