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JOURNALS // Zapiski Nauchnykh Seminarov POMI // Archive

Zap. Nauchn. Sem. POMI, 2011 Volume 396, Pages 144–154 (Mi znsl4656)

Beneš condition for discontinuous exponential martingale

R. Liptser

Department of Electrical Engineering Systems, Tel Aviv University, Tel Aviv, Israel

Abstract: It is known that the Girsanov exponent $\mathfrak z_t$, being solution of Doléans-Dade equation $\mathfrak z_t=1+\int_0^t\mathfrak z_s\alpha(s)\,dB_s$ generated by Brownian motion $B_t$ and a random process $\alpha(t)$ with $\int_0^t\alpha^2(s)\,ds<\infty$ a.s., is the martingale provided that the Beneš condition
$$ |\alpha(t)|^2\le\mathrm{const.}\big[1+\sup_{s\in[0,t]}B^2_s\big],\quad\forall\ t>0, $$
holds true. In this paper, we show that $\int_0^t\alpha(s)\,dB_s$ can be replaced by a purely discontinuous square integrable martingale $M_t$ paths from the Skorokhod space $ \mathbb D_{[0,\infty)}$ having jumps $\alpha(s)\triangle M_t>-1$. The method of proof differs from the original Beneš proof.

Key words and phrases: Girsanov's exponential martingale, uniform integrability.

UDC: 519.1+519.2

Received: 29.08.2011

Language: English


 English version:
Journal of Mathematical Sciences (New York), 2013, 188:6, 717–723

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© Steklov Math. Inst. of RAS, 2024