Adriana Moreo

PHASE SEPARATION INDUCED BY ORBITAL DEGREES OF FREEDOM IN MODELS FOR MANGANITES WITH JAHN-TELLER PHONONS

The two-orbital Kondo model with classical Jahn-Teller phonons is studied using Monte Carlo techniques. The observed phase diagram is rich, and includes a novel regime of phase separation induced by the orbital degrees of freedom. Experimental consequences of our results are discussed. In addition, the optical conductivity

Problems with Finite Density Simulations of Lattice QCD

sigma(omega)

Lattice SU(N) OCD at finite temperature and density in the strong coupling limit

of the model is presented. It is shown to have several similarities with experimental measurements for manganites.

The strong coupling limit of SU(2) QCD at finite baryon density

We present a discussion of problems that have arisen in attempts to understand the behavior of lattice QCD at high densities. The effects observed in the lattice simulations do not seem to be consistent with what we expect from the usual ideas of chiral symmetry breaking. In particular, at zero quark mass, there does not seem to be a massive baryon at finite density.

A numerical study of lattice QED with dynamical fermions

Abstract We study the strong coupling limit of lattice SU( N ) QCD at finite temperature ( T ) and chemical potential (μ) using the dimer technique and analytical approximations. For N ⩾3 we show the existence of a phase transition where chiral symmetry is restored. The order of the transition is discussed. When N = 2 a baryonic condensate appears at nonzero density, leading to a rich phase diagram which is also analyzed.

QUASIPARTICLE DISPERSION OF THE T-J AND HUBBARD MODELS

Abstract The thermodynamics is studied of SU(2) gauge theory with staggered fermions at finite baryon density and zero temperature in the strong coupling limit. Monte Carlo simulation and mean field analysis give a consistent picture indicating that no chiral phase transition occurs at g 2 = ∞ although the mesonic condensate 〈 ψ ψ〉 turns out to vanish for all non-zero chemical potentials.

Quasiparticle dispersion of the {ital t}-{ital J} and Hubbard models

Abstract Using the pseudo-fermion method U(1) lattice gauge theory with dynamical staggered fermions is studied. The plaqette energy, the chiral order parameter and the Polyakov line have been measured. With fermions of mass 0.20 and 0.25 a phase transition is observed, separating the strong coupling regime from a phase where chiral symmetry is restored.

Spin dynamics of hole doped Y2-xCxBaNiO5.

The spectral weight {ital A}(p,{omega}) of the two-dimensional {ital t}-{ital J} and Hubbard models has been calculated using exact diagonalization and quantum Monte Carlo techniques, at several densities 0.5{le}{l_angle}{ital n}{r_angle}{le}1.0. The photoemission ({omega}{lt}0) region contains two dominant distinct features, namely a low-energy quasiparticle peak with bandwidth of order {ital J}, and a broad valence band peak at energies of order {ital t}. This behavior {ital persists} away from half-filling, as long as the antiferromagnetic correlations are robust. The results give support to theories of the copper oxide materials based on the behavior of holes in antiferromagnets, and they also provide theoretical guidance for the interpretation of experimental photoemission data for the cuprates.

A comment on the Nielsen-Ninomiya theorem☆

The spectral weight {ital A}(p,{omega}) of the two-dimensional {ital t}-{ital J} and Hubbard models has been calculated using exact diagonalization and quantum Monte Carlo techniques, at several densities 0.5{le}{l_angle}{ital n}{r_angle}{le}1.0. The photoemission ({omega}{lt}0) region contains two dominant distinct features, namely a low-energy quasiparticle peak with bandwidth of order {ital J}, and a broad valence band peak at energies of order {ital t}. This behavior {ital persists} away from half-filling, as long as the antiferromagnetic correlations are robust. The results give support to theories of the copper oxide materials based on the behavior of holes in antiferromagnets, and they also provide theoretical guidance for the interpretation of experimental photoemission data for the cuprates.

Phase diagram of noncompact scalar electrodynamics

We propose an electronic model for the recently discovered hole doped compound