# Evaluation of the operatorial Q-system for non-compact super spin chains

## TL;DR

This paper develops a method to explicitly evaluate the operatorial Q-system for non-compact super spin chains, including applications to the one-loop planar N=4 super Yang-Mills theory, by transforming infinite sums into finite matrix representations.

## Contribution

It introduces a novel oscillator-based approach to compute the full operatorial Q-system for non-compact super spin chains, enabling explicit finite matrix forms.

## Key findings

- Explicit finite matrix form of Q-operators for non-compact spin chains
- Application to one-loop N=4 SYM with BMN vacuum
- Method to handle infinite sums in Lax operators

## Abstract

We present an approach to evaluate the full operatorial Q-system of all $\mathfrak{u}(p,q|r+s)$-invariant spin chains with representations of Jordan-Schwinger type. In particular, this includes the super spin chain of planar $\mathcal{N}=4$ super Yang-Mills theory at one loop in the presence of a diagonal twist. Our method is based on the oscillator construction of Q-operators. The Q-operators are built as traces over Lax operators which are degenerate solutions of the Yang-Baxter equation. For non-compact representations these Lax operators may contain multiple infinite sums that conceal the form of the resulting functions. We determine these infinite sums and calculate the matrix elements of the lowest level Q-operators. Transforming the Lax operators corresponding to the Q-operators into a representation involving only finite sums allows us to take the supertrace and to obtain the explicit form of the Q-operators in terms of finite matrices for a given magnon sector. Imposing the functional relations, we then bootstrap the other Q-operators from those of the lowest level. We exemplify this approach for non-compact spin $-s$ spin chains and apply it to $\mathcal{N}=4$ SYM at the one-loop level using the BMN vacuum as an example.