Dispersion of E8 particles in the spin-1/2 antiferromagnetic XXZ chain BaCo2V2O8 in a transverse magnetic field

The one-dimensional spin-1/2 antiferromagnetic with Heisenberg-Ising (XXZ) anisotropy is a great model system to explore fundamental physics concepts. In zero applied magnetic field, it hosts spinon excitations which are confined into pairs by interchain coupling and in a longitudinal magnetic field it enters a critical regime known as a Tomonaga-Luttinger Liquid characterised by Bethe string excitations. These features have been explored using the compounds BaCo2V2O8 and SrCo2V2O8. In BaCo2V2O8 a transverse magnetic field has also been found to also suppress the antiferromagnetic order and induce a one-dimensional quantum critical point classified by the exceptional E8 Lie algebra which is characterized by 8 gapped excitations (massive particles). Here we propose to explore the dispersion of the E8 particles in BaCo2V2O8 and make comparison to recent theories.