Investigating quark-gluon plasma (QGP) is not trivial. Even finding out how hot it is presents difficulties. The yield of photons from the early formation stages of the plasma is a good “thermometer” for the QGP, and several detailed measurements have been made by collaborations at Brookhaven National Laboratory and the Large Hadron Collider. However, a precise theoretical understanding of the physical mechanisms driving this photon production is still lacking.
Now, in a paper published in Physical Review Letters, Gökçe Başar and colleagues at Stony Brook University, New York, and collaborators propose a mechanism for photon production in QGPs based on a well-known feature of QCD: the conformal anomaly. As a classical system, QCD possesses a special symmetry (conformal invariance) that is broken by quantum effects. Başar et al. show that the anomalous breaking of this symmetry in the presence of strong magnetic fields, such as the ones present in the QGP, can lead to a novel mechanism for photon production. They also show that an estimate of the photons produced through this mechanism corresponds to known experimental signals. However, further detailed analysis is needed to firmly understand the role of the proposed mechanism in the context of the QGP, and such results are eagerly awaited. – Abhishek Agarwal