8,847 research outputs found
The Schwarzian Theory - Origins
In this paper we further study the 1d Schwarzian theory, the universal
low-energy limit of Sachdev-Ye-Kitaev models, using the link with 2d Liouville
theory. We provide a path-integral derivation of the structural link between
both theories, and study the relation between 3d gravity, 2d Jackiw-Teitelboim
gravity, 2d Liouville and the 1d Schwarzian. We then generalize the Schwarzian
double-scaling limit to rational models, relevant for SYK-type models with
internal symmetries. We identify the holographic gauge theory as a 2d BF theory
and compute correlators of the holographically dual 1d particle-on-a-group
action, decomposing these into diagrammatic building blocks, in a manner very
similar to the Schwarzian theory.Comment: 40 pages + appendices, v3: corrected several equations in section 5,
added discussion on particle on a group, typos corrected and references
added, matches published versio
Holographic estimate of heavy quark diffusion in a magnetic field
We study the influence of a background magnetic field on the 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.
Vortices in Quantum Spin Systems
We examine spin vortices in ferromagnetic quantum Heisenberg models with
planar anisotropy on two-dimensional lattices. The symmetry properties and the
time evolution of vortices built up from spin-coherent states are studied in
detail. Although these states show a dispersion typical for wave packets,
important features of classical vortices are conserved. Moreover, the results
on symmetry properties provide a construction scheme for vortex-like
excitations from exact eigenstates, which have a well-controlled time
evolution. Our approach works for arbitrary spin length both on triangular and
square lattices.Comment: Remarks added and conclusions enlarged, version to be published in
European Physical Journal
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
Defects in Jackiw-Teitelboim Quantum Gravity
We classify and study defects in 2d Jackiw-Teitelboim gravity. We show these
are holographically described by a deformation of the Schwarzian theory where
the reparametrization mode is integrated over different coadjoint orbits of the
Virasoro group. We show that the quantization of each coadjoint orbit is
connected to 2d Liouville CFT between branes with insertions of Verlinde loop
operators. We also propose an interpretation for the exceptional orbits. We use
this perspective to solve these deformations of the Schwarzian theory,
computing their partition function and correlators. In the process, we define
two geometric observables: the horizon area operator and the geodesic
length operator . We show this procedure is structurally related to
the deformation of the particle-on-a-group quantum mechanics by the addition of
a chemical potential. As an example, we solve the low-energy theory of complex
SYK with a U(1) symmetry and generalize to the non-abelian case.Comment: 66 pages, v4: clarifications added, typos corrected, matches
published versio
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
Clocks and Rods in Jackiw-Teitelboim Quantum Gravity
We specify bulk coordinates in Jackiw-Teitelboim (JT) gravity using a
boundary-intrinsic radar definition. This allows us to study and calculate
exactly diff-invariant bulk correlation functions of matter-coupled JT gravity,
which are found to satisfy microcausality. We observe that quantum gravity
effects dominate near-horizon matter correlation functions. This shows that
quantum matter in classical curved spacetime is not a sensible model for
near-horizon matter-coupled JT gravity. This is how JT gravity, given our
choice of bulk frame, evades an information paradox. This echoes into the
quantum expectation value of the near-horizon metric, whose analysis is
extended from the disk model to the recently proposed topological completion of
JT gravity. Due to quantum effects, at distances of order the Planck length to
the horizon, a dramatic breakdown of Rindler geometry is observed.Comment: 37 pages + appendices, v4: improved discussion on conformal anomaly
and choice of bulk observable, added appendix on massive bulk correlators and
global conformal blocks, corrected several equations in section 5 and
appendix E, typos corrected, matches published versio
An Investigation of AdS Backreaction and Holography
We investigate a dilaton gravity model in AdS 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
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