Constraints on Quantum Gravity and the Photon Mass from Gamma Ray Bursts

Lorentz Invariance Violation in Quantum Gravity (QG) models or a non-zero photon mass, $m_gamma$, would lead to an energy-dependent propagation speed for photons, such that photons of different energies from a distant source would arrive at different times, even if they were emitted simultaneously. By developing source-by-source, Monte Carlo-based forward models for such time delays from Gamma Ray Bursts, and marginalising over empirical noise models describing other contributions to the time delay, we derive constraints on $m_gamma$ and the QG length scale, $ell_{rm QG}$, using spectral lag data from the BATSE satellite. We find $m_gamma < 4.0 times 10^{-5} , h , {rm eV}/c^2$ and $ell_{rm QG} < 5.3 times 10^{-18} , h , {rm , GeV^{-1}}$ at 95% confidence, and demonstrate that these constraints are robust to the choice of noise model. The QG constraint is among the tightest from studies which consider multiple Gamma Ray Bursts and the constraint on $m_gamma$, although weaker than from using radio data, provides an independent constraint which is less sensitive to the effects of dispersion by electrons.

Constraints on Equivalence Principle Violation from Gamma Ray Bursts

Theories of gravity that obey the Weak Equivalence Principle have the same Parametrised Post-Newtonian parameter $gamma$ for all particles at all energies. The large Shapiro time delays of extragalactic sources allow us to put tight constraints on differences in $gamma$ between photons of different frequencies from spectral lag data, since a non-zero $Delta gamma$ would result in a frequency-dependent arrival time. The majority of previous constraints have assumed that the Shapiro time delay is dominated by a few local massive objects, although this is a poor approximation for distant sources. In this work we consider the cosmological context of these sources by developing a source-by-source, Monte Carlo-based forward model for the Shapiro time delays by combining constrained realisations of the local density field using the BORG algorithm with unconstrained large-scale modes. Propagating uncertainties in the density field reconstruction and marginalising over an empirical model describing other contributions to the time delay, we use spectral lag data of Gamma Ray Bursts from the BATSE satellite to constrain $Delta gamma < 3.4 times 10^{-15}$ at $1 sigma$ confidence between photon energies of $25 {rm , keV}$ and $325 {rm , keV}$.