Study of time lags in HETE-2 Gamma-Ray Bursts with redshift: search for astrophysical effects and Quantum Gravity signature

The study of time lags between spikes in Gamma-Ray Burst light curves in different energy bands as a function of redshift may lead to the detection of effects due to Quantum Gravity. We present an analysis of 15 Gamma-Ray Bursts with measured redshift, detected by the HETE-2 mission in order to measure time lags related to astrophysical effects and search for Quantum Gravity signature in the framework of an extra-dimension string model. The wavelet transform method is used both for de-noising the light curves and for the detection of sharp transitions. The use of photon tagged data allows us to consider various energy ranges and to evaluate systematic effects due to selections and cuts. The analysis of maxima and minima of the light curves leads to no significant Quantum Gravity effect. A lower limit at 95% Confidence Level on the Quantum Gravity scale parameter of 2x10**15 GeV is set.