# Quillen–Lichtenbaum conjecture

(Redirected from Quillen-Lichtenbaum conjecture)

In mathematics, the Quillen–Lichtenbaum conjecture is a conjecture relating étale cohomology to algebraic K-theory introduced by Quillen (1975, p. 175), who was inspired by earlier conjectures of Lichtenbaum (1973). Kahn (1997) and Rognes & Weibel (2000) proved the Quillen–Lichtenbaum conjecture at the prime 2 for some number fields. Rost and Voevodsky have announced proofs of the Bloch–Kato conjecture, which implies the Quillen–Lichtenbaum conjecture for all primes.

## Statement

The conjecture in Quillen's original form states that if A is a finitely-generated algebra over the integers and l is prime, then there is a spectral sequence analogous to the Atiyah-Hirzebruch spectral sequence, starting at

$E_2^{pq}=H^p_\text{etale}(\text{Spec }A[\ell^{-1}], Z_\ell(-q/2)),$ (which is understood to be 0 if q is odd)

and abutting to

$K_{-p-q}A\otimes Z_\ell$

for −p − q > 1 + dim A.

## K theory of the integers

Assuming the Quillen–Lichtenbaum conjecture and the Vandiver conjecture, the K-groups of the integers, Kn(Z), are given by:

• 0 if n = 0 mod 8 and n > 0, Z if n = 0
• Z ⊕ Z/2 if n = 1 mod 8 and n > 1, Z/2 if n = 1.
• Z/ckZ/2 if n = 2 mod 8
• Z/8dk if n = 3 mod 8
• 0 if n = 4 mod 8
• Z if n = 5 mod 8
• Z/ck if n = 6 mod 8
• Z/4dk if n = 7 mod 8

where ck/dk is the Bernoulli number B2k/k in lowest terms and n is 4k − 1 or 4k − 2 (Weibel 2005).