Kappa Plane Wave Modes and Continuous Squeezing in Quantum Field Theory

We introduce a new family of field modes in flat spacetime – termed $\kappa$-plane wave modes – constructed from $\kappa$-dependent linear combinations of Minkowski plane waves. These modes define a one-parameter family of vacua, $\mathrm{\mid }{0}_{\kappa }⟩$, that smoothly interpolate between different quantizations, reducing to the Minkowski vacuum in the limit $\kappa \to 0$. We show that $\mathrm{\mid }{0}_{\kappa }⟩$ is uniquely characterized as a continuous-mode squeezed vacuum, with frequency-dependent squeezing parameter $r(\nu )$ satisfying $\tanh r(\nu )=e^{-\pi \nu \mathrm{/}\kappa }$. We also derive two Bogoliubov transformations between $\kappa$-plane wave and $\kappa$-Rindler operators, which exhibit a universal form and smoothly interpolate between all known mode decompositions, including those of Minkowski, Rindler, and Unruh quantizations as limiting cases.