M. Velkovsky et E. Shuryak, QCD WITH LARGE NUMBER OF QUARKS - EFFECTS OF THE INSTANTON-ANTI-INSTANTON PAIRS, Physics letters. Section B, 437(3-4), 1998, pp. 398-402
We calculate the contribution of instanton - anti-instanton (I (I) ove
r bar) pairs to the vacuum energy of QCD-like theories with N-f light
fermions, using the saddle point method. A qualitative change of behav
ior is found around N-f = 6. We discuss the relation of this phenomeno
n to the mechanism of chiral symmetry breaking and the asymptotic of t
he perturbative series associated with I (I) over bar contributions. (
C) 1998 Published by Elsevier Science B.V. All rights reserved.