### The coin turning walk

Probability Seminar

22nd May 2019, 4:00 pm – 5:00 pm

Main Maths Building, SM3

Let $S$ be the random walk obtained from ``coin turning” with some sequence $\{p_n\}_{n\ge 2}$, as introduced in (Engl\"ander, J.; Volkov, S. Turning a coin over instead of tossing it. J. Theor. Probab. 31 (2018), 1097--1118.). In this paper we investigate the scaling limits of $S$ in the spirit of the classical Donsker invariance principle, both for the heating and for the cooling dynamics. We prove that an invariance principle, albeit with a non-classical scaling, holds for ``not too small" sequences, the order const$\cdot n^{-1}$ (critical cooling regime) being the threshold. At and below this critical order, the scaling behavior is dramatically different from the one above it. The same order is also the critical one for the Weak Law of Large Numbers to hold. In the critical cooling regime, an interesting process emerges: it is a continuous, piecewise linear, recurrent process, for which the one-dimensional marginals are Beta-distributed. We also investigate the recurrence of the walk and its scaling limit, as well as the ergodicity and mixing of the $n$th step of the walk.

This is joint work with Stas Volkov (Lund) and Zhenhua Wang (Boulder).

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