Mean field theory of effective spin models as a baryon fugacity expansion

TY - JOUR

T1 - Mean field theory of effective spin models as a baryon fugacity expansion

AU - Greensite, Jeffrey Paul

AU - Splittorff, Kim

PY - 2012/10/1

Y1 - 2012/10/1

N2 - The free energy of effective spin or "Polyakov line" models with a chemical potential, based on the U(N) group, does not depend on the chemical potential. In a mean field-inspired expansion, we show how the condition of unit determinant, taking U(N) to SU(N), reintroduces the chemical potential, and allows us to express the free energy, as a function of mean field variational parameters, in terms of an expansion in the baryon (rather than the quark) fugacity at each lattice site. We solve the SU(3) mean field equations numerically to determine the phase diagram and compute observables. We also calculate the first corrections to the leading order mean field results, and find that these can significantly shift the endpoint of a line of first order transitions. The problem of deriving an effective spin model from full QCD is discussed.

AB - The free energy of effective spin or "Polyakov line" models with a chemical potential, based on the U(N) group, does not depend on the chemical potential. In a mean field-inspired expansion, we show how the condition of unit determinant, taking U(N) to SU(N), reintroduces the chemical potential, and allows us to express the free energy, as a function of mean field variational parameters, in terms of an expansion in the baryon (rather than the quark) fugacity at each lattice site. We solve the SU(3) mean field equations numerically to determine the phase diagram and compute observables. We also calculate the first corrections to the leading order mean field results, and find that these can significantly shift the endpoint of a line of first order transitions. The problem of deriving an effective spin model from full QCD is discussed.

U2 - 10.1103/PhysRevD.86.074501

DO - 10.1103/PhysRevD.86.074501

M3 - Journal article

SN - 1550-7998

VL - 86

JO - Physical Review D (Particles, Fields, Gravitation and Cosmology)

JF - Physical Review D (Particles, Fields, Gravitation and Cosmology)

IS - 7

M1 - 074501

ER -