Arxiv:1905.06698V2 [Math.AT] 6 Dec 2019 Prtr Tsatisfies It Operator
Submitted exclusively to the London Mathematical Society doi:10.1112/0000/000000 The circle action on topological Hochschild homology of complex cobordism and the Brown–Peterson spectrum John Rognes Abstract ′ We specify exterior generators in π∗THH(MU)= π∗(MU) ⊗ E(λn | n ≥ 1) and π∗THH(BP )= π∗(BP ) ⊗ E(λn | n ≥ 1), and calculate the action of the σ-operator on these graded rings. ′ In particular, σ(λn)=0 and σ(λn) = 0, while the actions on π∗(MU) and π∗(BP ) are expressed in terms of the right units ηR in the Hopf algebroids (π∗(MU),π∗(MU ∧ MU)) and (π∗(BP ),π∗(BP ∧ BP )), respectively. 1. Introduction Let S be the sphere spectrum. For any (associative) S-algebra R, the topological Hoch- schild homology spectrum THH(R) is the geometric realization of a cyclic spectrum [q] 7→ ∧q THH(R)q = R ∧ R , see [9] and [19]. The skeleton filtration of THH(R) leads to a spectral sequence 1 Eq,∗ = πq+∗(skqTHH(R), skq−1THH(R)) =⇒ πq+∗THH(R) , whose (E1, d1)-term is the normalized chain complex associated to the simplicial graded abelian group ∧q [q] 7→ π∗THH(R)q = π∗(R ∧ R ) . The cyclic structure specifies a natural circle action on THH(R), which we shall treat as 1 1 1 a right action. The cofiber sequence 1+ → S+ → S is split by a retraction S+ → 1+ and a 1 1 1 1 stable section S → S+. We write σ for the composite map THH(R) ∧ S → THH(R) ∧ S+ → THH(R) and call the induced homomorphism σ : π∗THH(R) → π∗+1THH(R) the (right) σ- 2 operator.
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