Limit on leptonic photon interactions from SN 1987 a

If massless leptonic photons associated to electron, muon or tau leptonic number exist they would be emitted from supernova 1987a via the annihilation process νν → γ l γ l. By requiring that this process does not carry away most of the energy that can be radiated by the supernova we obtain an upper limit on the leptonic photon coupling constants to be less than 1.6 × 10 −11. This limit is a few orders of magnitude better than the limit obtained from the (g−2) experiment on muon magnetic moment or the limit which is expected from the analysis of high energy neutrino data. Recently, a few papers devoted to leptonic photons, first discussed by Okun in ref. [1], have been published [2, 3, 4, 5]. According to Okun [1, 2], it is assumed that if leptonic quantum numbers corresponding to the three lepton families (ν e , e), (ν µ , µ), (ν τ , τ) are strictly conserved these doublets could carry leptonic charges, which are sources of electronic, muonic and tauonic massless pho-tons, respectively. Okun considered the various consequences of this hypothesis and discussed possible experiments which might indicate the existence of these new vector particles. In particular , he pointed out that the additional gauge symmetries connected with new leptonic photons would produce a problem of triangle anomalies, which need special attention. To avoid this problem an anomaly-free scheme was suggested in which a single leptonic photon γ l had the same coupling α l to both the (ν µ , µ) and (ν τ , τ) doublets and was decoupled from (ν e , e) [2]. In the framework of this scheme there are no ν µ ↔ ν e oscillations, however transitions between muon and tau neutrinos are allowed. From the existing experimental data on muon magnetic moment upper limit α l ≤ 10 −5 × α could be obtained, where α=1/137 is the fine structure constant (hereafter we assume that α l ≡ α µ ≡ α τ). The improved limit on α l could be obtained from the analysis of high energy neutrino data. The idea is as follows [2]. If leptonic photons exist they might result from the decay π → µνγ l of charged pions copiously produced by high energy protons in the neutrino target. The γ l 's would penetrate the downstream shielding and would be observed in neutrino …