Krylov Complexity in Free and Interacting Scalar Field Theories with Bounded Power Spectrum

We study a notion of operator growth known as Krylov complexity in free and interacting massive scalar quantum field theories in $d$-dimensions at finite temperature. We consider the effects of mass, one-loop self-energy due to perturbative interactions, and finite ultraviolet cutoffs in continuous momentum space. These deformations change the behavior of Lanczos coefficients and Krylov complexity and induce effects such as the "staggering" of the former into two families, a decrease in the exponential growth rate of the latter, and transitions in their asymptotic behavior. We also discuss the relation between the existence of a mass gap and the property of staggering, and the relation between our ultraviolet cutoffs in continuous theories and lattice theories.Comment: 44 pages, 12 figures. Comments are welcome. V2: Note added at the end of the Introduction. Added references and footnotes, corrected typos, modified Figure 5, improved argument in Sec. 2.2, added a discussion of large-N limit in Sec. 3.3 and added an additional future direction in Sec.