RUI: Dissipative Dynamics of the Quark Gluon Plasma

理解宇宙为什么是现在的样子，关键取决于我们对从时间开始到现在发生的各种相变的理解。这个链中的一个关键相变被称为夸克胶子等离子体(QGP)相变。这种相变的不同之处在于，它是唯一一种可以使用当前一代粒子加速器在实验上实现的相变。在布鲁克海文国家实验室的相对论重离子对撞机(RHIC)上已经进行的实验已经达到了触发夸克-胶子等离子体出现所需的温度；然而，产生的温度仅略高于2万亿摄氏度的相变温度。最近在大型强子对撞机(LHC)和欧洲核子研究中心(CERN)进行的更高碰撞能量下进行的实验已经产生了温度接近向等离子体相转变的临界温度的四倍的状态。QGP-物理理论工作的很大一部分致力于描述使用粘性流体动力学模型产生的物质的热化和随后的演化。这些模型在描述RHIC重离子碰撞期间产生的物质的集体流动方面取得了显着的成功。在这次事件中产生的粒子椭圆流的数据似乎与具有小剪切粘度的物质相容，该物质的剪切粘度接近“完美流体”的极限。然而，在粘性流体动力学模型的应用中仍然存在关键的不确定性，这可能会影响即将在大型强子对撞机(LHC)上进行的实验。主要的不确定性之一集中在何时是开始对碰撞中产生的物质进行粘性流体动力学描述的合适时间的问题上。传统的粘性流体力学处理依赖于一个隐含的假设，即系统在动量空间中非常接近热平衡和各向同性。在实践中，偏离热各向同性状态的演化可用粘性流体动力学演化来描述。然而，由于存在巨大的动量空间各向异性，这样的描述可能在碰撞后的最早时间就被打破。在这项工作中，我将推广和发展一种新的方法来推导夸克胶子等离子体演化的动力学方程，它放松了流体动力学描述中隐含的一个假设，即系统在动量空间中接近各向同性的假设。新方法重新组织了单粒子分布函数在由时空椭圆和各向异性温度描述的各向异性状态周围的展开式。得到的耦合偏微分方程组可以用来描述夸克胶子等离子体整个历史过程中系统的演化。所资助的研究应该会对我们理解极端相对论系统的非平衡动力学产生重大影响。还有一个最重要的教育目标是让本科生物理专业的学生参与一个积极的研究项目。该提议包括两名本科生研究助理，他们将接受分析和数值方法方面的培训。这种培训对美国科学项目未来的成功以及吸引有才华的学生投身科学事业至关重要。

An understanding of why the universe is the way it is right now depends critically on our understanding of the various phase transitions that have occurred since the beginning of time until now. A key phase transition in this chain is called the quark gluon plasma (QGP) phase transition. This phase transition has the distinction of being the only one that is experimentally accessible using the current generation of particle accelerators. Experiments already performed at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab have reached the temperature necessary to trigger the emergence of a quark-gluon plasma; however, the temperatures generated were only slightly higher than the phase transition temperature of 2 trillion degrees K. Experiments recently carried out at higher collision energies at the Large Hadron Collider (LHC) and CERN have generated states with temperatures approaching four times the critical temperature for the transition to the plasma phase. A large part of the QGP-physics theoretical effort is dedicated to describing the thermalization and subsequent evolution of the matter produced using viscous hydrodynamical models. The success of these models to describe the collective flow of the matter created during heavy ion collisions at RHIC is remarkable. It seems that the data for the elliptic flow of the particles created during the event is compatible with the matter having a small shear viscosity approaching the limit of a "perfect fluid." However, key uncertainties still remain in the application of viscous hydrodynamical models that may impact upcoming experiments at the Large Hadron Collider (LHC). One of the primary uncertainties centers on the question of when is the appropriate time to begin a viscous hydrodynamical description of the matter that is created in the collision. Traditional viscous hydrodynamical treatments rely on an implicit assumption that the system is very close to thermal equilibrium and isotropy in momentum space. In practice, the evolution of the deviations from a thermal isotropic state is described by viscous hydrodynamical evolution. However, such descriptions can break down at the earliest times after the collision due to the presence of large momentum-space anisotropies. In this work I will extend and develop a new method for deriving dynamical equations for the evolution of the quark gluon plasma which relaxes one of the assumptions implicit in hydrodynamical descriptions, namely the assumption that the system is nearly isotropic in momentum space. The new method reorganizes the expansion of the one particle distribution function around an anisotropic state described by space-time dependent ellipticities and an anisotropic temperature. The resulting coupled partial differential equations can be used to describe the evolution of the system during the entire history of the quark gluon plasma. The research funded should have a significant impact on our understanding the non-equilibrium dynamics of ultrarelativistic systems. There is also an overarching educational goal to involve undergraduate physics majors in an active research program. The proposal involves the inclusion of two undergraduate research assistants who will receive training in analytic and numerical methods. This kind of training is crucial to the future success of the United States scientific programs and to attracting talented students to scientific careers.