Question

How do messenger fields break SUSY in the MSSM?

Answer 1

there is a hidden sector where SUSY is spontaneously broken, there is a messenger superfield and there is a visible sector. There should be no direct coupling between the hidden sector and the visible sector. The spontaneous susy breaking in the hidden sector affects the messenger fields which in turn breaks susy in the visible sector keeping the soft terms. The messenger fields break susy in the visible sector only via loop