Seminormal Operators

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742

Kevin Clancey

Seminormal Operators

Springer-Verlag Berlin Heidelberg New York 1979

Author Kevin Clancey Department of Mathematics University of Georgia Athens, G A 3 0 6 0 2 USA

A M S Subject Classifications (1970): 47 B20, 4 7 A 6 5 ISBN 3 - 5 4 0 - 0 9 5 4 7 - 0 Springer-Verlag Berlin Heidelberg NewYork ISBN 0 - 3 8 ? - 0 9 5 4 7 - 0 Springer-Verlag NewYork Heidelberg Berlin Library of Congress Cataloging in Publication Data Clancey, Kevin, 1944Seminormal operators. (Lecture notes in mathematics; 742) Bibliography: p. Includes index. 1. Subnormal operators. I. Title. II. Series: Lecture notes in mathematics (Berlin); 742. QA3.L28 no. 742 [QA329.2] 510'.8s [515'.72] 79-20324 ISBN 0-387-09547-0 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under £354 of the German Copyright Law where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher. © by Springer-Verlag Berlin Heidelberg 1979 Printed in Germany Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr. 2141/3140-543210

Preface

These space.

notes

In the

operators created

have

stirs

(at least)

of

decade

been

obtained,

five

interest

with

several

the

is h a p p e n i n g .

seminormal

major

area.

sources

self-contained

seminormal

and

this

The

aim

of

which

have

on

appear

These

picture

operators

operators

results

some of w h i c h

in

different

what

a reasonably

concerned

past

of

to a p p r e c i a t e

area

are

of

some

this

it

these of

the

occurred

a Hilbert

class

mystifying

results

makes

on

have

and come

somewhat notes

of

from

difficult

is to p a i n t

developments

during

have

the

in t h e

last

ten

years. The in

1970

fact when

measure

A.

C.

of the

positive. C.

that

and

with

operators

PUTNAM

established

spectrum

Perhaps

BERGER

operator

R.

seminormal

a cyclic

two

PINCUS

studying

function)

for

invariant

arose

the

theory

HELTON and

of

as

began

in an o p e r a t o r introduced

a tracial

sented

via

integration

Pincus

immediately

principal

function.

a trace

form

up a g a i n s t

verified

this

on

CAREY

the

of

the

phase

the

work

generated

by

D.

a signed

measure

on t h e

have

shift

of

from

Carey

These

which

derivative

This

polynomials

algebra

authors

J.

operators.

this

these

and

principal

self-adjoint

has

by

hyponormal

self-commutator.

measure

Independently,

R. W.

to u n d e r s t a n d

class

1973

self-commutator.

analogue of

in

is

self-cor~mutator.

to as

star-algebra

a trace

bilinear

place

class

perturbations

the

class

any

obvious

Lebesgue

operator

obtained

that

(referred

in an a t t e m p t

has

shows

taking

dimensional

studying

that

result

bec