Shor-Movassagh chain leads to unusual integrable model

TL;DR

This paper proves the integrability of the free Shor-Movassagh chain model, explicitly constructing its Lax pair and boundary matrices, thus demonstrating quantum integrability despite the absence of crossing unitarity.

Contribution

The paper establishes the integrability of the free Shor-Movassagh chain and constructs its Lax pair and boundary K-matrices, providing a new exactly solvable case.

Findings

Proved integrability of the free Shor-Movassagh model.

Constructed explicit Lax pair for the open chain.

Derived boundary K-matrices compatible with integrability.

Abstract

The ground state of Shor-Movassagh chain can be analytically described by the Motzkin paths. There is no analytical description of the excited states, the model is not solvable. We prove the integrability of the model without interacting part in this paper [free Shor-Movassagh]. The Lax pair for the free Shor-Movassagh open chain is explicitly constructed. We further obtain the boundary $K$-matrices compatible with the integrability of the model on the open interval. Our construction provides a direct demonstration for the quantum integrability of the model, described by Yang-Baxter algebra. Due to the lack of crossing unitarity, the integrable open chain can not be constructed by the reflection equation (boundary Yang-Baxter equation).