On condensation properties of Bethe roots associated with the XXZ chain

I prove that the Bethe roots describing either the ground state or a certain class of “particle-hole” excited states of the XXZ spin-$1\mathrm{/}2$ chain in any sector with magnetisation $\mathfrak{m}\in [0;1\mathrm{/}2]$ exist and form, in the infinite volume limit, a dense distribution on a subinterval of $\mathbb{R}$. The results holds for any value of the anisotropy $\mathrm{\Delta }\ge -1$. In fact, I establish an even stronger result, namely the existence of an all order asymptotic expansion of the counting function associated with such roots. As a corollary, these results allow one to prove the existence and form of the infinite volume limit of various observables attached to the model -the excitation energy, momentum, the zero temperature correlation functions, so as to name a few- that were argued earlier in the literature.