Under a Galilean transformation, the coordinates and momenta of any system transform as: $$ t \rightarrow t',\\ \vec r\:' = \vec r + \vec vt,\\ \vec p\:' = \vec p + m\vec v $$ where $\vec v$ is velocity of frame moving w.r.t it. Now, what will be unitary transformation that can that will carry out this transformation. Let us say the total momentum of the system is $\vec P$ and its mass $M$ and its position $X$. I know how to write a single coordinate translation, but am not able to put all these together.
An Attempt : The transformation should contain :
$ \bf e^{i \vec p.\vec x} $ for translations and $ \bf e^{iHt}$ for time translations, but what about generators of Velocity transformations ?