"Bethe-Ansatz-free" eigenstates of spin-1/2 Richardson-Gaudin integrable models

Understand

In this work we construct the eigenstates of the most general spin-1/2 Richardson-Gaudin model integrable in an external magnetic field.

• This includes the possibility for fully anisotropic XYZ coupling such that the $S^x_iS^x_j$, $S^y_iS^y_j$ and $S^z_iS^z_j$ terms all have distinct coupling strengths.
• While insuring that integrability is maintained in the presence of an external field excludes the elliptic XYZ model which is only integrable at zero field, this work still covers a wide class of fully anisotropic (XYZ) models associated with non skew-symmetric r-matrices.
• The eigenstates, as constructed here, do not require any usable Bethe ansatz and therefore: no proper pseudo-vacuum, Bethe roots, or generalised spin raising (Gaudin) operators have to be defined.