Speed Variations of Cosmic Photons and Neutrinos from Loop Quantum Gravity

Abstract

Recently a series of analyses on the flight time of cosmic photons and neutrinos suggests that the speed of light \emph{in vacuo} takes the energy-dependent form $v(E)\simeq 1-E/E_{\text{LIV}}^{\gamma }$ with $E_{\text{LIV}}^{\gamma }\approx 3.6\times 10^{17}~\text{GeV}$, and meanwhile the speed of neutrinos is proposed to be $v(E)\simeq 1\pm E/E_{\text{LIV}}^{\nu }$ with $E_{\text{LIV}}^{\nu }\approx 6.5\times 10^{17}~\text{GeV}$ and $\pm {}$ representing the helicity dependence. This novel picture immediately urges us to provide a satisfactory theoretical explanation. Among all the attempts to predict the speed variations from quantum gravity, we find that loop quantum gravity can serve as a good candidate for explaining the aforementioned picture consistently.