We study sums of squares formulae from the perspective of normed bilinear maps and their Hopf constructions. We begin with the geometric properties of quadratic forms between euclidean spheres. Let F: Sm → Sn be a quadratic form. For every point q in the image, the inverse image F⁻¹ (q) is the intersection of Sm with a linear subspace wq, whose dimension can be determined easily. In fact, for every k ≤ m+1 with nonempty Yk = {q ∈ Sn: dim Wq = k}, the restriction F⁻¹ (Yk) → Yk is a great (k-1) - sphere bundle. The quadratic form F is the Hopf construction of a normed bilinear map if and only if it admits a pair of "poles" ±p such that dim Wp + dim W₋p = m+1. In this case, the inverse images of points on a "meridian", save possibly the poles, are mutually isoclinic. Furthermore, the collection of all poles forms a great sphere of relatively low dimension. We also prove that the classical Hopf fibrations are the only nonconstant quadratic forms which are harmonic morphisms in the sense that the composite with every real valued harmonic function is again harmonic. Hidden in a quadratic form F: Sm → Sn are nonsingular bilinear maps Rk x Rm-k⁺¹ → Rn, one for each point in the image, all representing the homotopy class of F, which lies in Im J. Moreover, every hidden nonsingular bilinear map can be homotoped to a normed bilinear map. The existence of one sums of squares formula, therefore, anticipates others which cannot be obtained simply by setting some of the indeterminates to zero. These geometric and topological properties of quadratic forms are then used, together with homotopy theory results in the literature, to deduce that certain sums of squares formulae cannot exist, notably of types [12,12,20] and [16,16,24]. We also prove that there is no nonconstant quadratic form S²⁵ → S²³. Sums of squares formulae with integer coefficients are equivalent to "intercalate matrices of colors with appropriate signs". This combinatorial nature enables us to establish a stronger nonexistence result: no sums of squares formula of type [16,16, 28] can exist if only integer coefficients are permitted. We also classify integral [10,10,16] formulae, and show that they all represent ±2Ʋ∈ π [s over 3]. With the aid of the KO theory of real projective spaces, we determine, for given δ ≤ 5 and s, the greatest possible r for which there exists an [r,s,s+δ] formula. An explicit solution of the classical Hurwitz-Radon matrix equations is also recorded. / Science, Faculty of / Mathematics, Department of / Graduate

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Submitted by TAÍSA FERNANDA DE LIMA QUEMEL null (taisafernanda.10@hotmail.com) on 2016-03-10T20:25:22Z No. of bitstreams: 1 Versão final_Dissertação_Taísa Quemel.pdf: 674351 bytes, checksum: 3498053a8bb53e50ac3119a10d45a0c5 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-03-11T12:17:58Z (GMT) No. of bitstreams: 1 quemel_tfl_me_sjrp.pdf: 674351 bytes, checksum: 3498053a8bb53e50ac3119a10d45a0c5 (MD5) / Made available in DSpace on 2016-03-11T12:17:58Z (GMT). No. of bitstreams: 1 quemel_tfl_me_sjrp.pdf: 674351 bytes, checksum: 3498053a8bb53e50ac3119a10d45a0c5 (MD5) Previous issue date: 2016-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo deste trabalho é mostrar que πn(X) é sempre abeliano quando n ≥ 2 e que π1(X) é abeliano quando X for um H-espaço e por fim calcular alguns grupos de homotopia utilizando sequência exata de uma fibração. / The goal of this work is to show that πn(X) is always abelian when n ≥ 2 and that π1(X) is abelian when X is an H-space and finally calculate some homotopy groups using the exact sequence of a fibration.

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This Thesis consists of four independent parts. In the first part I prove that the delooping, i.e.the classifying space, of a grouplike monoid is an $H$-space if and only if its multiplication is a homotopy homomorphism. This is an extension and clarification of a result of Sugawara. Furthermore I prove that the Moore loop space functor and the construction of the classifying space induce an adjunction on the corresponding homotopy categories. In the second part I extend a result of G. Dunn, by proving that the tensorproduct $C_{n_1}\otimes\dots \otimes C_{n_j}$ of little cube operads is a topologically equivalent suboperad of $C_{n_1 \dots n_j}$. In the third part I describe operads as algebras over a certain colored operad. By application of results of Boardman and Vogt I describe a model of the homotopy category of topological operads and algebras over them, as well as a notion of lax operads, i.e. operads whose axioms are weakened up to coherent homotopies. Here the W-construction, a functorial cofibrant replacement for a topological operad, plays a central role. As one application I construct a model for the homotopy category of topological categories. C. Berger claimed to have constructed an operad structure on the permutohedras, whose associated monad is exactly the Milgram-construction of the free two-fold loop space. In the fourth part I prove that this statement is not correct.