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New cyclic difference sets with Singer parameters. (English) Zbl 1043.05024
Summary: The main result in this paper is a general construction of $$\phi(m)/2$$ pairwise inequivalent cyclic difference sets with Singer parameters $$(v,k,\lambda)= (2^m-1, 2^{m-1}, 2^{m-2})$$ for any $$m \geqslant 3$$. The construction was conjectured by the second author at Oberwolfach in 1998. We also give a complete proof of related conjectures made by J.-S. No, H. Chung and M.-S. Yun [IEEE Trans. Inf. Theory 44, 1278–1282 (1998; Zbl 0912.94017)] and by J.-S. No, L. W. Golomb, G. Gong, H.-K. Lee and G. Gaal [ibid., 814–817 (1998; Zbl 0912.94016)] which produce another difference set for each $$m\geqslant 7$$ not a multiple of 3. Our proofs exploit Fourier analysis on the additive group of GF($$2^m$$) and draw heavily on the theory of quadratic forms in characteristic 2. By-products of our results are a new class of bent functions and a new short proof of the exceptionality of the Müller–Cohen–Matthews polynomials. Furthermore, following the results of this paper, there are today no sporadic examples of difference sets with these parameters; i.e. every known such difference set belongs to a series given by a constructive theorem.

##### MSC:
 05B10 Combinatorial aspects of difference sets (number-theoretic, group-theoretic, etc.) 11T06 Polynomials over finite fields
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