An anomaly in neutrino physics has several plausible explanations that don't require new physics. I would rate each of the beyond the Standard Model explanations in their paper lower than they do in plausibility by at least two stars.
A series of experiments studying neutrinos from intense radioactive sources have reported a deficit in the measured event rate which, in combination, has reached a statistical significance of ∼5σ.
In this paper, we explore avenues for explaining this anomaly, both within the Standard Model and beyond.
First, we discuss possible biases in the predicted cross section for the detection reaction νe+71Ga→e−+71Ge, which could arise from mismeasurement of the inverse process, 71Ge decay, or from the presence of as yet unknown low-lying excited states of 71Ga. The latter would imply that not all 71Ge decays go to the ground state of 71Ga, so the extraction of the ground state-to-ground state matrix element relevant for neutrino capture on gallium would be incorrect.
Second, we scrutinize the measurement of the source intensity in gallium experiments, and we point out that a ∼2% error in the branching ratios for 51Cr decay would be enough to explain the anomaly.
Third, we investigate the calibration of the radiochemical germanium extraction efficiency as a possible origin of anomaly.
From here.
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