On the Automorphism Group of a Binary Self-dual [120, 60, 24] Code (1210.2540v1)

Abstract: We prove that an automorphism of order 3 of a putative binary self-dual [120, 60, 24] code C has no fixed points. Moreover, the order of the automorphism group of C divides 2^a.3.5.7.19.23.29 where a is a nonegative integer. Automorphisms of odd composite order r may occur only for r=15, 57 or r=115 with corresponding cycle structures 15-(0,0,8;0), 57-(2,0,2;0) or 115-(1,0,1;0), respectively. In case that all involutions act fixed point freely we have |Aut(C)|<=920, and Aut(C) is solvable if it contains an element of prime order p>=7. Moreover, the alternating group A_5 is the only non-abelian composition factor which may occur.