On the full Boltzmann equations for Leptogenesis

We consider the full Boltzmann equations for standard and soft leptogenesis, instead of the usual integrated Boltzmann equations which assume kinetic equilibrium for all species. Decays and inverse decays may be inefficient for thermalising the heavy-(s)neutrino distribution function, leading to significant deviations from kinetic equilibrium. We analyse the impact of using the full kinetic equations in the case of a previously generated lepton asymmetry, and find that the washout of this initial asymmetry due to the interactions of the right-handed neutrino is larger than when calculated via the integrated equations. We also solve the full Boltzmann equations for soft leptogenesis, where the lepton asymmetry induced by the soft SUSY-breaking terms in sneutrino decays is a purely thermal effect, since at T=0 the asymmetry in leptons cancels the one in sleptons. In this case, we obtain that in the weak washout regime (K ~< 1) the final lepton asymmetry can change up to a factor four with respect to previous estimates.Comment: 34 pages, 6 figures, to be published in JCA

Low-energy renormalization of the electron dispersion of high-Tc_c superconductors

High-resolution ARPES studies in cuprates have detected low-energy changes in the dispersion and absorption of quasi-particles at low temperatures, in particular, in the superconducting state. Based on a new 1/N expansion of the t-J-Holstein model, which includes collective antiferromagnetic fluctuations already in leading order, we argue that the observed low-energy structures are mainly caused by phonons and not by spin fluctuations, at least, in the optimal and overdoped regime.Comment: 6 pages, 3 figure

Ground-state fidelity in one-dimensional gapless model

A general relation between quantum phase transitions and the second derivative of the fidelity (or the "fidelity susceptibility") is proposed. The validity and the limitation of the fidelity susceptibility in characterizing quantum phase transitions is thus established. Moreover, based on the bosonization method, general formulas of the fidelity and the fidelity susceptibility are obtained for a class of one-dimensional gapless systems known as the Tomonaga-Luttinger liquid. Applying these formulas to the one-dimensional spin-1/2 $XXZ$ model, we find that quantum phase transitions, even of the Beresinskii-Kosterlitz-Thouless type, can be signaled by the fidelity susceptibility.Comment: 4+ pages, no figure, published versio

Instantons and the singlet-coupling in the chiral quark model

Chiral quark model with a broken-U(3) flavor symmetry can be interpreted as the effective theory of the instanton-dominated non-perturbative QCD. This naturally suggests the possibility of a negative singlet/octet coupling ratio, which has been found, in a previous publication, to be compatible with the phenomenological description of the nucleon spin-flavor structure.Comment: 9 page

Neutron Scattering and the B_{1g} Phonon in the Cuprates

The momentum dependent lineshape of the out-of-phase oxygen vibration as measured in recent neutron scattering measurements is investigated. Starting from a microscopic coupling of the phonon vibration to a local crystal field, the phonon lineshift and broadening is calculated as a function of transfered momentum in the superconducting state of YBa$_{2}$Cu$_{3}$O$_{7}$. It is shown that the anisotropy of the density of states, superconducting energy gap, and the electron-phonon coupling are all crucial in order to explain these experiments.Comment: new figures and discussio

Galaxy Counts, Sizes, Colours and Redshifts in the Hubble Deep Field

We compare the galaxy evolution models of Bruzual & Charlot (1993) with the faint galaxy count, size and colour data from the Hubble and Herschel Deep Fields (Metcalfe et al 1996). For qo=0.05, we find that models where the SFR increases exponentially out to z>2 are consistent with all of the observational data. For qo=0.5, such models require an extra population of galaxies which are only seen at high redshift and then rapidly fade or disappear. We find that, whatever the cosmology, the redshift of the faint blue galaxies and hence the epoch of galaxy formation is likely to lie at z>2. We find no implied peak in the SFR at z=1 and we suggest that the reasons for this contradiction with the results of Madau et al (1996) include differences in faint galaxy photometry, in the treatment of spiral dust and in the local galaxy count normalisation.Comment: 8 pages, 5 eps figures, needs paspconf.st