3,974 research outputs found
What's new with the electroweak phase transition?
We review the status of non-perturbative lattice studies of the electroweak
phase transition. In the Standard Model, the complete phase diagram has been
reliably determined, and the conclusion is that there is no phase transition at
all for the experimentally allowed Higgs masses. In the Minimal Supersymmetric
Standard Model (MSSM), in contrast, there can be a strong first order
transition allowing for baryogenesis. Finally, we point out possibilities for
future simulations, such as the problem of CP-violation at the MSSM electroweak
phase boundary.Comment: LATTICE98(electroweak), 6 pages. List of references update
A Strong Electroweak Phase Transition up to m_H ~ 105 GeV
Non-perturbative lattice simulations have shown that there is no electroweak
phase transition in the Standard Model for the allowed Higgs masses, m_H \gsim
75 GeV. In the Minimal Supersymmetric Standard Model, in contrast, it has been
proposed that the transition should exist and even be strong enough for
baryogenesis up to m_H ~ 105 GeV, provided that the lightest stop mass is in
the range 100...160 GeV. However, this prediction is based on perturbation
theory, and suffers from a noticeable gauge parameter and renormalization scale
dependence. We have performed large-scale lattice Monte Carlo simulations of
the MSSM electroweak phase transition. Extrapolating the results to the
infinite volume and continuum limits, we find that the transition is in fact
stronger than indicated by 2-loop perturbation theory. This guarantees that the
perturbative Higgs mass bound m_H ~ 105 GeV is a conservative one, allows
slightly larger stop masses (up to ~ 165 GeV), and provides a strong motivation
for further studies of MSSM electroweak baryogenesis.Comment: 4 pages, 3 figure
First order thermal phase transition with 126 GeV Higgs mass
We study the strength of the electroweak phase transition in models with two
light Higgs doublets and a light SU(3)_c triplet by means of lattice
simulations in a dimensionally reduced effective theory. In the parameter
region considered the transition on the lattice is significantly stronger than
indicated by a 2-loop perturbative analysis. Within some ultraviolet
uncertainties, the finding applies to MSSM with a Higgs mass m_h approximately
126 GeV and shows that the parameter region useful for electroweak baryogenesis
is enlarged. In particular (even though only dedicated analyses can quantify
the issue), the tension between LHC constraints after the 7 TeV and 8 TeV runs
and frameworks where the electroweak phase transition is driven by light stops,
seems to be relaxed.Comment: Presented at 31st International Symposium on Lattice Field Theory -
LATTICE 201
Measuring infrared contributions to the QCD pressure
For the pressure (or free energy) of QCD, four-dimensional (4d) lattice data
is available at zero baryon density up to a few times the critical temperature
. Perturbation theory, on the other hand, has serious convergence problems
even at very high temperatures. In a combined analytical and three-dimensional
(3d) lattice method, we show that it is possible to compute the QCD pressure
from about to infinity. The numerical accuracy is good enough to
resolve in principle, e.g., logarithmic contributions related to 4-loop
perturbation theory.Comment: 3 pages; talk by Y. Schroder at Lattice2001(hightemp
Mesonic screening masses at high temperature and finite density
We compute the first perturbative correction to the static correlation
lengths of light quark bilinears in hot QCD with finite quark chemical
potentials. The correction is small and positive, with mu-dependence depending
on the relative sign of chemical potentials and the number of dynamical
flavors. The computation is carried out using a three-dimensional effective
theory for the lowest fermionic Matsubara mode. We also compute the full
correlator in free theory and find a rather complicated general mu-dependence
at shorter distances. Finally, rough comparisons with lattice simulations are
discussed.Comment: 24 pages, 5 figures, JHEP style. Minor corrections and
clarifications, version to appear in JHE
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
Three-dimensional U(1) gauge+Higgs theory as an effective theory for finite temperature phase transitions
We study the three-dimensional U(1)+Higgs theory (Ginzburg-Landau model) as
an effective theory for finite temperature phase transitions from the 1 K scale
of superconductivity to the relativistic scales of scalar electrodynamics. The
relations between the parameters of the physical theory and the parameters of
the 3d effective theory are given. The 3d theory as such is studied with
lattice Monte Carlo techniques. The phase diagram, the characteristics of the
transition in the first order regime, and scalar and vector correlation lengths
are determined. We find that even rather deep in the first order regime, the
transition is weaker than indicated by 2-loop perturbation theory. Topological
effects caused by the compact formulation are studied, and it is demonstrated
that they vanish in the continuum limit. In particular, the photon mass
(inverse correlation length) is observed to be zero within statistical errors
in the symmetric phase, thus constituting an effective order parameter.Comment: 42 pages, 14 figure
Four-loop logarithms in 3d gauge + Higgs theory
We discuss the logarithmic contributions to the vacuum energy density of the
three-dimensional SU(3) + adjoint Higgs theory in its symmetric phase, and
relate them to numerical Monte Carlo simulations. We also comment on the
implications of these results for perturbative and non-perturbative
determinations of the pressure of finite-temperature QCD.Comment: 3 pages, Lattice2002(nonzerot
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