The overdamped chiral magnetic wave

Abstract

About eight years ago it was predicted theoretically that a charged chiral plasma could support the propagation of the so-called chiral magnetic waves, which are driven by the anomalous chiral magnetic and chiral separation effects. This prompted intensive experimental efforts in search of signatures of such waves in relativistic heavy-ion collisions. In fact, several experiments have already reported a tentative detection of the predicted signal, albeit with a significant background contribution. Here, we critically reanalyze the theoretical foundations for the existence of the chiral magnetic waves. We find that the commonly used background-field approximation is not sufficient for treating the waves in hot chiral plasmas in the long-wavelength limit. Indeed, the back-reaction from dynamically induced electromagnetic fields turns the chiral magnetic wave into a diffusive mode. While the situation is slightly better in the strongly-coupled near-critical regime of quark-gluon plasma created in heavy-ion collisions, the chiral magnetic wave is still strongly overdamped due to the effects of electrical conductivity and charge diffusion. XIII Quark Confinement and the Hadron

Gapped momentum states

“…Important studies related to the possible manifestation and detection of the dispersion relation in (95) in Quark Gluon Plasma have been recently performed in Ref. [120].…”

Experimental searches for the chiral magnetic effect in heavy-ion collisions

“…These would be good tests of this background mechanism An anomalous transport model calculation suggests that including the Lorentz Force on quarks and antiquarks could even flip the sign of the elliptic flow difference between positively and negatively charged pions [184,185]. It was pointed out [186] that the propagation of the long-wavelength CMW could be badly interrupted by high electrical conductivity in dynamically induced electromagnetic fields and become a diffusive one. Even at small electrical conductivity, the CMW is still strongly over-damped due to the effects of electrical conductivity and charge diffusion.…”

Chiral sound waves in strained Weyl semimetals

“…Based on the same physics that gives rise to the chiral magnetic wave [25], but driven by axial elastic gauge fields, we have found a unidirectional chiral sound wave (CSW) which propagates longer and dissipates slower than the chiral magnetic wave making better prospects for its experimental detection. The key difference is that our CSW does not hybridize with plasmons to linear order in the derivative expansion and avoids the over-damping predicted in [26]. Instead, it does hybridize with standard acoustic phonons, what provides the way to its experimental detection.…”

“…More recently, the gravitational [18,19], conformal [20][21][22][23] and torsional [24] anomalies have also been incorporated to the play. Directly related to the chiral anomaly there is a prediction in the physics of the quark-gluon plasma, of the existence of a collective excitation called chiral magnetic wave [25] which have eluded experimental detection so far due to its strong hybridization with the plasmons [26]. The CMW is a collective, gapless excitation of the electronic fluid which corresponds to a coherent propagation of electric and chiral density waves coupled together by the chiral magnetic effect.…”

“…Hence, our wave does not couple to the electromagnetic fields at linear order and does not mix with the quickly dissipating plasmon modes. The CSW propagates longer and dissipates slower than the chiral magnetic wave [26].…”