On the set of bad primes in the study of Casas-Alvero Conjecture

Abstract

The Casas-Alvero conjecture predicts that every univariate polynomial over a field of characteristic zero having a common factor with each of its derivatives $H_i(f)$ is a power of a linear polynomial. One approach to proving the conjecture is to first prove it for polynomials of some small degree $d$, compile a list of bad primes for that degree (namely, those primes $p$ for which the conjecture fails in degree $d$ and characteristic $p$) and then deduce the conjecture for all degrees of the form $dp^\ell$, $\ell\in\mathbb{N}$, where $p$ is a good prime for $d$. In this paper we calculate certain distinguished monomials appearing in the resultant $R(f,H_i(f))$ and obtain a (non-exhaustive) list of bad primes for every degree $d\in\mathbb{N}\setminus\{0\}$.