202 research outputs found
Problem of the noise-noise correlation function in hot non-Abelian plasma
In this work on the basis of Kadomtsev's kinetic fluctuation theory we
present the more general expression for noise-noise correlation function in
effective theory for ultrasoft field modes.Comment: 3 pages, REVTeX
Electroweak Bubble Nucleation, Nonperturbatively
We present a lattice method to compute bubble nucleation rates at radiatively
induced first order phase transitions, in high temperature, weakly coupled
field theories, nonperturbatively. A generalization of Langer's approach, it
makes no recourse to saddle point expansions and includes completely the
dynamical prefactor. We test the technique by applying it to the electroweak
phase transition in the minimal standard model, at an unphysically small Higgs
mass which gives a reasonably strong phase transition (lambda/g^2 =0.036, which
corresponds to m(Higgs)/m(W) = 0.54 at tree level but does not correspond to a
positive physical Higgs mass when radiative effects of the top quark are
included), and compare the results to older perturbative and other estimates.
While two loop perturbation theory slightly under-estimates the strength of the
transition measured by the latent heat, it over-estimates the amount of
supercooling by a factor of 2.Comment: 48 pages, including 16 figures. Minor revisions and typo fixes,
nothing substantial, conclusions essentially unchange
Enhancement of the electronic contribution to the low temperature specific heat of Fe/Cr magnetic multilayer
We measured the low temperature specific heat of a sputtered
magnetic multilayer, as well as separate
thick Fe and Cr films. Magnetoresistance and magnetization
measurements on the multilayer demonstrated antiparallel coupling between the
Fe layers. Using microcalorimeters made in our group, we measured the specific
heat for and in magnetic fields up to for the multilayer. The
low temperature electronic specific heat coefficient of the multilayer in the
temperature range is . This is
significantly larger than that measured for the Fe or Cr films (5.4 and respectively). No magnetic field dependence of was
observed up to . These results can be explained by a softening of the
phonon modes observed in the same data and the presence of an Fe-Cr alloy phase
at the interfaces.Comment: 20 pages, 5 figure
Magnetic Fields Produced by Phase Transition Bubbles in the Electroweak Phase Transition
The electroweak phase transition, if proceeding through nucleation and growth
of bubbles, should generate large scale turbulent flow, which in turn generates
magnetic turbulence and hence magnetic fields on the scale of turbulent flow.
We discuss the seeding of this turbulent field by the motion of the dipole
charge layers in the phase transition bubble walls, and estimate the strength
of the produced fields.Comment: Revtex, 14 pages, 3 figures appended as uuencoded postscript-fil
Ergodic Properties of Classical SU(2) Lattice Gauge Theory
We investigate the relationship between the Lyapunov exponents of periodic
trajectories, the average and fluctuations of Lyapunov exponents of ergodic
trajectories, and the ergodic autocorrelation time for the two-dimensional
hyperbola billiard. We then study the fluctuation properties of the ergodic
Lyapunov spectrum of classical SU(2) gauge theory on a lattice. Our results are
consistent with the notion that this system is globally hyperbolic. Among the
many powerful theorems applicable to such systems, we discuss one relating to
the fluctuations in the entropy growth rate.Comment: 21 pages, 7 figure
Divergences in Real-Time Classical Field Theories at Non-Zero Temperature
The classical approximation provides a non-perturbative approach to
time-dependent problems in finite temperature field theory. We study the
divergences in hot classical field theory perturbatively. At one-loop, we show
that the linear divergences are completely determined by the classical
equivalent of the hard thermal loops in hot quantum field theories, and that
logarithmic divergences are absent. To deal with higher-loop diagrams, we
present a general argument that the superficial degree of divergence of
classical vertex functions decreases by one with each additional loop: one-loop
contributions are superficially linearly divergent, two-loop contributions are
superficially logarithmically divergent, and three- and higher-loop
contributions are superficially finite. We verify this for two-loop SU(N)
self-energy diagrams in Feynman and Coulomb gauges. We argue that hot,
classical scalar field theory may be completely renormalized by local (mass)
counterterms, and discuss renormalization of SU(N) gauge theories.Comment: 31 pages with 7 eps figure
Bjorken Flow, Plasma Instabilities, and Thermalization
At asymptotically high energies, thermalization in heavy ion collisions can
be described via weak-coupling QCD. We present a complete treatment of how
thermalization proceeds, at the parametric weak-coupling level. We show that
plasma instabilities dominate the dynamics, from immediately after the
collision until well after the plasma becomes nearly in equilibrium. Initially
they drive the system close to isotropy, but Bjorken expansion and increasing
diluteness makes the system again become more anisotropic. At time \tau ~
\alpha^(-12/5) Q^(-1) the dynamics become dominated by a nearly-thermal bath;
and at time \tau ~ \alpha^(-5/2) Q^(-1)$ the bath comes to dominate the energy
density, completing thermalization. After this time there is a nearly isotropic
and thermal Quark-Gluon Plasma.Comment: 22 pages, 5 figure
Simulating hot Abelian gauge dynamics
The time evolution of soft modes in a quantum gauge field theory is to first
approximation classical, but the equations of motion are non-local. We show how
they can be written in a local and Hamiltonian way in an Abelian theory, and
that this formulation is particularly suitable for numerical simulations. This
makes it possible to simulate numerically non-equilibrium processes such as the
phase transition in the Abelian Higgs model and and to study, for instance,
bubble nucleation and defect formation. Such simulations would also help to
understand phase transitions in more complicated gauge theories. Moreover, we
show that the existing analytical results for the time-evolution in a
pure-gauge theory correspond to a special class of initial conditions and that
different initial conditions can lead to qualitatively different behavior. We
compare the results of the simulations to analytical calculations and find an
excellent agreement.Comment: 18 pages, 5 figures, REVTe
Electroweak Baryogenesis in Non-minimal Composite Higgs Models
We address electroweak baryogenesis in the context of composite Higgs models,
pointing out that modifications to the Higgs and top quark sectors can play an
important role in generating the baryon asymmetry. Our main observation is that
composite Higgs models that include a light, gauge singlet scalar in the
spectrum [as in the model based on the symmetry breaking pattern SO(6)/SO(5)],
provide all necessary ingredients for viable baryogenesis. In particular, the
singlet leads to a strongly first-order electroweak phase transition and
introduces new sources of CP violation in dimension-five operators involving
the top quark. We discuss the amount of baryon asymmetry produced and the
experimental constraints on the model.Comment: 15 pages, 7 figure
Classical Lattice Gauge Fields with Hard Thermal Loops
We propose a formulation of the long-distance dynamics of gauge theories at
finite temperature on a lattice in Minkowski space, including the effects of
hard thermal loops on the dynamics of the long wavelength modes. Our approach
is based on the dual classical limits of quantum fields as waves and particles
in the infrared and ultraviolet limits, respectively. It exhibits manifest
invariance under space-dependent lattice gauge transformations and conserves
Gauss' law.Comment: 11 pages, plain latex file, with major revisions to include details
on the algorith
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