Speaker
Description
Despite the success of hydrodynamic models in describing heavy-ion collisions, there have long been questions about its regime of validity. Recently-derived conditions on the causality of the hydrodynamic equations [1] can give a concrete answer --- if evolution is acausal, it is not a faithful representation of the underlying QCD theory. It is now known that current simulation models reach acausal regimes, at least sometimes.
We study the phenomenological effects of this knowledge in the context of a comprehensive, multi-system model-to-data comparison that was originally performed by the JETSCAPE Collaboration [2]. Different ways are explored to include information about causality violation (and therefore the validity of the model) into the analysis, and its effects on the extracted physical properties. Specifically, when performing Bayesian inference we can include the information in the prior probability (quantifying our trust in the model based on the degree or frequency of causality violation), or in the model uncertainty (estimating an increased uncertainty when there is violation of causality). The resulting changes in the posterior give an indication of the uncertainty that is contributed by model (in)validity, and the importance of addressing these fundamental issues in our treatment of heavy-ion collisions.
As an additional study, we identify various causes of acausality in hydrodynamic simulations, and therefore the best targets for designing more realistic models.
References:
[1] Bemfica, Disconzi, Hoang, Noronha, Radosz, Phys.Rev.Lett. 126 (2021) 22, 222301
[2] JETSCAPE Collaboration, Phys.Rev.C 103 (2021) 5, 054904; Phys.Rev.Lett. 126 (2021) 24, 242301
| Category | Theory |
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