Spin dynamics and dark particle in a weak-coupled quantum Ising ladder

Emergent Ising_h² integrability is anticipated in a quantum Ising ladder composed of two weakly coupled, critical transverse field Ising chains. This integrable system is remarkable for including eight types of massive relativistic particles, with their scattering matrix and spectrum characterized by the D₈⁽¹⁾ Lie algebra. In this article, we delve into zero-temperature spin dynamics. By computing the dynamical structure factors from analytical form factor approach, we clearly identify dispersive single-particle excitations of (anti-) soliton and breathers as well as their multiparticle continua in the dynamical spectra. We show that the selection rule to the form factor, which is inherent in the charge-parity C of the theory, causes a significant result that C-odd particles, termed as dark particles, cannot be directly excited from the ground state through any local or quasi-local operations. Furthermore, the lightest dark particle is proposed to be generated and controlled through resonant absorption-resonant emission processes.