IRFU's Double Chooz group has just published some surprising results regarding the flux of antineutrinos generated by uranium and plutonium fission products in nuclear power reactors. A more precise estimate of this flux has revealed a +3% shift with respect to the predictions considered as the benchmark for the past 25 years. The re-analysis of the most important past reactor neutrino experimental results, in the light of this new flux prediction, lead to the so called 'reactor antineutrino anomaly'. Including other effects such as the evolution of the neutron lifetime and the presence of long-lived fission isotopes, the averaged shortfall in the number of antineutrinos detected at short baseline reactor experiments is almost 6%. The hypothesis according to which this anomaly can be explained by the existence of a new particle, a 4th "sterile” neutrino, ties in surprisingly well with other independent results.
If its existence is proven by forthcoming experiments this 4th neutrino, interacting only with gravity, should be added to the bestiary of the Standard Model of particle physics. It could have some impact on cosmology as well. Nonetheless, neutrino flux measurements will have to be performed less than ten meters from reactor cores to obtain irrefutable proof that the new particle exists. This is within the grasp of present-day techniques used in neutrino detection experiments, particularly in the case of Nucifer, a detector that is about to be used in a data-gathering mission on Osiris, the research reactor in Saclay. Other new proposals are being discussed by the particle physics community to test this anomaly, with new neutrino beam experiment (at CERN) or by deploying a Mci neutrino generator in large liquid scintillator detectors (like Borexino).
Authors of articles: M. Cribier, M. Fechner, Th. Lasserre, A. Letourneau, D. Lhuillier, G. Mention, Th. Mueller.
 K. Schreckenbach et al., Phys. Lett. 160B (1985) 325. A.A. Hahn, K. Schreckenbach et al., Phys. Lett. B218 (1989) 365.
 G. Mention et al., "Improved Predictions of Reactor Antineutrino Spectra" , available online , arXiv:1101.2755 [hep-ex].
 C. Guinti and M. Laveder, Phys. Rev. D82 (2010) 053005.
 Th. A. Mueller et al. "The Reactor Antineutrino Anomaly": arXiv:1101.2663 [hep-ex].