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Item Chiral hydrodynamics in strong external magnetic fields(2021) Ammon, Martin; Grieninger, Sebastian; Hernandez, Juan; Kaminski, Matthias; Koirala, Roshan; Leiber, Julian; Wu, Jackson; University of Alabama TuscaloosaShow more We construct the general hydrodynamic description of (3+1)-dimensional chiral charged (quantum) fluids subject to a strong external magnetic field with effective field theory methods. We determine the constitutive equations for the energy-momentum tensor and the axial charge current, in part from a generating functional. Furthermore, we derive the Kubo formulas which relate two-point functions of the energy-momentum tensor and charge current to 27 transport coefficients: 8 independent thermodynamic, 4 independent non-dissipative hydrodynamic, and 10 independent dissipative hydrodynamic transport coefficients. Five Onsager relations render 5 more transport coefficients dependent. We uncover four novel transport effects, which are encoded in what we call the shear-induced conductivity, the two expansion-induced longitudinal conductivities and the shear-induced Hall conductivity. Remarkably, the shear-induced Hall conductivity constitutes a novel non-dissipative transport effect. As a demonstration, we compute all transport coefficients explicitly in a strongly coupled quantum fluid via holography.Show more Item Quantum quenches in a holographic Kondo model(2017) Erdmenger, Johanna; Flory, Mario; Newrzella, Max-Niklas; Strydom, Migael; Wu, Jackson; University of Alabama TuscaloosaShow more We study non-equilibrium dynamics and quantum quenches in a recent gauge/gravity duality model for a strongly coupled system interacting with a magnetic impurity with SU(\(N\)) spin. At large N, it is convenient to write the impurity spin as a bilinear in Abrikosov fermions. The model describes an RG flow triggered by the marginally relevant Kondo operator. There is a phase transition at a critical temperature, below which an operator condenses which involves both an electron and an Abrikosov fermion field. This corresponds to a holographic superconductor in AdS 2 and models the impurity screening. We quench the Kondo coupling either by a Gaussian pulse or by a hyperbolic tangent, the latter taking the system from the condensed to the uncondensed phase or vice-versa. We study the time dependence of the condensate induced by this quench. The timescale for equilibration is generically given by the leading quasinormal mode of the dual gravity model. This mode also governs the formation of the screening cloud, which is obtained as the decrease of impurity degrees of freedom with time. In the condensed phase, the leading quasinormal mode is imaginary and the relaxation of the condensate is over-damped. For quenches whose final state is close to the critical point of the large N phase transition, we study the critical slowing down and obtain the combination of critical exponents zν = 1. When the final state is exactly at the phase transition, we find that the exponential ringing of the quasinormal modes is replaced by a power-law behaviour of the form ∼ t − a sin( b log t ). This indicates the emergence of a discrete scale invariance.Show more Item Quasinormal modes of charged magnetic black branes & chiral magnetic transport(2017) Ammon, Martin; Kaminski, Matthias; Koirala, Roshan; Leiber, Julian; Wu, Jackson; University of Alabama TuscaloosaShow more We compute quasinormal modes (QNMs) of the metric and gauge field perturbations about black branes electrically and magnetically charged in the Einstein-Maxwell-Chern-Simons theory. By the gauge/gravity correspondence, this theory is dual to a particular class of field theories with a chiral anomaly, in a thermal charged plasma state subjected to a constant external magnetic field, B. The QNMs are dual to the poles of the two-point functions of the energy-momentum and axial current operators, and they encode information about the dissipation and transport of charges in the plasma. Complementary to the gravity calculation, we work out the hydrodynamic description of the dual field theory in the presence of a chiral anomaly, and a constant external B. We find good agreement with the weak field hydrodynamics, which can extend beyond the weak B regime into intermediate regimes. Furthermore, we provide results that can be tested against thermodynamics and hydrodynamics in the strong B regime. We find QNMs exhibiting Landau level behavior, which become long-lived at large B if the anomaly coefficient exceeds a critical magnitude. Chiral transport is analyzed beyond the hydrodynamic approximation for the five (formerly) hydrodynamic modes, including a chiral magnetic wave.Show more Item Quasinormal modes of charged magnetic black branes & chiral magnetic transport(2017) Ammon, Martin; Kaminski, Matthias; Koirala, Roshan; Leiber, Julian; Wu, Jackson; University of Alabama TuscaloosaShow more Item Two-point functions in a holographic Kondo model(2017) Erdmenger, Johanna; Hoyos, Carlos; O’Bannon, Andy; Papadimitriou, Ioannis; Probst, Jonas; Wu, Jackson; University of Alabama TuscaloosaShow more We develop the formalism of holographic renormalization to compute two-point functions in a holographic Kondo model. The model describes a (0 + 1)-dimensional impurity spin of a gauged SU(\(N\)) interacting with a (1 + 1)-dimensional, large- N, strongly-coupled Conformal Field Theory (CFT). We describe the impurity using Abrikosov pseudo-fermions, and define an SU(\(N\))-invariant scalar operator \(O\) built from a pseudo-fermion and a CFT fermion. At large N the Kondo interaction is of the form \(O^{\dagger}O\), which is marginally relevant, and generates a Renormalization Group (RG) flow at the impurity. A second-order mean-field phase transition occurs in which \(O\) condenses below a critical temperature, leading to the Kondo effect, including screening of the impurity. Via holography, the phase transition is dual to holographic superconductivity in (1 + 1)-dimensional Anti-de Sitter space. At all temperatures, spectral functions of \(O\) exhibit a Fano resonance, characteristic of a continuum of states interacting with an isolated resonance. In contrast to Fano resonances observed for example in quantum dots, our continuum and resonance arise from a (0 + 1)-dimensional UV fixed point and RG flow, respectively. In the low-temperature phase, the resonance comes from a pole in the Green's function of the form \(-i\langle O \rangle^2\), which is characteristic of a Kondo resonance.Show more Item Universal magnetoresponse in QCD and N = 4 SYM(2018) Endrődi, Gergely; Kaminski, Matthias; Schäfer, Andreas; Wu, Jackson; Yaffe, Laurence; University of Alabama TuscaloosaShow more Using recent lattice data on the thermodynamics of QCD in the presence of a background magnetic field, we show that the ratio of transverse to longitudinal pressure exhibits, to good accuracy, a simple scaling behavior over a wide range of temperature and magnetic field, essentially depending only on the ratio \(T/\sqrt{B}\). We compare this QCD response to the corresponding magnetoresponse in maximally supersymmetric Yang Mills theory. Given suitable calibrations defining the comparison, we find excellent agreement. This may be viewed as a further test of the applicability of holographic models for hot QCD.Show more