Title
"The effective field theory for mass ratio of elementary excitations in spin chains with frustration and dimerization"
Shintaro Takayoshi (National Institute for Materials Science)
Abstract
Field theoretical approach is a powerful tool to investigate one-dimensional quantum magnets. We consider Heisenberg antiferromagnetic chain with next-nearest neighbor exchange interaction and bold-alternation, which can be related with corresponding sine-Gordon effective field theory through the bosonization technique. We investigate the excitation spectrum of this model for S=1/2 and 1 through both analytical and numerical methods, focusing on the mass ratio of second breather to soliton. In the result, the S=1/2 and 1 cases can be described with the same effective field theory. The mass ratio becomes $sqrt{3}$, the value predicted from sine-Gordon model when next-nearest neighbor coupling is introduced so that the marginal term in effective field theory vanishes ($J_2=J_{2{m c}}$). The universality class of transition, which happens with changing dimerization, is Tomonaga-Luttinger liquid and first order for $J_2<J_{2{m c}}$ and $J_2<J_{2{m c}}$, respectively. We also provide the formula for mass ratio by form factor perturbation theory and renormalization analysis, considering the marginal term as perturbation.
