Radiative neutrino masses

[BjHerrmann]

Dear all,

we are currently implementing a non-supersymmetric model including, in addition to the Standard Model, a couple of scalars and new fermions. One important feature of this model is that neutrino masses are generated radiatively at the one-loop level. In a simple case, it turns out that only two neutrinos will have masses, while the first one remains massless (roughly, this is due to the number of degrees of freedom available to generate the masses). The free parameters of the model are basically the masses of scalars and fermions as well as the couplings between them and the Standard Model fermions, which allows the generation of neutrino masses.

We have implemented the model in SARAH and generated a SPHENO version from it. While testing, we observe that in certain cases we have the first neutrino being massless as expected (in the output SLHA the mass is then strictly 0.00000E+00), while for other parameter configurations we obtain for the lightest mass values of the order 10^{-16} to 10^{-21}, which is numerically close to zero (given that they are double precision values), but not exactly.

My question is: can we consider that this is zero, or must we suspect that something is wrong with the model implementation? My feeling is that numerics is playing tricks with us here, or rather that such values are compatible with zero, but I am not quite sure? And how to verify this in practice?

Thank you for your help,
best regards,
Björn