Real-time holography: anomalous transport and non-hermitian systems

• Autores: Sergio Morales Tejera
• Directores de la Tesis: Karl Landsteiner (dir. tes.), Oscar Varela Rizo (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2023
• Idioma: inglés
• Número de páginas: 176
• Títulos paralelos:
  • Holografía en tiempo real: Transporte anómalo y sistemas no hermíticos.
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • In this thesis we investigate the real-time evolution of strongly coupled systems using holographic techniques. In particular, we study the anomalous transport in strongly coupled plasmas, such as the quark-gluon plasma, and the dynamics of non-hermitian PT -symmetric systems. First, we study the chiral vortical e ect (CVE) far from equilibrium in a strongly coupled holographic eld theory. Rotation is represented as a perturbation via a gravitomagnetic eld on top of a ve-dimensional charged AdS Vaidya metric. We also introduce a momentum relaxation mechanism through linear scalar eld backgrounds and study the CVE dynamics as a function of charges, temperature and momentum relaxation. We pay special attention to the e ects of the gravitational contribution to the axial anomaly in the CVE of the axial current. The far-from-equilibrium behaviour shows that the CVE builds up with a signi cant time delay compared to the quasi instantaneous equilibration of the background metric. We develop an analytical estimate of this delay and also compute the near-equilibrium quasinormal modes that determine the late time ring down. We then move on to the study of the out-of-equilibrium chiral magnetic e ect (CME). We consider the back-reaction of the magnetic eld on the geometry and monitor the pressure and the chiral magnetic current. Our results show that, in general, at small magnetic elds the pressure builds up faster than the CME current, while at strong magnetic elds the opposite is true. At large magnetic elds we also nd that equilibration is signi cantly delayed due to long-lived oscillations. We also match the parameters of our model to QCD parameters and draw conclusions that may be relevant to the realisation of the chiral magnetic e ect in heavy ion collisions. In particular, we nd an equilibration time of about 0:35 fm/c in the presence of the chiral anomaly for plasma temperatures of the order of T 300 - 400MeV: We also nd in holography that for collider energies like those achieved at RHIC, the lifetime of the magnetic eld is long enough to build up the chiral magnetic current, whereas the lifetime of the magnetic eld at the LHC seems to be too short. The CME is further studied in a generalised setup that includes topological charge dissipation. In holography, this is done by giving the bulk gauge eld a mass. We study the cases where axial charge is initially present in the plasma and where axial charge is initially generated. For small values of the anomalous dimension, the CME response is qualitatively equivalent in both cases. Large values of the anomalous dimension lead to faster dissipation. A parameter scan of the model shows that, like the CME current, the axial charge also oscillates for su ciently large magnetic eld and/or anomaly strength. We re ne the QCD matching and nd that the CME signal at the LHC can be comparable to the signal at RHIC, provided that there is at least three times as much axial charge in the plasma: nLHC 5 = 3nRHIC 5 . Finally, we study the evolution of non-Hermitian PT symmetric holographic eld theories when the couplings are varied with time, with particular emphasis on the question of non-unitary time vs. unitary time evolution. The notion of non-Hermitian PT -symmetric quantum theory has recently been generalised to gauge/gravity duality. We show that a non-unitary time evolution in the dual quantum theory corresponds to a violation of the Null Energy Condition (NEC) in the bulk of the asymptotically AdS spacetime. We nd that varying the non-Hermitian coupling causes the horizon of a bulk AdS black hole to shrink. On the other hand, varying the Hermitian coupling in the presence of a constant non-Hermitian coupling still violates the NEC, but results in a growing horizon. We also show that by introducing a non-Hermitian gauge eld, the time evolution can be made unitary, i.e. the NEC is obeyed in the bulk, and an exactly equivalent purely Hermitian description can be given