Finite Temperature Dynamical Structure Factor of Alternating Heisenberg   Chains
  We develop a low-temperature expansion for the finite temperature dynamical structure factor of the spin half Heisenberg chain with alternating nearest neighbour exchange in the limit of strong alternation of the exchange constants. We determine both the broadening of the low lying triplet lines and the contribution of the thermally activated intraband scattering. 
A. J. A. James, F. H. L. Essler, and R. M. Konik