Recently it was suggested that certain perturbations of integrable spin chains lead to a weak breaking integrability in the sense is preserved at first order coupling. Here we examine this claim using level spacing distribution. We find volume dependent crossover between and chaotic statistics which marks onset quantum behaviour, markedly different for vs. strong integrability. In particular, gapless case coupling as function $L$ scales with $1/L^2$ law opposed $1/L^3$ previously found case.

We study the nonequilibrium dynamics of quantum sine-Gordon model describing a pair Josephson-coupled one-dimensional bosonic quasicondensates. Motivated by experimentally accessible quench procedures where zero mode quasicondensates is weakly coupled to finite momentum modes, we develop Hamiltonian truncation scheme relying on mini-superspace treatment (MSTHA). apply this method simulate time evolution after both weak and strong quenches, injecting low or high energy density into system,...

The false vacuum is a metastable state that can occur in quantum field theory, and its decay was first studied semi-classically by Coleman. In this work we consider the 1+1 dimensional $\varphi^4$ which simplest model provides realisation of problem. We realise as quench study subsequent evolution using truncated Hamiltonian approach. thin wall limit, rate be described terms mass kink interpolating between vacua degenerate energy density difference true once degeneracy lifted symmetry...

We develop a truncated Hamiltonian method to investigate the dynamics of $(1+1)d~\phi^4$ theory following quantum quenches. The results are compared two different semi-classical approaches, self-consistent Gaussian approximation and Wigner approximation, used determine range validity these widely approaches. show that is strongly limited in comparison which for larger cutoffs practically exact parameter studied. find only valid when effective mass vicinity renormalised mass. Similarly not...

We study the non-equilibrium dynamics of quantum sine-Gordon model describing a pair Josephson-coupled one-dimensional bosonic quasi-condensates. Motivated by experimentally accessible quench procedures where zero mode quasi-condensates is weakly coupled to finite momentum modes, we develop novel Hamiltonian truncation scheme relying on mini-superspace treatment (MSTHA). apply this method simulate time evolution after both weak and strong quenches, injecting low or high energy density into...

We study the sine-Gordon quantum field theory at finite temperature by generalizing method of random surfaces to compute free energy and one-point functions exponential operators non-perturbatively. Focusing on gapped phase model, we demonstrate method's accuracy comparing our results predictions other methods exact in thermodynamic limit. find excellent agreement between approaches when is not too small with respect mass gap. Extending more general problems strongly interacting...

We study the effects of integrability breaking on relaxation dynamics (double) sine-Gordon model. Compared to previous studies, we apply an alternative viewpoint motivated by open-system physics separating phase field into homogeneous and inhomogeneous parts, describing a quantum pendulum (subsystem) interacting phononic bath (environment). To in model, perform quenches using mini-superspace-based truncated Hamiltonian approach developed recently simulate real-time evolution various...