Newton polygons of L-functions of polynomials x p + a x d - 1 with p≡-1 mod d

For prime p ? - 1 mod d and q a power of p, we obtain the slopes of the q-adic Newton polygons of L-functions of x d + a x d - 1 ? F q x with respect to finite characters ? when p is larger than an explicit bound depending only on d and log p ? q . The main tools are Dwork's trace formula and Zhu's rigid transform theorem.