arXiv subjects

Yasuo Umino

Publications and source records attributed to Yasuo Umino.

6 recordsLinked to original sources

arXiv2005

Critical behavior of strongly coupled lattice QCD at finite temperature

We study the critical behavior of lattice Quantum Chromodynamics (QCD) in the strong coupling approximation with Kogut-Susskind and Wilson fermions at finite temperature ($T$) and zero chemical potential. Using the Hamiltonian formulation we construct a mean field solution to the equation of motion at finite $T$ and use it to study the elementary thermal excitations and to extract some critical exponents characterizing the observed second order phase transition. We find similar critical behaviors for Kogut-Susskind and Wilson fermions at finite $T$

hep-lat↗

arXiv2002

Hamiltonian lattice QCD at finite density: equation of state in the strong coupling limit

The equation of state of Hamiltonian lattice QCD at finite density is examined in the strong coupling limit by constructing a solution to the equation of motion corresponding to an effective Hamiltonian describing the ground state of the many body system. This solution exactly diagonalizes the Hamiltonian to second order in field operators for all densities and is used to evaluate the vacuum energy density from which we obtain the equation of state. We find that up to and beyond the chiral symmetry restoration density the pressure of the quark Fermi sea can be negative indicating its mechanical instability. Our result is in qualitative agreement with continuum models and should be verifiable by future lattice simulations of strongly coupled QCD at finite density.

hep-ph↗

arXiv2002

Equation of state of strongly coupled Hamiltonian lattice QCD at finite density

We calculate the equation of state of strongly coupled Hamiltonian lattice QCD at finite density by constructing a solution to the equation of motion corresponding to an effective Hamiltonian using Wilson fermions. We find that up to and beyond the chiral symmetry restoration density the pressure of the quark Fermi sea can be negative indicating its mechanical instability. This result is in qualitative agreement with continuum models and should be verifiable by future numerical simulations.

hep-ph↗

arXiv2000

The 't Hooft interaction at finite T and $μ$: Beyond the mean field theory

We use the N-quantum approach (NQA) to quantum field theory to construct a solution of the two flavor effective instanton induced `t Hooft interaction model valid for any temperature (T) and chemical potential ($μ$) beyond the mean field theory. The model contains only the $\bar{q}q$ channels. In constructing this solution we calculate the masses, widths and coupling constants of bound $σ$ and resonant color $\bar{3}$ scalar diquark states. We find that the chemical potential induced by the interaction cancel exactly for all values of T in contrast to the Nambu-Jona-Lasinio model. Our method can also be extended to include the qq channels in the model Lagrangian and we discuss how the NQA can be used to study the properties of bound diquark states at finite T and $μ$.

hep-ph↗

arXiv2000

Diagonalization of the strongly coupled lattice QCD Hamiltonian

We construct a solution to the equation of motion of Hamiltonian lattice QCD in the strong coupling limit using Wilson fermions which exactly diagonalizes the Hamiltonian to second order in the field operators. This solution obeys the free lattice Dirac equation with a dynamical mass which is identified with the gap. The equation determining this gap is derived and it is found that the dynamical quark mass is a constant to lowest order in N_c but becomes momentum dependent once 1/N_c corrections are taken into account. We interpret our solution within the framework of the N-quantum approach to quantum field theory and discuss how our formalism may be systematically extended to study bound states at finite temperature and chemical potential.

hep-ph↗

arXiv1999

N-quantum approach to quantum field theory at finite T and $μ$: the NJL model

We extend the N-quantum approach to quantum field theory to finite temperature ($T$) and chemical potential ($μ$) and apply it to the NJL model. In this approach the Heisenberg fields are expressed using the Haag expansion while temperature and chemical potential are introduced simultaneously through a generalized Bogoliubov transformation. Known mean field results are recovered using only the first term in the Haag expansion. In addition, we find that at finite T and in the broken symmetry phase of the model the mean field approximation can not diagonalize the Hamiltonian. Inclusion of scalar and axial vector diquark channels in the SU(2)$_{rm f}$ $otimes$ SU(3)$_{\rm c}$ version of the model can lead to a lowering of the vacuum energy density. We discuss how to go beyond the mean field approximation by including higher order terms in the Haag expansion.

hep-ph↗