This monograph adopts an operational and functional analytic approach to the following problem: given a short exact sequence (group extension) 1 N G H 1 of finite groups, describe the irreducible representations of G by means of the structure of the group extension. This problem has attracted many mathematicians, including I. Schur, A.H. Clifford, and G. Mackey and, more recently, M. Isaacs, B. Huppert, Y.G. Berkovich & E.M. Zhmud, and J.M.G. Fell & R.S. Doran. The main topics are, on the one hand, Clifford Theory and the Little Group Method (of Mackey and Wigner) for induced representations, and, on the other hand, Kirillov's Orbit Method (for step-2 nilpotent groups of odd order) which establishes a natural and powerful correspondence between Lie rings and nilpotent groups. As an application, a detailed description is given of the representation theory of the alternating groups, of metacyclic, quaternionic, dihedral groups, and of the (finite) Heisenberg group.

TheLittle Group Method may be applied if and only if a suitable unitary 2-cocycle (the Mackey obstruction) is trivial. To overcome this obstacle, (unitary) projective representations are introduced and corresponding Mackey and Clifford theories are developed. The commutant of an induced representation and the relative Hecke algebra is also examined. Finally, there is a comprehensive exposition of the theory of projective representations for finite Abelian groups which is applied to obtain a complete description of the irreducible representations of finite metabelian groups of odd order.

The first monograph completely devoted to the representation theory of finite group extensions Includes new results on the projective representations of finite Abelian groups and their applications Provides a new, more operational and functional analytical perspective on the subject

Autorentext

Tullio Ceccherini-Silberstein graduated from the University of Rome La Sapienza in 1990 and obtained his PhD in mathematics from the University of California at Los Angeles in 1994. Since 1997 he has taught at the University of Sannio, Benevento (Italy). His main interests include harmonic and functional analysis, geometric and combinatorial group theory, ergodic theory and dynamical systems, and theoretical computer science. He is an editor of the journal Groups, Geometry, and Dynamics, published by the European Mathematical Society. He has published more than 90 research papers, 9 monographs, and 4 conference proceedings. Professor Michel Coornaert taught mathematics at the University of Strasbourg from 1992 until 2021. His research interests are in geometry, topology, group theory and dynamical systems. He is the author of many Springer volumes, including Topological Dimension and Dynamical Systems (2015), Cellular Automata and Groups (2010), Symbolic Dynamics and Hyperbolic Groups (1993) and Géométrie et théorie des groupes (1990).

Inhalt

• 1. Preliminaries. - 2. Clifford Theory. - 3. Abelian Extensions. - 4. The Little Group Method for Abelian Extensions. - 5. Examples and Applications. - 6. Central Extensions and the Orbit Method. - 7. Representations of Finite Group Extensions via Projective Representations. - 8. Induced Projective Representations. - 9. Clifford Theory for Projective Representations. - 10 Projective Representations of Finite Abelian Groups with Applications.