On the Neutrino Vector and Axial Vector Charge Radius

Abstract

Abstract.A Majorana neutrino is characterized by just one flavor diagonal electromagnetic form factor: the anapole moment, that in the static limit corresponds to the axial vector charge radius r 2 A . As is the case for the vector charge radius of a Dirac neutrino, proving that this quantity is a well defined physical quantity is non trivial. I will first describe briefly the origin of the long standing controversy about the physical or non physical nature of the neutrino charge radius. Then I will argue that, in contrast to Dirac neutrino electromagnetic form factors, for Majorana neutrinos cosmological and astrophysical arguments do not provide useful informations on r 2 A . Therefore this quantity has to be studied by means of terrestrial experiment. Finally, I will discuss the constraints that can be derived on r 2 A for the tau neutrino from a comprehensive analysis of the data on single photon production off Z-resonance, and I will conclude with a few comments on ν µ scattering data from the NuTeV, E734, CCFR and CHARM-II collaborations and on the limits implied for r 2 A for the muon neutrino.

Effects of neutrino magnetic moment and charge radius constraints and medium modifications of the nucleon form factors on the neutrino mean free path in dense matter

“…A , which can have a negative value for Dirac neutrinos [67,68]. For the Majorana neutrinos, only the anapole form factor g 1 (q 2 ) remains and thus the relevant quantity is solely R 2 A [62,64] in the EM interaction vertex with R 2 V = 0 [67,68]. The values of R 2 for the Dirac neutrino are at the order of (10 −3 fm) 2 [67][68][69].…”

“…For the Majorana neutrinos, only the anapole form factor g 1 (q 2 ) remains and thus the relevant quantity is solely R 2 A [62,64] in the EM interaction vertex with R 2 V = 0 [67,68]. The values of R 2 for the Dirac neutrino are at the order of (10 −3 fm) 2 [67][68][69].…”

Impact of medium modification of the nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter

“…A , which can have a negative value for Dirac neutrinos [36,37]. For Majorana neutrinos, only the anapole form factor g 1 (q 2 ) remains and thus the relevant quantity is solely R 2 A [31,33] in the EM interaction vertex with R 2 V = 0 [36,37].…”

Effect of neutrino electromagnetic form factors on the neutrino cross section in dense matter

“…In the limit of q 2 → 0, f 2ν and g 2ν , respectively, define the neutrino magnetic moment and the Charge Parity (CP) violating electric dipole moment [29,31], i.e.,…”