Phase diagram of the one-state potts model on the Cayley tree

The phase diagram of the one-state Potts model on the closed asymmetric Cayley tree with branching ratior=2 is obtained from the Bethe-Peierls map. The route to chaos, via the period doubling cascade, is obtained by considering the antiferromagnetic coupling limit. The connection of the Potts model with the percolation problem is shown by calculating the order parameter, its susceptibility, the internal energy, and the specific heat as well as their asymptotic behavior at the paramagnetic-ferromagnetic critical point. Due to the type of the lattice and to the polynomial character of the map, this is the simplest known example of a McKay-Berker-Kirkpatrick spin-glass.     

Metastability and nucleation for the Blume-Capel model. Different mechanisms of transition

We study metastability and nucleation for the Blume-Capel model: a ferromagnetic nearest neighbor two-dimensional lattice system with spin variables taking values in {–1,0, +1}. We consider large but finite volume, small fixed magnetic fieldh, and chemical potential in the limit of zero temperature; we analyze the first excursion from the metastable –1 configuration to the stable +1 configuration. We compute the asymptotic behavior of the transition time and describe the typical tube of trajectories during the transition. We show that, unexpectedly, the mechanism of transition changes abruptly when the lineh=2 is crossed.     

Metastability in the Two-Dimensional Ising Model with Free Boundary Conditions

We investigate metastability in the two dimensional Ising model in a square with free boundary conditions at low temperatures. Starting with all spins down in a small positive magnetic field, we show that the exit from this metastable phase occurs via the nucleation of a critical droplet in one of the four corners of the system. We compute the lifetime of the metastable phase analytically in the limit T 0, h 0 and via Monte Carlo simulations at fixed values of T and h and find good agreement. This system models the effects of boundary domains in magnetic storage systems exiting from a metastable phase when a small external field is applied.     

Theory of the Ising model on a Cayley tree

The Ising model on a Cayley tree is known to exhibit a phase transition of continuous order. In this paper we present a complete and quantitative analysis of the leading singular term in the free energy which is associated with this phase transition. We have been able to solve this problem by considering the distribution of zeros of the partition function. The most interesting new feature in our results is a contribution to the free energy which performs singular oscillations as the magnetic field approaches zero.     

Metastability of the liquid-vapor transition and related effects

The Becker-Döring and Fisher nucleation kinetic theories of metastability of the liquid-vapor transition are outlined and compared with Temperley's theory based on equilibrium statistical mechanics, and it is claimed that the two approaches are in effect the same—a point that has been made by O. Penrose based on a different argument. The theoretical 27T _c/32 for the limit of superheat is known to be in reasonable agreement with experiment. The tensile strengths of liquids have been measured by many methods which have appeared to be in conflict, but it is claimed that the conflicts can be resolved by invoking rectified diffusion of gas into a bubble performing forced oscillations in a periodic pressure field and by considering the structure of the free surface of a liquid. The transition layer almost certainly contains a region in which the velocity of sound is low. A brief account of cavitation effects is given.     

A Note on the Metastability of the Ising Model: The Alternate Updating Case

We study the metastable behavior of the two-dimensional Ising model in the case of an alternate updating rule: parallel updating of spins on the even (odd) sublattice are permitted at even (odd) times. We show that although the dynamics is different from the Glauber serial case the typical exit path from the metastable phase remains the same.     

Metastability in Glauber Dynamics in the Low-Temperature Limit: Beyond Exponential Asymptotics

We consider Glauber dynamics of classical spin systems of Ising type in the limit when the temperature tends to zero in finite volume. We show that information on the structure of the most profound minima and the connecting saddle points of the Hamiltonian can be translated into sharp estimates on the distribution of the times of metastable transitions between such minima as well as the low lying spectrum of the generator. In contrast with earlier results on such problems, where only the asymptotics of the exponential rates is obtained, we compute the precise pre-factors up to multiplicative errors that tend to 1 as T0. As an example we treat the nearest neighbor Ising model on the 2 and 3 dimensional square lattice. Our results improve considerably earlier estimates obtained by Neves–Schonmann,⁽¹⁾ Ben Arous–Cerf,⁽²⁾ and Alonso–Cerf.⁽³⁾ Our results employ the methods introduced by Bovier, Eckhoff, Gayrard, and Klein in refs. 4 and 5.     

