A. Vaquero

Geometric algorithm for abelian-gauge models

Motivated by the sign problem in several systems, we have developed a geometric simulation algorithm based on the strong coupling expansion which can be applied to abelian pure gauge models. We have studied the algorithm in the U(1) model in 3 and 4 dimensions, and seen that it is practical and is similarly efficient to the standard heat-bath algorithm, but without the ergodicity problems which comes from the presence of vortices. We have also applied the algorithm to the Ising gauge model at the critical point, and we find hints of a better asymptotic behaviour of the autocorrelation time, which therefore suggests the possibility of a smaller dynamical critical exponent with respect to the standard heat-bath algorithm.

QCD with two flavors of Wilson fermions: The QCD vacuum, the Aoki vacuum and other vacua

We discuss the vacuum structure of QCD with two flavors of Wilson fermions. We derive two possible scenarios: (i) If the spectral density

Progress in numerical simulations of systems with a θ-vacuum like term: The two- and three-dimensional Ising model within an imaginary magnetic field

{\ensuremath{\rho}}_{U}(\ensuremath{\lambda},\ensuremath{\kappa})

Parity realization in vector-like theories from fermion bilinears

of the overlap Hamiltonian in a fixed background gauge field is not symmetric in

Recent results for the proton spin decomposition from lattice QCD

\ensuremath{\lambda}

Spectral Flow and Index Theorem for Staggered Fermions

, Hermiticity is violated and Hermiticity violation effects could influence numerical determinations of the

Parity realization in Lattice QCD with Ginsparg-Wilson fermions

\ensuremath{\eta}

Results on the disconnected contributions for hadron structure

meson mass if we are not near enough to the continuum limit, where Hermiticity should be recovered; (ii) otherwise we argue that, under certain assumptions, new phases appear beside the Aoki phase, which can be characterized by a nonvanishing vacuum expectation value of

Nucleon electromagnetic and axial form factors with N

i{\overline{\ensuremath{\psi}}}_{u}{\ensuremath{\gamma}}_{5}{\ensuremath{\psi}}_{u}+i{\overline{\ensuremath{\psi}}}_{d}{\ensuremath{\gamma}}_{5}{\ensuremath{\psi}}_{d}

_\textrm{f}=2

, and with vacuum states that cannot be connected with the Aoki vacua by parity-flavor symmetry transformations. Quenched numerical simulations suggest that the second scenario is more likely realized.