# Tesi etd-07032009-204654

Thesis type
Tesi di laurea specialistica
Author
D'ANTONIO, GIACOMO
URN
etd-07032009-204654
Title
Orlik-Solomon algebras and Hyperplane Arrangements
Struttura
SCIENZE MATEMATICHE, FISICHE E NATURALI
Corso di studi
MATEMATICA
Supervisors
relatore Prof. Gaiffi, Giovanni
Parole chiave
• configuration spaces
• braids
• braid arrangement
• extended action
• representations symmetric group
• orlik-solomon algebra
• hyperplane arrangements
Data inizio appello
24/07/2009;
Consultabilità
Completa
Riassunto analitico
This work fits into the topic of hyperplane arrangements; this is a widely studied subject involving many different areas of mathematics (combinatorics, commutative algebra, topology, group theory, representation theory, etc..).
To each hyperplane arrangement are associated certain combinatorial data; it turns out that the cohomology algebra of the complement of a complex hyperplane arrangement is uniquely determined by these combinatorial data. A famous isomorphic model for this algebra is the so-called Orlik-Solomon algebra. In the first part of the thesis
(chapters 1-3) we study the topology of the complement of a complex hyperplane arrangement; in chapter 1 we review in detail the general theory of hyperplane arrangements, in chapter 2 we specialize to the braid arrangement and prove
some explicit results and in chapter 3 we prove the isomorphism between the Orlik-Solomon algebra and the cohomology algebra of the complement.

In the second part of the thesis (chapters 4 and 5) we study some cohomology representations of the symmetric group \$S_n\$. In chapter 4 we study the action of \$S_n\$ on the complement of the braid arrangement (the so-called pure
braid space); we introduce an extended action of the symmetric group \$S_{n+1}\$ on \$n+1\$ elements that allows for a simple computation of the character of the action of \$S_n\$. We also study some properties of \$H^*(M(B_n); C)\$ as graded \$S_n\$-module. In chapter 5 we study the action of \$S_n\$ on the configuration space of \$n\$ points in \$R^d\$; it turns out that an argument similar to the case of the pure braid space applies. In particular we build an extended \$S_{n+1}\$-action and use it to study in detail the action of \$S_n\$.

In the appendices we prove some fundamental results in algebraic topology and group actions that are important for the preceding discussion: the thom isomorphism and the theorem of transfer.
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