Renormalized mean-field theory of the neutron scattering in cuprate superconductors

The magnetic excitation spectrum of the t-t'-J-model is studied in mean-field theory and compared to inelastic neutron-scattering (INS) experiments on YBCO and BSCCO superconductors. Within the slave-particle formulation the dynamical spin response is calculated from a renormalized Fermi liquid with an effective interaction ~J in the magnetic particle--hole channel. We obtain the so-called 41meV resonance at wave vector (pi,pi) as a collective spin-1 excitation in the d-wave superconducting state. It appears sharp (undamped), if the underlying Fermi surface is hole-like with a sufficient next-nearest-neighbor hopping t'<0. The double-layer structure of YBCO or BSCCO is not important for the resonance to form. The resonance energy \omega_{res} and spectral weight at optimal doping come out comparable to experiment. The observed qualitative behavior of \omega_{res} with hole filling is reproduced in the underdoped as well as overdoped regime. A second, much broader peak becomes visible in the magnetic excitation spectrum if the 2D wave-vector is integrated over. It is caused by excitations across the maximum gap, and in contrast to the resonance its energy is almost independent of doping. At energies above or below \omega_{res} the commensurate resonance splits into incommensurate peaks, located off (pi,pi). Below \omega_{res} the intensity pattern is of `parallel' type and the dispersion relation of incommensurate peaks has a negative curvature. This is in accordance with recent INS experiments on YBCO.Comment: 17pp including 14 figure

The (not so) controversial role of DNA methylation in epigenetic inheritance across generations.

It has been demonstrated originally in plants that phenotypic traits, such as floral symmetry, can be caused by changes of methylation patterns of specific genes. Such traits can be transgenerationally inherited for multiple generations and remain associated with cytosine methylation patterns. Whether genomic methylation may also contribute to epigenetic inheritance across generations in vertebrates and notably in mammals is still more controversial. One reason for this tentativeness is the dual occurrence of global genomic de-methylation first in pre-implantation embryos and subsequently in primordial germ cells (PGCs) of mammals. Although gene focused cases of epigenetic inheritance associated with genomic DNA methylation have been well studied mostly in rodents (such as imprinted genes and the Agouti viable yellow, Avy, allele), it is still a matter of debate whether genomic DNA methylation may provide a more general mechanism for the epigenetic inheritance of acquired traits across generations. We review the current literature on this topic with a focus on the potential role of DNA methylation for epigenetic inheritance across generations in mammals