The neutrino charge radius as a probe of physics beyond the standard model

In this paper, we review the search of possible physics effects beyond the standard model on the electromagnetic charge and anapole form factors, fQ(q2) and fA(q2), for a no massive Dirac neutrino, when these quantities are calculated in the frame of an effective electroweak Yang-Mills theory, which induces the most general SUL(2)–invariant Lorentz tensor structure of nonrenormalizable type for the WWγ vertex. We found that in this frame, besides the standard model contribution, the additional contribution to fQ(q2) and fA(q2) (fQOW(q2) and fAOW(q2), respectively) are gauge independent and finite functions of q2 after adopting a renormalization scheme. These form factors, fQOW(q2) and fAOW(q2), get contribution at the one loop level only from the proper neutrino electromagnetic vertex. Besides, the relation fQeff(q2) = q2fAeff(q2)(fQeff(q2) = fQSM(q2)+fQOW(q2),fAeff(q2) = fASM(q2)+fAOW(q2)) is still fulfilled and hence the relation aveff = eff/6(aveff = avSM+avOW,eff = SM+OW) is obtained, just as in the SM. Using the experimental constraint on the anomalous WWγ vertex, a value for the additional contribution to the charge radius of ‖OW‖≲10−34 cm2 is gotten, which is one order of magnitude lower than the SM value.