Search for Lorentz Invariance Violation from stacked Gamma-Ray Burst spectral lag data

Abstract

A number of works have claimed detections of a turn-over in the spectral lag data for individual Gamma-Ray Bursts (GRBs), caused by an energy-dependent speed of light, which could be a possible manifestation of Lorentz invariance violation (LIV). Here, we stack the spectral lag data from a total of 37 GRBs (with a total of 91 measurements), to verify if the combined data is consistent with a unified model consisting of intrinsic astrophysical emission, along with another contribution due to LIV. We then carry out Bayesian model comparison to ascertain if this combined spectral lag data shows a preference for an energy-dependent speed of light, as compared to only an intrinsic astrophysical emission mechanism. We do not find a decisive evidence for such an energy-dependent speed of light for two different models of LIV. When we assume a constant intrinsic lag coupled with an unknown intrinsic scatter, we do not find any evidence for LIV. However, when we use GRB-dependent parameters to model the intrinsic emission, we get decisive evidence for LIV violation. We then carry out a search for LIV Standard Model Extension using this dataset as well as an independent search using a separate dataset consisting of rest-frame spectral lags. Finally, none of the models considered here with any of the aforementioned assumptions provide a good fit to the stacked spectral lag data, indicating that there is still missing Physics in the model for intrinsic spectral lags.

Observational constraints on varying fundamental constants in a minimal CPC model

“…BD theory and other extensions of the current standard model naturally lead to the concept that fundamental couplings are indeed expected to vary. Some examples of varying physical couplings proposals are studies of variation of the fine-structure constant α [49,50,51,52,53,54,55,56,57], of the Newton's gravitational constant G [58,59,60,61,62,63,64,65], and of the speed of light c [66,67,68,69,70,71,72,73,74,75,76,77,78,79]. The common feature of these works is to take only one of the couplings as a function of the cosmological time while disregarding possible variations of the others.…”

Gamma-Ray Cosmology and Tests of Fundamental Physics

“…It should be noted that even though these time-delay analyses achieve strong constraints on the LIV scale M, assumptions have to made about the intrinsic time spread of the emission. This problem is starting to be addressed both for AGN flares [207] and GRBs [208,209] in a systematic way, but further work appears to be needed to disentangle intrinsic from possible line-of-sight effects [210].…”

“…LHAASO could even reach a sensitivity to LIV of the order of ∼20 E Pl [218]. These limits will, of course, depend on a better understanding of the intrinsic time lags, which need to be incorporated in the data analysis [209,210]. Furthermore, optical follow-up observations will be of paramount importance in order to determine the redshift and hence the distance of GRBs.…”

A search for the variation of speed of light using galaxy cluster gas mass fraction measurements

“…Another specific class of alternative models consider the possibility of variation of some of the fundamental constants of Physics, such as the fine-structure constant α [17][18][19][20][21][22][23][24][25], Newton's gravitational constant G [26][27][28][29][30][31][32][33] or the speed of light c [34][35][36][37][38][39][40][41][42][43]. In this work, we focus on testing the supposition of the constancy of the speed of light, which constitutes one of the most basic and sacro-sanct tenets of Physics.…”

“…[56] used a model-independent method to reconstruct the temporal evolution of the speed of light, and the results were in agreement to the value measured at z = 0. Complementary to these tests on the redshiftdependent speed of light, searches for energy-dependent speed of light (as predicted by certain Lorentz-violating standard model extension models) have also been carried out using spectral lags of Gamma-ray bursts [43].…”