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On several varieties of cacti and their relations

Ralph M Kaufmann

Algebraic & Geometric Topology 5 (2005) 237–300

arXiv: math.QA/0209131


Motivated by string topology and the arc operad, we introduce the notion of quasi-operads and consider four (quasi)-operads which are different varieties of the operad of cacti. These are cacti without local zeros (or spines) and cacti proper as well as both varieties with fixed constant size one of the constituting loops. Using the recognition principle of Fiedorowicz, we prove that spineless cacti are equivalent as operads to the little discs operad. It turns out that in terms of spineless cacti Cohen’s Gerstenhaber structure and Fiedorowicz’ braided operad structure are given by the same explicit chains. We also prove that spineless cacti and cacti are homotopy equivalent to their normalized versions as quasi-operads by showing that both types of cacti are semi-direct products of the quasi-operad of their normalized versions with a re-scaling operad based on >0. Furthermore, we introduce the notion of bi-crossed products of quasi-operads and show that the cacti proper are a bi-crossed product of the operad of cacti without spines and the operad based on the monoid given by the circle group S1. We also prove that this particular bi-crossed operad product is homotopy equivalent to the semi-direct product of the spineless cacti with the group S1. This implies that cacti are equivalent to the framed little discs operad. These results lead to new CW models for the little discs and the framed little discs operad.

cacti, (quasi-)operad, string topology, loop space, bi-crossed product, (framed) little discs, quasi-fibration
Mathematical Subject Classification 2000
Primary: 55P48
Secondary: 55P35, 16S35
Forward citations
Received: 9 January 2004
Revised: 16 March 2005
Accepted: 30 March 2005
Published: 15 April 2005
Ralph M Kaufmann
Department of Mathematics
University of Connecticut
196 Auditorium Road
Storrs CT 06269-3009