3,288 research outputs found
Relativistic dissipative hydrodynamics with spontaneous symmetry breaking
In this paper we consider dissipative hydrodynamic equations for systems with
continuous broken symmetries. We first present the case of superfluidity, in
which the symmetry U(1) is broken and then generalize to the chiral symmetry
. The corresponding new transport coefficients are
introduced.Comment: 5 pages, RevTeX Minor changes, version accepted for publicatio
Dynamical obstruction in a constrained system and its realization in lattices of superconducting devices
Hard constraints imposed in statistical mechanics models can lead to
interesting thermodynamical behaviors, but may at the same time raise
obstructions in the thoroughfare to thermal equilibration. Here we study a
variant of Baxter's 3-color model in which local interactions and defects are
included, and discuss its connection to triangular arrays of Josephson
junctions of superconductors and \textit{kagom\'e} networks of superconducting
wires. The model is equivalent to an Ising model in a hexagonal lattice with
the constraint that the magnetization of each hexagon is or 0. For
ferromagnetic interactions, we find that the system is critical for a range of
temperatures (critical line) that terminates when it undergoes an exotic first
order phase transition with a jump from a zero magnetization state into the
fully magnetized state at finite temperature. Dynamically, however, we find
that the system becomes frozen into domains. The domain walls are made of
perfectly straight segments, and domain growth appears frozen within the time
scales studied with Monte Carlo simulations. This dynamical obstruction has its
origin in the topology of the allowed reconfigurations in phase space, which
consist of updates of closed loops of spins. As a consequence of the dynamical
obstruction, there exists a dynamical temperature, lower than the (avoided)
static critical temperature, at which the system is seen to jump from a
``supercooled liquid'' to a ``polycrystalline'' phase. In contrast, for
antiferromagnetic interactions, we argue that the system orders for
infinitesimal coupling because of the constraint, and we observe no interesting
dynamical effects
Hydrodynamics with spontaneous symmetry breaking: application to relativistic heavy ion collisions
In this paper we apply hydrodynamics for systems with continuous broken
symmetries to heavy ion collisions in the framework of (1+1) dimensional
Bjorken model. The temperature profile with respect to proper time determined
in that context exhibits no differences with the ideal fluid. On the contrary,
it is shown that the profile obtained when M\"{u}ller-Israel-Stewart second
order theory of dissipation is included on top of standard hydrodynamics
indicates a slower cooling of the system.Comment: 5 pages, 2 figures, version accepted for publication as a Brief
Report in Physical Review
Three-sublattice Skyrmion crystal in the antiferromagnetic triangular lattice
The frustrated classical antiferromagnetic Heisenberg model with
Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied
under a magnetic field by means of semiclassical calculations and large-scale
Monte Carlo simulations. We show that even a small DM interaction induces the
formation of an Antiferromagnetic Skyrmion crystal (AF-SkX) state. Unlike what
is observed in ferromagnetic materials, we show that the AF-SkX state consists
of three interpenetrating Skyrmion crystals (one by sublattice), and most
importantly, the AF-SkX state seems to survive in the limit of zero
temperature. To characterize the phase diagram we compute the average of the
topological order parameter which can be associated to the number of
topological charges or Skyrmions. As the magnetic field increases this
parameter presents a clear jump, indicating a discontinuous transition from a
spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the
spin structure factor. For higher fields, a second (probably continuous)
transition occurs into a featureless paramagnetic phase.Comment: 8 pages, 8 figure
Ground states of quantum kagome antiferromagnets in a magnetic field
We study the ground state properties of a quantum antiferromagnet in the
kagome lattice in the presence of a magnetic field, paying particular attention
to the stability of the plateau at magnetization 1/3 of saturation. While the
plateau is reinforced by certain deformations of the lattice, like the
introduction of structural defect lines and against an Ising anisotropy, ground
state correlations are seen to be quite different and the undistorted SU(2)
case appears to be rather special.Comment: 3 pages, 3 figures, contribution to the Japanese-French symposium on
"Quantum magnetism in spin, charge and orbital systems", Paris 1-4 October
200
Diagnosing order by disorder in quantum spin systems
In this paper we study the frustrated J1-J2 quantum Heisenberg model on the
square lattice for J2 > 2J1, in a magnetic field. In this regime the classical
system is known to have a degenerate manifold of lowest energy configurations,
where standard thermal order by disorder occurs. In order to study its quantum
version we use a path integral formulation in terms of coherent states. We show
that the classical degeneracy in the plane transverse to the magnetic field is
lifted by quantum fluctuations. Collinear states are then selected, in a
similar pattern to that set by thermal order by disorder, leaving a Z2
degeneracy. A careful analysis reveals a purely quantum mechanical effect given
by the tunneling between the two minima selected by fluctuations. The effective
description contains two planar (XY -like) fields conjugate to the total
magnetization and the difference of the two sublattice magnetizations. Disorder
in either or both of these fields produces the locking of their conjugate
observables. Furthermore, within this scenario we argue that the quantum state
is close to a product state.Comment: 8 pages, 3 figure
Creating agent platforms to host agent-mediated services that share resources
After a period where the Internet was exclusively filled with content,
the present
efforts are moving towards services, which handle the raw information to
create
value from it. Therefore labors to create a wide collection of
agent-based services
are being perfomed in several projects, such as Agentcities does.
In this work we present an architecture for agent platforms named
a-Buildings. The
aim of the proposed architecture is to ease the creation, installation,
search and
management of agent-mediated services and the share of resources among
services.
To do so the a-Buildings architecture creates a new level of abstraction
on top of
the standard FIPA agent platform specification.
Basically, an a-Building is a service-oriented platform which offers a
set of
low level services to the agents it hosts. We define low level services
as those
required services that are neccesary to create more complex high level
composed
services.Postprint (published version
Statistical transmutation in doped quantum dimer models
We prove a "statistical transmutation" symmetry of doped quantum dimer models
on the square, triangular and kagome lattices: the energy spectrum is invariant
under a simultaneous change of statistics (i.e. bosonic into fermionic or
vice-versa) of the holes and of the signs of all the dimer resonance loops.
This exact transformation enables to define duality equivalence between doped
quantum dimer Hamiltonians, and provides the analytic framework to analyze
dynamical statistical transmutations. We investigate numerically the doping of
the triangular quantum dimer model, with special focus on the topological Z2
dimer liquid. Doping leads to four (instead of two for the square lattice)
inequivalent families of Hamiltonians. Competition between phase separation,
superfluidity, supersolidity and fermionic phases is investigated in the four
families.Comment: 3 figure
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