Tracing CP-violation in Lepton Flavor Violating Muon Decays

Although the Lepton Flavor Violating (LFV) decay $\mu^+\to e^+ \gamma$ is forbidden in the Standard Model (SM), it can take place within various theories beyond the SM. If the branching ratio of this decay saturates its present bound [{\it i.e.,} Br$(\mu^+ \to e^+\gamma)\sim 10^{-11}$], the forthcoming experiments can measure the branching ratio with high precision and consequently yield information on the sources of LFV. In this letter, we show that for polarized $\mu^+$, by studying the angular distribution of the transversely polarized positron and linearly polarized photon we can derive information on the CP-violating sources beyond those in the SM. We also study the angular distribution of the final particles in the decay $\mu^+\to e^+_1 e^- e^+_2$ where $e^+_1$ is defined to be the more energetic positron. We show that transversely polarized $e_1^+$ can provide information on a certain combination of the CP-violating phases of the underlying theory which would be lost by averaging over the spin of $e^+_1$.Comment: 6 pages, 2 figure

Sediment transport in steep channels with large roughness elements

Most sediment transport equations overestimate the bedload transport rate by several times when applied to mountain rivers. This is due to the fact that the presence of large relatively immobile boulders, which disrupt the flow, is generally not taken into account. Sediment transport in steep channels with boulders was herein investigated using 41 laboratory experiments carried out on a tilting flume for three slopes (S = 6.7%, 9.9%, and 13%). Sediment transport, mean flow velocities and morphology-describing variables were measured regularly during the experiments. The sediment transport capacity is clearly decreasing with dimensionless boulder distance and is better estimated in terms of critical discharge for incipient motion of mobile sediments than in terms of bed shear stress. A sediment transport formula based on excess discharge relative to a critical value, which depends not only on the channel slope but also on the boulder spatial density, is herein developed

Double Exchange Models: Self Consistent Renormalisation

We propose a scheme for constructing classical spin Hamiltonians from Hunds coupled spin-fermion models in the limit J_H/t \to \infinity. The strong coupling between fermions and the core spins requires self-consistent calculation of the effective exchange in the model, either in the presence of inhomogeneities or with changing temperature. In this paper we establish the formalism and discuss results mainly on the ``clean'' double exchange model, with self consistently renormalised couplings, and compare our results with exact simulations. Our method allows access to system sizes much beyond the reach of exact simulations, and we can study transport and optical properties of the model without artificial broadening. The method discussed here forms the foundation of our papers Phys. Rev. Lett. 91, 246602 (2003), and Phys. Rev. Lett. 92, 126602 (2004).Comment: 11 pages revtex. Final version, to appear in EPJ

Unitary Quantum Physics with Time-Space Noncommutativity

In this work quantum physics in noncommutative spacetime is developed. It is based on the work of Doplicher et al. which allows for time-space noncommutativity. The Moyal plane is treated in detail. In the context of noncommutative quantum mechanics, some important points are explored, such as the formal construction of the theory, symmetries, causality, simultaneity and observables. The dynamics generated by a noncommutative Schrodinger equation is studied. We prove in particular the following: suppose the Hamiltonian of a quantum mechanical particle on spacetime has no explicit time dependence, and the spatial coordinates commute in its noncommutative form (the only noncommutativity being between time and a space coordinate). Then the commutative and noncommutative versions of the Hamiltonian have identical spectra.Comment: 18 pages, published versio

Effective Lagrangians and Parity-Conserving Time-Reversal Violation at Low Energies

Using effective Lagrangians, we argue that any time-reversal-violating but parity-conserving effects are too small to be observed in flavor-conserving nuclear processes without dramatic improvement in experimental accuracy. In the process we discuss other arguments that have appeared in the literature.Comment: Revised manuscript, 11 pages, RevTex, epsf.st

Bosonization in the two-channel Kondo model

The bosonization of the $S=1/2$ anisotropic two-channel Kondo model is shown to yield two equivalent representations of the original problem. In a straight forward extension of the Emery-Kivelson approach, the interacting resonant level model previously derived by the Anderson-Yuval technique is obtained. In addition, however, a ``($\sigma$,$\tau$)'' description is also found. The strong coupling fixed point of the ($\sigma$,$\tau$) model was originally postulated to be related to the intermediate coupling fixed point of the two-channel Kondo model. The equivalence of the $\sigma$,$\tau$ model to the two-channel Kondo model is formally established. A summary of what one may learn from a simple study of these different representations is also given.Comment: 5 pages, latex (uses revtex and epsf macros) with 1 postscript figur

Influence of welding residual stresses on stable crack growth in tubular K-joints under compressive fatigue loadings

Tubular bridge design has to deal with fatigue issues. The fatigue susceptibility of these bridges, composed of circular hollow section profiles welded together in K-joints, is mainly due to stress concentrations, to welding imperfections and to tensile residual stresses induced by the welding process. Since these residual stresses are unknown for K-joints, measurements were carried out in vicinity of weld toes using the incremental hole-drilling method, X-ray diffraction and neutron diffraction in particular. Re-sults from these techniques show that on the first millimeters from the surface, the most important tensile re-sidual stresses are oriented perpendicular to the weld and reach the yield strength. According to experimental investigations on two large scale specimens, it is established that tensile residual stresses have a strong influ-ence down to a depth of 2-3 mm from the surface, allowing cracks to propagate in compressive joints. Prelim-inary Finite Element Analyses are presented in this paper