We construct a free-probability quantum Yang-Mills theory on the two
dimensional plane, determine the Wilson loop expectation values, and show that
this theory is the $N=\infty$ limit of U(N) quantum Yang-Mills theory on the
plane.
In a two-state free probability space $(A, \phi, \psi)$, we define an
algebraic two-state free Brownian motion to be a process with two-state freely
independent increments whose two-state free cumulant generating function is
quadratic. Note that a priori, the distribution of the process with respect to
the second state $\psi$ is arbitrary. We show, however, that if $A$ is a von
Neumann algebra, the states $\phi, \psi$ are normal, and $\phi$ is faithful,
then there is only a one-parameter family of such processes.
We investigate in more detail the two-state free convolution semigroups of
pairs of measures whose Jacobi parameters are linear in the convolution
parameter $t$. These semigroups were constructed in arXiv:1001.1540, where we
also showed that measures with the analogous property for the usual and free
convolution are exactly the classical, resp. free Meixner classes. The class of
measures in this paper has not been considered explicitly before, but we show
that it also has Meixner-type properties.
We prove that the q-Gaussian distribution introduced by Bozejko and Speicher
is freely infinitely divisible for all q between zero and one.
We show that a convolution semigroup of measures has Jacobi parameters linear
in the convolution parameter $t$ if and only if the measures come from the
Meixner class. Moreover, we prove the parallel result, in a more explicit way,
for the free convolution and the free Meixner class. We then construct the
class of measures satisfying the same property for the two-state free
convolution. This class has not been considered explicitly before, but we
describe its relation to the two-state free Laha-Lukacs characterization, and
to the $q=0$ case of quadratic harnesses.
The operator $L_\mu: f \mapsto \int \frac{f(x) - f(y)}{x - y} d\mu(y)$ is,
for a compactly supported measure $\mu$ with an $L^3$ density, a closed,
densely defined operator on $L^2(\mu)$. We show that the operator $Q = p
L_\mu^2 - q L_\mu$ has polynomial eigenfunctions if and only if $\mu$ is a free
Meixner distribution. The only time $Q$ has orthogonal polynomial
eigenfunctions is if $\mu$ is a semicircular distribution. More generally, the
only time the operator $p (L_\nu L_\mu) - q L_\mu$ has orthogonal polynomial
eigenfunctions is when $\mu$ and $\nu$ are related by a Jacobi shift.