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Digital archive of theses discussed at the University of Pisa


Thesis etd-12062011-191704

Thesis type
Tesi di dottorato di ricerca
Thesis title
Zeros and degrees of characters of finite groups
Academic discipline
Course of study
tutor Prof. Dolfi, Silvio
relatore Prof. Navarro, Gabriel
  • Character theory
  • irreducible character degrees
  • real irreducible characters
  • Vanishing and non-vanishing elements
Graduation session start date
This thesis addresses some questions about the relationship between the structure of finite groups and the set of their character degrees (Chapters 2 and 5) and the set of their vanishing elements (Chapters 3 and 4).

In Chapter 2,we study the groups G such that
whenever $1\neq\chi,\psi \in$ Irr(G) have the same degree,then there exists an automorphism $\alpha$ of G such that $\chi=\psi^{\alpha}$. We call AC the class of such groups G. In Section 2.2, we give a tight description of the
structure of solvable groups in AC. In Section 2.3, we discuss the problem of determining all the simple groups in AC.

In Chapter 3, we generalize some recent results regarding the relationship between the structure of a group and his vanishing elements.

In Chapter 4, we solve a new problem concerning vanishing elements and characters with prescribed fields of values. Let F be a subfield of $\mathbb{C}$, we write Irr$_{F}$(G) for the set of those $\chi$ in Irr(G) such that $\chi(g) \in F$ for all $g \in G$. Then we consider $F=\mathbb{R}$ and the set of real-valued (or real) irreducible characters of G.
The main goal of Chapter 4 states that if $\chi(x) \neq 0$ for all real $\chi$ in Irr(G) and all 2-elements x in G, then
G has a normal Sylow 2-subgroup.

Finally, in Chapter 5, we come back to an old problem by R. Gow (in 1975), on the groups whose irreducible character degrees can be linearly ordered by divisibility. Gow's main result is not complete: there are three undecided cases. In Chapter 5 we will settle two of these three cases.