Interferometry for rotating sources

Ong

2017

Peripheral collisions of heavy ions can give rise to extremely intense magnetic fields. It has been suggested that these fields might invalidate the holographic description of the corresponding quark-gluon plasmas, assuming that these can be modelled by strongly coupled field theories. In the case of the plasmas produced in collisions at the RHIC facility (including in the beam energy scans), it is known how to deal with this problem: one has to take into account the large angular momenta generated in these plasmas, and the effects of the baryonic chemical potential. But this does not work for the plasmas produced in peripheral collisions at the LHC. However, these results neglect some (less significant) aspects of bulk physics; could it be that the problem is resolved by taking into account these lower-order effects? Here we use a bulk dilatonic field (fully compatible with boundary data, as well as with the asymptotically AdS character of the bulk geometry) as a model of these effects, and show that this is unlikely to be the solution. Thus, the existence of a consistent holographic description of the most extreme LHC plasmas remains open to question.

Section: The Quark-gluon Plasma In the Lhcmentioning

confidence: 99%

On the existence of a holographic description of the LHC quark–gluon plasmas

Ong

2017

“…On the other hand, it has recently become clear that local rotation might also be important in these systems, and this might manifest itself in the form of such phenomena as the "chiral vortical effect": see [15] for a review. Now the large magnetic fields in the QGP mentioned above are in fact closely associated with very large angular momentum densities [16][17][18][19][20][21][22][23][24]; see [25,26] for recent in-depth analyses. The angular momentum arises in the same way as the magnetic field, and the corresponding vectors are (to a good approximation) parallel [26] (that is, perpendicular to the reaction plane).…”

Section: Rotation/magnetism and The Quark-gluon Plasmamentioning

confidence: 99%

“…It turns out, very 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][21][22][23][24][25], or as a shearing motion [16][17][18]26]. (The two are not mutually exclusive, and in fact in a real plasma the two forms would coexist, but for clarity we treat them separately.)…”

Section: Rotation/magnetism and The Quark-gluon Plasmamentioning

confidence: 99%

A rotation/magnetism analogy for the quark–gluon plasma

2016

In peripheral heavy ion collisions, the Quark-Gluon Plasma that may be formed often has a large angular momentum per unit energy. This angular momentum may take the form of (local) rotation. In many physical systems, rotation can have effects analogous to those produced by a magnetic field; thus, there is a risk that the effects of local rotation in the QGP might be mistaken for those of the large genuine magnetic fields which are also known to arise in these systems. Here we use the gauge-gravity duality to investigate this, and we find indeed that, with realistic parameter values, local rotation has effects on the QGP (at high values of the baryonic chemical potential) which are not only of the same kind as those produced by magnetic fields, but which can in fact be substantially larger. Furthermore, the combined effect of rotation and magnetism is to change the shape of the main quark matter phase transition line in an interesting way, reducing the magnitude of its curvature; again, local rotation contributes to this phenomenon at least as strongly as magnetism.

“…It has in fact long been known that, precisely in the case of peripheral collisions, a very large amount of angular momentum is transferred to the plasma [37][38][39][40][41][42][43][44][45][46][47][48]; this arises from exactly the same circumstances that give rise to the magnetic field, and the two effects are inseparable. From the field theory point of view, it is not obvious why this is relevant.…”

Section: The Qgp At the Rhic And In The Beam Energy Scansmentioning

confidence: 99%

“…There are essentially two ways [40] in which angular momentum can be transferred to the QGP in a peripheral collision: as vorticity [41][42][43][44][45][46]48], or as shear [37][38][39]47]. We begin with an exploration, using the gauge-gravity duality, of the consequences of including the latter.…”

Section: Fixing the Parameters: Theorymentioning

confidence: 99%

Field theories without a holographic dual

2016

In applying the gauge-gravity duality to the quark-gluon plasma, one models the plasma using a particular kind of field theory with specified values of the temperature, magnetic field, and so forth. One then assumes that the bulk, an asymptotically AdS black hole spacetime with properties chosen to match those of the boundary field theory, can be embedded in string theory. But this is not always the case: there are field theories with no bulk dual. The question is whether these theories might include those used to study the actual plasmas produced at such facilities as the RHIC experiment or the relevant experiments at the LHC. We argue that, provided that due care is taken to include the effects of the angular momentum associated with the magnetic fields experienced by the plasmas produced by peripheral collisions, the existence of the dual can be established for the RHIC plasmas. In the case of the LHC plasmas, the situation is much more doubtful.