Hint of nonstandard Mikheyev-Smirnov-Wolfenstein dynamics in solar neutrino conversion

Motivated by the recent low-threshold measurements of the solar B-8 neutrino spectrum performed by Borexino, Super-Kamiokande and the Sudbury Neutrino Observatory-all now monitoring the transition regime between low-energy (vacuumlike) and high-energy (matter-dominated) flavor conversions-we consider the role of subdominant dynamical terms induced by new flavor-changing interactions. We find that the presence of such perturbations with strength similar to 10(-1) G(F) is now favored, offering a better description of the anomalous behavior suggested by the new results, whose spectrum shows no sign of the typical low-energy upturn predicted by the standard Mikheyev-Smirnov-Wolfenstein (MSW) mechanism. Our findings, if interpreted in a 2-flavor scheme, provide a hint of such new interactions at the similar to 2 sigma level, which is rather robust with respect to 3-flavor effects possibly induced by nonzero 0(13).