Action functional for kappa-Minkowski Noncommutative Spacetime
We examine some alternative possibilities for an action functional for $κ$-Minkowski noncommutative spacetime, with an approach which should be applicable to other spacetimes with coordinate-dependent commutators of the spacetime coordinates ($[x_μ,x_ν]=f_{μ,ν}(x)$). Early works on $κ$-Minkowski focused on $κ$-Poincaré covariance and the dependence of the action functional on the choice of Weyl map, renouncing to invariance under cyclic permutations of the factors composing the argument of the action functional. A recent paper (hep-th/0307149), by Dimitrijevic, Jonke, Moller, Tsouchnika, Wess and Wohlgenannt, focused on a specific choice of Weyl map and, setting aside the issue of $κ$-Poincaré covariance of the action functional, introduced in implicit form a cyclicity-inducing measure. We provide an explicit formula for (and derivation of) a choice of measure which indeed ensures cyclicity of the action functional, and we show that the same choice of measure is applicable to all the most used choices of Weyl map. We find that this ``cyclicity-inducing measure'' is not covariant under $κ$-Poincaré transformations. We also notice that the cyclicity-inducing measure can be straightforwardly derived using a map which connects the $κ$-Minkowski spacetime coordinates and the spacetime coordinates of a ``canonical'' noncommutative spacetime, with coordinate-independent commutators.