Complex exponential construction of planar Brownian motion

ID: complex-exponential-construction-of-planar-brownian-motion

For independent one-dimensional Brownian motions , the real and imaginary parts of are continuous local martingales with equal bracket and zero cross bracket. The Divergence of a driftless Brownian exponential clock makes , and the common-clock time change of orthogonal local martingales makes planar Brownian motion started at . The exponential never vanishes, proving that this Brownian motion never hits zero. Recurrent visits of to arbitrarily negative levels prove visits arbitrarily near zero at arbitrarily large Brownian times.

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