Michael N. Schmitt (Naval War College - International Law Department; University of Exeter Law School) has posted
The Syrian Intervention: Assessing the Possible International Law Justifications (89 International Law Studies 744 (2013)) on SSRN. Here is the abstract:
This article examine the various legal justifications that might be offered to justify a US strike against Syria in response to its use of chemical weapons. They include Security Council authorization, self-defense, collective defense, assistance to the "new" government, maintaining accountability for a violation of the prohibition on using chemical weapons, and humanitarian intervention. It suggest that only the last provides a colorable basis for attacking Syria.