We define Grothendieck-Witt spectra in the setting of Poincaré ∞-categories, show that they fit into an extension with a K-and an L-theoretic part and deduce localisation sequences for Verdier quotients. As special cases we obtain generalisations of Karoubi's fundamental and periodicity theorems for rings in which 2 need not be invertible.A novel feature of our approach is the systematic use of ideas from cobordism theory by interpreting the hermitian Q-construction as an algebraic cobordism category. We also use this to give a new description of the LA-spectra of Weiss and Williams.
CONTENTS
IntroductionRecollection 1 Poincaré-Verdier sequences and additive functors 1.1 Poincaré-Verdier sequences 1.2 Split Poincaré-Verdier sequences and Poincaré recollements 1.3 Poincaré-Karoubi sequences 1.4 Examples of Poincaré-Verdier sequences 1.5 Additive and localising functors 2 The hermitian Q-construction and algebraic cobordism categories 2.1 The hermitian Q-construction 2.2 The cobordism category of a Poincaré ∞-category 2.3 Algebraic surgery 2.4 The additivity theorem 2.5 Fibrations between cobordism categories 2.6 Additivity in K-Theory 3 Structure theory for additive functors 3.1 Cobordisms of Poincaré functors 3.2 Isotropic decompositions of Poincaré ∞-categories 3.3 The group-completion of an additive functor 3.4 The spectrification of an additive functor 3.5 Bordism invariant functors 3.6 The bordification of an additive functor 3.7 The genuine hyperbolisation of an additive functor 4 Grothendieck-Witt theory 4.1 The Grothendieck-Witt space 4.2 The Grothendieck-Witt spectrum 4.3 The Bott-Genauer sequence and Karoubi's fundamental theorem 4.4 L-theory and the fundamental fibre square 4.5 The real algebraic K-theory spectrum and Karoubi periodicity 4.6 LA-theory after Weiss and Williams Date: September 16, 2020. 144 B.2 Schlichting's Grothendieck-Witt-spectrum of a ring with 2 invertible 146 References 150which we term the fundamental fibre square. Now, in [HM] Hesselholt and Madsen promoted the Grothendieck-Witt spectrum GW s cl ( , ) into the genuine fixed points of what they termed the real algebraic K-theory KR s cl ( , ), a genuine C 2 -spectrum. We similarly produce a functor KR ∶ Cat p ∞ ⟶ Sp gC 2 using the language of spectral Mackey functors, with the property that the isotropy separation square of KR(C, Ϙ) is precisely the fundamental fibre square above, so that in particular KR(C, Ϙ) gC 2 ≃ GW(C, Ϙ) and KR(C, Ϙ) C 2 ≃ L(C, Ϙ); here (−) gC 2 and (−) C 2 ∶ S gC 2 → S denote the genuine and geometric fixed points functors, respectively. Combined with the comparison results of [HS20] this affirms the conjecture of Hesselholt and Madsen, that the geometric fixed points of the real algebraic K-theory spectrum of a discrete ring are a version of Ranicki's L-theory.As the ultimate expression of periodicity, we then enhance our extension of Karoubi's periodicity to the following statement in the language of genuine homotopy theory:
Theorem D. The boundary map of the metabolic Poincaré-Verdier sequence provides a...