The raise and peel model of a one-dimensional fluctuating interface (model A) is extended by considering one source (model B) or two sources (model C) at the boundaries. The Hamiltonians describing the three processes have, in the thermodynamic limit, spectra given by conformal field theory. The probabilities of the different configurations in the stationary states of the three models are not only related but have interesting combinatorial properties. We show that by extending Pascal’s triangle (which gives solutions to linear relations in terms of integer numbers), to an hexagon, one obtains integer solutions of bilinear relations. These solutions not only give the weights of the various configurations in the three models but also give an insight into the connections between the probability distributions in the stationary states of the three models. Interestingly enough, Pascal’s hexagon also gives solutions to a Hirota’s difference equation.
The raise and peel model is a one-dimensional nonlocal stochastic model where adsortion happens locally and desorption is nonlocal.The model depends on the single parameter u that is the ratio among the desorption and adsorption rates.At a special value of this parameter (u = 1) the model has interesting features.The spectrum is described by a conformal field theory (central charge c = 0), and its stationary probability density is related to the equilibrium distribution of a two dimensional system.The phase diagram of the model, as a function of the parameter u, has a massive phase (gapped phase) and a massless (gapless phase) whose critical exponents vary continuously with u.In this monography we study a one-parameter extension of the raise and peel model at u = 1, that depends on the additional parameter p.The new model exhibits conformal invariance for the whole range of values of its parameter p, and it is in the same universality class as the usual raise and peel model.The single difference between the models is the value of the sound velocity v s (p) which is a function of p.The methods used in this monography are the exact diagonalization of the evolution operator of the stochastic model (Hamiltonian), for small lattice sizes and Monte Carlo simulations.
We investigate a non-equilibrium one-dimensional model known as the raise and peel model describing a growing surface which grows locally and has non-local desorption. For specific values of adsorption ( u a ) and desorption ( u d ) rates, the model shows interesting features. At u a = u d , the model is described by a conformal field theory (with conformal charge c = 0) and its stationary probability can be mapped onto the ground state of the XXZ quantum chain. Moreover, for the regime u a ⩾ u d , the model shows a phase in which the avalanche distribution is scale-invariant. In this work, we study the surface dynamics by looking at avalanche distributions using a finite-sized scaling formalism and explore the effect of adding a wall to the model. The model shows the same universality for the cases with and without a wall for an odd number of tiles removed, but we find a new exponent in the presence of a wall for an even number of tiles released in an avalanche. New insights into the effect of parity on avalanche distributions are discussed and we provide a new conjecture for the probability distribution of avalanches with a wall obtained by using an exact diagonalization of small lattices and Monte Carlo simulations.
We consider the problem of correlation functions in the stationary states of one-dimensional stochastic models having conformal invariance. If one considers the space dependence of the correlators, the novel aspect is that although one considers systems with periodic boundary conditions, the observables are described by boundary operators. From our experience with equilibrium problems one would have expected bulk operators. Boundary operators have correlators having critical exponents being half of those of bulk operators. If one studies the space-time dependence of the two-point function, one has to consider one boundary and one bulk operators. The Raise and Peel model has conformal invariance as can be shown in the spin 1/2 basis of the Hamiltonian which gives the time evolution of the system. This is an XXZ quantum chain with twisted boundary condition and local interactions. This Hamiltonian is integrable and the spectrum is known in the finite-size scaling limit. In the stochastic base in which the process is defined, the Hamiltonian is not local anymore. The mapping into an SOS model, helps to define new local operators. As a byproduct some new properties of the SOS model are conjectured. The predictions of conformal invariance are discussed in the new framework and compared with Monte Carlo simulations.
Pascal's triangle is widely used as a pedagogical tool to explain the "first-order" multiplet patterns that arise in the spectra of
INS coupled spin-1/2 systems in magnetic resonance. Various other combinatorial structures, which may be well-known in the broader field of quantum dynamics, appear to have largely escaped the attention of the magnetic resonance community with a few exceptions, despite potential usefulness. In this brief set of lecture notes, we describe a "quantum Pascal pyramid" (OEIS https://oeis.org/A268533) as a generalization of Pascal's triangle, which is shown to directly map the relationship between multispin operators of arbitrary spin product rank
q (
Z^Nq) and population operators for states with magnetic quantum number
m (
S^Nm), and - as a consequence - obtain the general form of the intensity ratios of multiplets associated with antiphase single-quantum coherences, with an expression given in terms of the Jacobi polynomials. An extension of the de Moivre-Laplace theorem, beyond the trivial case
q=0, is applied to the
q-th columns of the quantum Pascal pyramid, and is given in terms of a product of the
q-th order Hermite polynomials and a Gaussian distribution, reproducing the well-known functional forms of the solutions of the quantum harmonic oscillator and the classical limit of Hermite-Gaussian modes in laser physics (Allen et al.,
Phys. Rev. A.,
45, 1992). This is used to approximate the Fourier-transformed spectra of
Z^Nq-associated multiplets of arbitrary complexity. Finally, an exercise is shown in which the first two columns of the quantum Pascal pyramid are used to calculate the previously known symmetry-constrained upper bound on
Iz→Sz polarization transfer in
INS spin systems.
Up to now the raise and peel model was the single known example of a one-dimensional stochastic process where one can observe conformal invariance. The model has one-parameter. Depending on its value one has a gapped phase, a critical point where one has conformal invariance and a gapless phase with changing values of the dynamical critical exponent
z. In this model, adsorption is local but desorption is not. The raise and strip model presented here in which desorption is also nonlocal, has the same phase diagram. The critical exponents are different as are some physical properties of the model. Our study suggest the possible existence of a whole class of stochastic models in which one can observe conformal invariance.