Stringent Neutron-Star Limits on Large Extra Dimensions

Supernovae (SNe) are copious sources for Kaluza-Klein (KK) gravitons which are generic for theories with large extra dimensions. These massive particles are produced with average velocities ≃0.5c so that many of them are gravitationally retained by the SN core. Every neutron star thus has a halo of KK gravitons which decay into νν̅ , e⁺e^-, and γγ on time scales ≃10⁹ years. The EGRET γ-flux limits ( E_γ≃100MeV) for nearby neutron stars constrain the compactification scale for n = 2 extra dimensions to M≳500TeV, and M≳30TeV for n = 3. The requirement that neutron stars are not excessively heated by KK decays implies M≳1700TeV for n = 2, and M≳60TeV for n = 3.