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Jun 28 at 14:22 comment added Michael Hardy @Wicher : You can use MathJax in comments and write $\operatorname{cov}(X_s,X_t) = 1/6 - |s-t|(1-|s-t|).$ Or $$ \operatorname{cov}(X_s,X_t) = \frac16 - |s-t|(1-|s-t|). $$
Jun 28 at 11:25 comment added Wicher @WillSawin Yes this gives a covariance function cov(X_s,X_t)=1/6-|s-t|(1-|s-t|).
May 2, 2012 at 1:17 comment added Will Sawin One could normalize so that the average value of the BB over the entire circle was always $0$.
Nov 23, 2010 at 0:28 comment added Simon Lyons Thanks for your reply. After some more research, I stumbled across this article: emis.de/journals/EJP-ECP/_ejpecp/ECP/include/getdocf87c.pdf Apparently Levy developed the theory of Brownian motion indexed by spheres. The variance of the process in Levy's definition doesn't quite match what I had in mind, so I guess I need to rethink things.
Nov 22, 2010 at 22:37 comment added Michael Hardy It's not clear that we could still speak of the value of the BB at a point, but we could still speak of the difference between the values of the BB at two different points. If the circumference of the circle is 1, then there are two distances between the two points---the lengths of each of the two arcs connecing them---and the sum of the two distances is 1. It can then be deduced that the variance of the difference between the values of the BB at the two points is just the product of those two distances.
Nov 22, 2010 at 20:26 history answered Michael Hardy CC BY-SA 2.5