Resumen de Hawking radiation in NS5 and little string theory
Oscar Lorente Espin
In this thesis we have focused on semi-classical methods that enables us to obtain non-thermal spectra for the vast majority of black holes. This fact is due to taking into account the backreaction of the metric, when the black hole emits, imposing energy conservation. Specifically we have studied NS5 and Little String Theory (LST) black holes. We have calculated the Hawking radiation for both models, obtaining a non-thermal spectrum for NS5, whereas a purely thermal spectrum for LST. This last fact is due to the peculiar behavior of LST, whose temperature is independent of its mass. After a brief outline in Chapter 1 about properties of black holes, where we have introduced the information loss paradox, we have reviewed in the Chapter 2 how curved space-times, e.g. black hole backgrounds, create particles. Hawking demonstrated that black holes has temperature thus emit thermal radiation, and calculated its flux without taking into account the back-reaction of the metric. Afterwards we have presented two semi-classical methods, i.e. the tunneling approach and the complex path method, that somehow solve the information loss paradox stated by the work of Hawking. In Chapter 3 we have applied both semi-classical methods plus the covariant anomaly method in NS5 and Little String Theory (LST) black holes. We have calculated some thermodynamical quantities as the temperature and the entropy; furthermore, after reducing the ten-dimensional theory to a two-dimensional effective theory, we have calculated the emission rate and the corresponding fluxes taking into account the back-reaction of the metric. In Chapter 4 we have calculated the emission of fermions by NS5 and LST obtaining identical results as for scalar particles. In Chapter 5 we have presented a novel method in order to introduce quantum perturbations directly in the black hole metric, that accounts for back-reaction effects. This method has been applied in a general stationary spherically symmetric metric, recovering similar results as in the semi-classical methods presented in the previous chapters. Moreover, when we have applied this method in LST black hole we have obtained similar results as in string one-loop theory. Finally, in Chapter 6 we have calculated and compared some thermodynamical quantities as the entropy, using both Einstein frame and conformal frame.
