Let $\mathcal{D}_1$, $\mathcal{D}_2$ and $\mathcal{D}_3$ be three distributions defined on some space $\mathcal{X}$.
Assume $\mathcal{D}_1 = \mathcal{D}_2 + \mathcal{D}_3$
and $\mathcal{D}_1$ is assumed to be known and for example it's a (multi) variate normal distribution, what can we say about $\mathcal{D}_2$ and $\mathcal{D}_3$, are they also gaussian? The problem has many degrees of freedom but I just want to get some intuition about what those distributions could be.
WHat happen if we generalize the problem to other classical laws and to exponential families ?