(European Space Agency) ESA’s Integral gamma-ray observatory has provided results that will dramatically affect the search for physics beyond Einstein. It has shown that any underlying quantum ‘graininess’ of space must be at much smaller scales than previously predicted.
Einstein’s General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric. Yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach.
GRB 041219A took place on 19 December 2004 and was immediately recognised as being in the top 1% of GRBs for brightness. It was so bright that Integral was able to measure the polarisation of its gamma rays accurately.
Dr Laurent and colleagues searched for differences in the polarisation at different energies, but found none to the accuracy limits of the data.
Some theories suggest that the quantum nature of space should manifest itself at the ‘Planck scale’: the minuscule 10-35 of a metre, where a millimetre is 10-3 m.
However, Integral’s observations are about 10 000 times more accurate than any previous and show that any quantum graininess must be at a level of 10-48 m or smaller.
“This is a very important result in fundamental physics and will rule out some string theories and quantum loop gravity theories,” says Dr Laurent.
One of the experimental tests of Lorentz invariance violation is to measure the helicity dependence of the propagation velocity of photons originating in distant cosmological obejcts. Using a recent determination of the distance of the Gamma-Ray Burst GRB 041219A, for which a high degree of polarization is observed in the prompt emission, we are able to improve by 4 orders of magnitude the existing constraint on Lorentz invariance violation, arising from the phenomenon of vacuum birefringence.
Using a recent determination of the distance of GRB041219A for which a high degree of polarization is observed, we were able to increase by 4 orders of magnitude the existing constraint on Lorentz invariance violations, arising from birefringence. Turned into a constraint on the coupling of dimension 5 Lorentz violating interactions, that is of corrections of order [formula] to the dispersion relations, this gives the very stringent constraint less than 10^-14. Most presumably, this means that such operators are vanishing, which might point towards a symmetry such as supersymmetry in action. In that case, the pressure is on the next corrections of order [formula] corresponding to operators of dimension 6. We showed that, although astrophysical constraints are not yet really constraining, they are getting closer to the relevant regime ( of order 1 or smaller). Our result can be compared to the limits derived using the possible energy dependence of the group velocity of photons in distant GRBs derived with Fermi. However, written in the same way as we did in this work, this limit was less than 0.8 that is much less constraining.
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