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Class of solvable reaction-diffusion processes on Cayley tree

Considering the most general one-species reaction-diffusion processes on a Cayley tree, it has been shown that there exist two integrable models. In the first model, the reactions are the various creation processes, i.e. $\circ\circ\to\bullet\circ$, $\circ\circ\to\bullet\bullet$ and $\circ\bullet\to\bullet\bullet$, and in the second model, only the diffusion process $\bullet\circ\to\circ\bullet$ exists. For the first model, the probabilities $P_l(m;t)$, of finding $m$ particles on $l$-th shell of Cayley tree, have been found exactly, and for the second model, the functions $P_l(1;t)$ have been calculated. It has been shown that these are the only integrable models, if one restricts himself to $L+1$-shell probabilities $P(m_0,m_1,...,m_L;t)$s.