Yang-Lee zeros of the Ising model on the closed Cayley tree

The Yang-Lee zeros of the partition function of the ferro-, antiferro- and of the partially antiferromagnetic anisotropic Ising models defined on the closed symmetric Cayley tree are studied. The applicability of the Yang-Lee theorem to the antiferromagnetic systems is shown to be a consequence of the invariance of the unit circle under the Bethe-Peierls map. The relationship as well as the distinction between the set of zeros and the Julia set is established. The fractal dimension of the Julia set is shown to be equal to one in the low temperature phase and to be a decreasing function of the temperature in the paramagnetic phase of the three systems.     

An exact formulation of the Blume-Emery-Griffiths model on a two-fold Cayley tree model

A two-fold Cayley tree graph with fully q-coordinated sites is constructed and the spin-1 Ising Blume-Emery-Griffiths model on the constructed graph is solved exactly using the exact recursion equations for the coordination number q = 3. The exact phase diagrams in (kT/J, K/J ) and (kT/J, D/J) planes are obtained for various values of constants D/J and K/J, respectively, and the tricritical behavior is found. It is observed that when the negative biquadratic exchange (K) and the positive crystal-field (D) interactions are large enough, the tricritical point disappears in the (kT/J, K/J) plane. On the other hand, the system always exhibits a tricritical behavior in the phase diagram of (kT/J, D/J) plane. Received 8 June 2001 and Received in final form 28 September 2001     

Susceptibility divergence of the spin 1 Ising model on the Cayley tree

The temperature T₂(1), below which the zero-field isothermal susceptibility diverges for the spin 1 Ising model on the M-generation Cayley tree, in the limit as M → ∞, is located. The general approach follows closely that of Falk for the spin $\text{1}\text{2}$ problem. Pruning and retraction identities are used to find upper and lower bounds on the bond-length dependence of the general two-spin correlation function and thence on the susceptibility. A conjecture is advanced regarding the divergence of the higher-order susceptibilities.     

On the transition from ferromagnetism to antiferromagnetism on twofold Cayley tree

Summary A fixed-point conversion theorem which shows the transition from ferromagnetism to antiferromagnetism on twofold Cayley tree is proved. The ferromagnetic and antiferromagnetic maps are shown to be related by an involution and in zero field the stable fixed points of the ferromagnetic map are converted to a stable two-cycle of the antiferromagnetic map. A reduced one-dimensional analysis in zero field yields precisely the same results.     

More results on the Ashkin-Teller model

We analyze the low-temperature phase diagram of the Ashkin-Teller model for real values of the quadratic and quartic coupling constants.     

Behavior of the effective fields for a regular ising model on the Cayley tree

A regular Ising model with nearest-neighbor interactions ofJ and–J(J>0) on a Cayley tree of coordination number 3 is investigated for the behavior of effective fields in a uniform external field. The effective fields show periodic and also aperiodic structures in the temperature-field plane. At absolute zero temperature, the equations determining effective fields are reduced to a nonlinear, one-dimensional, iterative equation. Arithmetic furcations of period and a screening of the furcations are observed.     

Exactly solvable reaction diffusion models on a Cayley tree

The most general reaction-diffusion model on a Cayley tree with nearest-neighbor interactions is introduced, which can be solved exactly through the empty-interval method. The stationary solutions of such models, as well as their dynamics, are discussed. Concerning the dynamics, the spectrum of the evolution Hamiltonian is found and shown to be discrete, hence there is a finite relaxation time in the evolution of the system towards its stationary state.     

Spin-glass and spin-crystal phase transition of a regular Ising model on the Cayley tree

A regular Ising model with nearest-neighbour interaction of +J and -J on a Cayley tree is reported to show a phase transition from the paramagnetic phase to the spin-glass and spin-crystal phase in a uniform external field below a critical value h_c.