[1] DESY Theory Grp, D-22603 Hamburg, Germany
[2] Sao Paulo State Univ, Inst Fis Teor, BR-01140070 Sao Paulo, Brazil
[3] Univ Fed Rio Grande do Norte, Escola Ciencias & Tecnol, BR-59072970 Natal, RN, Brazil
[4] Univ Andres Bello, Fac Ciencias Exactas, Dept Ciencias Fis, Santiago, Chile