Impact of cosmology on Lorentz Invariance Violation constraints from GRB time-delays

Abstract

Putting constraints on a possible Lorentz Invariance Violation (LIV) from astrophysical sources such as gamma-ray bursts (GRBs) is essential for finding evidences of new theories of quantum gravity (QG) that predict an energy-dependent speed of light. This search has its own difficulties, so usually, the effect of the cosmological model is understudied, with the default model being a fixed-parameters $\Lambda$CDM. In this work, we use various astrophysical datasets to study the effect of a number of dark energy models on LIV constraints. To this end, we combine two public time-delay GRB datasets with the supernovae Pantheon dataset, several measurements of angular baryonic acoustic oscillations (BAO), the cosmic microwave background (CMB) distance prior and an optional GRB or quasars dataset. For the LIV parameter $\alpha$, we find the expected from previous works average value of $\alpha \sim 4 \times 10^{-4}$, corresponding to $E_{QG}\ge 10^{17}$ GeV for both time-delay (TD) datasets, with the second one being more sensitive to the cosmological model. The cosmology results in a minimum 20\% deviation in our constraints on the energy. Interestingly, adding the TD points makes the DE models less-preferable statistically and shifts the value of the parameter $c/(H_0 r_d)$ down, making it smaller than the expected value. We observe that possible LIV measurements critically depend on the transparency of the assumptions behind the published data concerning cosmology, and taking this into account may be an important contribution in the case of possible detection.

Probing for Lorentz Invariance Violation in Pantheon Plus Dominated Cosmology

“…As in our previous paper [64], we denote a LIV = α and b is replaced with β, to avoid mixing this parameter with b = c/(H 0 r d ).…”

“…It is particularly important when averaging over multiple GRBs due to the different redshifts employed. In [64], we obtained that the effect of adding cosmology may be significant for certain models and datasets. The biggest unknown in such a study is the intrinsic time delay-i.e., the possibility that the high and low-energy photons were not emitted at the same time.…”

“…Figure 1. Current upper limits of E QG : P1 [22], P2 [56], P3 [47], P4 [62], P5 [63], P6 [57], P7 [55], P8 [58], P9 [59], P10 [60], P11 [54], P12 [61], P13 [64], P14 [64], P15 [52]. The red line signifies the Planck energy.…”

“…In a previous paper [64], we started our investigation on how cosmology affects such constraints. LIV can be constrained either from the different energy bands of a single event or from averaging over multiple events, or both.…”

“…Since we do not have a good enough model of the GRB progenitor to predict the intrinsic time delay, we need to approximate it with a toy model. In [64], we used the standard approximation that assumes a constant (over the energy or the luminosity) intrinsic time delay, common for all the GRBs.…”