Wolfgang Unger

Chiral and deconfinement aspects of the QCD transition

We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with 2 + 1 flavors of quarks using the p4, asqtad, and HISQ/tree actions. Lattices with temporal extent N-tau = 6, 8, and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory with two massless flavors and analyzed using O(N) scaling fits to the chiral condensate and susceptibility. We find consistent estimates from the HISQ/tree and asqtad actions and our main result is T-c = 154 +/- 9 MeV.

Conformality in many-flavour lattice QCD at strong coupling

A bstractIt is widely believed that chiral symmetry is spontaneously broken at zero temperature in the strong coupling limit of staggered fermions, for any number of colors and flavors. Using Monte Carlo simulations, we show that this conventional wisdom, based on a mean-field analysis, is wrong. For sufficiently many fundamental flavors, chiral symmetry is restored via a bulk, first-order transition. This chirally symmetric phase appears to be analytically connected with the expected conformal window of many-flavor continuum QCD. We perform simulations in the chirally symmetric phase at zero quark mass for various system sizes L, and measure the torelon mass, the Dirac spectrum and the hadron spectrum. All masses go to zero with 1/L. L is hence the only infrared length scale. Thus, the strong-coupling chirally restored phase appears as a convenient laboratory to study IR-conformality. Finally, we present a conjecture for the phase diagram of lattice QCD as a function of the bare coupling and the number of quark flavors.

Continuous time Monte Carlo for lattice QCD in the strong coupling limit

We present results for lattice QCD in the limit of infinite gauge coupling, obtained from a worm-type Monte Carlo algorithm on a discrete spatial lattice but with continuous Euclidean time. This is obtained by sending both the anisotropy parameter gamma^2 \sim a/a_t and the number of time-slices N_\tau to infinity, keeping the ratio \gamma^2/N_\tau \sim aT fixed. The obvious gain is that no continuum extrapolation N_\tau -> \infty has to be carried out. Moreover, the algorithm is faster and the sign problem disappears. We compare our computations with those on discrete lattices. We determine the phase diagram as a function of temperature and baryon chemical potential.

Thermodynamics of strongly-coupled lattice QCD in the chiral limit

In the strong coupling limit,

Quark Mass Dependence of the QCD Critical End Point in the Strong Coupling Limit

n

arXiv : Strong-Coupling Lattice QCD on Anisotropic Lattices

-point functions in lattice QCD with staggered fermions can be rewritten exactly as sums over constrained configurations of monomers, dimers, and baryon loops covering the spacetime lattice. Worm algorithms provide efficient global sampling methods over such ensembles, and are particularly efficient in the chiral limit. We study the thermodynamics of strongly-coupled U(3) and SU(3) lattice QCD with one massless staggered fermion using such methods, and compare the results with the relativistic pion gas down to low temperatures O(15 MeV).

A surprise with many-flavor staggered fermions in the strong coupling limit

Strong coupling lattice QCD in the dual representation allows to study the full

Towards corrections to the strong coupling limit of staggered lattice QCD

\mu

Strong-coupling lattice QCD on anisotropic lattices

-

Strong-Coupling Lattice QCD on Anisotropic Lattices : arXiv

T