Vyaas Ramakrishnan, Shantanu Desai

We reanalyze the spectral lag data for 56 GRBs in the cosmological rest frame to search for Lorentz Invariance Violation using frequentist inference. For this purpose, we use the technique of profile likelihood to deal with the nuisance parameters corresponding to a constant astrophysical spectral lag in the GRB rest frame and the unknown intrinsic scatter, while the parameter of interest is the energy scale ($E_{QG}$) for LIV. With this method, we do not obtain a global minimum for $\chi^2$ as a function of $E_{QG}$ up to the Planck scale. Therefore, we can set one-sided lower limits on $E_{QG}$ in a seamless manner. The 95% c.l. lower limits which we obtain on $E_{QG}$ are then given by $E_{QG}\geq 1.22 \times 10^{15}$ GeV and $E_{QG}\geq 6.64\times 10^{5}$ GeV, for linear and quadratic LIV, respectively. Therefore, this work represents yet another proof of principles application of profile likelihood in the search for LIV using GRB spectral lags.