Let $\sum_{i=1}^n\sum_{j=n+1}^m\epsilon_i\epsilon_jb_ib_j$ be Rademacher Chaos of degree two (here $b_k\in R$ and $\epsilon_k$ are Rademacher random variables) and such tat $\epsilon_m=-\sum_{k=1}^{m-1}\epsilon_k$.
I would like to bound from above the following expectation:
$ E\left(\exp\left(\sum_{i=1}^n\sum_{j=m}^u\epsilon_i\epsilon_jb_ib_j\right)\right) $