I'm looking for some scientific papers to get a better grasp of synthetic options mainly the valuation, eventual time decay etc.. I've looked in my university library and only but I only found obscure references.
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As mentioned in the comments, you will most likely not find much literature on simple synthetic positions such as the synthetic long stock. This is simply a way to obtain a highly leveraged version of the same risk profile as a long stock position - hence, analyzing the risk profile is redundant. However, there are a few papers on taking more advanced synthetic positions to replicate complicated options structures. See for example:
Tilley, James A., and Gary D. Latainer. "A Synthetic Option Framework for Asset Allocation." Financial Analysts Journal 41, no. 3 (1985): 32-43. http://www.jstor.org/stable/4478840.
Valuation is is in general completely trivial, since the value of a synthetic position is simply the sum of the values of its components.