Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram
Abstract
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:more »
- Publication Date:
- Research Org.:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF)
- OSTI Identifier:
- 1756459
- Alternate Identifier(s):
- OSTI ID: 1851464
- Grant/Contract Number:
- SC0011090
- Resource Type:
- Published Article
- Journal Name:
- Physical Review D
- Additional Journal Information:
- Journal Name: Physical Review D Journal Volume: 102 Journal Issue: 9; Journal ID: ISSN 2470-0010
- Publisher:
- American Physical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 79 ASTRONOMY AND ASTROPHYSICS; Astronomy & Astrophysics; Physics; critical phenomena; phase transitions; hydrodynamic models; QCD phase transitions; relativistic heavy-ion collisions; hydrodynamics; relativistic hydrodynamics
Citation Formats
Rajagopal, Krishna, Ridgway, Gregory W., Weller, Ryan, and Yin, Yi. Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram. United States: N. p., 2020.
Web. doi:10.1103/PhysRevD.102.094025.
Rajagopal, Krishna, Ridgway, Gregory W., Weller, Ryan, & Yin, Yi. Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram. United States. https://doi.org/10.1103/PhysRevD.102.094025
Rajagopal, Krishna, Ridgway, Gregory W., Weller, Ryan, and Yin, Yi. Mon .
"Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram". United States. https://doi.org/10.1103/PhysRevD.102.094025.
@article{osti_1756459,
title = {Understanding the out-of-equilibrium dynamics near a critical point in the QCD phase diagram},
author = {Rajagopal, Krishna and Ridgway, Gregory W. and Weller, Ryan and Yin, Yi},
abstractNote = {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.},
doi = {10.1103/PhysRevD.102.094025},
journal = {Physical Review D},
number = 9,
volume = 102,
place = {United States},
year = {Mon Nov 30 00:00:00 EST 2020},
month = {Mon Nov 30 00:00:00 EST 2020}
}
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https://doi.org/10.1103/PhysRevD.102.094025
https://doi.org/10.1103/PhysRevD.102.094025
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