Boundary Theory for Symmetric Markov Processes

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516 Martin L. Silverstein

Boundary Theoryfor Symmetric Markov Processes

Springer-Verlag Berlin. Heidelberg. New York 19?6

Author Martin L. Silverstein Department of Mathematics University of Southern California University Park Los Angeles, California 90007 USA

Library of Congress Ca~alogiag ia pdblieation Data

Silverstein, Martin /. 1939Boundary theory for symmetric Markov processes. (Lecture notes in mathematics ; 516) Bibliography: p. Includes index. i. Markov processes. 2. Semigroups. 3. Symmetry groups. I. Title. If. Series: Lecture notes in mathematics "Berlin) ; 516. QA3.L28 no. 516 [QA274.7] 510'.8s [519.2'33] 76-10683

AMS Subject Classifications (1970): 60J 25, 60J 45, 60J 50

ISBN 3-540-07688-3 Springer-Verlag Berlin Heidelberg 9 New 9 York ISBN 0-387-07688-3 Springer-Verlag New York Heidelberg 9 Berlin 9 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 w 54 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. 9by Springer-Verlag Berlin - Heidelberg 1976 Printed in Germany Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr.

Dedicated to the m e m o r y JOSEPH

of m y father

SILVERSTEIN

Introduction. Let This means

Pt' t > 0 be a submarkovian

that each

Pt

semigroup

maps bounded measurable

on a measurable

space

X.=

functions into bounded meas-

urable functions and that

(0.1)

O O.

A l s o i t is u s u a l l y n e c e s s a r y

to impose

h o p e t o do a n y s e r i o u s w o r k .

(0.3) where the

whenever

O P t f whenever f>_ O.

This volume is concerned with the general problem tent classifying markovian

submarkovian

sernigroup

Pt'

semigroups

case when both the

(0.6)

dx

o n X.

Pt

Pt'

of a n a l y z i n g a n d t o s o m e e x -

t > O, w h i c h d o m i n a t e a f i x e d s u b -

t > O.

There are good technical

measure

the first if

and

Pt

reasons

for restricting

a~e symmetric

with respect

This meansthat

IdxPtf(x)g(x) = Idxf(x)ptg(x)

attention to the special to a g i v e n r e f e r e n c e

VI

at least w h e n

f, g are bounded and integrable.

The restriction will be in effect

throughout the volume. Once s y m m e t r y

is imposed, it is convenient to modify the regularity

condition (0. 3) and (0.4).

In place of (0. 3) w e a s s u m e that each

with respect to bounded almost everywhere convergence. symmetry

condition (0.6), guarantees that each

s y m m e t r i c contraction on the Hilbert space a s s u m e that the extended operators

This, together with the

Pt extends uniquely to a bounded

L 2(X, dx).

In place of (0.4) w e

Pt f o r m a semigroup which is continuous

relative to the strong operator topology on LZ(X,dx).

(0.4')

Pt iS continuous

This m e a n s that