The absolutely Koszul and Backelin-Roos properties for spaces of quadrics of small codimension

Rasoul Ahangari Maleki, Liana M. Şega

Published 2018-10-13Version 1

Let $\kk$ be a field and let $R$ be a standard graded quadratic $\kk$-algebra with $\dim_{\kk}R_2\le 3$. We construct a graded surjective Golod homomorphism $\varphi \colon P\to R$ such that $P$ is a complete intersection of codimension at most $3$. Furthermore, we show that $R$ is absolutely Koszul (that is, every finitely generated $R$-module has finite linearity defect) if and only if $R$ is Koszul if and only if $R$ is not a trivial fiber extension of a standard graded $\kk$-algebra with Hilbert series $(1+2t-2t^3)(1-t)^{-1}$. In particular, we recover earlier results on the Koszul property of Backelin, Conca and D'Al\`i.