The nuclear aspects of flavour changing neutral current (FCNC) processes,
predicted by various new-physics models to occur in the presence of nuclei, are
examined by computing the relevant nuclear matrix elements within the context
of the quasi-particle RPA using realistic strong two-body forces. One of our
aims is to explore the role of the non-standard interactions (NSI) in the
leptonic sector and specifically: (i) in lepton flavour violating (LFV)
processes involving the neutral particles νℓ and ν~ℓ,
ℓ=e,μ,τ and (ii) in charged lepton flavour violating (cLFV)
processes involving the charged leptons ℓ− or ℓ+. As concrete
nuclear systems we have chosen the stopping targets of μ−→e−
conversion experiments, i.e. the 48Ti nucleus of the PRIME/PRISM
experiment at J-PARC and the 27Al of the COMET at J-PARC as well
as of the Mu2e at Fermilab. These experiments have been designed to reduce the
single event sensitivity down to 10−16--10−18 in searching for
charged lepton mixing events. Our goal is, by taking advantage of our detailed
nuclear structure calculations and using the present limits or the sensitivity
of the aforementioned exotic μ−→e− experiments, to put
stringent constraints on the parameters of NSI Lagrangians.Comment: 8 pages, 4 figures, 3 Tables, Physics Letters B accepte