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The expected area of the filled planar Brownian loop is \(\pi/5\). (English) Zbl 1107.82023

Summary: Let \(B_{t}\), \(0\leq t \leq 1\) be a planar Brownian loop (a Brownian motion conditioned so that \(B_{0}= B_{1})\). We consider the compact hull obtained by filling in all the holes, i.e. the complement of the unique unbounded component of the complement of \(B [0,1]\). We show that the expected area of this hull is \(\pi /5\). The proof uses, perhaps not surprisingly, the Schramm Loewner Evolution (SLE). As a consequence of this result, using Yor’s formula for the law of the index of a Brownian loop, we find that the expected area of the region inside the loop having index zero is \(\pi/30\); this value could not be obtained directly using Yor’s index description.

MSC:

82B41 Random walks, random surfaces, lattice animals, etc. in equilibrium statistical mechanics
60J65 Brownian motion

Online Encyclopedia of Integer Sequences:

Decimal expansion of 2*Pi.

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