Riemann-Roch for the ring $\mathbb Z$

Abstract

We show that by working over the absolute base $\mathbb S$ (the categorical version of the sphere spectrum) instead of $\mathbb S[\pm 1]$ improves our previous Riemann-Roch formula for $\overline{{\rm Spec\,}\mathbb Z}$. The formula equates the (integer-valued) Euler characteristic of an Arakelov divisor with the sum of the degree of the divisor (using logarithms with base 2) and the number $1$, thus confirming the understanding of the ring $\mathbb Z$ as a ring of polynomials in one variable over the absolute base $\mathbb S$, namely $\mathbb S[X], 1+1=X+X^2$.