## 20D06 Simple groups: alternating groups and groups of Lie type [See also 20Gxx]

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- The classification of isotrivially fibred surfaces with p_g=q=2, and topics on Beauville surfaces (2010)
- In our thesis we treat mainly two topics: the classification of isotrivially fibred surfaces with p_g=q=2, and the construction of new Beauville surfaces. An isotrivially fibred surface is a smooth projective surface endowed with a morphism onto a smooth curve such that all the smooth fibres are isomorphic to each other. The first goal of this thesis is to classify the isotrivially fibred surfaces with p_g=q=2 completing and extending a result by Zucconi. As an important byproduct, we provide new examples of minimal surfaces of general type with p_g=q=2 and K^2=4,5 and the first example with K^2=6. We say that a surface S is isogenous to a product of curves if S = (C times F )/G, for C and F smooth curves and G a finite group acting freely on C times F. Beauville surfaces are a special case of surfaces isogenous to a product. In this thesis we include part of a joint work with Shelly Garion, in which we construct new Beauville surfaces with group G either PSL(2,p^e), or A_n, or S_n, proving a conjecture of Bauer, Catanese and Grunewald. The proofs rely on probabilistic group theoretical results of Liebeck and Shalev, and on classical results of Macbeath. The thesis is divided into three chapters, which are subdivided in several sections. In the first chapter we treat the problem of the classification of isotrivially fibred surfaces with p_g=q=2. We start by recalling some basic facts and theorems about fibred surfaces and surfaces isogenous to a higher product of curves. Then we solve the classification problem using techniques coming from both geometry and combinatorial group theory. In the second chapter we deal with Beauville surfaces. First we give a group theoretical characterization of them. Then we enunciate a theorem of Liebeck and Shalev that we use for the construction of Beauville surfaces with group A_n or S_n. Afterwards we also study Beauville surfaces with group PSL(2,p^e). In the third chapter we give a description of the locus, in the moduli space of surfaces of general type, corresponding to the surfaces isogenous to a product with p_g=q=2 described in the first chapter. Indeed, by the results proven by Catanese, this locus is a union of connected components, whose number can be computed using a theorem of Bauer and Catanese. In the same way we are able to provide an asymptotic result about the number of connected components of the moduli space corresponding to certain families of Beauville surfaces with group either PSL(2,p^e), or A_n, or (mathbb{Z}/nmathbb{Z})^2 as p and n go to infinity.