Effective Lagrangian with vector mesons : Linear response theory

The soliton breathing mode is investigated in the framework of linear response theory within a Skyrme model vector meson stabilized. The effective Lagrangian considered includes the $\rho$ (introduced following the standard prescription of nonlinear chiral symmetry) and the $\omega$ mesons. The monopole response function is found to have a pronounced peak which is identified to the $P11$ (Roper) resonance. The results are compared to those obtained within the local approximation.Comment: 8 pages of plain Latex and 2 figures (available from the author), preprint LPN 93-12 and IPNO/TH 93-4

An infrared singularity in the damping rate for longitudinal gluons in hot QCD

We calculate $\gamma_l(0)$, the damping rate for longitudinal on-shell gluons with zero momentum in hot QCD using the hard-thermal-loop (htl) scheme. We find it to be divergent in the infrared, which means that in this scheme $\gamma_l(0)$ is different from $\gamma_t(0)$, the corresponding damping rate for transverse gluons which is known to be finite. This result suggests that the htl scheme is infrared sensitive and thus may need to be improved upon in this sector. We discuss this issue after we present our calculation.Comment: 11 pages, RevTeX. Two signs corrected. Same result but substantially rewritten with more emphasis on the infrared problem. References adde

A scenario for leptogenesis at the TeV scale

We propose a scenario of thermal leptogenesis at the TeV scale in the context of an extension of the Standard Model with 4 generations. We also add one right-handed Majorana neutrino for each generation to generate left handed neutrino masses via see-saw. The r\^{o}le of the fourth lepton doublet is not much different from that of a supersymmetric partner, so the leptogenesis consequences of a four generation scenario are indicators of a more generic picture. We obtain a value for the baryon asymmetry of the Universe in accordance with observations by solving the full set of coupled Boltzmann equations for this model.Comment: 4 pages, 2 figures, late

Sum rules for four-spinon dynamic structure factor in XXX model

In the context of the antiferromagnetic spin 1/2 Heisenberg quantum spin chain (XXX model), we estimate the contribution of the exact four-spinon dynamic structure factor $S_4$ by calculating a number of sum rules the total dynamic structure factor $S$ is known to satisfy exactly. These sum rules are: the static susceptibility, the integrated intensity, the total integrated intensity, the first frequency moment and the nearest-neighbor correlation function. We find that the contribution of $S_4$ is between 1% and 2.5%, depending on the sum rule, whereas the contribution of the exact two-spinon dynamic structure factor $S_2$ is between 70% and 75%. This is consistent with the expected scattering weight of states from outside the spin-wave continuum. The calculations are numerical and Monte Carlo based. Good statistics are obtained.Comment: 21 pages, Revtex, 02 figure

Neutrino Physics, Lepton Flavour Violation and the LHC

We briefly review flavour violation in the lepton sector: starting from neutrino oscillations and their implications, we consider several charged lepton flavour violating observables at high and low energies. We present new physics models and discuss the r\^ole of the latter in disentangling them. In particular, we show how the interplay of different observables allows to derive important information on the underlying mechanism of lepton flavour violation. As an example, we discuss the impact of a type-I SUSY seesaw concerning lepton flavour violation at low energies and at colliders (LHC and a future Linear Collider).Comment: 10 pages, 11 figures. Plenary talk at the 25th Rencontres de Blois on Particle Physics and Cosmology, Blois, France, 26-31 May 2013 1 reference adde