Consider the stochastic heat equation $partial_t u = (frac{varkappa}{2})Delta u+sigma(u)dot{F}$, where the solution $u:=u_t(x)$ is indexed by $(t,x)in (0, infty)timesR^d$, and $dot{F}$ is a centered Gaussian noise that is white in time and has spatia
lly-correlated coordinates. We analyze the large-$|x|$ fixed-$t$ behavior of the solution $u$ in different regimes, thereby study the effect of noise on the solution in various cases. Among other things, we show that if the spatial correlation function $f$ of the noise is of Riesz type, that is $f(x)propto |x|^{-alpha}$, then the fluctuation exponents of the solution are $psi$ for the spatial variable and $2psi-1$ for the time variable, where $psi:=2/(4-alpha)$. Moreover, these exponent relations hold as long as $alphain(0, dwedge 2)$; that is precisely when Dalangs theory implies the existence of a solution to our stochastic PDE. These findings bolster earlier physical predictions.
We consider a family of nonlinear stochastic heat equations of the form $partial_t u=mathcal{L}u + sigma(u)dot{W}$, where $dot{W}$ denotes space-time white noise, $mathcal{L}$ the generator of a symmetric Levy process on $R$, and $sigma$ is Lipschitz
continuous and zero at 0. We show that this stochastic PDE has a random-field solution for every finite initial measure $u_0$. Tight a priori bounds on the moments of the solution are also obtained. In the particular case that $mathcal{L}f=cf$ for some $c>0$, we prove that if $u_0$ is a finite measure of compact support, then the solution is with probability one a bounded function for all times $t>0$.
