The main goal of this thesis is a contribution to the classification of all incidence geometries of rank two on which some group PSL(2,q), q a prime power, acts flag-transitively. Actually we require that the action be RWPRI (residually weakly primitive) and (2T)1 (doubly transitive on every residue of rank one). In fact our definition of RWPRI requires the geometry to be firm (each residue of rank one has at least two elements) and RC (residually connected). The main goal is achieved in this thesis. It is stated in our "Main Theorem". The proof of this theorem requires more than 60pages. Quite surprisingly, our proof in the direction of the main goal uses essentially the classification of all subgroups of PSL(2,q), a famous result provided in Dickson’s book "Linear groups: With an exposition of the Galois field theory", section 260, in which the group is called Linear Fractional Group LF(n, pn). Our proof requires to work with all ordered pairs of subgroups up to conjugacy. The restrictions such as RWPRI and (2T)1 allow for a complete analysis. The geometries obtained in our "Main Theorem" are bipartite graphs; and also locally 2-arc-transitive graphs in the sense of Giudici, Li and Cheryl Praeger. These graphs are interesting in their own right because of the numerous connections they have with other fields of mathematics.

In this paper linear representations of finite groups are introduced, and the associated character theory with it. Some work of linear representations of the dihedral group $D_n$ and the symmetric group $S_n$ is presented. \\We also take a look at the finite matrix groups $\textbf{GL}(\mathbb{F}_q)$ and $\textbf{SL}(\mathbb{F}_q)$. The character table for $\textbf{SL}(\mathbb{F}_4)$ and its representation spaces in an implicit form are calculated. We define the standard representation $\varphi $ of $\textbf{SL}(\mathbb{F}_q)$ and prove that it is irreducible for an arbitrary finite field $\mathbb{F}_q$.

Based on Cohn and Umans’ group-theoretic method, we embed matrix multiplication into several group algebras, including those of cyclic groups, dihedral groups, special linear groups and Frobenius groups. We prove that SL2(Fp) and PSL2(Fp) can realize the matrix tensor ⟨p, p, p⟩, i.e. it is possible to encode p × p matrix multiplication in the group algebra of such a group. We also find the lower bound for the order of an abelian group realizing ⟨n, n, n⟩ is n3. For Frobenius groups of the form Cq Cp, where p and q are primes, we find that the smallest admissible value of q must be in the range p4/3 ≤ q ≤ p2 − 2p + 3. We also develop an algorithm to find the smallest q for a given prime p.

The main goal of this thesis is a contribution to the classification of all incidence geometries<p>of rank two on which some group PSL(2,q), q a prime power, acts flag-transitively.<p>Actually we require that the action be RWPRI (residually weakly primitive) and (2T)1<p>(doubly transitive on every residue of rank one). In fact our definition of RWPRI requires<p>the geometry to be firm (each residue of rank one has at least two elements) and RC<p>(residually connected).<p><p>The main goal is achieved in this thesis.<p>It is stated in our "Main Theorem". The proof of this theorem requires more than 60pages.<p><p>Quite surprisingly, our proof in the direction of the main goal uses essentially the classification<p>of all subgroups of PSL(2,q), a famous result provided in Dickson’s book "Linear groups: With an exposition of the Galois field theory", section 260, in which the group is called Linear Fractional Group LF(n, pn).<p><p>Our proof requires to work with all ordered pairs of subgroups up to conjugacy.<p><p>The restrictions such as RWPRI and (2T)1 allow for a complete analysis.<p><p>The geometries obtained in our "Main Theorem" are bipartite graphs; and also locally 2-arc-transitive<p>graphs in the sense of Giudici, Li and Cheryl Praeger. These graphs are interesting in their own right because of<p>the numerous connections they have with other fields of mathematics. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Bruhat-Tits buildings are a fundamental concept in the study of linear algebraic groups over general fields. The general goal of this thesis is to introduce buildings in the basic case of SLd(Qp) and to explicitly describe some of their geometrical and combinatorial properties - building are abstract simplicial complexes. After the general construction (Chapter 1) we focus in detail to the case of SL2(Qp). We work with simplices using certain matrix representatives. We explicitly describe the building and give a formula for graph distance. In Chapter 3 we consider the general case SLd(Qp), d ≥ 2. There we introduce a new concept of distance formulas. In Chapter 4 we prove some theorems which are satisfied by buildings in general. Chapter 5 studies the problem of determining so-called gallery distance of two simplices. In the last Chapter 6 we generalize the distance formulas to the case of three vertices. 1