387 research outputs found
Holographic Lattices Give the Graviton an Effective Mass
We discuss the DC conductivity of holographic theories with translational
invariance broken by a background lattice. We show that the presence of the
lattice induces an effective mass for the graviton via a gravitational version
of the Higgs mechanism. This allows us to obtain, at leading order in the
lattice strength, an analytic expression for the DC conductivity in terms of
the size of the lattice at the horizon. In locally critical theories this leads
to a power law resistivity that is in agreement with an earlier field theory
analysis of Hartnoll and Hofman.Comment: 16 pages, 2 figures, JHEP style, v2: added references. To comply with
UK open access requirements, the text of the (much shorter) peer-reviewed
version can be downloaded from http://www.damtp.cam.ac.uk/user/tong/pub.htm
Segmented strings coupled to a B-field
This work was supported by the Center of Mathematical Sciences and Applications at
Harvard University
Adventures in Holographic Dimer Models
We abstract the essential features of holographic dimer models, and develop
several new applications of these models. First, semi-holographically coupling
free band fermions to holographic dimers, we uncover novel phase transitions
between conventional Fermi liquids and non-Fermi liquids, accompanied by a
change in the structure of the Fermi surface. Second, we make dimer vibrations
propagate through the whole crystal by way of double trace deformations,
obtaining nontrivial band structure. In a simple toy model, the topology of the
band structure experiences an interesting reorganization as we vary the
strength of the double trace deformations. Finally, we develop tools that would
allow one to build, in a bottom-up fashion, a holographic avatar of the Hubbard
model.Comment: 22 pages, 8 figures; v2: brief description of case of pure D5 lattice
added in sec.3; v3: minor typo fixed; v4: minor change
Holographic Aspects of Fermi Liquids in a Background Magnetic Field
We study the effects of an external magnetic field on the properties of the
quasiparticle spectrum of the class of 2+1 dimensional strongly coupled
theories holographically dual to charged AdS black holes at zero
temperature. We uncover several interesting features. At certain values of the
magnetic field, there are multiple quasiparticle peaks representing a novel
level structure of the associated Fermi surfaces. Furthermore, increasing
magnetic field deforms the dispersion characteristics of the quasiparticle
peaks from non-Landau toward Landau behaviour. At a certain value of the
magnetic field, just at the onset of Landau-like behaviour of the Fermi liquid,
the quasiparticles and Fermi surface disappear.Comment: 18 pages, 10 figures. Revised some of the terminology: changed
non-separable solutions to infinite-sum solution
Chaotic Strings in AdS/CFT.
Holographic theories with classical gravity duals are maximally chaotic; i.e., they saturate the universal bound on the rate of growth of chaos [J. Maldacena, S. H. Shenker, and D. Stanford, J. High Energy Phys. 08 (2016) 106JHEPFG1029-847910.1007/JHEP08(2016)106]. It is interesting to ask whether this property is true only for leading large N correlators or if it can show up elsewhere. In this Letter, we consider the simplest setup to tackle this question: a Brownian particle coupled to a thermal ensemble. We find that the four-point out-of-time-order correlator that diagnoses chaos initially grows at an exponential rate that saturates the chaos bound, i.e., with a Lyapunov exponent λ_{L}=2π/β. However, the scrambling time is parametrically smaller than for plasma excitations, t_{*}∼βlogsqrt[λ] instead of t_{*}∼βlogN^{2}. Our result shows that, at least in certain cases, maximal chaos can be attained in the probe sector without the explicit need of gravitational degrees of freedom.Funded by SCOAP3
Non-relativistic metrics from back-reacting fermions
It has recently been pointed out that under certain circumstances the
back-reaction of charged, massive Dirac fermions causes important modifications
to AdS_2 spacetimes arising as the near horizon geometry of extremal black
holes. In a WKB approximation, the modified geometry becomes a non-relativistic
Lifshitz spacetime. In three dimensions, it is known that integrating out
charged, massive fermions gives rise to gravitational and Maxwell Chern-Simons
terms. We show that Schrodinger (warped AdS_3) spacetimes exist as solutions to
a gravitational and Maxwell Chern-Simons theory with a cosmological constant.
Motivated by this, we look for warped AdS_3 or Schrodinger metrics as exact
solutions to a fully back-reacted theory containing Dirac fermions in three and
four dimensions. We work out the dynamical exponent in terms of the fermion
mass and generalize this result to arbitrary dimensions.Comment: 26 pages, v2: typos corrected, references added, minor change
What If Alexander Hamilton Had Been Argentinean? A Comparison of the Early Monetary Experiences of Argentina and the United States
The contrast between the early nineteenth century Argentinean experience of high inflation and the American experience of low inflation is interpreted in terms of a dynamic monetary model of optimal taxation. It is argued that the two countries' experiences diverged because of the different constraints they faced in financing wartime government expenditures. In the presence of frequent wars, ever-tightening access to foreign capital, and an inadequate tax base, Argentina's use of the inflation tax may be viewed as an optimal solution to its wartime problems. By contrast, with the exception of the Revolutionary War, the absence of such constraints in the United States required full-tax smoothing, with only a temporary use of the inflation tax during wartime. Such policies were embodied in Alexander Hamilton's fiscal package of 1790, which allowed the United States to bond-finance most subsequent wartime expenditures.
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