On conformal Komar currents in LRS spacetimes

Abstract: For locally rotationally symmetric (LRS) spacetimes, we construct two equivalent forms of the Komar current derived from a conformal Killing vector. One is a kinematic construction and the other is in terms of the matter quantities on the spacetime. The required conservation condition for the current is derived and discussed in various instances, and the implications of the conservation of the current, and in the case of a vanishing current, are analyzed. A relationship between the conservation criterion and the presence of trapped surfaces in the spacetime is found and discussed. We also show that for LRS II metrics with constant metric time component, the current is always conserved. In the presence of a conformal Killing horizon, properties of the current are analyzed and restrictions on, and some implications for the physical spacetime variables, in the vicinity of the horizon, are obtained. Finally, with respect to the conformal Killing horizon, the associated Noether charge is shown to be proportional to the surface gravity, establishing the thermodynamic interpretation of the Noether charge.