Tunneling across dilaton-axion black holes

In this work we study both charged and uncharged particles tunneling across the horizon of spherically symmetric dilaton-axion black holes using Parikh-Wilczek tunneling formalism. Such black hole solutions have much significance in string theory based models. For different choices of the dilaton and axion couplings with the electromagnetic field, we show that the tunneling probability depends on the difference between initial and final entropies of the black hole. Our results, which agree with similar results obtained for other classes of black holes, further confirm the usefulness of Parikh-Wilczek formalism to understand Hawking radiation. The emission spectrum is shown to agree with a purely thermal spectrum only in the leading order. The modification of the proportionality factor in the area-entropy relation in the Bekenstein-Hawking formula has been determined.