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Spontaneous CP breaking in QCD and the axion potential: an effective Lagrangian approach
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. The Niels Bohr Institute, Denmark.
2017 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 12, article id 104Article in journal (Refereed) Published
Abstract [en]

Using the well-known low-energy effective Lagrangian of QCD - valid for small (non-vanishing) quark masses and a large number of colors - we study in detail the regions of parameter space where CP is spontaneously broken/unbroken for a vacuum angle theta = pi. In the CP broken region there are first order phase transitions as one crosses theta = pi, while on the (hyper)surface separating the two regions, there are second order phase transitions signalled by the vanishing of the mass of a pseudo Nambu-Goldstone boson and by a divergent QCD topological susceptibility. The second order point sits at the end of a first order line associated with the CP spontaneous breaking, in the appropriate complex parameter plane. When the effective Lagrangian is extended by the inclusion of an axion these features of QCD imply that standard calculations of the axion potential have to be revised if the QCD parameters fall in the above mentioned CP broken region, in spite of the fact that the axion solves the strong-CP problem. These last results could be of interest for axionic dark matter calculations if the topological susceptibility of pure Yang-Mills theory falls off sufficiently fast when temperature is increased towards the QCD deconfining transition.

Place, publisher, year, edition, pages
Springer, 2017. no 12, article id 104
Keywords [en]
1/N Expansion, Anomalies in Field and String Theories
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-221376DOI: 10.1007/JHEP12(2017)104ISI: 000418374200005Scopus ID: 2-s2.0-85039415318OAI: oai:DiVA.org:kth-221376DiVA, id: diva2:1175106
Note

QC 20180117

Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2018-01-17Bibliographically approved

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