  The sharp growth and distortion theorems are established for slice monogenic
extensions of univalent functions on the unit disc $\mathbb D\subset \mathbb C$
in the setting of Clifford algebras, based on a new convex combination
identity. The analogous results are also valid in the quaternionic setting for
slice regular functions and we can even prove the Koebe type one-quarter
theorem in this case. Our growth and distortion theorems for slice regular
(slice monogenic) extensions to higher dimensions of univalent holomorphic
functions hold without extra geometric assumptions, in contrast to the setting
of several complex variables in which the growth and distortion theorems fail
in general and hold only for some subclasses with the starlike or convex
assumption.
