A recent experiment LSND at Los Alamos has provided\cite{ 1} an indication of $\overline{ \nu}_{ \mu} - \overline{ \nu}_e$ oscillations with $\Delta m^2$ of order 1ev$^2$ or greater and $\sin^2 2 \theta_{ e \mu}$ between $2 \times 10^{ -3}$ and $10^{ 2}$. Such a value of $\Delta m^2$ for $\nu_{ \mu} - \nu_e$ oscillations was not expected in the standard see-saw model\cite{ 2} suggested by SO(10) with a large mass hierarchy because it leads to too large a value of $m(\nu_{ \tau})$ to fit cosmological constraints. Furthermore within that model the LSND result is inconsistent with the indications of oscillations from both atmospheric neutrinos\cite{ 3} and solar neutrinos.\cite{ 4}
Categories: hep-ph