Kappa vacua: Infinite number of new vacua in two-dimensional quantum field theory

We uncover an infinite number of vacua in two-dimensional quantum field theory, the Klein-Gordon field for simplicity, by conceiving a new mode that is classified by a real positive parameter $\kappa$. We show each mode has a distinct vacuum, say $\kappa$-vacuum. This new mode is a generalization of the Unruh-Minkowski mode. Moreover, the Minkowski and Rindler vacua are special cases of the $\kappa$-vacuum for $\kappa =1$ and $\kappa \to \mathrm{\infty }$, respectively.