  We study signatures of quantum chaos in (1+1)D Quantum Field Theory (QFT)
models. Our analysis is based on the method of Hamiltonian truncation, a
numerical approach for the construction of low-energy spectra and eigenstates
of QFTs that can be considered as perturbations of exactly solvable models. We
focus on the double sine-Gordon, also studying the massive sine-Gordon and
${\phi^4}$ model, all of which are non-integrable and can be studied by this
method with sufficiently high precision from small to intermediate perturbation
strength. We analyze the statistics of level spacings and of eigenvector
components, both of which are expected to follow Random Matrix Theory
predictions. While level spacing statistics are close to the Gaussian
Orthogonal Ensemble as expected, on the contrary, the eigenvector components
follow a distribution markedly different from the expected Gaussian. Unlike in
the typical quantum chaos scenario, the transition of level spacing statistics
to chaotic behaviour takes place already in the perturbative regime. On the
other hand, the distribution of eigenvector components does not appear to
change or approach Gaussian behaviour, even for relatively large perturbations.
Moreover, our results suggest that these features are independent of the choice
of model and basis.
