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Scale invariance vs conformal invariance

Nakayama, Yu (2015) Scale invariance vs conformal invariance. Physics Reports, 569 . pp. 1-93. ISSN 0370-1573. doi:10.1016/j.physrep.2014.12.003.

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In this review article, we discuss the distinction and possible equivalence between scale invariance and conformal invariance in relativistic quantum field theories. Under some technical assumptions, we can prove that scale invariant quantum field theories in d=2 space–time dimensions necessarily possess the enhanced conformal symmetry. The use of the conformal symmetry is well appreciated in the literature, but the fact that all the scale invariant phenomena in d=2 space–time dimensions enjoy the conformal property relies on the deep structure of the renormalization group. The outstanding question is whether this feature is specific to d=2 space–time dimensions or it holds in higher dimensions, too. As of January 2014, our consensus is that there is no known example of scale invariant but non-conformal field theories in d=4 space–time dimensions under the assumptions of (1) unitarity, (2) Poincaré invariance (causality), (3) discrete spectrum in scaling dimensions, (4) existence of scale current and (5) unbroken scale invariance in the vacuum. We have a perturbative proof of the enhancement of conformal invariance from scale invariance based on the higher dimensional analogue of Zamolodchikov’s cc-theorem, but the non-perturbative proof is yet to come. As a reference we have tried to collect as many interesting examples of scale invariance in relativistic quantum field theories as possible in this article. We give a complementary holographic argument based on the energy-condition of the gravitational system and the space–time diffeomorphism in order to support the claim of the symmetry enhancement. We believe that the possible enhancement of conformal invariance from scale invariance reveals the sublime nature of the renormalization group and space–time with holography. This review is based on a lecture note on scale invariance vs conformal invariance, on which the author gave lectures at Taiwan Central University for the 5th Taiwan School on Strings and Fields.

Item Type:Article
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URLURL TypeDescription Paper
Nakayama, Yu0000-0002-1747-5147
Additional Information:© 2014 Elsevier B.V. Accepted 11 December 2014, Available online 24 December 2014. This lecture note is prepared for the 5th Taiwan School on Strings and Fields. The author would like to thank the organizers, in particular C.M. Chen for the host, and all the participants for kind invitation and stimulating discussions. I also thank all the people I talked with for stimulating discussions on the subject. I, in particular, thank S. El-Showk, C. Ho, S. Rey and S. Rychkov for collaborations, and P. Argyres, D. Bak, K. Balasubramanian, J. Cardy, S. Deser, P. Di Vecchia, S. Dubovsky, M. Duff, A. Edery, H. Elvang, J. Fortin, P. Horava, Y. Iwasaki, R. Jackiw, C. Keeler, A. Konechny, S. Kuzenko, Z. Komargodski, S.S. Lee, R. Myers, A. Migdal, E. Mottola, S. Mukohyama, C. Nunez, H. Osborn, J. Polchinski, A. Shapere, K. Skenderis, S. Solodukhin, A. Stergiou and Y. Tachikawa for discussions and correspondence.
Group:Walter Burke Institute for Theoretical Physics
Subject Keywords:Scale invariance; Conformal invariance; Renormalization group; Holography
Record Number:CaltechAUTHORS:20150501-085852165
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Official Citation:Yu Nakayama, Scale invariance vs conformal invariance, Physics Reports, Volume 569, 28 March 2015, Pages 1-93, ISSN 0370-1573, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57138
Deposited By: Ruth Sustaita
Deposited On:01 May 2015 16:49
Last Modified:10 Nov 2021 21:08

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