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Yu Tian

Publications and source records attributed to Yu Tian.

At least 343 records · Page 19Linked to original sources
arXiv2018

Holographic RG flow of thermo-electric transports with momentum dissipation

We construct the holographic renormalization group (RG) flow of thermo-electric conductivities when the translational symmetry is broken. The RG flow is probed by the intrinsic observers hovering on the sliding radial membranes. We obtain the RG flow by solving a matrix-form Riccati equation. The RG flow provides a high-efficient numerical method to calculate the thermo-electric conductivities of strongly coupled systems with momentum dissipation. As an illustration, we recover the AC thermo-electric conductivities in the Einstein-Maxwell-axion model. Moreover, in several homogeneous and isotropic holographic models which dissipate the momentum and have the finite density, it is found that the RG flow of a particular combination of DC thermo-electric conductivities does not run. As a result, the DC thermal conductivity on the boundary field theory can be derived analytically, without using the conserved thermal current.

hep-th↗
arXiv2018

A Deep Generative Adversarial Architecture for Network-Wide Spatial-Temporal Traffic State Estimation

This study proposes a deep generative adversarial architecture (GAA) for network-wide spatial-temporal traffic state estimation. The GAA is able to combine traffic flow theory with neural networks and thus improve the accuracy of traffic state estimation. It consists of two Long Short-Term Memory Neural Networks (LSTM NNs) which capture correlation in time and space among traffic flow and traffic density. One of the LSTM NNs, called a discriminative network, aims to maximize the probability of assigning correct labels to both true traffic state matrices (i.e., traffic flow and traffic density within a given spatial-temporal area) and the traffic state matrices generated from the other neural network. The other LSTM NN, called a generative network, aims to generate traffic state matrices which maximize the probability that the discriminative network assigns true labels to them. The two LSTM NNs are trained simultaneously such that the trained generative network can generate traffic matrices similar to those in the training data set. Given a traffic state matrix with missing values, we use back-propagation on three defined loss functions to map the corrupted matrix to a latent space. The mapping vector is then passed through the pre-trained generative network to estimate the missing values of the corrupted matrix. The proposed GAA is compared with the existing Bayesian network approach on loop detector data collected from Seattle, Washington and that collected from San Diego, California. Experimental results indicate that the GAA can achieve higher accuracy in traffic state estimation than the Bayesian network approach.

eess.SP↗
arXiv2017

Charged BTZ-like black hole solutions and the diffusivity-butterfly velocity relation

We show that there exists a class of charged BTZ-like black hole solutions in Lifshitz spacetime with a hyperscaling violating factor. The charged BTZ is characterized by a charge-dependent logarithmic term in the metric function. As concrete examples, we give five such charged BTZ-like black hole solutions and the standard charged BTZ metric can be regarded as a special instance of them. In order to check the recent proposed universal relations between diffusivity and the butterfly velocity, we first compute the diffusion constants of the standard charged BTZ black holes and then extend our calculation to arbitrary dimension $d$, exponents $z$ and $θ$. Remarkably, the case $d=θ$ and $z=2$ is a very special in that the charge diffusion $D_c$ is a constant and the energy diffusion $D_e$ might be ill-defined, but $v^2_Bτ$ diverges. We also compute the diffusion constants for the case that the DC conductivity is finite but in the absence of momentum relaxation.

hep-th↗
arXiv2017

Hyperscaling violating black hole solutions and Magneto-thermoelectric DC conductivities in holography

We derive new black hole solutions in Einstein-Maxwell-Axion-Dilaton theory with a hyperscaling violation exponent. We then examine the corresponding anomalous transport exhibited by cuprate strange metals in the normal phase of high-temperature superconductors via gauge/gravity duality. Linear temperature dependence resistivity and quadratic temperature dependence inverse Hall angle can be achieved. In the high temperature regime, the heat conductivity and Hall Lorenz ratio are proportional to the temperature. The Nernst signal first increases as temperature goes up but it then decreases with increasing temperature in the high temperature regime.

hep-th↗
arXiv2017

Wilsonian RG-flow approach to holographic transport with momentum dissipation

We systematically present a new approach for studying the coupled linear transport of holographic systems. In this approach, the set of equations for the linear perturbations can be reduced to a first-order nonlinear ordinary differential equation expressed as the radial (renormalization group) flow equation of the transport matrices. As an important application, we use this approach to compute the DC and AC conductivities of a holographic model with momentum dissipation, which can be easily read off from the nonlinear flow equations. This method also works for transport in the presence of an external magnetic field.

