183 research outputs found
Thermodynamics of trajectories of the one-dimensional Ising model
We present a numerical study of the dynamics of the one-dimensional Ising
model by applying the large-deviation method to describe ensembles of dynamical
trajectories. In this approach trajectories are classified according to a
dynamical order parameter and the structure of ensembles of trajectories can be
understood from the properties of large-deviation functions, which play the
role of dynamical free-energies. We consider both Glauber and Kawasaki
dynamics, and also the presence of a magnetic field. For Glauber dynamics in
the absence of a field we confirm the analytic predictions of Jack and Sollich
about the existence of critical dynamical, or space-time, phase transitions at
critical values of the "counting" field . In the presence of a magnetic
field the dynamical phase diagram also displays first order transition
surfaces. We discuss how these non-equilibrium transitions in the 1 Ising
model relate to the equilibrium ones of the 2 Ising model. For Kawasaki
dynamics we find a much simple dynamical phase structure, with transitions
reminiscent of those seen in kinetically constrained models.Comment: 23 pages, 10 figure
Signatures of many-body localisation in a system without disorder and the relation to a glass transition
We study a quantum spin systemâadapted from a facilitated spin model for classical glassesâwith local bilinear interactions and without quenched disorder which seems to display characteristic signatures of a many-body localisation (MBL) transition. From direct diagonalisation of small systems, we find a change in certain dynamical and spectral properties at a critical value of a coupling, from those characteristic of a thermalising phase to those characteristic of a MBL phase. The system we consider is known to have a quantum phase transition in its ground-state in the limit of large size, related to a first-order active-to-inactive phase transition in the stochastic trajectories of an associated classical model of glasses. Our results here suggest that this first-order transition in the low-lying spectrum may influence the rest of the spectrum of the system in the large size limit. These findings may help understand the connection between MBL and structural glass transitions
Activity phase transition for constrained dynamics
We consider two cases of kinetically constrained models, namely East and
FA-1f models. The object of interest of our work is the activity A(t) defined
as the total number of configuration changes in the interval [0,t] for the
dynamics on a finite domain. It has been shown in [GJLPDW1,GJLPDW2] that the
large deviations of the activity exhibit a non-equilibirum phase transition in
the thermodynamic limit and that reducing the activity is more likely than
increasing it due to a blocking mechanism induced by the constraints. In this
paper, we study the finite size effects around this first order phase
transition and analyze the phase coexistence between the active and inactive
dynamical phases in dimension 1. In higher dimensions, we show that the finite
size effects are also determined by the dimension and the choice of boundary
conditions.Comment: 38 pages, 3 figure
Mixed population Minority Game with generalized strategies
We present a quantitative theory, based on crowd effects, for the market
volatility in a Minority Game played by a mixed population. Below a critical
concentration of generalized strategy players, we find that the volatility in
the crowded regime remains above the random coin-toss value regardless of the
"temperature" controlling strategy use. Our theory yields good agreement with
numerical simulations.Comment: Revtex file + 3 figure
Multibaryons in the collective coordinate approach to the SU(3) Skyrme model
We obtain the rotational spectrum of strange multibaryon states by performing
the SU(3) collective coordinate quantization of the static multi-Skyrmions.
These background configurations are given in terms of rational maps, which are
very good approximations and share the same symmetries as the exact solutions.
Thus, the allowed quantum numbers in the spectra and the structure of the
collective Hamiltonians we obtain are also valid in the exact case. We find
that the predicted spectra are in overall agreement with those corresponding to
the alternative bound state soliton model.Comment: 16 pages, 1 figur
Topographic Control of Order in Quasi-2D Granular Phase Transitions
We experimentally investigate the nature of 2D phase transitions in a quasi-2D granular fluid. Using a surface decorated with periodically spaced dimples we observe interfacial tension between coexisting granular liquid and crystal phases. Measurements of the orientational and translational order parameters and associated susceptibilities indicate that the surface topography alters the order of the phase transition from a two-step continuous one to a first-order liquid-solid one. The interplay of boundary inelasticity and geometry, either order promoting or inhibiting, controls whether it is the granular crystal or the granular fluid which makes contact with the edge. This order induced wetting has important consequences, determining how coexisting phases separate spatially
Absence of dissipation in trajectory ensembles biased by currents
We consider biased ensembles of trajectories associated with large deviations of currents in equilibrium systems. The biased ensembles are characterised by non-zero currents and lack the time-reversal symmetry of the equilibrium state. In cases where the equilibrium system has an inversion symmetry which is broken by the bias, we show that the biased ensembles retain a generalised time-reversal symmetry, involving a spatial transformation that inverts the current. This means that these ensembles lack dissipation. Hence, they differ significantly from non-equilibrium steady states where currents are induced by external forces. One consequence of this result is that maximum entropy assumptions (MaxEnt/MaxCal), widely used for modelling thermal systems away from equilibrium, have quite unexpected implications, including apparent superfluid behaviour in a classical model of shear flow
Jamming percolation and glassy dynamics
We present a detailed physical analysis of the dynamical glass-jamming
transition which occurs for the so called Knight models recently introduced and
analyzed in a joint work with D.S.Fisher \cite{letterTBF}. Furthermore, we
review some of our previous works on Kinetically Constrained Models.
The Knights models correspond to a new class of kinetically constrained
models which provide the first example of finite dimensional models with an
ideal glass-jamming transition. This is due to the underlying percolation
transition of particles which are mutually blocked by the constraints. This
jamming percolation has unconventional features: it is discontinuous (i.e. the
percolating cluster is compact at the transition) and the typical size of the
clusters diverges faster than any power law when . These
properties give rise for Knight models to an ergodicity breaking transition at
: at and above a finite fraction of the system is frozen. In
turn, this finite jump in the density of frozen sites leads to a two step
relaxation for dynamic correlations in the unjammed phase, analogous to that of
glass forming liquids. Also, due to the faster than power law divergence of the
dynamical correlation length, relaxation times diverge in a way similar to the
Vogel-Fulcher law.Comment: Submitted to the special issue of Journal of Statistical Physics on
Spin glasses and related topic
Zero mode quantization of multi-Skyrmions
A zero mode quantization of the minimal energy SU(2) Skyrmions for nucleon
numbers four to nine and seventeen is described. This involves quantizing the
rotational and isorotational modes of the configurations. For nucleon numbers
four, six and eight the ground states obtained are in agreement with the
observed nuclear states of Helium, Lithium and Beryllium. However, for nucleon
numbers five, seven, nine and seventeen the spins obtained conflict with the
observed isodoublet nuclear states.Comment: 37 pages, LaTeX, 4 figures. More careful treatment of double covers,
reference adde
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