# Theoretical Ideas about Neutrino Mass

• Lincoln Wolfenstein

## Abstract

What insight does theory give us about neutrino masses? When parity was discovered in 1957 it was immediately suggested that the neutrino was a massless Weyl particle having only two components, the left-handed v L and the right-handed anti-particle $$\bar v_R .$$ With the advent of the standard model all fermions start out as Weyl particles: these are the left-handed doublets
$$\begin{array}{*{20}c} {\left( {\begin{array}{*{20}c} {v_e } \\ e \\ \end{array} } \right)_L } & {\left( {\begin{array}{*{20}c} {v_\mu } \\ \mu \\ \end{array} } \right)_L } & {\left( {\begin{array}{*{20}c} {v_\tau } \\ \tau \\ \end{array} } \right)_L } \\ {\left( {\begin{array}{*{20}c} u \\ d \\ \end{array} } \right)_L } & {\left( {\begin{array}{*{20}c} c \\ s \\ \end{array} } \right)_L } & {\left( {\begin{array}{*{20}c} t \\ b \\ \end{array} } \right)_L } \\ \end{array}$$
(1)
and the right-handed singlets
$$\begin{array}{*{20}c} {\begin{array}{*{20}c} {e_R } & {\mu _R } & {\tau _R } \\ \end{array} } \\ {\begin{array}{*{20}c} {u_R } & {d_R } & {c_R } & {s_R } & {t_R } & {b_R .} \\ \end{array} } \\ \end{array}$$
.

### Keywords

Chlorine Gallium Mellon