New necessary conditions for (negative) Latin square type partial difference sets in abelian groups

Abstract

Partial difference sets (for short, PDSs) with parameters ($n^2$, $r(n-\epsilon)$, $\epsilon n+r^2-3\epsilon r$, $r^2-\epsilon r$) are called Latin square type (respectively negative Latin square type) PDSs if $\epsilon=1$ (respectively $\epsilon=-1$). In this paper, we will give restrictions on the parameter $r$ of a (negative) Latin square type partial difference set in an abelian group of non-prime power order. As far as we know no previous general restrictions on $r$ were known. Our restrictions are particularly useful when $a$ is much larger than $b$. As an application, we show that if there exists an abelian negative Latin square type PDS with parameter set $(9p^{4s}, r(3p^{2s}+1),-3p^{2s}+r^2+3r,r^2+r)$, $1 \le r \le \frac{3p^{2s}-1}{2}$, $p\equiv 1 \pmod 4$ a prime number and $s$ is an odd positive integer, then there are at most three possible values for $r$. For two of these three $r$ values, J. Polhill gave constructions in 2009.