Bounds on hep neutrinos

The excess of highest energy solar-neutrino events recently observed by Superkamiokande can be in principle explained by anomalously high hep-neutrino flux Φν(hep). Without using SSM calculations, from the solar luminosity constraint we derive that Φν(hep)/S13 cannot exceed the SSM estimate by more than a factor three. If one makes the additional hypothesis that hep neutrino production occurs where the 3He concentration is at equilibrium, helioseismology gives an upper bound which is (less then) two times the SSM prediction. We argue that the anomalous hep-neutrino flux of order of that observed by Superkamiokande cannot be explained by astrophysics, but rather by a large production cross-section.