Quark mass effects in octet baryon magnetic polarisabilities via lattice QCD

TL;DR

This study investigates how changing quark masses affect octet baryon magnetic polarisabilities using lattice QCD, revealing direct and indirect effects linked to quark mass variations and constituent quark model insights.

Contribution

It introduces a fractional charge formalism in lattice QCD to analyze quark mass effects on baryon magnetic polarisabilities, providing new insights into direct and environmental influences.

Findings

Increasing charged quark mass decreases its magnetic contribution.

Increasing spectator quark mass indirectly increases magnetic polarisability.

Reduction in constituent quark magnetic moment explains the direct mass dependence.

Abstract

The quark mass dependence of octet baryon magnetic polarisabilities is examined at the level of individual quark-sector contributions in the uniform background-field approach of lattice QCD. The aim is to understand the direct impact of increasing the mass of a quark flavour on the magnetic polarisability and indirect or environmental effects associated with changing the mass of spectator quarks, insensitive to the background magnetic field. Noting the need to set the electric charge of some quark flavours to zero, a fractionally charged baryon formalism is introduced. We find that increasing the mass of the charged quark flavour directly causes its contribution to the magnetic polarisability to decrease. However, increasing the mass of the spectator quark flavour indirectly acts to increase the magnetic polarisability. To gain a deeper understanding of these effects, we evaluate the predictions of the constituent quark model in this context. While the model provides a compelling explanation for the environmental effect of varying the spectator quark mass, an explanation of the direct mass dependence is more complicated as competing factors combine in the final result. The lattice results indicate the key factor is a reduction in the constituent quark magnetic moment with increasing quark mass, as it governs the strength of the magnetic transition to the nearby decuplet baryon.