11.07.2015 Views

International Congress of Mathematicians

International Congress of Mathematicians

International Congress of Mathematicians

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790 Liming GèSuppose (A,T) is a C*-probability space. We assume that r is a trace. Afamily A,,, i £ I, <strong>of</strong> unital * subalgebras <strong>of</strong> A are called free with respect to r ifT(AIA 2 • • • A n ) = 0 whenever Aj £ A h , ti fi 1 • • • fi 1 t n (*i and t 3 may be the same)and T(AJ) = 0 for 1 < j < n and every n in N. A family <strong>of</strong> subsets (or elements)<strong>of</strong> A are said to be free if the unital * subalgebras they generate are free.Note that freeness is a highly noneommutative notion, the non-commutativity(or algebraic freeness) <strong>of</strong> free random variables is encoded in the definition. Recallsome basic concepts in free probability theory.Semicircular elements: The Gaussian laws in classical theory is replaced bythe semicircular laws. The semicircular law centered at a and <strong>of</strong> radius r is thedistribution p a>r : C[x] —¥ C such thatoi-a+rßa,r(v>(xj) = —2 /

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