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Persistence of iterated partial sums

Amir DemboJian DingFuchang Gao — 2013

Annales de l'I.H.P. Probabilités et statistiques

Let S n ( 2 ) denote the iterated partial sums. That is, S n ( 2 ) = S 1 + S 2 + + S n , where S i = X 1 + X 2 + + X i . Assuming X 1 , X 2 , ... , X n are integrable, zero-mean, i.i.d. random variables, we show that the persistence probabilities p n ( 2 ) : = max 1 i n S i ( 2 ) l t ; 0 c 𝔼 | S n + 1 | ( n + 1 ) 𝔼 | X 1 | , with c 6 30 (and c = 2 whenever X 1 is symmetric). The converse inequality holds whenever the non-zero min ( - X 1 , 0 ) is bounded or when it has only finite third moment and in addition X 1 is squared integrable. Furthermore, p n ( 2 ) n - 1 / 4 for any non-degenerate squared integrable, i.i.d., zero-mean X i . In contrast, we show that for any 0 l t ; γ l t ; 1 / 4 there exist integrable, zero-mean...

Markovian perturbation, response and fluctuation dissipation theorem

Amir DemboJean-Dominique Deuschel — 2010

Annales de l'I.H.P. Probabilités et statistiques

We consider the Fluctuation Dissipation Theorem (FDT) of statistical physics from a mathematical perspective. We formalize the concept of “linear response function” in the general framework of Markov processes. We show that for processes out of equilibrium it depends not only on the given Markov process () but also on the chosen perturbation of it. We characterize the set of all possible response functions for a given Markov process and show that at equilibrium they all satisfy the FDT. That is,...

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