Chiral order and fluctuations in multi-flavour QCD |
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Authors: | S Descotes-Genon L Girlanda J Stern |
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Institution: | (1) Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK , GB;(2) Dipartimento di Fisica, Università di Padova and INFN, Via Marzolo 8, 35131 Padova, Italy , IT;(3) Groupe de Physique Théorique, Institut de Physique Nucléaire, 91406 Orsay-Cedex, France , FR |
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Abstract: | Multi-flavour chiral perturbation theory (PT) may exhibit instabilities due to vacuum fluctuations of sea pairs. Keeping the fluctuations small would require a very precise fine tuning of the low-energy constants and to , . A small deviation from these critical values - like the one suggested by the phenomenology of OZI-rule violation in the
scalar channel - is amplified by huge numerical factors inducing large effects of vacuum fluctuations. This would lead in
particular to a strong Nf dependence of chiral symmetry breaking (SB) and a suppression of the multi-flavour chiral order parameters. A simple resummation is shown to cure the instability
of PT, but it modifies the standard expressions of some O(p
2
) and O(p
4
) low-energy parameters in terms of observables. On the other hand, for r= m
s
/m > 15, the two-flavour condensate is not suppressed, due to the contribution induced by massive vacuum pairs. Thanks to the latter, the standard two-flavour PT is protected from multi-flavour instabilities and could provide a well-defined expansion scheme in powers of non-strange
quark masses.
Received: 31 July 2002 / Revised version: 6 November 2002 / Published online: 15 January 2003
RID="a"
ID="a" e-mail: sdg@hep.phys.soton.ac.uk
RID="b"
ID="b" e-mail: luca.girlanda@pd.infn.it * Present address: ECT*, Villa Tambosi, Strada delle Tabarelle 286, 38050 Trento, Italy
RID="c"
ID="c" e-mail: stern@ipno.in2p3.fr |
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Keywords: | |
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