The tail distribution of the partition function for directed polymer in the weak disorder phase

We investigate the upper tail distribution of the partition function of the directed polymer in a random environment on ${\mathbb{Z}}^d$ in the weak disorder phase. We show that the distribution of the infinite volume partition function $W_{\mathrm{\infty }}^{\beta }$ displays a power-law decay, with an exponent $p^{\ast }(\beta )\in [1+\frac{2}{d},\mathrm{\infty })$. We also prove that the distribution of the suprema of the point-to-point and point-to-line partition functions display the same behavior. On the way to these results, we prove a technical estimate of independent interest: the $L^p$-norm of the partition function at the time when it overshoots a high value $A$ is comparable to $A$. We use this estimate to extend the validity of many recent results that were proved under the assumption that the environment is upper bounded.