Motivated by credit risk modelling, we consider a type of default times whose probability law can have atoms, where standard intensity and density hypotheses in the enlargement of filtrations are not satisfied. We propose a generalized density approach in order to treat such random times in the framework of progressive enlargement of filtrations. We determine the compensator process of the random time and study the martingale and semimartingale processes in the enlarged filtration which are important for the change of probability measures and the evaluation of credit derivatives. The generalized density approach can also be applied to model simultaneous default events in the multi-default setting.
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