Twisted Classical Poincar\'{e} Algebras

We consider the twisting of Hopf structure for classical enveloping algebra $U(\hat{g})$, where $\hat{g}$ is the inhomogenous rotations algebra, with explicite formulae given for $D=4$ Poincar\'{e} algebra $(\hat{g}={\cal P}_4).$ The comultiplications of twisted $U^F({\cal P}_4)$ are obtained by conjugating primitive classical coproducts by $F\in U(\hat{c})\otimes U(\hat{c}),$ where $\hat{c}$ denotes any Abelian subalgebra of ${\cal P}_4$, and the universal $R-$matrices for $U^F({\cal P}_4)$ are triangular. As an example we show that the quantum deformation of Poincar\'{e} algebra recently proposed by Chaichian and Demiczev is a twisted classical Poincar\'{e} algebra. The interpretation of twisted Poincar\'{e} algebra as describing relativistic symmetries with clustered 2-particle states is proposed.