Maria-Paola Lombardo

Finite density QCD via an imaginary chemical potential

We study QCD at nonzero temperature and baryon density in the framework of nthe analytic continuation from imaginary chemical potential. We carry out nsimulations of QCD with four flavor of staggered fermions, and reconstruct the nphase diagram in the temperature-imaginary mu plane. We consider ansatze for nthe analytic continuation of the critical line and other observables motivated nboth by theoretical considerations and mean field calculations in four fermion nmodels and random matrix theory. We determine the critical line, and the nanalytic continuation of the chiral condensate, up to mu_B approx. 500 MeV. nThe results are in qualitative agreement with the predictions of model field ntheories, and consistent with a first order chiral transition. The correlation nbetween the chiral transition and the deconfinement transition observed at nmu=0 persists at nonzero density.

Evidence for a conformal phase in SU(N) gauge theories

We discuss the existence of a conformal phase in SU(N) gauge theories in four dimensions. In this lattice study, we explore the model in the bare parameter space, varying the lattice coupling and bare mass. Simulations are carried out with three colors and 12 flavors of dynamical staggered fermions in the fundamental representation. The analysis of the chiral order parameter and the mass spectrum of the theory indicates the restoration of chiral symmetry at zero temperature and the presence of a Coulomb-like phase, depicting a scenario compatible with the existence of an infrared stable fixed point at nonzero coupling. Our analysis supports the conclusion that the onset of the conformal window for QCD-like theories is smaller than N(f) = 12, before the loss of asymptotic freedom at 16 and 1/ 2 flavors. We discuss open questions and future directions.

RESULTS ON FINITE DENSITY QCD

A brief summary of the formulation of QCD at finite chemical potental, μ, is presented. The failure of the quenched approximation to the problem is reviewed. Results are presented for dynamical simulations of the theory at strong and intermediate couplings. We find that the problems associated with the quenched theory persist: the onset of non-zero quark number does seem to occur at a chemical potential ≈ m x 2 . However analysis of the Lee-Yang zeros of the grand canonical partition function in the complex fugacity plane, (eμ/T), does show signals of critical behaviour in the expected region of chemical potential. Results are presented for a simulation at finite density of the Gross-Neveu model on a 163 lattice near to the chiral limit. Contrary to our simulations of QCD no pathologies were found when μ passed through the value m x 2 .

SYMMETRIES AND SPECTRUM OF SU(2) LATTICE GAUGE THEORY AT FINITE CHEMICAL POTENTIAL

Abstract We study SU(2) Lattice Gauge Theory with dynamical fermions at non-zero chemical potential μ. The symmetries special to SU(2) for staggered fermions on the lattice are discussed explicitly and their relevance to spectroscopy and condensates at non-zero chemical potential are considered. Using the molecular dynamics algorithm on small lattices we find qualitative changes in the theorys spectroscopy at small and large values of μ. This preliminary study should lay the groundwork for future large scale simulations.

The critical points of strongly coupled lattice QCD at nonzero chemical potential

We study QCD at nonzero quark density, zero temperature, infinite coupling using the Glasgow algorithm. An improved complex zero analysis gives a critical point

On the particle spectrum and the conformal window

{ensuremath{mu}}_{c}

Behaviour of the topological susceptibility in two colour QCD across the finite density transition

in agreement with that of chiral symmetry restoration computed with strong coupling expansions, and monomer-dimer simulations. We observe, however, two unphysical critical points: the onset for the number density

Finite density [might well be easier] at finite temperature

{ensuremath{mu}}_{0}

Pathologies of quenched lattice QCD at nonzero density and its effective potential.

, and

One, two, zero: Scales of strong interactions

{ensuremath{mu}}_{s}