hep-th↗
arXiv2017

Study of radially excited $D_s(2^1S_0)$ and $D^+_{sJ}(2632)$

The $J^P=0^-$ radial excitation $D_s(2^1S_0)$ is anticipated to have mass $2650$ MeV (denoted with $D_s(2650)$) though it has not been observed. $D_s(2650)$ is anticipated to be observed in inclusive $e^+e^-$ and $pp$ collisions in $D^*K$ channel. $D_s(2650)$ can be produced from hadronic decays of higher excited resonances. In a $^3P_0$ model, hadronic production of $D_s(2650)$ has been studied, relevant decay widths have been estimated. The hadronic decays of $D_s(3P)$ have been explored in detail, and the dominant decay channels have been pointed out. Two hadronic decay channels of $D^+_{sJ}(2632)$ were observed by SELEX, but have not been observed by any other experiment. Hadronic decays of $D^+_{sJ}(2632)$ in different assignments have been explored in the $^3P_0$ model. In view of the hadronic decay manner of $D^+_{sJ}(2632)$ , we conclude that $D^+_{sJ}(2632)$ cannot be a conventional charmed strange $c\bar s$ meson.

hep-ph↗
arXiv2017

From Prigogine to Raychaudhuri

It is highlighted by Prigogine that there are two additional universal behaviors associated with the entropy production rate besides the four laws of thermodynamics. One is that the entropy production rate decreases when the system approaches the steady state, and the other is that the entropy production rate reaches its minimal value at the steady state. Motivated by the black hole thermodynamics and AdS/CFT correspondence, we resort to Raychaudhuri equation to prove that these two universal behaviors are also obeyed by the black hole entropy. In particular, our result together with the four laws of black hole thermodynamics further indicates that the holographic gravity should be universal, not restricted only within the context of AdS/CFT correspondence.

hep-th↗
arXiv2017

Statical Structures of the BCS-like Holographic Superfluid in AdS4 Spacetime

We investigate in detail the m^{2}=0 Abelian Higgs model in AdS4, which is considered as the holographic dual of the most BCS-like superfluid. In homogeneous and isotropic superfluid solutions, we calculate the sound speeds, square of which approaches to 1/2 with increasing chemical potential (lowering temperature). Then we present the single dark soliton solutions, which becomes thinner with increasing chemical potential. For the first time, we also find the interesting double and triple dark soliton solutions, which is unexpected and shows the possibility of more complicated static configurations. Finally, we investigate vortex solutions. For winding number n=1, the vortex becomes thinner with increasing chemical potential. At a given chemical potential, with increasing winding number, firstly the vortex becomes bigger and the charge density depletion becomes larger, then the charge density depletion settles down at a certain value and the growth of the vortex size is found to obey a scaling symmetry.

hep-th↗
arXiv2017

Nonlinear Conductivity of a Holographic Superconductor Under Constant Electric Field

The dynamics of a two-dimensional superconductor under a constant electric field $E$ is studied by using the gauge/gravity correspondence. The pair breaking current induced by $E$ first increases to a peak value and then decreases to a constant value at late time, where the superconducting gap goes to zero, corresponding to a normal conducting phase. The peak value of the current is found to increase linearly with respect to the electric field. Moreover, the nonlinear conductivity, defined as an average of the conductivity in the superconducting phase, scales as $\sim E^{-2/3}$ for large $E$ when the system is close to the critical temperature, which agrees with predictions from solving the time dependent Ginzburg-Landau equation.

hep-th↗
arXiv2017

Direction- and Salt-Dependent Ionic Current Signatures for DNA Sensing with Asymmetric Nanopores

Solid-state nanopores are promising tools for single molecule detection of both DNA and proteins. In this study, we investigate the patterns of ionic current blockades as DNA translocates into or out of the geometric confinement of such conically shaped pores. We studied how the geometry of a nanopore affects the detected ionic current signal of a translocating DNA molecule over a wide range of salt concentration. The blockade level in the ionic current depends on the translocation direction at a high salt concentration, and at lower salt concentrations we find a non-intuitive ionic current decrease and increase within each single event for the DNA translocations exiting from confinement. We use recently developed DNA rulers with markers and finite element calculations to explain our observations. Our calculations explain the shapes of the signals observed at all salt concentrations and show that the unexpected current decrease and increase are due to the competing effects of ion concentration polarization and geometric exclusion of ions. Our analysis shows that over a wide range of geometry, voltage and salt concentrations we are able to understand the ionic current signals of DNA in asymmetric nanopores enabling signal optimization in molecular sensing applications.

physics.bio-ph↗
arXiv2016

Linear and quadratic in temperature resistivity from holography

We present a new black hole solution in the asymptotic Lifshitz spacetime with a hyperscaling violating factor. A novel computational method is introduced to compute the DC thermoelectric conductivities analytically. We find that both the linear-T and quadratic-T contributions to the resistivity can be realized, indicating that a more detailed comparison with experimental phenomenology can be performed in this scenario.

hep-th↗
arXiv2016

Hadronic production of $D(2550)$, $D^*(2600)$, $D(2750)$, $D^*_1(2760)$ and $D^*_3(2760)$

