New Supernova Limit on Large Extra Dimensions: Bounds on Kaluza-Klein Graviton Production

If large extra dimensions exist in nature, supernova (SN) cores will emit large fluxes of Kaluza-Klein gravitons, producing a cosmic background of these particles with energies and masses up to about 100 MeV. Radiative decays then give rise to a diffuse cosmic -ray background with E_100MeV which is well in excess of the observations if more than 0. 5%--1% of the SN energy is emitted into the new channel. For two extra dimensions we derive a conservative bound on their radius of R0. 910^-4mm; for three extra dimensions it is R1. 910^-7mm.