CHIRAL-SYMMETRY BREAKING IN THE NAMBU-JONA-LASINIO MODEL IN EXTERNAL CONSTANT ELECTROMAGNETIC-FIELD

Dynamical chiral symmetry breaking (D chi SB) is studied in the Nambu- Jona-Lasinio model for an arbitrary combination of external constant e lectric and magnetic fields. In 3 + 1 dimensions it is shown that the critical coupling constant increases with increasing of the value of t he second invariant of electromagentic field E.B, i.e. the second inva riant inhibits D chi SB. The case of 2+1 dimensions is simpler because there is only one Lorentz invariant of electromagnetic field and any combination of constant fields can be reduced to cases either purely m agnetic or purely electric field. (C) 1998 Elsevier Science B.V.