91 research outputs found
Conformal perturbation theory
Statistical systems near a classical critical point have been intensively
studied both from theoretical and experimental points of view. In particular,
correlation functions are of relevance in comparing theoretical models with the
experimental data of real systems. In order to compute physical quantities near
a critical point one needs to know the model at the critical (conformal) point.
In this line, recent progresses in the knowledge of conformal field theories,
through the conformal bootstrap, give the hope to get some interesting results
also outside of the critical point. In this note we will review and clarify
how, starting from the knowledge of the critical correlators, one can calculate
in a safe way their behavior outside the critical point. The approach
illustrated requires the model to be just scale invariant at the critical
point. We will clarify the method by applying it to different kind of
perturbations of the Ising model.Comment: 21 pages, Version to appear on PR
Magneto-transport from momentum dissipating holography
We obtain explicit expressions for the thermoelectric transport coefficients
of a strongly coupled, planar medium in the presence of an orthogonal magnetic
field and momentum-dissipating processes. The computations are performed within
the gauge/gravity framework where the momentum dissipation mechanism is
introduced by including a mass term for the bulk graviton. Relying on the
structure of the computed transport coefficients and promoting the parameters
to become dynamical functions, we propose a holography inspired phenomenology
open to a direct comparison with experimental data from the cuprates.Comment: 23 page
Chasing the cuprates with dilatonic dyons
Magnetic field and momentum dissipation are key ingredients in describing
condensed matter systems. We include them in gauge/gravity and systematically
explore the bottom-up panorama of holographic IR effective field theories based
on bulk Einstein-Maxwell Lagrangians plus scalars. The class of solutions here
examined appear insufficient to capture the phenomenology of charge transport
in the cuprates. We analyze in particular the temperature scaling of the
resistivity and of the Hall angle. Keeping an open attitude, we illustrate weak
and strong points of the approach.Comment: 30 pages, 2 figures, Version to appear in JHE
3+1D Massless Weyl spinors from bosonic scalar-tensor duality
We consider the fermionization of a bosonic free theory characterized by the
3+1D scalar - tensor duality. This duality can be interpreted as the
dimensional reduction, via a planar boundary, of the 4+1D topological BF
theory. In this model, adopting the Sommerfield tomographic representation of
quantized bosonic fields, we explicitly build a fermionic operator and its
associated Klein factor such that it satisfies the correct anticommutation
relations. Interestingly, we demonstrate that this operator satisfies the
massless Dirac equation and that it can be identified with a 3+1D Weyl spinor.
Finally, as an explicit example, we write the integrated charge density in
terms of the tomographic transformed bosonic degrees of freedom
Holography in flat spacetime: 4D theories and electromagnetic duality on the border
We consider a free topological model in 5D euclidean flat spacetime, built
from two rank-2 tensor fields. Despite the fact that the bulk of the model does
not have any particular physical interpretation, on its 4D planar edge
nontrivial gauge field theories are recovered, whose features are entirely
determined by the gauge and discrete symmetries of the bulk. In particular no
4D dynamics can be obtained without imposing a Time Reversal invariance in the
bulk. Remarkably, one of the two possible edge models selected by the Time
Reversal symmetries displays a true electromagnetic duality, which relates
strong and weak coupling regimes. Moreover this same model, when considered
on-shell, coincides with the Maxwell theory, which therefore can be thought of
as a 4D boundary theory of a seemingly harmless 5D topological model.Comment: 21 pages, plain LaTeX, no figures. Version to appear on JHE
Analytic DC thermo-electric conductivities in holography with massive gravitons
We provide an analytical derivation of the thermo-electric transport
coefficients of the simplest momentum-dissipating model in gauge/gravity where
the lack of momentum conservation is realized by means of explicit graviton
mass in the bulk. We rely on the procedure recently described by Donos and
Gauntlett in the context of Q-lattices and holographic models where momentum
dissipation is realized through non-trivial scalars. The analytical approach
confirms the results found previously by means of numerical computations.Comment: 9 pages, no figures, minor comments added, version to appear on PR
Duality and Dimensional Reduction of 5D BF Theory
A planar boundary introduced \`a la Symanzik in the 5D topological BF theory,
with the only requirement of locality and power counting, allows to uniquely
determine a gauge invariant, non topological 4D Lagrangian. The boundary
condition on the bulk fields is interpreted as a duality relation for the
boundary fields, in analogy with the fermionization duality which holds in the
3D case. This suggests that the 4D degrees of freedom might be fermionic,
although starting from a bosonic bulk theory. The method we propose to
dimensionally reduce a Quantum Field Theory and to identify the resulting
degrees of freedom can be applied to a generic spacetime dimension.Comment: 13 pages, plain LaTeX, version to appear on EPJ
A holographic perspective on phonons and pseudo-phonons
We analyze the concomitant spontaneous breaking of translation and conformal
symmetries by introducing in a CFT a complex scalar operator that acquires a
spatially dependent expectation value. The model, inspired by the holographic
Q-lattice, provides a privileged setup to study the emergence of phonons from a
spontaneous translational symmetry breaking in a conformal field theory and
offers valuable hints for the treatment of phonons in QFT at large. We first
analyze the Ward identity structure by means of standard QFT techniques,
considering both spontaneous and explicit symmetry breaking. Next, by
implementing holographic renormalization, we show that the same set of Ward
identities holds in the holographic Q-lattice. Eventually, relying on the
holographic and QFT results, we study the correlators realizing the symmetry
breaking pattern and how they encode information about the low-energy spectrum.Comment: 31+1 pages, version accepted on JHE
Thermo-electric transport in gauge/gravity models
In this review, we summarize recent results in the study of the thermo-electric transport properties of holographic models exhibiting mechanism of momentum dissipation. These models are of particular interests if applied to understand the transport mechanisms of strongly coupled condensed matter systems such as the high-temperature superconductors. After a brief introduction in which we point out the discrepancies between the experimentally measured transport properties of these materials and the prediction of the weakly coupled theory of Fermi Liquid, we will review the basic aspects of AdS/CFT correspondence and how gravitational models could help in understanding the peculiar properties of strongly coupled condensed matter systems
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