Hadronic decays of radially excited $2D$ $D(2^3D_1)$, $D(2^3D_3)$, $D(2D_2)$ and $D(2D^\prime_2)$ have been studied in a $^3P_0$ model. All OZI-allowed decay channels of these $2D$ $D$ resonances have been given, and relevant decay widths have been calculated. $D(2550)$, $D^*(2600)$, $D(2750)$, $D^*_1(2760)$ and $D^*_3(2760)$ can be produced in hadronic decays of $D(2^3D_1)$, $D(2^3D_3)$, $D(2D_2)$ and $D(2D^\prime_2)$. In different assignments, hadronic decay widths and some relevant ratios from the $2D$ $D$ resonances to $D(2550)$, $D^*(2600)$, $D(2750)$, $D^*_1(2760)$ or $D^*_3(2760)$ final states have been predicted, which may provide some more information to identify these resonances in forthcoming experiments.

hep-ph↗
arXiv2016

Zero Temperature Holographic Superfluids with Two Competing Orders

We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one band superfluid phases, the coexistent superfluid phase has also been found in the AdS soliton background for the first time. We construct the complete phase diagram in the $e-μ$ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of pole of optical conductivity at $ω=0$ indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the non-smoothness at the critical points as the order parameter of condensate, which indicates that the phase transitions can also be identified by the behavior of sound speed. Moreover, as expected from the boundary conformal field theory, the sound speed saturates to $\frac{1}{\sqrt{2}}$ at the large chemical potential limit for our two band holographic superfluid model.

hep-th↗
arXiv2016

Towards Quantum Turbulence in Finite Temperature Bose-Einstein Condensates

Motivated by the various indications that holographic superfluid is BCS like at the standard quantization but BEC like at the alternative quantization, we have implemented the alternative quantization in the dynamical holographic superfluid for the first time. With this accomplishment, we further initiate the detailed investigation of quantum turbulence in finite temperature BEC by a long time stable numerical simulation of bulk dynamics, which includes the two body decay of vortex number caused by vortex pair annihilation, the onset of superfluid turbulence signaled by Kolmogorov scaling law, and a direct energy cascade demonstrated by injecting energy to the turbulent superfluid. All of these results share the same patterns as the holographic superfluid at the standard quantization, thus suggest that these should be universal features for quantum turbulence at temperatures order of the critical temperature.

hep-th↗
arXiv2016

Nonlinear Transport in a Two Dimensional Holographic Superconductor

The problem of nonlinear transport in a two dimensional superconductor with an applied oscillating electric field is solved by the holographic method. The complex conductivity can be computed from the dynamics of the current for both near- and non-equilibrium regimes. The limit of weak electric field corresponds to the near equilibrium superconducting regime, where the charge response is linear and the conductivity develops a gap determined by the condensate. A larger electric field drives the system into a superconducting non-equilibrium steady state, where the nonlinear conductivity is quadratic with respect to the electric field. Keeping increasing the amplitude of applied electric field results in a far-from-equilibrium non-superconducting steady state with a universal linear conductivity of one. In lower temperature regime we also find chaotic behavior of superconducting gap, which results in a non-monotonic field dependent nonlinear conductivity.

hep-th↗
arXiv2016

Note on Zero Temperature Holographic Superfluids

In this note, we have addressed various issues on zero temperature holographic superfluids. First, inspired by our numerical evidence for the equality between the superfluid density and particle density, we provide an elegant analytic proof for this equality by a boost trick. Second, using not only the frequency domain analysis but also the time domain analysis from numerical relativity, we identify the hydrodynamic normal modes and calculate out the sound speed, which is shown to increase with the chemical potential and saturate to the value predicted by the conformal field theory in the large chemical potential limit. Third, the generic non-thermalization is demonstrated by the fully non-linear time evolution from a non-equilibrium state for our zero temperature holographic superfluid. Furthermore, a conserved Noether charge is proposed in support of this behavior.

hep-th↗
arXiv2016

Modave Lectures on Applied AdS/CFT with Numerics

These lecture notes are intended to serve as an introduction to applied AdS/CFT with numerics for an audience of graduate students and others with little background in the subject. The presentation begins with a poor man's review of current status of quantum gravity, where AdS/CFT correspondence is believed to be the well formulated quantum gravity in the anti-de Sitter space. Then we present the basic ingredients in applied AdS/CFT and introduce the relevant numerics for solving differential equations into which the bulk dynamics collapses. To demonstrate how to apply AdS/CFT with numerics, we take the zero temperature holographic superfluid as a concrete example for case study. In passing, we also present some new results, which include the numerical evidence as well as an elegant analytic proof for the equality between the superfluid density and particle density, namely $ρ_s=ρ$, and the saturation to the predicted value $\frac{1}{\sqrt{2}}$ by conformal field theory for the sound speed in the large chemical potential limit.

gr-qc↗