82 research outputs found
Hall conductivity from dyonic black holes
A class of strongly interacting 2+1 dimensional conformal field theories in a
transverse magnetic field can be studied using the AdS/CFT duality. We compute
zero momentum hydrodynamic response functions of maximally supersymmetric 2+1
dimensional SU(N) Yang-Mills theory at the conformal fixed point, in the large
N limit. With background magnetic field B and electric charge density rho, the
Hall conductivity is found to be rho/B. The result, anticipated on kinematic
grounds in field theory, is obtained from perturbations of a four dimensional
AdS black hole with both electric and magnetic charges.Comment: 1+13 pages. TT correlator corrected. Typos corrected and added ref
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Quantum Critical Response at the Onset of Spin Density Wave Order in Two-dimensional Metals
We study the frequency dependence of the electron self-energy and the optical conductivity in a recently developed field theory of the spin-density-wave quantum phase transition in two-dimensional metals. We focus on the interplay between the Fermi surface “hot spots” and the remainder of the “cold” Fermi surface. Scattering of electrons off the fluctuations of the spin-density-wave order parameter, , is strongest at the hot spots; we compute the conductivity due to this scattering in a rainbow approximation. We point out the importance of composite operators, built of products of the primary electron or fields: These have important effects also away from the hot spots. The simplest composite operator, , leads to deviations from Landau Fermi-liquid behavior on the entire Fermi surface. We also find an intermediate frequency window in which the cold electrons lose their quasiparticle form due to effectively one-dimensional scattering processes. The latter processes are part of umklapp scattering, which leads to singular contributions to the optical conductivity at the lowest frequencies at zero temperature.Physic
Quantum oscillations and black hole ringing
We show that strongly coupled field theories with holographic gravity duals
at finite charge density and low temperatures can undergo de Haas - van Alphen
quantum oscillations as a function of an external magnetic field. Exhibiting
this effect requires computation of the one loop contribution of charged bulk
fermions to the free energy. The one loop calculation is performed using a
formula expressing determinants in black hole backgrounds as sums over
quasinormal modes. At zero temperature, the periodic nonanalyticities in the
magnetic susceptibility as a function of the inverse magnetic field depend on
the low energy scaling behavior of fermionic operators in the field theory, and
are found to be softer than in weakly coupled theories. We also obtain
numerical and WKB results for the quasinormal modes of charged bosons in dyonic
black hole backgrounds, finding evidence for nontrivial periodic behavior as a
function of the magnetic field.Comment: 1+53 pages. 9 figures. v2: important changes to sections 3.4 - 3.6.
contribution of branch cut poles include
Landscape of superconducting membranes
The AdS/CFT correspondence may connect the landscape of string vacua and the
`atomic landscape' of condensed matter physics. We study the stability of a
landscape of IR fixed points of N=2 large N gauge theories in 2+1 dimensions,
dual to Sasaki-Einstein compactifications of M theory, towards a
superconducting state. By exhibiting instabilities of charged black holes in
these compactifications, we show that many of these theories have charged
operators that condense when the theory is placed at a finite chemical
potential. We compute a statistical distribution of critical superconducting
temperatures for a subset of these theories. With a chemical potential of one
milliVolt, we find critical temperatures ranging between 0.24 and 165 degrees
Kelvin.Comment: 1+34 pages. 3 figures. v2 references added, typos fixe
Transport near the Ising-nematic quantum critical point of metals in two dimensions
We consider two-dimensional metals near a Pomeranchuk instability which breaks 90∘ lattice rotation symmetry. Such metals realize strongly coupled non-Fermi liquids with critical fluctuations of an Ising-nematic order. At low temperatures, impurity scattering provides the dominant source of momentum relaxation and, hence, a nonzero electrical resistivity. We use the memory matrix method to compute the resistivity of this non-Fermi liquid to second order in the impurity potential, without assuming the existence of quasiparticles. Impurity scattering in the d-wave channel acts as a random “field” on the Ising-nematic order. We find contributions to the resistivity with a nearly linear temperature dependence, along with more singular terms; the most singular is the random-field contribution which diverges in the limit of zero temperature.Physic
GlioPredictor: A deep learning model for identification of high-risk adult IDH-mutant glioma towards adjuvant treatment planning
