π½
p
2
-maximal curves with many automorphisms are Galois-covered by the Hermitian curve
Abstract Let π½ be the finite field of order q 2. It is sometimes attributed to Serre that any curve π½-covered by the Hermitian curve H q + 1 : y q + 1 = x q + x ${{\mathcal{H}}_{q+1}}:{{y}^{q+1}}={{x }^{q}}+x$ is also π½-maximal. For prime numbers q we show that every π½-maximal curve x $\mathcal{x}$ of genus g β₯ 2 with | Aut(π³) | > 84(g β 1) is Galois-covered by H q + 1 . ${{\mathcal{H}}_{q+1}}.$ The hypothesis on | Aut(π³) | is sharp, since there exists an π½-maximal curve x $\mathcal{x}$ for q = 71 of genus g = 7 with | Aut(π³) | = 84(7 β 1) which is not Galois-covered by the Hermitian curve H 72 . ${{\mathcal{H}}_{72}}.$