夸克-胶子等离子体的旋转与磁性类比：深度探讨与现实参数下的影响

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本文探讨了夸克-胶子等离子体（QGP）在周围重离子碰撞中的一种特性，即其可能携带的角动量。在这些碰撞过程中，形成的QGP每单位能量往往具有相当大的角动量，这可能导致局部区域呈现出旋转性质。这种旋转效应对物理系统的动态行为有类似磁场的作用，因此可能会引发误解，误以为观察到的是真实的强磁场效应。作者Brett McInnes在新加坡国立大学的研究中，利用规范引力对偶（gauge-gravity duality），这是一种理论框架，它将量子场论与引力理论联系起来，尤其是在阿贝尔-雅可比恩-辛格霍夫曼猜想（AdS/CFT correspondence）的背景下。通过这个工具，研究者得以在相对论性引力理论的框架下分析QGP中的旋转效应。文章指出，当QGP处于较高的baryonic chemical potential（巴氏化学势）条件下，局部旋转的影响不仅与磁场产生的效应类型相同，而且可能会产生额外的影响，这些效应可能在没有磁场存在的环境中不明显。这表明，在探索和理解这些高温、高密度状态下的量子色动力学（QCD）现象时，区分旋转与磁场效应的重要性。通过使用规范引力对偶，研究者能够量化并预测这些旋转效应，从而帮助实验物理学家在解析实验数据时避免混淆，并深化对夸克-胶子等离子体内部结构及其相互作用的理解。这项工作对于核物理、高能物理学以及可能的宇宙早期条件下的极端环境研究具有重要意义，因为它揭示了非传统物理机制如何影响基本粒子的行为。本文提供了一个关键的理论基础，用于解读和预测夸克-胶子等离子体中旋转效应的观测结果，以及其潜在的实际应用价值。

176 B. McInnes / Nuclear Physics B 911 (2016) 173–190

black holes with event horizons which (prior to the introduction of angular momentum) have

the local geometry of a sphere, and, second, black holes with event horizons which (prior to the

introduction of angular momentum) have the local geometry of a ﬂat plane.

It turns out, ve

ry remarkably, that this classiﬁcation precisely reﬂects the two basic ways

[19] in which angular momentum is manifested in the QGP in the aftermath of a heavy-ion

collision: as local rotation (vorticity) [20–25], or as a shearing motion [16–18,26]. (The two are

not mutually exclusive, and in fact in a real plasma the tw

o forms would co-exist, but for clarity

we treat them separately.) Here we are concerned with local rotation or vorticity, and one ﬁnds

that this corresponds to the case of asymptotically AdS black holes with topologically spherical

event horizons: that is, to the simplest extension of the asymptotically ﬂat dyonic K

err–Newman

metric to the AdS context. Even this “simplest” generalisation can give rise to surprises, however.

We are interested in studying the temperature of the plasma and its baryonic chemical poten-

tial. The quantity which is holographically dual to the temperature of the QGP is of course the

wking temperature of the bulk black hole, which depends both on its electromagnetic charges

and on its angular momentum. As we will see, the dual of the baryonic chemical potential is also

a certain combination of the char

ges and the angular momentum parameter. In this very general

sense, holography indicates that there must indeed be some kind of analogy between local rota-

tion and a magnetic ﬁeld in the dual plasma. Notice that an observ

ation which is immediate on

one side of the duality is far from it on the other: this is the point of holography.

These considerations allo

w us to formulate the analogy in a concrete way; so we can begin to

answer some basic questions. Does local rotation always change the temperature and chemical

potential in the same direction as does a magnetic ﬁeld—that is, does it always reinforce the

magnetic effect or sometimes tend to counteract it?

Which of the two effects is dominant? Do

local rotation and magnetism modify the shape of the phase transition line, and, if so, how do the

two effects compare?

In f

act, the problem of understanding the behaviour of the temperature and chemical potential

corresponding to a dyonic, topologically spherical AdS black hole is not straightforward: for two

reasons. First, unlike the parameters of an asymptotically ﬂat black hole, the geometric param-

eters of a rotating AdS black hole are not related in an

y simple way to its physical properties.

For example, the mass parameter M is not the physical mass of the black hole (see equations (3)

below). Second, holography does not relate the boundary parameters to the physical parameters

of the black hole in as simple a way as in the non-rotating, non-magnetic case: for e

xample, the

baryonic chemical potential of the boundary theory is not proportional to the electric charge on

the black hole here (see equation (14) below), as it is in the familiar case of the dyonic AdS–

Reissner–Nordström black hole.

In short, the answers to our questions are unclear: the

y can only be settled by means of a de-

tailed investigation, which we propose to carry out here. We stress that the holographic model of

these extremely complex systems may well be severely over-simpliﬁed, so that accurate numer-

ical predictions are not to be e

xpected here. Our emphasis is on more qualitative questions. The

answers to these questions may guide more quantitative investigations of these basic properties

of the QGP.

In fact, in the case of shearing angular momentum, it was found in [54] that unexpected behaviour does occur in some

cases: it can happen that increasing the shearing angular momentum has the opposite effect to that of a large magnetic

ﬁeld (though never enough to counteract the latter entirely—in this sense, shearing angular momentum has a “weaker”

effect than magnetism).

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