Mathematical Proceedings of the Cambridge Philosophical Society

Exel's crossed product and relative Cuntz–Pimsner algebras

a1 School of Mathematical and Physical Sciences, University of Newcastle, NSW 2308, Australia. e-mail:

Article author query
brownlowe n   [Google Scholar] 
raeburn i   [Google Scholar] 


We consider Exel's new construction of a crossed product of a $C^*$-algebra $A$ by an endomorphism $\alpha$. We prove that this crossed product is universal for an appropriate family of covariant representations, and we show that it can be realised as a relative Cuntz–Pimsner algbera. We describe a necessary and sufficient condition for the canonical map from $A$ into the crossed product to be injective, and present several examples to demonstrate the scope of this result. We also prove a gauge-invariant uniqueness theorem for the crossed product.

(Received March 30 2005)
(Revised October 20 2005)


1 This research has been supported by the Australian Research Council.