[1] Univ Complutense Madrid, Dept Fis Teor, E-28040 Madrid, Spain
[2] Univ Complutense Madrid, IPARCOS, Ciencias Fis, E-28040 Madrid, Spain
[3] Univ Aveiro, Dept Matemat, Campus Santiago, P-3810183 Aveiro, Portugal
[4] Ctr Res & Dev Math & Applicat, Campus Santiago, P-3810183 Aveiro, Portugal
[5] Dublin Inst Adv Studies, Sch Theoret Phys, Burlington Rd, Dublin, Ireland
[6] Natl Univ Ireland Maynooth, Dept Comp Sci, Maynooth, Ireland