Phenomenology of Space Time Fluctuations

TL;DR

This paper explores how quantum gravitational space-time fluctuations could cause observable effects on cosmic rays and particle stability, providing strong constraints on models of quantum gravity through astrophysical observations.

Contribution

It demonstrates that space-time fluctuations can lead to forbidden particle decays and affect cosmic ray propagation, offering new constraints on quantum gravity models.

Findings

Lower energy cosmic ray observations constrain space-time fluctuation models.

Fluctuations could enable forbidden particle decay reactions.

Proposed loopholes may prevent some predicted effects.

Abstract

Quantum gravitational effects may induce stochastic fluctuations in the structure of space-time, to produce a characteristic foamy structure. It has been known for some time now that these fluctuations may have observable consequences for the propagation of cosmic ray particles over cosmological distances. While invoked as a possible explanation for the detection of the puzzling cosmic rays with energies in excess of the threshold for photopion production (the so-called super-GZK particles), we demonstrate here that lower energy observations may provide strong constraints on the role of a fluctuating space-time structure. We note also that the same fluctuations, if they exist, imply that some decay reactions normally forbidden by elementary conservation laws, become kinematically allowed, inducing the decay of particles that are seen to be stable in our universe. Due to the strength of the prediction, we are led to consider this finding as the most severe constraint on the classes of models that may describe the effects of gravity on the structure of space-time. We also propose and discuss several potential loopholes of our approach, that may affect our conclusions. In particular, we try to identify the situations in which despite a fluctuating energy-momentum of the particles, the reactions mentioned above may not take place.