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110
Electron stars for holographic metallic criticality
 Phys.Rev. D83 (2011) 046003, arXiv:1008.2828 [hepth
"... We refer to the ground state of a gravitating, charged ideal fluid of fermions held at a finite chemical potential as an ‘electron star’. In a holographic setting, electron stars are candidate gravity duals for strongly interacting finite fermion density systems. We show how electron stars develop a ..."
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Cited by 56 (7 self)
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We refer to the ground state of a gravitating, charged ideal fluid of fermions held at a finite chemical potential as an ‘electron star’. In a holographic setting, electron stars are candidate gravity duals for strongly interacting finite fermion density systems. We show how electron stars develop an emergent Lifshitz scaling at low energies. This IR scaling region is a consequence of the two way interaction between emergent quantum critical bosonic modes and the finite density of fermions. By integrating from the IR region to an asymptotically AdS4 spacetime, we compute basic properties of the electron stars, including their electrical conductivity. We emphasize the challenge of connecting UV and IR physics in strongly interacting finite density systems. ar
The Bicycle Model
 in the Northeast Asian Economic Cooperation”, An Unpublished Paper, Korea Development Institute
, 2000
"... In this paper, we investigate a timesensitive image retrieval problem, in which given a query keyword, a query time point, and optionally user information, we retrieve the most relevant and temporally suitable images from the database. Inspired by recently emerging interests on query dynamics in in ..."
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Cited by 23 (5 self)
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In this paper, we investigate a timesensitive image retrieval problem, in which given a query keyword, a query time point, and optionally user information, we retrieve the most relevant and temporally suitable images from the database. Inspired by recently emerging interests on query dynamics in information retrieval research, our timesensitive image retrieval algorithm can infer users ’ implicit search intent better and provide more engaging and diverse search results according to temporal trends of Web user photos. We model observed image streams as instances of multivariate point processes represented by several different descriptors, and develop a regularized multitask regression framework that automatically selects and learns stochastic parametric models to solve the relations between image occurrence probabilities and various temporal factors that influence them. Using Flickr datasets of more than seven million images of 30 topics, our experimental results show that the proposed algorithm is more successful in timesensitive image retrieval than other candidate methods, including ranking SVM, a PageRankbased image ranking, and a generative temporal topic model.
A Holographic Quantum Critical Point at Finite Magnetic Field and Finite Density
 JHEP
, 2010
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Stellar spectroscopy: Fermions and holographic Lifshitz criticality
 JHEP
"... Electron stars are fluids of charged fermions in Antide Sitter spacetime. They are candidate holographic duals for gauge theories at finite charge density and exhibit emergent Lifshitz scaling at low energies. This paper computes in detail the field theory Green’s function GR(ω, k) of the gaugeinv ..."
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Cited by 21 (2 self)
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Electron stars are fluids of charged fermions in Antide Sitter spacetime. They are candidate holographic duals for gauge theories at finite charge density and exhibit emergent Lifshitz scaling at low energies. This paper computes in detail the field theory Green’s function GR(ω, k) of the gaugeinvariant fermionic operators making up the star. The Green’s function contains a large number of closely spaced Fermi surfaces, the volumes of which add up to the total charge density in accordance with the Luttinger count. Excitations of the Fermi surfaces are long lived for ω. kz. Beyond ω ∼ kz the fermionic quasiparticles dissipate strongly into the critical Lifshitz sector. Fermions near this critical dispersion relation give interesting contributions to the optical conductivity. ar X iv
Electron star birth: A continuous phase transition at nonzero density
"... We show that charged black holes in Antide Sitter spacetime can undergo a third order phase transition at a critical temperature in the presence of charged fermions. In the low temperature phase, a fraction of the charge is carried by a fermion fluid located a finite distance from the black hole. I ..."
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Cited by 19 (3 self)
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We show that charged black holes in Antide Sitter spacetime can undergo a third order phase transition at a critical temperature in the presence of charged fermions. In the low temperature phase, a fraction of the charge is carried by a fermion fluid located a finite distance from the black hole. In the zero temperature limit the black hole is no longer present and all charge is sourced by the fermions. The solutions exhibit the low temperature entropy density scaling s ∼ T 2/z anticipated from the emergent IR criticality of recently discussed electron stars. ar
Holographically smeared Fermi surface: Quantum oscillations and Luttinger count in electron stars,” [arXiv:1011.2502
"... We apply a small magnetic field to strongly interacting matter with a gravity dual description as an electron star. These systems are both metallic and quantum critical at low energies. The resulting quantum oscillations are shown to be of the KosevichLifshitz form characteristic of Fermi liquid th ..."
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Cited by 18 (3 self)
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We apply a small magnetic field to strongly interacting matter with a gravity dual description as an electron star. These systems are both metallic and quantum critical at low energies. The resulting quantum oscillations are shown to be of the KosevichLifshitz form characteristic of Fermi liquid theory. It is seen that only fermions at a single radius in the electron star contribute to the oscillations. We proceed to show that the Fermi surface area extracted from the quantum oscillations does not obey the simplest statement of the Luttinger theorem, that is, it is not universally proportional to the total charge density. It follows that our system is a nonFermi liquid that nonetheless exhibits KosevichLifshitz quantum oscillations. We explain how the Luttinger count is recovered via a field theoretic description involving a continuum of ‘smeared ’ fermionic excitations. ar
Universal linear in temperature resistivity from black hole superradiance,” arXiv:1208.4102 [hepth
"... Observations across many families of unconventional materials motivative the search for robust mechanisms producing linear in temperature d.c. resistivity. BKT quantum phase transitions are commonplace in holographic descriptions of finite density matter, separating critical and ordered phases. We s ..."
