1,754 research outputs found
Invariant random subgroups of strictly diagonal limits of finite symmetric groups
We classify the ergodic invariant random subgroups of strictly diagonal
limits of finite symmetric groups
Approximations of standard equivalence relations and Bernoulli percolation at p\_u
The goal of this note is to announce certain results in orbit equivalence
theory, especially concerning the approximation of p.m.p. standard equivalence
relations by increasing sequence of sub-relations, with applications to the
behavior of the Bernoulli percolation on graphs at the threshold pu. R\'esum\'e
en Fran\c{c}ais. Approximations de relations d'\'equivalence standards et
percolation de Bernoulli \`a p\_u
Classical and Quantum Implications of the Causality Structure of Two-Dimensional Spacetimes with Degenerate Metrics
The causality structure of two-dimensional manifolds with degenerate metrics
is analysed in terms of global solutions of the massless wave equation. Certain
novel features emerge. Despite the absence of a traditional Lorentzian Cauchy
surface on manifolds with a Euclidean domain it is possible to uniquely
determine a global solution (if it exists), satisfying well defined matching
conditions at the degeneracy curve, from Cauchy data on certain spacelike
curves in the Lorentzian region. In general, however, no global solution
satisfying such matching conditions will be consistent with this data.
Attention is drawn to a number of obstructions that arise prohibiting the
construction of a bounded operator connecting asymptotic single particle
states. The implications of these results for the existence of a unitary
quantum field theory are discussed.Comment: 27 pages LaTex (6 Figures), Journal of Mathematical Physics
(Accepted
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