We describe the Z 2 -graded central polynomials for the matrix algebra of order two, M 2 (K ), and for the algebras M 1,1 (E) and E ⊗ E over an infinite field K , char K = 2. Here E is the infinite-dimensional Grassmann algebra, and M 1,1 (E) stands for the algebra of the 2 × 2 matrices whose entries on the diagonal belong to E 0 , the centre of E, and the off-diagonal entries lie in E 1 , the anticommutative part of E. It turns out that in characteristic 0 the graded central polynomials for M 1,1 (E) and E ⊗ E are the same (it is well known that these two algebras satisfy the same polynomial identities when char K = 0). On the contrary, this is not the case in characteristic p > 2. We describe systems of generators for the Z 2 -graded central polynomials for all these algebras.Finally we give a generating set of the central polynomials with involution for M 2 (K ). We consider the transpose and the symplectic involutions.MSC: 16R10; 16R20; 16R40; 15A75
IntroductionAn important task in the study of algebras with polynomial identities is the description of the central polynomials in a given algebra. The existence of central polynomials for the matrix algebras M n (K ) over a field K was proved by means of direct construction by Formanek [8] and by Razmyslov [19]. Note that Razmyslov also found central polynomials for other important classes of algebras. These are the following. Let E be the infinite dimensional Grassmann algebra of a vector space V with a basis e 1 , e 2 , . . .; then E has a basis consisting of 1 and the products e i 1 e i 2 . . . e i k , i 1 < i 2 < · · · < i k , k ≥ 1. The multiplication in E is induced by e i e j = −e j e i and e 2 i = 0. The algebra E has a natural Z 2 -grading defined as follows: E = E 0 ⊕ E 1 where E i is the span of all basic elements such that k ≡ i (mod 2), i = 0, 1. Now let M n (E) be the n × n matrix algebra over E. Set M a,b the subalgebra of M a+b (E) that consistis of the block matrices having two blocks on the main diagonal, of sizes a × a and b × b whose elements * Corresponding author.