Unitary Perturbations of Masas in Type Ii1 Factors
نویسندگان
چکیده
The main result of this paper is the inequality d(u,N(A))/31 ≤ ‖EA − EuAu∗ ‖∞,2 ≤ 4d(u,N(A)), where A is a masa in a separably acting type II1 factor N , u ∈ N is a unitary, N(A) is the group of normalizing unitaries, d is the distance measured in the ‖ ·‖2-norm, and ‖ · ‖∞,2 is a norm defined on the space of bounded maps on N by ‖φ‖∞,2 = sup{‖φ(x)‖2 : ‖x‖ ≤ 1}. This result implies that a unitary which almost normalizes a masa must be close to a normalizing unitary. The inequality also shows that every singular masa is α-strongly singular for α = 1/31. Partially supported by a grant from the National Science Foundation.
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