Status of four-neutrino mass schemes: A global and unified approach to current neutrino oscillation data

We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes $(3+1)$ and $(2+2).$ We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including the Liquid Scintillation Neutrino Detector (LSND). If we combine only solar and atmospheric neutrino data, $(3+1)$ schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefer $(2+2)$ models. When combining all data in a global analysis, the $(3+1)$ mass scheme gives a slightly better fit than the $(2+2)$ case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with only Δmₛₒₗ² and Δmₐₜₘ² at 99.9% C.L. with respect to the four-neutrino best-fit model. We perform a detailed analysis of the goodness of fit to identify which subset of the data is in disagreement with the best-fit solution in a given mass scheme.