Gauge parameter dependence in the background field gauge and the construction of an invariant charge

By using the enlarged BRS transformations we control the gauge parameter dependence of Green functions in the background field gauge. We show that it is unavoidable -- also if we consider the local Ward identity -- to introduce the normalization gauge parameter $\xi_o$, which enters the Green functions of higher orders similarly to the normalization point $\kappa$. The dependence of Green functions on $\xi_o$ is governed by a further partial differential equation. By modifying the Ward identity we are able to construct in 1-loop order a gauge parameter independent combination of 2-point vector and background vector functions. By explicit construction of the next orders we show that this combination can be used to construct a gauge parameter independent RG-invariant charge. However, it is seen that this RG-invariant charge does not satisfy the differential equation of the normalization gauge parameter $\xi_o$, and, hence, is not $\xi_o$-independent as required.Comment: 29 pages, LaTe

La Unión Europea, en el camino hacia una Comunidad de Derecho Constitucional

En este trabajo se aborda, en primer lugar, un resumen de los principales pasos en el proceso de integración europea, subrayando los aspectos más relevantes desde el punto de vista del Derecho Constitucional. Se detiene especialmente en el análisis de la Carta de Derechos Fundamentales de la Unión Europea, y posteriormente en el proceso frustrado de ratificación del Tratado por el que se establece una Constitución para Europa. El autor sugiere una serie de alternativas para que pueda seguir avanzándose en la integración, y sostiene que Europa ya es una Comunidad de Derecho Constitucional

Conditions for Adiabatic Spin Transport in Disordered Systems

We address the controversy concerning the necessary conditions for the observation of Berry phases in disordered mesoscopic conductors. For this purpose we calculate the spin-dependent conductance of disordered two-dimensional structures in the presence of inhomogeneous magnetic fields. Our numerical results show that for both, the overall conductance and quantum corrections, the relevant parameter defining adiabatic spin transport scales with the square root of the number of scattering events, in generalization of Stern's original proposal [Phys. Rev. Lett. 68, 1022 (1992)]. This could hinder a clear-cut experimental observation of Berry phase effects in diffusive metallic rings.Comment: 5 pages, 4 figures. To appear in Phys. Rev. B (Rapid Communications