Generalizing the Noether Theorem for Hopf-Algebra Spacetime Symmetries

Over these past few years several quantum-gravity research groups have been exploring the possibility that in some Planck-scale nonclassical descriptions of spacetime one or another form of nonclassical spacetime symmetries might arise. One of the most studied scenarios is based on the use of Hopf algebras, but previous attempts were not successful in deriving constructively the properties of the conserved charges one would like to obtain from the Hopf structure, and this in turn did not allow a crisp physical characterization of the new concept of spacetime symmetry. Working within the example of κ-Minkowski noncommutative spacetime, known to be particularly troublesome from this perspective, we observe that these past failures in the search of the charges originated from not recognizing the crucial role that the noncommutative transformation parameters play in the symmetry analysis. We show that, if indeed one introduces appropriate noncommutative transformation parameters, all the steps of the Noether analysis can be easily performed, obtaining an explicit formula for the charges carried by fields that are solutions of the equation of motion.