Roberto Casalbuoni^*

• Department of Physics, University of Florence, INFN, Florence, Italy and Galileo Galilei Institute for Theoretical Physics, Florence, Italy

Joaquim Gomis^†

• PH-TH Division, CERN, CH -1211 Geneva 23, Switzerland and Departament d’Estructura i Constituents de la Matèria, Facultat de Física, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain

Giorgio Longhi^‡

• Department of Physics, University of Florence and INFN, Florence, Italy

• ^*casalbuoni@fi.infn.it
• ^†gomis@ecm.ub.es
• ^‡longhi@fi.infn.it