Identification of isocitrate dehydrogenase (IDH)-mutant glioma patients at high risk of early progression is critical for radiotherapy treatment planning. Currently tools to stratify risk of early progression are lacking. We sought to identify a combination of molecular markers that could be used to identify patients who may have a greater need for adjuvant radiation therapy machine learning technology. 507 WHO Grade 2 and 3 glioma cases from The Cancer Genome Atlas, and 1309 cases from AACR GENIE v13.0 datasets were studied for genetic disparities between IDH1-wildtype and IDH1-mutant cohorts, and between different age groups. Genetic features such as mutations and copy number variations (CNVs) correlated with IDH1 mutation status were selected as potential inputs to train artificial neural networks (ANNs) to predict IDH1 mutation status. Grade 2 and 3 glioma cases from the Memorial Sloan Kettering dataset (n = 404) and Grade 3 glioma cases with subtotal resection (STR) from Northwestern University (NU) (n = 21) were used to further evaluate the best performing ANN model as independent datasets. IDH1 mutation is associated with decreased CNVs of EGFR (21% vs. 3%), CDKN2A (20% vs. 6%), PTEN (14% vs. 1.7%), and increased percentage of mutations for TP53 (15% vs. 63%), and ATRX (10% vs. 54%), which were all statistically significant (p \u3c 0.001). Age \u3e 40 was unable to identify high-risk IDH1-mutant with early progression. A glioma early progression risk prediction (GlioPredictor) score generated from the best performing ANN model (6/6/6/6/2/1) with 6 inputs, including CNVs of EGFR, PTEN and CDKN2A, mutation status of TP53 and ATRX, patient\u27s age can predict IDH1 mutation status with over 90% accuracy. The GlioPredictor score identified a subgroup of high-risk IDH1-mutant in TCGA and NU datasets with early disease progression (p = 0.0019, 0.0238, respectively). The GlioPredictor that integrates age at diagnosis, CNVs of EGFR, CDKN2A, PTEN and mutation status of TP53, and ATRX can identify a small cohort of IDH-mutant with high risk of early progression. The current version of GlioPredictor mainly incorporated clinically often tested genetic biomarkers. Considering complexity of clinical and genetic features that correlate with glioma progression, future derivatives of GlioPredictor incorporating more inputs can be a potential supplement for adjuvant radiotherapy patient selection of IDH-mutant glioma patients
Theory of the Nernst effect near quantum phase transitions in condensed matter, and in dyonic black holes
We present a general hydrodynamic theory of transport in the vicinity of
superfluid-insulator transitions in two spatial dimensions described by
"Lorentz"-invariant quantum critical points. We allow for a weak impurity
scattering rate, a magnetic field B, and a deviation in the density, \rho, from
that of the insulator. We show that the frequency-dependent thermal and
electric linear response functions, including the Nernst coefficient, are fully
determined by a single transport coefficient (a universal electrical
conductivity), the impurity scattering rate, and a few thermodynamic state
variables. With reasonable estimates for the parameters, our results predict a
magnetic field and temperature dependence of the Nernst signal which resembles
measurements in the cuprates, including the overall magnitude. Our theory
predicts a "hydrodynamic cyclotron mode" which could be observable in ultrapure
samples. We also present exact results for the zero frequency transport
co-efficients of a supersymmetric conformal field theory (CFT), which is
solvable by the AdS/CFT correspondence. This correspondence maps the \rho and B
perturbations of the 2+1 dimensional CFT to electric and magnetic charges of a
black hole in the 3+1 dimensional anti-de Sitter space. These exact results are
found to be in full agreement with the general predictions of our hydrodynamic
analysis in the appropriate limiting regime. The mapping of the hydrodynamic
and AdS/CFT results under particle-vortex duality is also described.Comment: 44 pages, 4 figures; (v3) Added new subsection highlighting negative
Hall resistance at hole densities smaller than 1/
Families of IIB duals for nonrelativistic CFTs
We show that the recent string theory embedding of a spacetime with
nonrelativistic Schrodinger symmetry can be generalised to a twenty one
dimensional family of solutions with that symmetry. Our solutions include IIB
backgrounds with no three form flux turned on, and arise as near horizon limits
of branewave spacetimes. We show that there is a hypersurface in the space of
these theories where an instability appears in the gravitational description,
indicating a phase transition in the nonrelativistic field theory dual. We also
present simple embeddings of duals for nonrelativistic critical points where
the dynamical critical exponent can take many values z \neq 2.Comment: 1+25 pages. References adde
Deformations of Lifshitz holography
The simplest gravity duals for quantum critical theories with z=2 `Lifshitz'
scale invariance admit a marginally relevant deformation. Generic black holes
in the bulk describe the field theory with a dynamically generated momentum
scale Lambda as well as finite temperature T. We describe the thermodynamics of
these black holes in the quantum critical regime where T >> Lambda^2. The
deformation changes the asymptotics of the spacetime mildly and leads to
intricate UV sensitivities of the theory which we control perturbatively in
Lambda^2/T.Comment: 1+27 pages, 12 figure
Black hole determinants and quasinormal modes
We derive an expression for functional determinants in thermal spacetimes as
a product over the corresponding quasinormal modes. As simple applications we
give efficient computations of scalar determinants in thermal AdS, BTZ black
hole and de Sitter spacetimes. We emphasize the conceptual utility of our
formula for discussing `1/N' corrections to strongly coupled field theories via
the holographic correspondence.Comment: 28 pages. v2: slightly improved exposition, references adde
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