String inspired models with millimeter scale extra dimensions provide a natural way to understand an ultralight sterile neutrino needed for a simultaneous explanation of the solar, atmospheric and Liquid Scintillation Neutrino Detector neutrino oscillation results. The sterile neutrino is the bulk neutrino $\left({\nu }_B\right)$ postulated to exist in these models, and it becomes ultralight in theories that prevent the appearance of its direct mass terms. Its Kaluza-Klein (KK) states then add new oscillation channels for the electron neutrino emitted from the solar core. We show that successive Mikheyev-Smirnov-Wolfenstein transitions of solar ${\nu }_e$ to the lower lying KK modes of ${\nu }_B$ in conjunction with vacuum oscillations between the ${\nu }_e$ and the zero mode of ${\nu }_B$ provide a new way to fit the solar neutrino data. The characteristic predictions can be tested by solar neutrino observations and forthcoming solar neutrino experiments. We discuss both intermediate and low string scale models where the desired spectrum can emerge naturally.

• Received 26 February 2001

DOI:https://doi.org/10.1103/PhysRevD.64.073001