Credit spreads

I'm currently working on my dissertation on the credit spread puzzle. Basically, there is a wide gap between corporate bond yields and expected default losses, which imply that default risks can only explain a small proportion of the spread. This is commonly known as the credit spread puzzle.

Well, I've been reading several recent research papers to summarize what the answers to this puzzle could be. This isn't the difficult part, what is difficult is being able to criticize the papers, undermine their models and justify my arguments. In a theoretical dissertation, we're supposed to select 8-12 journal articles and present them. Firstly, these articles have a certain level of technical sophistication, and I am unable to completely comprehend the modelling details. How am I going to succinctly criticize the models or suggest ways to improve them? Secondly, my knowledge on credit risk is probably close to nothing, and it'll take a huge effort to produce something outstanding (yeah, I know I should have started a few months back). And lastly, I have only a week left to finish it...

Anyway, in case you're interested in this area, which is still a major current research theme, I can provide you with a good reference list that I've been collecting for some time. A good paper to look at is Hull, Predescu and White (2004), where they mention the possible answers as tax and liqudity factors, risk premium, traders' expectations, nondiversifiable risks and diversifiable risks.