Review of Systematic Investigations of the Rout/Rside ratio in HBT at RHIC

We review the significant difference in the ratio R{sub out}/R{sub side} between experiment and theory in heavy-ion collisions at RHIC. This ratio is expected to be strongly correlated with the pion emission duration. Hydrodynamic models typically calculate a value that approximately equal to 1.5 and moderately dependent on k{sub T} whereas the experiments report a value close to unity and independent of k{sub T}. We review those calculations in which systematic variations in the theoretical assumptions were reported. We find that the scenario of second order phase transition or cross-over has been given insufficient attention, and may play an important role in resolving this discrepancy