Tate twist

In number theory and algebraic geometry, the Tate twist, named after John Tate, is an operation on Galois modules.

For example, if K is a field, G_K is its absolute Galois group, and ρ : G_K → Aut_Qp(V) is a representation of G_K on a finite-dimensional vector space V over the field Q_p of p-adic numbers, then the Tate twist of V, denoted V(1), is the representation on the tensor product V⊗Q_p(1), where Q_p(1) is the p-adic cyclotomic character (i.e. the Tate module of the group of roots of unity in the separable closure K^s of K). More generally, if m is a positive integer, the mth Tate twist of V, denoted V(m), is the tensor product of V with the m-fold tensor product of Q_p(1). Denoting by Q_p(−1) the dual representation of Q_p(1), the -mth Tate twist of V can be defined as

$V\otimes \mathbf {Q} _{p}(-1)^{\otimes m}.$