Tensor meson exchange at low energies

We complete the analysis of meson resonance contributions to chiral low-energy constants of O(p⁴) by including all quark–antiquark bound states with orbital angular momentum ≤1. Different tensor meson Lagrangians used in previous work are shown to produce the same final results for the low-energy constants, once QCD short-distance constraints are properly implemented. We also discuss the possible relevance of axial-vector mesons with odd C-parity (J^PC=1^+-).     

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Influence of molecular weight on the short‐channel effect in polymer‐based field‐effect transistors

In this study, we demonstrate how the intrinsic properties of a polymer can influence the electrical characteristics of organic field‐effect transistors (OFETs). OFETs fabricated with three batches of poly[2‐methoxy,5‐(3′,7′‐dimethyl‐octyloxy)]‐p‐phenylene vinylene (MDMO‐PPV) were investigated. The properties of the polymers were initially investigated using Fourier transform infrared spectroscopy (FTIR), impedance spectroscopy (IS), gel permeation chromotography (GPC), and cyclic voltammetry (CV), respectively. The structure and purity of the polymer batches were found to be very comparable, but the molecular weight (M_n and M_w) and polydispersity (PDI = M_w/M_n), varied between the samples and the HOMO and LUMO levels of the polymers were found to depend on the molecular weight properties. OFETs were then fabricated with the polymers and electrically characterized. It was observed that the channel current and the field‐effect mobility increase with increasing polymer molecular weight. The output characteristics of the transistors, on the other hand, were found to depend on the PDI of the polymer. Saturation of the channel current occurs at higher source–drain voltages and short‐channel behavior was observed to start at longer channel lengths for polymers with a higher PDI. This behavior is observed to be thickness dependent, and the short‐channel behavior was more pronounced for thicker MDMO‐PPV films. These results are explained in terms of influences of chain packing and ordering and high bulk currents on the FET output and transistor parameters. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 117–124, 2012     

Quark mass matrices in left-right symmetric gauge theories

The most general left-right symmetry for SU(2)_L×SU(2)_R×U(1) gauge theories with any number of flavours and with at most two scalar multiplets transforming as $\text{q}\text{q}$ bilinears is analyzed. In order to get additional constraints on the structure of quark mass matrices, all possible horizontal groups (continuous or discrete) are investigated. We give a complete classification of physically inequivalent quark mass matrices for four and six flavours. It is argued that our methods and results are also applicable in the case of dynamical symmetry breaking. Parity invariance and horizontal symmetry are shown to imply CP conservation on the lagrangian level. For all non-trivial three-generation models there is spontaneous CP violation, which in most cases turns out to be naturally small. Several six-flavour models predict $\text{m}{}_{\mathrm{<mtext>t</mtext>}}\text{?m}{}_{\mathrm{<mtext>b</mtext>}}\text{(}\text{m}{}_{\mathrm{<mtext>u</mtext>}}\text{m}{}_{\mathrm{<mtext>c</mtext>}}\text{m}{}_{\mathrm{<mtext>d</mtext>}}\text{m}{}_{\mathrm{<mtext>s</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and are, therefore, already ruled out experimentally. In the remaining few realistic models, predictions for the weak mixing angles are made.