Solvability of Parabolic Anderson Equation with Fractional Gaussian Noise

This paper provides necessary as well as sufficient conditions on the Hurst parameters so that the continuous time parabolic Anderson model partial derivative u/partial derivative t = 1/2 Delta+u(W)over dot on [0, infinity) x R-d with d >= 1 has a unique random field solution, where W(t, x) is a fractional Brownian sheet on [0, infinity) x R-d and formally (W)over dot = partial derivative(d+1)/partial derivative(t)partial derivative x(1)...partial derivative x(d) W(t, x). When the noise W(t, x) is white in time, our condition is both necessary and sufficient when the initial data u(0, x) is bounded between two positive constants. When the noise is fractional in time with Hurst parameter H-0 > 1/2, our sufficient condition, which improves the known results in the literature, is different from the necessary one.