Robust constraint on Lorentz violation using Fermi-LAT gamma-ray burst data

Abstract

Models of quantum gravity suggest that the vacuum should be regarded as a medium with quantum structure that may have non-trivial effects on photon propagation, including the violation of Lorentz invariance. Fermi Large Area Telescope (LAT) observations of gammaray bursts (GRBs) are sensitive probes of Lorentz invariance, via studies of energy-dependent timing shifts in their rapidly-varying photon emissions. In this paper we analyze the Fermi-LAT measurements of high-energy gamma rays from GRBs with known redshifts, allowing for the possibility of energy-dependent variations in emission times at the sources as well as a possible non-trivial refractive index in vacuo for photons. We use statistical estimators based on the irregularity, kurtosis and skewness of bursts that are relatively bright in the 100 MeV to multi-GeV energy band to constrain possible dispersion effects during propagation. We find that the energy scale characterizing a linear energy dependence of the refractive index should exceed a few ×10 17 GeV, and we estimate the sensitivity attainable with additional future sources to be detected by Fermi-LAT.

Limits on neutrino Lorentz violation from multimessenger observations of TXS 0506+056

“…A less radical hypothesis would be that Lorentz invariance is an emergent symmetry in the low-energy limit, but is subject to modification that increases with energy. This is indeed the suggestion that has been made in a number of different theoretical frameworks, including the 'space-time foam' expected in models of quantum gravity [15], phenomenological models suggested by features of cosmic-ray physics [16] and other considerations [17], the suggestion that Lorentz invariance may be 2 The redshift of TXS 0506+056 is not very large, and the estimates of ∆t and the energy of the neutrino are not very accurate, so this estimate does not include the small effects associated with the expansion of the Universe during propagation. 3 Henceforth, we use natural units in which the conventional velocity of light c = 1.…”

“…which is over 6 orders of magnitude stronger than the limit obtained previously [3] from an analysis of the neutrino signal from supernova 1987A 6 . The sensitivity (1) is, nevertheless, an order of magnitude weaker than the robust limit on photon Lorentz violation [2], so refers directly to the neutrino.…”

“…Over the past two decades, since the publication of [1], considerable effort has been put by many experimental collaborations into constraining different forms of Lorentz violation, and specifically a linear coefficient M 1 in the velocity v of energetic photons: ∆v = −E/M 1 , using distant time-dependent astrophysical sources of energetic photons such as pulsars, gamma-ray bursts (GRBs) and active galactic nuclei (AGNs). However, analyses of possible Lorentz violation in photon propagation have been beset by difficulties in disentangling intrinsic time delays in the sources from time delays accumulated during propagation, and we consider that the strongest robust limit on M 1 for photons is between 10 17 and 10 18 GeV [2]. There have also been analyses of possible Lorentz violation in neutrino propagation from Supernova 1987A and in a terrestrial neutrino beam, but these are sensitive only to M 1 ∼ 2 × 10 11 GeV and potentially ∼ 4 × 10 8 GeV, respectively [3].…”

“…Again, the large distance of 6 In calculating (1) we used the standard cosmological ΛCDM model with dark energy and dark matter contributions Ω Λ = 0.7 and Ω M = 0.3, respectively, and Hubble expansion rate H 0 = 68 km/s/Mpc. See [2] for detailed derivation of (1). 7 In fact, we are unaware of neutrino experiments that have sought to test Lorentz invariance in the way proposed here.…”

Commutative or noncommutative spacetime? Two length scales of noncommutativity

“…This is also the point of view of many authors when looking for light velocity modifications as a probe of Lorentz-invariance violation (LIV) (see Refs. [34][35][36] and references therein). In particular, special attention has been devoted to gammaray bursts (GRB).…”