Aernout C. D. van Enter
University of Groningen

Talk 1


Title : First-Order Transitions in the Presence of Continuous Symmetries

Abstract We present a number of results where there is a first-order 
transition in temperature in the presence of a continuous symmetry. 
These include strongly nonlinear nearest-neighbor 2- and 
more-dimensional vector (classical or quantum XY or Heisenberg) models, 
possibly with annealed dilution,  nematic liquid-crystal models, and 3- 
and more-dimensional lattice gauge models. A peculiar aspect of our 
results is that the proofs do not necessarily provide information on the 
nature of the low-temperature phases.

Talk 2

Title: Gibbsian and non-Gibbsian measures

Non-Gibbsian measures first appeared as an explanation for  the
"Renormalization Group peculiarities" which were discovered
more than twentyfive years ago by Griffiths and Pearce. Some of the 
questions they asked have been answered, but others   are still widely open.
The problems they raised have led to the study of non-Gibbsian states 
(probability measures). We discuss  some further related developments, 
in particular  applications to nonequilibrium questions and disordered 
models.