Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram
© 2020 authors. Published by the American Physical Society. Upcoming experimental programs, including the Beam Energy Scan at RHIC, will look for signatures of a possible critical point in the QCD phase diagram in fluctuation observables. To understand and predict these signatures, one must account...
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| Format: | Article |
| Language: | English |
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American Physical Society (APS)
2022
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| Online Access: | https://hdl.handle.net/1721.1/142199 |
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| author | Rajagopal, Krishna Ridgway, Gregory W Weller, Ryan Yin, Yi |
| author2 | Massachusetts Institute of Technology. Center for Theoretical Physics |
| author_facet | Massachusetts Institute of Technology. Center for Theoretical Physics Rajagopal, Krishna Ridgway, Gregory W Weller, Ryan Yin, Yi |
| author_sort | Rajagopal, Krishna |
| collection | MIT |
| description | © 2020 authors. Published by the American Physical Society. Upcoming experimental programs, including the Beam Energy Scan at RHIC, will look for signatures of a possible critical point in the QCD phase diagram in fluctuation observables. To understand and predict these signatures, one must account for the fact that the dynamics of any critical fluctuations must be out-of-equilibrium: because of critical slowing down, the fluctuations cannot stay in equilibrium as the droplet of quark gluon plasma produced in a collision expands and cools. Furthermore, their out-of-equilibrium dynamics must also influence the hydrodynamic evolution of the cooling droplet. The recently developed Hydro+ formalism allows for a consistent description of both the hydrodynamics and the out-of-equilibrium fluctuations, including the feedback between them. We shall provide an explicit demonstration of how this works, setting up a Hydro+ simulation in a simplified setting: a rapidity-independent fireball undergoing radial flow with an equation of state in which we imagine a critical point close to the μB=0 axis of the phase diagram. Within this setup, we show that we can quantitatively capture nonequilibrium phenomena, including critical fluctuations over a range of scales and memory effects. Furthermore, we illustrate the interplay between the dynamics of the fluctuations and the hydrodynamic flow of the fireball: as the fluid cools and flows, the dynamical fluctuations lag relative to how they would evolve if they stayed in equilibrium; there is then a backreaction on the flow itself due to the out-of-equilibrium fluctuations; and, in addition, the radial flow transports fluctuations outwards by advection. Within our model, we find that the backreaction from the out-of-equilibrium fluctuations does not yield dramatically large effects in the hydrodynamic variables. Further work will be needed in order to check this quantitative conclusion in other settings but, if it persists, this will considerably simplify future modeling. |
| first_indexed | 2024-09-23T12:40:10Z |
| format | Article |
| id | mit-1721.1/142199 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T12:40:10Z |
| publishDate | 2022 |
| publisher | American Physical Society (APS) |
| record_format | dspace |
| spelling | mit-1721.1/1421992023-07-19T16:19:33Z Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram Rajagopal, Krishna Ridgway, Gregory W Weller, Ryan Yin, Yi Massachusetts Institute of Technology. Center for Theoretical Physics Massachusetts Institute of Technology. Department of Physics © 2020 authors. Published by the American Physical Society. Upcoming experimental programs, including the Beam Energy Scan at RHIC, will look for signatures of a possible critical point in the QCD phase diagram in fluctuation observables. To understand and predict these signatures, one must account for the fact that the dynamics of any critical fluctuations must be out-of-equilibrium: because of critical slowing down, the fluctuations cannot stay in equilibrium as the droplet of quark gluon plasma produced in a collision expands and cools. Furthermore, their out-of-equilibrium dynamics must also influence the hydrodynamic evolution of the cooling droplet. The recently developed Hydro+ formalism allows for a consistent description of both the hydrodynamics and the out-of-equilibrium fluctuations, including the feedback between them. We shall provide an explicit demonstration of how this works, setting up a Hydro+ simulation in a simplified setting: a rapidity-independent fireball undergoing radial flow with an equation of state in which we imagine a critical point close to the μB=0 axis of the phase diagram. Within this setup, we show that we can quantitatively capture nonequilibrium phenomena, including critical fluctuations over a range of scales and memory effects. Furthermore, we illustrate the interplay between the dynamics of the fluctuations and the hydrodynamic flow of the fireball: as the fluid cools and flows, the dynamical fluctuations lag relative to how they would evolve if they stayed in equilibrium; there is then a backreaction on the flow itself due to the out-of-equilibrium fluctuations; and, in addition, the radial flow transports fluctuations outwards by advection. Within our model, we find that the backreaction from the out-of-equilibrium fluctuations does not yield dramatically large effects in the hydrodynamic variables. Further work will be needed in order to check this quantitative conclusion in other settings but, if it persists, this will considerably simplify future modeling. 2022-04-29T15:48:29Z 2022-04-29T15:48:29Z 2020 2022-04-29T15:40:21Z Article http://purl.org/eprint/type/JournalArticle https://hdl.handle.net/1721.1/142199 Rajagopal, Krishna, Ridgway, Gregory W, Weller, Ryan and Yin, Yi. 2020. "Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram." Physical Review D, 102 (9). en 10.1103/PHYSREVD.102.094025 Physical Review D Attribution-NonCommercial-ShareAlike 4.0 https://creativecommons.org/licenses/by/4.0 application/pdf American Physical Society (APS) APS |
| spellingShingle | Rajagopal, Krishna Ridgway, Gregory W Weller, Ryan Yin, Yi Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title | Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title_full | Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title_fullStr | Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title_full_unstemmed | Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title_short | Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram |
| title_sort | understanding the out of equilibrium dynamics near a critical point in the qcd phase diagram |
| url | https://hdl.handle.net/1721.1/142199 |
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