Upper bound on all products of R-parity violating couplings λ′ and λ″ from proton decay

We prove that any product of R-parity violating couplings λ′ (L-violating) and λ″ (B-violating) can be strongly restricted by proton decay data. For any pair λ′ and λ″ the decay exists at least at one loop level. For squark masses below 1 TeV we find the conservative bounds |λ′ · λ″| < 10−9 in absence of squark flavor mixing, and |λ′ · λ″| < 10−11 when this mixing is taken into account. We study the dependence of the bounds on the flavor basis in which R-parity breaking couplings are determined.