On constacyclic codes of length 4 p s over F p m + u F p m

For any odd prime p such that p m ź 1 ( m o d 4 ) , the structures of all λ -constacyclic codes of length 4 p s over the finite commutative chain ring F p m + u F p m ( u 2 = 0 ) are established in terms of their generator polynomials. If the unit λ is a square, each λ -constacyclic code of length 4 p s is expressed as a direct sum of an - α -constacyclic code and an α -constacyclic code of length 2 p s . In the main case that the unit λ is not a square, it is shown that any nonzero polynomial of degree