In this note we prove an anolog
of Amitsur’s theorem for central polynomials.
Theorem. Let F be an infinite field, f(x) = f(x1,⋯,xr), g(x) = g(xr+1,⋯,xs)two noncommutative polynomials in disjoint sets of variables. Assume thatf(x1,⋯,xr) ⋅g(xr+1,⋯,xs) is central but not an identity for Fk. Then both f(x) andg(x) are central polynomials for Fk.