Abnormal number of Nambu-Goldstone bosons in the color-asymmetric dense color superconducting phase of a Nambu–Jona-Lasinio–type model

D. Blaschke, D. Ebert, K. G. Klimenko, M. K. Volkov, and V. L. Yudichev
Phys. Rev. D 70, 014006 – Published 27 July 2004
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Abstract

We consider an extended Nambu–Jona-Lasinio model including both (qq¯) and (qq) interactions with two light-quark flavors in the presence of a single (quark density) chemical potential. In the color superconducting phase of the quark matter the color SUc(3) symmetry is spontaneously broken down to SUc(2). If the usual counting of Goldstone bosons would apply, five Nambu-Goldstone (NG) bosons corresponding to the five broken color generators should appear in the mass spectrum. Unlike that expectation, we find only three gapless diquark excitations of quark matter. One of them is an SUc(2) singlet; the remaining two form an SUc(2) (anti)doublet and have a quadratic dispersion law in the small momentum limit. These results are in agreement with the Nielsen-Chadha theorem, according to which NG bosons in Lorentz-noninvariant systems, having a quadratic dispersion law, must be counted differently. The origin of the abnormal number of NG bosons is shown to be related to a nonvanishing expectation value of the color charge operator Q8 reflecting the lack of color neutrality of the ground state. Finally, by requiring color neutrality, two massive diquarks are argued to become massless, resulting in a normal number of five NG bosons with the usual linear dispersion laws.

  • Received 16 March 2004

DOI:https://doi.org/10.1103/PhysRevD.70.014006

©2004 American Physical Society

Authors & Affiliations

D. Blaschke*

  • Fachbereich Physik, Universität Rostock, D-18051 Rostock, Germany
  • Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia

D. Ebert

  • Institut für Physik, Humboldt-Universität zu Berlin, D-12489 Berlin, Germany

K. G. Klimenko

  • Institute of High Energy Physics, 142281 Protvino, Moscow Region, Russia

M. K. Volkov and V. L. Yudichev§

  • Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia

  • *Electronic address: david.blaschke@physik.uni-rostock.de
  • Electronic address: debert@physik.hu-berlin.de
  • Electronic address: kklim@mx.ihep.su
  • §Electronic address: yudichev@thsun1.jinr.ru

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Vol. 70, Iss. 1 — 1 July 2004

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