248 research outputs found
Simulating the Electroweak Phase Transition in the SU(2) Higgs Model
Numerical simulations are performed to study the finite temperature phase
transition in the SU(2) Higgs model on the lattice. In the presently
investigated range of the Higgs boson mass, below 50 GeV, the phase transition
turns out to be of first order and its strength is rapidly decreasing with
increasing Higgs boson mass. In order to control the systematic errors, we also
perform studies of scaling violations and of finite volume effects.Comment: 46 pages with 16 figures, DESY-94-15
Defect fugacity, Spinwave Stiffness and T_c of the 2-d Planar Rotor Model
We obtain precise values for the fugacities of vortices in the 2-d planar
rotor model from Monte Carlo simulations in the sector with {\em no} vortices.
The bare spinwave stiffness is also calculated and shown to have significant
anharmonicity. Using these as inputs in the KT recursion relations, we predict
the temperature T_c = 0.925, using linearised equations, and using next higher order corrections, at which vortex unbinding commences
in the unconstrained system. The latter value, being in excellent agreement
with all recent determinations of T_c, demonstrates that our method 1)
constitutes a stringent measure of the relevance of higher order terms in KT
theory and 2) can be used to obtain transition temperatures in similar systems
with modest computational effort.Comment: 7 pages, 4 figure
CO2-related vasoconstriction superimposed on ischemic medullary brain autonomic nuclei may contribute to sudden death
Introduction: In 2015, a multinational randomized controlled phase IV clinical trial of adaptive servoventilation for the management of heart failure with central sleep apnea was halted in progress because more patients in the study group were dying than in the control group. One year later, another large clinical trial reported results on the effectiveness of continuous positive airway pressure (CPAP) in preventing sudden death and other cardiovascular events such as heart attack and stroke in patients with preexisting vascular disease as well as obstructive sleep apnea. Background: Sudden unexpected death has been associated with many types of small and nonmalignant medullary brain lesions, like demyelination plaques \u2014 largely asymptomatic until they caused sudden death. Many such medullary lesions, typically without hemorrhage or mass effect, have in themselves been previously considered relatively harmless \u2014 in cases where they have been known to be present. Discussion: Why did not the improved pulmonary ventilation and subsequently improved gas exchange provided during the CPAP and servoventilation clinical trials help to resolve any ischemic lesions that may have been present both in the heart and in the medulla, thereby tending to normalize interactions between the vagal neural structures and the heart? CO2 is a potent dilator of brain vasculature, thereby increasing blood flow to the brain. When ventilation is increased, even if only to improve it back toward normal from a depressed steady-state level, the alveolar partial pressure of carbon dioxide is decreased, likely resulting in a converse relative vasoconstriction in the brain, thereby reducing blood flow in the brain, especially in watershed areas like the solitary tract nucleus. In normal physiology, this is demonstrated impressively by the ability of hyperventilation to induce loss of consciousness. Conclusions: The findings of several clinical trials recently reported, taken together with neuropathology case studies reported elsewhere, suggest that additional research is warranted in regard to the mechanisms by which focal medullary autonomic brain ischemia may be related to sudden death in general medical illnesses \u2014 and how it may additionally be influenced by changes in arterial CO2 levels
Numerical tests of the electroweak phase transition and thermodynamics of the electroweak plasma
The finite temperature phase transition in the SU(2) Higgs model at a Higgs
boson mass GeV is studied in numerical simulations on
four-dimensional lattices with time-like extensions up to . The effects
of the finite volume and finite lattice spacing on masses and couplings are
studied in detail. The errors due to uncertainties in the critical hopping
parameter are estimated. The thermodynamics of the electroweak plasma near the
phase transition is investigated by determining the relation between energy
density and pressure.Comment: latex2e, 32 pages, 11 figures with epsfig; A few comments and a new
table are adde
Electroweak phase transition by four dimensional simulations
The finite temperature phase transition in the SU(2)-Higgs model at a Higgs
boson mass GeV is studied in numerical simulations on four
dimensional lattices with time-like extensions up to . is
extrapolated to the continuum limit and a comparison with the perturbative
prediction is made. A one-loop calculation to the coupling anisotropies of the
SU(2)-Higgs model on lattices with asymmetric lattice spacings is presented.
Our numerical simulations show that the above perturbative result is applicable
in the phenomenologically interesting parameter region.Comment: 3 pages, Latex, 3 figures, Talk presented at LATTICE96(electroweak)
by Z. Fodo
Identification of the critical temperature from non-equilibrium time-dependent quantities
We present a new procedure able to identify and measure the critical
temperature. This method is based on the divergence of the relaxation time
approaching the critical point in quenches from infinite temperature. We
introduce a dimensionless quantity that turns out to be time-independent at the
critical temperature. The procedure does not need equilibration and allows for
a relatively fast identification of the critical temperature. The method is
first tested in the ferromagnetic Ising model and then applied to the
one-dimensional Ising spin glass with power-law interactions. Here we always
find a finite critical temperature also in presence of a uniform external
field, in agreement with the mean-field picture for the low temperature phase
of spin glasses.Comment: 6 pages, 10 figure
Critical aging of a ferromagnetic system from a completely ordered state
We adapt the non-linear model to study the nonequilibrium critical
dynamics of O(n) symmetric ferromagnetic system. Using the renormalization
group analysis in dimensions we investigate the pure relaxation
of the system starting from a completely ordered state. We find that the
average magnetization obeys the long-time scaling behavior almost immediately
after the system starts to evolve while the correlation and response functions
demonstrate scaling behavior which is typical for aging phenomena. The
corresponding fluctuation-dissipation ratio is computed to first order in
and the relation between transverse and longitudinal fluctuations is
discussed.Comment: 5 pages, revtex
Rejection-free Geometric Cluster Algorithm for Complex Fluids
We present a novel, generally applicable Monte Carlo algorithm for the
simulation of fluid systems. Geometric transformations are used to identify
clusters of particles in such a manner that every cluster move is accepted,
irrespective of the nature of the pair interactions. The rejection-free and
non-local nature of the algorithm make it particularly suitable for the
efficient simulation of complex fluids with components of widely varying size,
such as colloidal mixtures. Compared to conventional simulation algorithms,
typical efficiency improvements amount to several orders of magnitude
Monte Carlo Simulations of Short-time Critical Dynamics with a Conserved Quantity
With Monte Carlo simulations, we investigate short-time critical dynamics of
the three-dimensional anti-ferromagnetic Ising model with a globally conserved
magnetization (not the order parameter). From the power law behavior of
the staggered magnetization (the order parameter), its second moment and the
auto-correlation, we determine all static and dynamic critical exponents as
well as the critical temperature. The universality class of is the same
as that without a conserved quantity, but the universality class of non-zero
is different.Comment: to appear in Phys. Rev.
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