In the Coxeter group W (R) generated by the root system R, let T (R) be the number of conjugacy classes having no eigenvalue +1 and let S(R) be the number of conjugacy classes having no eigenvalue −1. The algebra H W (R) of observables of the rational Calogero model based on the root system R possesses T (R) independent traces; the same algebra, considered as an associative superalgebra with respect to a certain natural parity, possesses S(R) even independent supertraces and no odd trace or supertrace. The numbers T (R) and S(R) are determined for all irreducible root systems (hence for all root systems). It is shown that T (R) ≤ S(R), and T (R) = S(R) if and only if superalgebra H W (R) contains a Klein operator (or, equivalently, W (R) ∋ −1).Keywords: Trace; supertrace; Cherednik algebra; algebra of observables; Calogero model.
Mathematics Subject Classification: 17B80, 16W551. Definitions and generalities
TracesLet A be an associative superalgebra with parity π. All expressions of linear algebra are given for homogeneous elements only and are supposed to be extended to inhomogeneous elements via linearity.A linear function str on A is called a supertrace ifA linear function tr on A is called a trace if
S.E. Konstein and R. StekolshchikLet A 1 and A 2 be associative superalgebras with parities π 1 and π 2 , respectively. Define the tensor product A = A 1 ⊗A 2 as a superalgebra with the product (a 1 ⊗a 2 )(b 1 ⊗b 2 ) = (a 1 b 1 )⊗(a 2 b 2 ) (no sign factors in this formula) and the parity π defined by the formula π(a ⊗ b) = π 1 (a) + π 2 (b).Let T i be a trace on A i . Clearly, the function T such thatis an even supertrace on A .
Klein operatorLet A be an associative superalgebra with parity π. Following M.Vasiliev, see, e.g.[21], we say that an element K ∈ A is a Klein operator a if π(K) = 0, K f = (−1) π( f ) f K for any f ∈ A and K 2 = 1. Every Klein operator belongs to the anticenter of the superalgebra A , see [18], p.41. b Any Klein operator, if exists, establishes an isomorphism between the space of even traces and the space of even supertraces on A . Namely, if f → T ( f ) is an even trace, then f → T ( f K) is a supertrace, and if f → S( f ) is an even supertrace, then f → S( f K) is a trace.
Group algebraLet V = R n and G ⊂ End(V ) be a finite group. The group algebra C[G] of G consists of all linear combinations ∑ g∈W (R) α gḡ , where α g ∈ C. We distinguish g considered as an element of the group G ⊂ End(V ) from the same elementḡ ∈ C[G] considered as an element of the group algebra. The addition in C[G] is defined as follows:and the multiplication is defined by setting g 1 g 2 = g 1 g 2 .Note that the additions in C[G] and in End(V ) differ. For example, if I ∈ G is unity and the matrix J = −I from End(V ) belongs to G, then I + J = 0 in End(V ) while I + J = 0 in C[G].
Root systemsLet V = R N be endowed with a non-degenerate symmetric bilinear form (·, ·) and the vectors a i constitute an orthonormal basis in V , i.e. Co-published by Atlantis Press and Taylor & Francis Copyright: the authors 29...