440 research outputs found
O(2) symmetry breaking vs. vortex loop percolation
We study with lattice Monte Carlo simulations the relation of global O(2)
symmetry breaking in three dimensions to the properties of a geometrically
defined vortex loop network. We find that different definitions of constructing
a network lead to different results even in the thermodynamic limit, and that
with typical definitions the percolation transition does not coincide with the
thermodynamic phase transition. These results show that geometrically defined
percolation observables need not display universal properties related to the
critical behaviour of the system, and do not in general survive in the field
theory limit.Comment: 14 pages; references added, version to appear in Phys.Lett.
The Phase Diagram of Three-Dimensional SU(3) + Adjoint Higgs Theory
We study the phase diagram of the three-dimensional SU(3)+adjoint Higgs
theory with lattice Monte Carlo simulations. A critical line consisting of a
first order line, a tricritical point and a second order line, divides the
phase diagram into two parts distinguished by =0 and /=0. The location
and the type of the critical line are determined by measuring the condensates
and , and the masses of scalar and vector excitations.
Although in principle there can be different types of broken phases,
corresponding perturbatively to unbroken SU(2)xU(1) or U(1)xU(1) symmetries, we
find that dynamically only the broken phase with SU(2)xU(1)-like properties is
realized. The relation of the phase diagram to 4d finite temperature QCD is
discussed.Comment: 21 pages, 8 figure
Non-perturbative plaquette in 3d pure SU(3)
We present a determination of the elementary plaquette and, after the
subsequent ultraviolet subtractions, of the finite part of the gluon
condensate, in lattice regularization in three-dimensional pure SU(3) gauge
theory. Through a change of regularization scheme to MSbar and a matching back
to full four-dimensional QCD, this result determines the first non-perturbative
contribution in the weak-coupling expansion of hot QCD pressure.Comment: 6 pages, 4 figures, talk presented at Lattice 2005 (Non-zero
temperature and density
Quark Number Susceptibility of High Temperature QCD
We use three dimensional reduced effective field theory (EQCD) and lattice calculations to determine the quark number susceptibility of QCD at high temperature. We find our results to agree well with known perturbative expansion as well as with other lattice data
Non-abelian plasma instabilities for strong anisotropy
We numerically investigate gauge field instabilities in anisotropic SU(2)
plasmas using weak field initial conditions. The growth of unstable modes is
stopped by non-abelian effects for moderate anisotropy. If we increase the
anisotropy the growth continues beyond the non-abelian saturation bound. We
find strong indications that the continued growth is not due to over-saturation
of infrared field modes, but instead due to very rapid growth of high momentum
modes which are not unstable in the weak field limit. The saturation amplitude
strongly depends on the initial conditions. For strong initial fields we do not
observe the sustained growth.Comment: 28 pages, 17 figure
High-T QCD and dimensional reduction: measuring the Debye mass
We study the high-temperature phase of SU(2) and SU(3) QCD using lattice
simulations of an effective 3-dimensional SU(N) + adjoint Higgs -theory,
obtained through dimensional reduction. We investigate the phase diagram of the
3D theory, and find that the high-T QCD phase corresponds to the metastable
symmetric phase of the 3D theory. We measure the Debye screening mass m_D with
gauge invariant operators; in particular we determine the O(g^2) and O(g^3)
corrections to m_D. The corrections are seen to be large, modifying the
standard power-counting hierarchy in high temperature QCD.Comment: 3 pages, Latex, 3 figures. Presented by K. Rummukainen at Lattice '9
Three-dimensional physics and the pressure of hot QCD
We update Monte Carlo simulations of the three-dimensional SU(3) + adjoint
Higgs theory, by extrapolating carefully to the infinite volume and continuum
limits, in order to estimate the contribution of the infrared modes to the
pressure of hot QCD. The sum of infrared contributions beyond the known 4-loop
order turns out to be a smooth function, of a reasonable magnitude and specific
sign. Unfortunately, adding this function to the known 4-loop terms does not
improve the match to four-dimensional lattice data, in spite of the fact that
other quantities, such as correlation lengths, spatial string tension, or quark
number susceptibilities, work well within the same setup. We outline possible
ways to reduce the mismatch.Comment: 14 page
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