Abstract
We investigate the effect of external magnetic fields on equilibration in the improved holographic QCD theory in the deconfined phase using the AdS/CFT correspondence. In particular we calculate the quasinormal mode spectra in the corresponding black brane solutions and study their dependence on temperature, momentum and magnetic field, both in the scalar and the shear channels. We find complex patterns in the motion of quasinormal modes on the complex plane, including certain cross overs between the lowest lying modes under varying magnetic field, momentum and temperature. We also discover a critical value of the magnetic field Bc above which the hydrodynamic approximation breaks down, as the imaginary part of the first excited quasi-normal mode in the shear channel becomes smaller than that of the hydro mode.
Highlights
Introduction and summaryQuantum Chromodynamics exhibits a host of interesting phenomena when put under a strong external magnetic field B
The latter paper does not report any quasinormal mode (QNM) of this type in magnetically charged black brane solutions [51] whereas we find an example of such modes here
In the subsection we investigate temperature, magnetic field and momentum dependence of the shear channel QNM spectrum
Summary
Quantum Chromodynamics exhibits a host of interesting phenomena when put under a strong external magnetic field B. As one observes, this crossing happens between the hydro mode and the second excited quasi-normal mode in the shear channel, signalling a breakdown of hydrodynamics beyond a certain value of momentum (that depends on T and B) This phenomenon was observed in [52,53,54] and recently in [31,32,33] in the context of holographic QCD and [55,56] for holographic superfluids. We observe that the hydrodynamic mode in the shear channel is overtaken by the first excited quasi-normal mode above a certain value of B, that depends on the values of T and k This is breakdown of hydro approximation beyond a critical magnetic field B. This turned out to be due to an error in our code that we fixed in this version and we do not find any perturbative instability in the system
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