arXiv subjects
Publications and source records attributed to Aner Shalev.
We prove that random d-regular Cayley graphs of the symmetric group asymptotically almost surely have girth at least (log_{d-1}|G|)^{1/2}/2 and that random d-regular Cayley graphs of simple algebraic groups over F_q asymptotically almost surely have girth at least log_{d-1}|G|/dim(G). For the symmetric p-groups the girth is between log log |G| and (log|G|)^alpha with alpha<1. Several conjectures and open questions are presented.
Waring's classical problem deals with expressing every natural number as a sum of g(k) k-th powers. Recently there has been considerable interest in similar questions for nonabelian groups, and simple groups in particular. Here the k-th power word is replaced by an arbitrary nontrivial group word w, and the goal is to express group elements as short products of values of w. We give a best possible and somewhat surprising solution for this Waring type problem for various finite simple groups, showing that a product of length two suffices to express all elements. We also show that the set of values of w is very large, improving various results obtained previously. Along the way we also obtain new results of independent interest on character values and class squares in symmetric groups. Our methods involve algebraic geometry, representation theory, probabilistic arguments, as well as three prime theorems from additive number theory (approximating Goldbach's Conjecture).
We study permutation groups of given minimal degree without the classical primitivity assumption. We provide sharp upper bounds on the order of a permutation group of minimal degree m and on the number of its elements of any given support. These results contribute to the foundations of a non-commutative coding theory. A main application of our results concerns the Hidden Subgroup Problem for the symmetric group in Quantum Computing. We completely characterize the hidden subgroups of the symmetric group that can be distinguished from identity with weak Quantum Fourier Sampling, showing these are exactly the subgroups with bounded minimal degree. This implies that the weak standard method for the symmetric group has no advantage whatsoever over classical exhaustive search.
We employ concepts and tools from the theory of finite permutation groups in order to analyse the Hidden Subgroup Problem via Quantum Fourier Sampling (QFS) for the symmetric group. We show that under very general conditions both the weak and the random-strong form (strong form with random choices of basis) of QFS fail to provide any advantage over classical exhaustive search. In particular we give a complete characterisation of polynomial size subgroups, and of primitive subgroups, that can be distinguished from the identity subgroup with the above methods. Furthermore, assuming a plausible group theoretic conjecture for which we give supporting evidence, we show that weak and random-strong QFS for the symmetric group have no advantage whatsoever over classical search.