Holographic estimate of heavy quark diffusion in a magnetic field

We study the influence of a background magnetic field on the $J/\psi$ vector meson in a DBI-extension of the soft wall model, building upon our earlier work Phys. Rev. D91, 086002 (2015). In this specific holographic QCD model, we discuss the heavy quark number susceptibility and diffusion constants of charm quarks and their dependence on the magnetic field by either a hydrodynamic expansion or by numerically solving the differential equation. This allows us to determine the response of these transport coefficients to the magnetic field. The effects of the latter are considered both from a direct as indirect (medium) viewpoint. As expected, we find a magnetic field induced anisotropic diffusion, with a stronger diffusion in the longitudinal direction compared to the transversal one. We backup, at least qualitatively, our findings with a hanging string analysis of heavy quark diffusion in a magnetic field. From the quark number susceptibility we can extract an estimate for the effective deconfinement temperature in the heavy quark sector, reporting consistency with the phenomenon of inverse magnetic catalysis.Comment: 27 pages. v2: extra discussions and references, compatible with version accepted by Phys.Rev.

Radiation Gauge in AdS/QCD: inadmissibility and implications on spectral functions in the deconfined phase

We point out a subtlety in choosing the radiation gauge (A_z=0 combined with the Lorenz gauge) for gauge fields in AdS/QCD for black hole backgrounds. We then demonstrate the effect of this on the momentum-dependence of the spectral functions of the J/psi vector meson, showing a spreading with momentum and a breaking of isotropy, in contrast to previous results in the literature. We also discuss the dependence on a background magnetic field, following our earlier proposed model.Comment: 10 pages, v2: added reference, version accepted for publicatio

Fraud deterrence in dynamic Mirrleesian economies

Social and private insurance schemes rely on legal action to deter fraud and tax evasion. This observation guides the authors to introduce a random state verification technology in a dynamic economy with private information. With some probability, an agent's skill level becomes known to the planner, who prescribes a punishment if the agent is caught misreporting. The authors show how deferring consumption can ease the provision of incentives. As a result, the marginal benefit may be below the marginal cost of investment in the constrained-efficient allocation, suggesting a subsidy on savings. They characterize conditions such that the intertemporal wedge is negative in finite horizon economies. In an infinite horizon economy, the authors find that the constrained-efficient allocation converges to a high level of consumption, full insurance, and no labor distortions for any probability of state verification.Insurance ; Fraud

The Schwarzian Theory - A Wilson Line Perspective

We provide a holographic perspective on correlation functions in Schwarzian quantum mechanics, as boundary-anchored Wilson line correlators in Jackiw-Teitelboim gravity. We first study compact groups and identify the diagrammatic representation of bilocal correlators of the particle-on-a-group model as Wilson line correlators in its 2d holographic BF description. We generalize to the Hamiltonian reduction of SL(2,R) and derive the Schwarzian correlation functions. Out-of-time ordered correlators are determined by crossing Wilson lines, giving a 6j-symbol, in agreement with 2d CFT results.Comment: 28 pages + appendices, v3: corrected discussion on representation theory and improved discussion on higher-point functions in appendices, references added, typos corrected, matches published versio

An Investigation of AdS2_2 Backreaction and Holography

We investigate a dilaton gravity model in AdS$_2$ proposed by Almheiri and Polchinski and develop a 1d effective description in terms of a dynamical boundary time with a Schwarzian derivative action. We show that the effective model is equivalent to a 1d version of Liouville theory, and investigate its dynamics and symmetries via a standard canonical framework. We include the coupling to arbitrary conformal matter and analyze the effective action in the presence of possible sources. We compute commutators of local operators at large time separation, and match the result with the time shift due to a gravitational shockwave interaction. We study a black hole evaporation process and comment on the role of entropy in this model.Comment: 32 pages, 6 figures, v3: typos corrected and references added, matches published versio