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Cited by 17 (3 self)
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Observations across many families of unconventional materials motivative the search for robust mechanisms producing linear in temperature d.c. resistivity. BKT quantum phase transitions are commonplace in holographic descriptions of finite density matter, separating critical and ordered phases. We show that at a holographic BKT critical point, if the unstable operator is coupled to the current via irrelevant operators, then a linear contribution to the resistivity is universally obtained. We also obtain broad power law tails in the optical conductivity, that shift spectral weight from the Drude peak as well as interband energy scales. We give a partial realization of this scenario using an EinsteinMaxwellpseudoscalar bulk theory. The instability is a vectorial mode at nonzero wavevector, which is communicated to the homogeneous current via irrelevant coupling to an ionic lattice. ar
FRW solutions and holography from uplifted AdS/CFT, arXiv:1108.5732
, 2000
"... Starting from concrete AdS/CFT dual pairs, one can introduce ingredients which produce cosmological solutions, including metastable de Sitter and its decay to nonaccelerating FRW. We present simple FRW solutions sourced by magnetic flavor branes and analyze correlation functions and particle and bra ..."
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Cited by 17 (7 self)
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Starting from concrete AdS/CFT dual pairs, one can introduce ingredients which produce cosmological solutions, including metastable de Sitter and its decay to nonaccelerating FRW. We present simple FRW solutions sourced by magnetic flavor branes and analyze correlation functions and particle and brane dynamics. To obtain a holographic description, we exhibit a timedependent warped metric on the solution and interpret the resulting redshifted region as a Lorentzian low energy effective field theory in one fewer dimension. At finite times, this theory has a finite cutoff, a propagating lower dimensional graviton and a finite covariant entropy bound, but at late times the lower dimensional Planck mass and entropy go off to infinity in a way that is dominated by contributions from the low energy effective theory. This opens up the possibility of a precise dual at late times. We reproduce the timedependent growth of the number of degrees of freedom in the system via a count of available microscopic states in the corresponding magnetic brane construction. Work supported in part by US Department of Energy contract DEAC0276SF00515. Contents
The Pauli exclusion principle at strong coupling: Holographic matter and momentum space
 JHEP
"... For free fermions at finite density, the Pauli exclusion principle is responsible for the existence of a Fermi surface and the consequent presence of low energy spectral weight over a finite range of momenta. We investigate the extent to which this effect occurs in strongly interacting quantum matte ..."
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Cited by 11 (2 self)
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For free fermions at finite density, the Pauli exclusion principle is responsible for the existence of a Fermi surface and the consequent presence of low energy spectral weight over a finite range of momenta. We investigate the extent to which this effect occurs in strongly interacting quantum matter with a holographic dual. We obtain the low energy currentcurrent spectral weight in two holographic frameworks at finite density: systems exhibiting semilocal quantum criticality (with a low temperature entropy density vanishing like s ∼ T η), and a probe D3/D5 system. For the semilocal theory with 0 < η < 2 we find a sharp discontinuity in the transverse spectral weight at a nonzero momentum k?. The case η = 1 is found to have additional symmetries and is soluble even at nonzero temperature. We show that this case exhibits a robust linear in temperature resistivity in the presence of random charged impurities. For the probe D3/D5 system we find an analytic expression for the low energy spectral weight as a function of momentum. The spectral weight is supported below a specific momentum k? and is exponentially suppressed at higher momenta.a rX iv
Largedensity field theory, viscosity, and “2kF” singularities from string duals
"... We analyze systems where an effective largeN expansion arises naturally in gauge theories without a large number of colors: a sufficiently large charge density alone can produce a perturbative string (’tHooft) expansion. One example is simply the wellknown NS5/F1 system dual to AdS3×T 4×S3, here v ..."
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Cited by 11 (0 self)
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We analyze systems where an effective largeN expansion arises naturally in gauge theories without a large number of colors: a sufficiently large charge density alone can produce a perturbative string (’tHooft) expansion. One example is simply the wellknown NS5/F1 system dual to AdS3×T 4×S3, here viewed as a 5+1 dimensional theory at finite density. This model is completely stable, and we find that the existing stringtheoretic solution of this model yields two interesting results. First, it indicates that the shear viscosity is not corrected by α′ effects in this system. For flow perpendicular to the F1 strings the viscosity to entropy ratio take the usual value 1/4π, but for flow parallel to the F1’s it vanishes as T 2 at low temperature. Secondly, it encodes singularities in correlation functions coming from lowfrequency modes at a finite value of the momentum along the T 4 directions. This may provide a strong coupling analogue of finite density condensed matter systems for which fermionic constituents of larger operators contribute socalled “2kF ” singularities. In the NS5/F1 example, stretched strings on the gravity side play the role of these composite operators. We explore the analogue for our system of the Luttinger relation between charge density and the volume bounded by these singular surfaces. This model provides a clean example where the stringtheoretic UV completion of the gravity dual to a finite density field theory plays a significant and calculable role.