Phase structure of a generalized Nambu Jona-Lasinio model with Wilson fermions in the mean field or large NN-expansion

We analyze the vacuum structure of a generalized lattice Nambu--Jona-Lasinio model with two flavors of Wilson fermions, such that its continuum action is the most general four-fermion action with 'trivial' color interactions, and having a $SU(2)_V x SU(2)_A$ symmetry in the chiral limit. The phase structure of this model in the space of the two four-fermion couplings shows, in addition to the standard Aoki phases, new phases with $!= 0$, in close analogy to similar results recently suggested by some of us for lattice QCD with two degenerate Wilson fermions. This result shows how the phase structure of an effective model for low energy QCD cannot be entirely understood from Wilson Chiral Perturbation Theory, based on the standard QCD chiral effective Lagrangian approach.Comment: 24 pages, 3 figures, sent to Nuclear Physics

Hacedores de frontera. Estudios sobre el contexto social de la frontera en la España Medieval. [Reseña]

Reseña de: Manuel Alejandro Rodríguez de la Peña (dir.), Hacedores de frontera. Estudios sobre el contexto social de la frontera en la España Medieval, CEU Ediciones, Madrid 2009, 346 pp

XXXVI Semana de Estudios Medievales de Estella «Ricos y pobres. Opulencia y desarraigo en el Occidente Medieval». [Crónica]

XXXVI Semana de Estudios Medievales de Estella, (20-24 de julio de 2009

Idade Média: Tempo do mundo, tempo dos homens, tempo de Deus. [Reseña]

Reseña de: José Antônio DE CAMARGO RODRIGUES DE SOUZA (org.), Idade Média: Tempo do mundo, tempo dos homens, tempo de Deus, EST Edições, Porto Alegre 2006, 535 pp

Topological Index Theorem on the Lattice through the Spectral Flow of Staggered Fermions

We investigate numerically the spectral flow introduced by Adams for the staggered Dirac operator on realistic (quenched) gauge configurations. We obtain clear numerical evidence that the definition works as expected: there is a clear separation between crossings near and far away from the origin, and the topological charge defined through the crossings near the origin agrees, for most configurations, with the one defined through the near-zero modes of large taste-singlet chirality of the staggered Dirac operator. The crossings are much closer to the origin if we improve the Dirac operator used in the definition, and they move towards the origin as we decrease the lattice spacing.Comment: References added. Slight changes to the tex

Le coeur du roi, les Capetiens et les sépultures multiples XIII e -XV e siècles [Reseña]

Reseña de Alexandre Bande, "Le coeur du roi, les Capetiens et les sépultures multiples XIIIe -XVe siècles", Ed. Tallander, París, 2009, 255 pp