Effects of physics beyond the standard model on the neutrino charge radius: an effective Lagrangian approach

anchez, H. Novales--S\'; Rosado, A.; an, V. Santiago--Ol\'; Toscano, J. J.

Effects of physics beyond the standard model on the neutrino charge radius: an effective Lagrangian approach

Authors

anchez, H. Novales--S\'

Rosado, A.

an, V. Santiago--Ol\'

Toscano, J. J.

Description

In this work, we look for possible new physics effects on the electromagnetic charge and anapole form factors, $f_Q(q^2)$ and $f_A(q^2)$, for a massless Dirac neutrino, when these quantities are calculated in the context of an effective electroweak Yang-Mills theory, which induces the most general $SU_L(2)$--invariant Lorentz tensor structure of nonrenormalizable type for the $WWγ$ vertex. It is found that in this context, besides the standard model contribution, the additional contribution to $f_{Q}(q^2)$ and $f_{A}(q^2)$ ($f_{Q}^{O_W}(q^2)$ and $f_{A}^{O_W}(q^2)$, respectively) are gauge independent and finite functions of $q^2$ after adopting a renormalization scheme. These form factors, $f_{Q}^{O_W}(q^2)$ and $f_{A}^{O_W}(q^2)$, get contribution at the one loop level only from the proper neutrino electromagnetic vertex. Besides, the relation $f_{Q}^{eff}(q^2)=q^2f_{A}^{eff}(q^2)$ ($f_{Q}^{eff}(q^2)=f_{Q}^{SM}(q^2)+f_{Q}^{O_W}(q^2)$, $f_{A}^{eff}(q^2)=f_{A}^{SM}(q^2)+f_{A}^{O_W}(q^2)$) is still fulfilled and hence the relation $a_ν^{eff} = < r^2_ν > ^{eff} /6$ ($a_ν^{eff} = a_ν^{SM}+ a_ν^{O_W}$, $<r^2_ν > ^{eff} = < r^2_ν > ^{SM}+< r^2_ν > ^{O_W}$)is gotten, 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 $|< r^2_ν >^{O_W}| \lsim 10^{-34} cm^2$ is obtained, which is one order of magnitude lower than the SM value.
9 pages, 3 figures