2,188 research outputs found
Spinodal decomposition to a lamellar phase: effects of hydrodynamic flow
Results are presented for the kinetics of domain growth of a two-dimensional
fluid quenched from a disordered to a lamellar phase. At early times when a
Lifshitz-Slyozov mechanism is operative the growth process proceeds
logarithmically in time to a frozen state with locked-in defects. However when
hydrodynamic modes become important, or the fluid is subjected to shear, the
frustration of the system is alleviated and the size and orientation of the
lamellae attain their equilibrium values.Comment: 4 Revtex pages, 4 figures, to appear in Physical Review Letter
Lattice Boltzmann Algorithm for three-dimensional liquid crystal hydrodynamics
We describe a lattice Boltzmann algorithm to simulate liquid crystal
hydrodynamics in three dimensions. The equations of motion are written in terms
of a tensor order parameter. This allows both the isotropic and the nematic
phases to be considered. Backflow effects and the hydrodynamics of topological
defects are naturally included in the simulations, as are viscoelastic effects
such as shear-thinning and shear-banding. We describe the implementation of
velocity boundary conditions and show that the algorithm can be used to
describe optical bounce in twisted nematic devices and secondary flow in
sheared nematics with an imposed twist.Comment: 12 pages, 3 figure
Rheology of cholesteric blue phases
Blue phases of cholesteric liquid crystals offer a spectacular example of
naturally occurring disclination line networks. Here we numerically solve the
hydrodynamic equations of motion to investigate the response of three types of
blue phases to an imposed Poiseuille flow. We show that shear forces bend and
twist and can unzip the disclination lines. Under gentle forcing the network
opposes the flow and the apparent viscosity is significantly higher than that
of an isotropic liquid. With increased forcing we find strong shear thinning
corresponding to the disruption of the defect network. As the viscosity starts
to drop, the imposed flow sets the network into motion. Disclinations break-up
and re-form with their neighbours in the flow direction. This gives rise to
oscillations in the time-dependent measurement of the average stress.Comment: 4 pages, 4 figure
Low temperature phase diagram and critical behaviour of the four-state chiral clock model
The low temperature behaviour of the four-state chiral clock () model
is reexamined using a systematic low temperature series expansion of the free
energy. Previously obtained results for the low temperature phases are
corrected and the low temperature phase diagram is derived. In addition, the
phase transition from the modulated region to the high temperature paraphase is
shown to belong to the universality class of the 3d-XY model.Comment: 17 pages in ioplppt style, 3 figure
Polarized 3 parton production in inclusive DIS at small x
Azimuthal angular correlations between produced hadrons/jets in high energy
collisions are a sensitive probe of the dynamics of QCD at small x. Here we
derive the triple differential cross section for inclusive production of 3
polarized partons in DIS at small x using the spinor helicity formalism. The
target proton or nucleus is described using the Color Glass Condensate (CGC)
formalism. The resulting expressions are used to study azimuthal angular
correlations between produced partons in order to probe the gluon structure of
the target hadron or nucleus. Our analytic expressions can also be used to
calculate the real part of the Next to Leading Order (NLO) corrections to
di-hadron production in DIS by integrating out one of the three final state
partons.Comment: 5 pages, 6 figures; version accepted for publication in Physics
Letters
Feynman parametrization and Mellin summation at finite temperature
We show that the Mellin summation technique (MST) is a well defined and
useful tool to compute loop integrals at finite temperature in the
imaginary-time formulation of thermal field theory, especially when interested
in the infrared limit of such integrals. The method makes use of the Feynman
parametrization which has been claimed to have problems when the analytical
continuation from discrete to arbitrary complex values of the Matsubara
frequency is performed. We show that without the use of the MST, such problems
are not intrinsic to the Feynman parametrization but instead, they arise as a
result of (a) not implementing the periodicity brought about by the possible
values taken by the discrete Matsubara frequencies before the analytical
continuation is made and (b) to the changing of the original domain of the
Feynman parameter integration, which seemingly simplifies the expression but in
practice introduces a spurious endpoint singularity. Using the MST, there are
no problems related to the implementation of the periodicity but instead, care
has to be taken when the sum of denominators of the original amplitude
vanishes. We apply the method to the computation of loop integrals appearing
when the effects of external weak magnetic fields on the propagation of scalar
particles is considered.Comment: 16 pages, 1 figure. Discussion expanded. References added. Published
versio
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