Generalizing the method of Wilczek and collaborators we provide a derivation of Hawking radiation from charged black holes using only covariant gauge and gravitational anomalies. The reliability and universality of the anomaly cancellation approach to Hawking radiation is also discussed.

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From an appropriate expression for the effective action, the Hawking radiation from charged black holes is derived, using only covariant boundary conditions at the event horizon. The connection of our approach with the Unruh vacuum and the recent analysis [1,2,3] of Hawking radiation using anomalies is established. Introduction:Hawking radiation arises upon the quantisation of matter in a background spacetime with an event horizon. It therefore plays an important role in black hole physics. Apart from Hawking's [4] original derivation, there are other approaches [5,6], although none is completely clinching or conclusive. This has led researchers to consider alternative derivations providing new insights into the problem. Here we discuss another approach that is based solely on the structure of the effective action and boundary conditions at the event horizon. We therefore guarantee the universality of Hawking radiation which ought to be determined by properties at the event horizon only-a feature that is usually lacking in approaches based on effective actions [7,8]. To put our work in a proper perspective, however, it is desirable to elaborate on the recent approaches [1, 2, 3] to the Hawking effect which rely on the cancellation of gauge and gravitational anomalies.An anomaly, it might be recalled, is a breakdown of some classical symmetry due to the process of quantisation. For example, a gauge anomaly is an anomaly in gauge symmetry, taking the form of nonconservation of the gauge current. Similarly, a gravitational anomaly occurs from a breaking of general covariance, taking the form of nonconservation of the energy momentum tensor (For reviews see, [9,10]). The simplest manifestation of these (gauge and gravitational) anomalies, which is also relevant for the present discussion, occurs for 1 + 1 dimensional chiral fields.Recently, Robinson and Wilczek [1], followed by Iso, Umetsu and Wilczek [2], gave a new derivation of the Hawking effect. They found that, by the process of dimensional reduction, effective field theories become two dimensional and chiral near the event horiazon of a black hole. This leads to the occurrence of gauge and gravitational anomalies. The Hawking flux is necessary to cancel these anomalies.An essential aspect of [1,2] is that a two dimensional chiral theory admits two types of anomalous currents (and/or energy momentum tensors)-the consistent and the covariant [9,10,11,12,13,14]-which are actually related by local counterterms. The covariant divergence of these currents and energy momentum tensors yields either the consistent or covariant form of the anomaly. Then the Hawking flux was derived in [1, 2] by a cancellation of the consistent anomaly but the boundary condition necessary to fix the parameters was obtained from a vanishing of the covariant current at the horizon [2]. It was also observed [16] that an incorrect result for the charge flux would be obtained if, instead, the vanishing of the consistent current at the horizon was taken as the boundary condition.The approach o...

In any generally covariant theory of gravity, we show the relationship between the linearized asymptotically conserved current and its non-linear completion through the identically conserved current. Our formulation for conserved charges is based on the Lagrangian description, and so completely covariant. By using this result, we give a prescription to define quasi-local conserved charges in any higher derivative gravity. As applications of our approach, we demonstrate the angular momentum invariance along the radial direction of black holes and reproduce more efficiently the linearized potential on the asymptotic AdS space.

We extend our recent work on the quasilocal formulation of conserved charges to a theory of gravity containing a gravitational Chern-Simons term. As an application of our formulation, we compute the off-shell potential and quasilocal conserved charges of some black holes in threedimensional topologically massive gravity. Our formulation for conserved charges reproduces very effectively the well-known expressions on conserved charges and the entropy expression of black holes in the topologically massive gravity. *