Colective Effects from Induced Behaviour

We present a solvable model for describing quantitatively situations where the individual behaviour of agents in a group "percolates" to collective behaviour of the group as a whole as a result of mutual influence between the agents.Comment: 6 pages, 6 figures, EPJ macro

A two step algorithm for learning from unspecific reinforcement

We study a simple learning model based on the Hebb rule to cope with "delayed", unspecific reinforcement. In spite of the unspecific nature of the information-feedback, convergence to asymptotically perfect generalization is observed, with a rate depending, however, in a non- universal way on learning parameters. Asymptotic convergence can be as fast as that of Hebbian learning, but may be slower. Moreover, for a certain range of parameter settings, it depends on initial conditions whether the system can reach the regime of asymptotically perfect generalization, or rather approaches a stationary state of poor generalization.Comment: 13 pages LaTeX, 4 figures, note on biologically motivated stochastic variant of the algorithm adde

Study of the phase structure of an SU(3) Higgs model at finite temperature

Karsch F, Seiler E, Stamatescu IO. Study of the phase structure of an SU(3) Higgs model at finite temperature. Physics Letters, B. 1985;157(1):60-64.We analyse numerically an SU(3) Higgs model with complete symmetry breaking and radial degree of freedom on asymmetric, periodic lattices. The character of both the Higgs and deconfining transitions is found to depend on the Higgs self-coupling and on a parameter which may simulate the number of flavours. In particular, an increase in the latter leads to the disappearance of the deconfining transition for small Higgs masses

The SU(2) adjoint Higgs model at positive temperature: a Monte Carlo study

Karsch F, Seiler E, Stamatescu IO. The SU(2) adjoint Higgs model at positive temperature: a Monte Carlo study. Physics Letters, B. 1983;131(1-3):138-144.We investigate the phase structure of the Georgi-Glashow model at positive temperature, realized by using an asymmetric 6 3 ×3 lattice. We find a clear signal for the deconfining phase transition at all values of the Higgs coupling constant. On the other hand, there is no unambiguous signal for a transition between a "Higgs" and a "symmetric" phase at moderate [beta]; very high values of [beta] cannot be studied with the icosahedral subgroup used here, because of the freezing transition. We use some new observables as probes of the different behaviour of the system at different values of the Higgs coupling constant

Investigation of a Toy Model for Frustration in Abelian Lattice Gauge Theory

We introduce a lattice model with local U(1) gauge symmetry which incorporates explicit frustration in d >2. The form of the action is inspired from the loop expansion of the fermionic determinant in standard lattice QED. We study through numerical simulations the phase diagram of the model, revealing the existence of a frustrated (antiferromagnetic) phase for d=3 and d=4, once an appropriate order parameter is identified.Comment: 7 pages, 7 figure

Controlling Complex Langevin simulations of lattice models by boundary term analysis

One reason for the well known fact that the Complex Langevin (CL) method sometimes fails to converge or converges to the wrong limit has been identified long ago: it is insufficient decay of the probability density either near infinity or near poles of the drift, leading to boundary terms that spoil the formal argument for correctness. To gain a deeper understanding of this phenomenon, in a previous paper we have studied the emergence of such boundary terms thoroughly in a simple model, where analytic results can be compared with numerics. Here we continue this type of analysis for more physically interesting models, focusing on the boundaries at infinity. We start with abelian and non-abelian one-plaquette models, then we proceed to a Polyakov chain model and finally to high density QCD (HDQCD) and the 3D XY model. We show that the direct estimation of the systematic error of the CL method using boundary terms is in principle possible.Comment: 17 pages, 11 figure