On the derivation of exact eigenstates of the generalized squeezing   operator
  We construct the states that are invariant under the action of the generalized squeezing operator $\exp{(z{a^{\dagger k}}-z^*a^k)}$ for arbitrary positive integer $k$. The states are given explicitly in the number representation. We find that for a given value of $k$ there are $k$ such states. We show that the states behave as $n^{-k/4}$ when occupation number $n\to\infty$. This implies that for any $k\geq3$ the states are normalizable. For a given $k$, the expectation values of operators of the form $(a^{\dagger} a)^j$ are finite for positive integer $j < (k/2-1)$ but diverge for integer $j\geq (k/2-1)$. For $k=3$ we also give an explicit form of these states in the momentum representation in terms of Bessel functions. 
Andrey Pereverzev and Eric R. Bittner