Extensions in FormCalc 5.3

We present a new tool for editing Feynman diagrams as well as several extensions in version 5.3 of the package FormCalc for the calculation of Feynman diagrams.Comment: 8 pages, contribution to the proceedings of the ACAT workshop, Amsterdam, April 23-27, 200

Diagrammatic Monte Carlo study of the Fr\"ohlich polaron dispersion in 2D and 3D

We present results for the solution of the large polaron Fr\"ohlich Hamiltonian in 3-dimensions (3D) and 2-dimensions (2D) obtained via the Diagrammatic Monte Carlo (DMC) method. Our implementation is based on the approach by Mishchenko [A.S. Mishchenko et al., Phys. Rev. B 62, 6317 (2000)]. Polaron ground state energies and effective polaron masses are successfully benchmarked with data obtained using Feynman's path integral formalism. By comparing 3D and 2D data, we verify the analytically exact scaling relations for energies and effective masses from 3D$\to$2D, which provides a stringent test for the quality of DMC predictions. The accuracy of our results is further proven by providing values for the exactly known coefficients in weak- and strong coupling expansions. Moreover, we compute polaron dispersion curves which are validated with analytically known lower and upper limits in the small coupling regime and verify the first order expansion results for larger couplings, thus disproving previous critiques on the apparent incompatibility of DMC with analytical results and furnishing useful reference for a wide range of coupling strengths

Compression failure mechanisms in unidirectional composites

Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model

Interplay between Hbs and bsgamma in the MSSM with Non-Minimal Flavour Violation

We investigate the constraints on flavour-changing neutral heavy Higgs-boson decays H-> b \bar s from b -> s gamma bounds on the flavour-mixing parameters of the MSSM with non-minimal flavour violation (NMFV). In our analysis we include the contributions from the SM and new physics due to general flavour mixing in the squark mass matrices. We study the case of one and two non-zero flavour-mixing parameters and find that in the latter case the interference can raise the Higgs flavour-changing branching ratios by one or two orders of magnitude with respect to previous predictions based on a single non-zero parameter and in agreement with present constraints from $B$ physics. In the course of our work we developed a new "FeynArts" model file for the NMFV MSSM and added the necessary code for the evaluation to "FormCalc". Both extensions are publicly available.Comment: LaTeX2e, 15 pages, 4 figures. Computation improved and figures replaced accordingly. Some references added. Main conclusions remain untouche

Complete electroweak one-loop radiative corrections to top-pair production at TESLA -- a comparison

Electroweak one-loop radiative corrections to the process e^+ e^- -> t tbar are revisited. Two groups from Karlsruhe and Bielefeld/Zeuthen performed independent calculations of both (virtual and soft) QED contributions and weak virtual corrections. For the angular distribution an agreement of at least eight digits for the weak corrections and of at least seven digits for additional photonic corrections is established.Comment: 12 pages, minor improvement of soft photon correction

FormCalc 8: Better Algebra and Vectorization

We present Version 8 of the Feynman-diagram calculator FormCalc. New features include in particular significantly improved algebraic simplification as well as vectorization of the generated code. The Cuba Library, used in FormCalc, features checkpointing to disk for all integration algorithms.Comment: 7 pages, LaTeX, proceedings contribution to ACAT 2013, Beijing, China, 16-21 May 201

The effect of resin toughness and modulus on compressive failure modes of quasi-isotropic graphite/epoxy laminates

Compressive failure mechanisms in quasi-isotropic graphite/epoxy laminates were characterized for both unnotched and notched specimens and also following damage by impact. Two types of fibers (Thornel 300 and 700) and four resin systems (Narmco 5208, American Cyanamid BP907, and Union Carbide 4901/MDA and 4901/mPDA) were studied. For all material combinations, failure of unnotched specimens was initiated by kinking of fibers in the 0-degree plies. A major difference was observed, however, in the mode of failure propagation after the 0-degree ply failure. The strength of quasi-isotropic laminates in general increased with increasing resin tensile modulus. The laminates made with Thornel 700 fibers exhibited slightly lower compressive strengths than did the laminates made with Thornel 300 fibers. The notch sensitivity as measured by the hole strength was lowest for the BP907 resin and highest for the 5208 resin. For the materials studied, however, the type of fiber had no effect on the notch sensitivity

CP violating asymmetry in H±→W±h1H^\pm\to W^\pm h_1 decays

The CP violating asymmetry from the decay rates $H^\pm\to W^\pm h_1$ of charged Higgs bosons into the lightest neutral Higgs boson and a $W^\pm$ boson is calculated and discussed in the complex MSSM. The contributions from all complex phases are considered, especially from the top-squark trilinear coupling, which induces a large contribution to the CP asymmetry.Comment: 19 pages, 10 figures, version published in JHE