Nonsinglet contributions to the structure function g1_{1} at small-x

Nonsinglet contributions to the g_1(x,Q^2) structure function are calculated in the double-logarithmic approximation of perturbative QCD in the region x \ll 1. Double logarithmic contributions of the type (\alpha_s \ln ^2 (1/x))^k which are not included in the GLAP evolution equations are shown to give a stronger rise at small-x than the extrapolation of the GLAP expressions. Further enhancement in the small-x region is due to non-ladder Feynman graphs which in the DLA of the unpolarized structure functions do not contribute. Compared to the conventional GLAP method (where neither the whole kinematical region which gives the double logs nor the non-ladder graphs are taken into account) our results lead to a growth at small-x which, for HERA parameters, can be larger by up to factor of 10 or more

Response of the electric field gradient in ion implanted BaTiO3_{3} to an external electric field

Single crystalline, ferroelectric BaTiO$_{3}$ as material with the highest piezoelectric constants among the perovskites with ordered sublattices was implanted with $^{111}$In($^{111}$Cd). The electric field gradient at the Ti position was measured with perturbed $\gamma-\gamma$-angular correlation spectroscopy (PAC) while the crystal was exposed to an external electric field. A quadratic dependence could be observed: $\nu_{Q}$(E) = (34.8(1) + 0.16(4) E/kV/mm + 0.080(2) E$^{2}$/kV$^{2}$/mm$^{2}$) MHz. Point charge model calculations reproduce the linear change of Vzz, but not the quadratic term. The polarizability of the host ions of BaTiO$_{3}$ is known to be nonlinear with respect to an electric field. The resulting quadratic shift of the electron density is reflected in the strength of the EFG

High-energy behaviour in a non-Abelian gauge theory ; 1, Tn−−>m_{n --> m }in the leading ln s approximation

This is the first part of an attempt to find a unitary high-energy description of a spontaneously broken non-Abelian gauge theory. The author calculates the high-energy behaviour of n to m amplitudes in the leading ln s approximation. The author starts from tree approximations and then only use dispersion relations and unitarity equations for elastic and inelastic amplitudes in the multi-Regge limit. The resulting amplitudes have multi-Regge behaviour with simple pole exchange, and satisfy s-channel unitarity in all channels. There is, however, no vacuum quantum number exchange (pomeron) in this approximation. The author briefly outlines a scheme which may lead to a unitary description of the pomeron. (17 refs)