arXiv subjects

Gang Li

Publications and source records attributed to Gang Li.

At least 595 records · Page 33Linked to original sources

arXiv2018

Entanglement of remote material qubits through nonexciting interaction with single photons

We propose a scheme to entangle multiple material qubits through interaction with single photons via non-exciting processes associated with strongly coupling systems. The basic idea is based on the material state dependent reflection and transmission for the input photons. Thus, the material qubits in several systems can be entangled when one photon interacts with each system in cascade and the photon paths are mixed by the photon detection. The character of non-exciting of the material qubits does not change the state of material qubit and thus ensures the possibility of purifying entangled states by using more photons under realistic imperfect parameters. It also guarantees directly scaling up the scheme to entangle more qubits. Detailed analysis of fidelity and success probability of the scheme in the frame of an optical Fabry-Pérot (FP) cavity based strongly coupling system is presented. It is shown that a two-qubit entangled state with fidelity above 0.99 is promised with only two photons by using currently feasible experimental parameters. Our scheme can also be directly implemented on other strongly coupled system.

quant-ph↗

arXiv2018

Measuring the ratio of $HWW$ and $HZZ$ couplings through $W^+W^-H$ production

For a generic Higgs boson, measuring the relative sign and magnitude of its couplings with the $W$ and $Z$ bosons is essential in determining its origin. Such a test is also indispensable for the 125-GeV Higgs boson. We propose that the ratio of the $HWW$ and $HZZ$ couplings $λ_{WZ}$ can be directly determined through the $W^+W^-H$ production, where $H$ denotes a generic Higgs boson, owing to the tree-level interference effect. While this is impractical at the LHC due to the limited sensitivity, it can be done at future $e^+e^-$ colliders, such as a 500-GeV ILC with the beam polarization $P(e^-,e^+)=(-0.8,+0.3)$ in the $jj\ell^{\pm}bb$ and $\ell^{\pm}\ell^{\pm}\ell^{\mp}jj$ channels. The discovery potential of a general ratio and the power to discriminate it from the SM value are studied in detail. Combining the cross section of $e^+e^-\to W^+ W^- H$ with the measurements of $HZZ$ coupling at the HL-LHC, one can further improve the sensitivity of $λ_{WZ}$.

hep-ph↗

arXiv2018

On Collaborative Compressive Sensing Systems: The Framework, Design and Algorithm

Based on the maximum likelihood estimation principle, we derive a collaborative estimation framework that fuses several different estimators and yields a better estimate. Applying it to compressive sensing (CS), we propose a collaborative CS (CCS) scheme consisting of a bank of $K$ CS systems that share the same sensing matrix but have different sparsifying dictionaries. This CCS system is expected to yield better performance than each individual CS system, while requiring the same time as that needed for each individual CS system when a parallel computing strategy is used. We then provide an approach to designing optimal CCS systems by utilizing a measure that involves both the sensing matrix and dictionaries and hence allows us to simultaneously optimize the sensing matrix and all the $K$ dictionaries. An alternating minimization-based algorithm is derived for solving the corresponding optimal design problem. With a rigorous convergence analysis, we show that the proposed algorithm is convergent. Experiments are carried out to confirm the theoretical results and show that the proposed CCS system yields significant improvements over the existing CS systems in terms of the signal recovery accuracy.

cs.IT↗

arXiv2018

An astrophysical interpretation of the remarkable g-mode frequency groups of the rapidly rotating $γ$ Dor star, KIC 5608334

The Fourier spectrum of the $γ$-Dor variable KIC 5608334 shows remarkable frequency groups at $\sim$3, $\sim$6, $\sim$9, and 11--12\,d$^{-1}$. We explain the four frequency groups as prograde sectoral g modes in a rapidly rotating star. Frequencies of intermediate-to-high radial order prograde sectoral g modes in a rapidly rotating star are proportional to $|m|$ (i.e., $ν\propto |m|$) in the co-rotating frame as well as in the inertial frame. This property is consistent with the frequency groups of KIC 5608334 as well as the period vs. period-spacing relation present within each frequency group, if we assume a rotation frequency of $2.2$\,d$^{-1}$, and that each frequency group consists of prograde sectoral g modes of $|m| = 1, 2, 3,$ and 4, respectively. In addition, these modes naturally satisfy near-resonance conditions $ν_i\approxν_j+ν_k$ with $m_i=m_j+m_k$. We even find exact resonance frequency conditions (within the precise measurement uncertainties) in many cases, which correspond to combination frequencies.

astro-ph.SR↗

arXiv2018

Nonhomogeneous Dirichlet problems without the Ambrosetti-Rabinowitz condition

We consider the existence of solutions of the following $p(x)$-Laplacian Dirichlet problem without the Ambrosetti-Rabinowitz condition: $-\mbox{div}(|\nabla u|^{p(x)-2}\nabla u)=f(x,u) \text{ in }Ω,$ and $u=0,\text{ on }\partial Ω.$ We give a new growth condition and we point out its importance for checking the Cerami compactness condition. We prove the existence of solutions of the above problem via the critical point theory, and also provide some multiplicity properties. Our results extend previous work by Q. Zhang and C. Zhao, Existence of strong solutions of a $p(x)$-Laplacian Dirichlet problem without the Ambrosetti-Rabinowitz condition, Comp. Math. Appl. 69 (2015), 1-12, and we establish the existence of solutions under weaker hypotheses on the nonlinear term.

math.AP↗

arXiv2018

Recent Advances in Efficient Computation of Deep Convolutional Neural Networks

Deep neural networks have evolved remarkably over the past few years and they are currently the fundamental tools of many intelligent systems. At the same time, the computational complexity and resource consumption of these networks also continue to increase. This will pose a significant challenge to the deployment of such networks, especially in real-time applications or on resource-limited devices. Thus, network acceleration has become a hot topic within the deep learning community. As for hardware implementation of deep neural networks, a batch of accelerators based on FPGA/ASIC have been proposed in recent years. In this paper, we provide a comprehensive survey of recent advances in network acceleration, compression and accelerator design from both algorithm and hardware points of view. Specifically, we provide a thorough analysis of each of the following topics: network pruning, low-rank approximation, network quantization, teacher-student networks, compact network design and hardware accelerators. Finally, we will introduce and discuss a few possible future directions.

cs.CV↗

arXiv2018

Two-stage energy release process of a confined flare with double HXR peaks

A complete understanding of the onset and subsequent evolution of confined flares has not been achieved. Earlier studies mainly analyzed disk events so as to reveal their magnetic topology and cause of confinement. In this study, taking advantage of a tandem of instruments working at different wavelengths of X-rays, EUVs, and microwaves, we present dynamic details of a confined flare observed on the northwestern limb of the solar disk on July 24th, 2016. The entire dynamic evolutionary process starting from its onset is consistent with a loop-loop interaction scenario. The X-ray profiles manifest an intriguing double-peak feature. From spectral fitting, it is found that the first peak is non-thermally dominated while the second peak is mostly multi-thermal with a hot (~10 MK) and a super-hot (~30 MK) component. This double-peak feature is unique in that the two peaks are clearly separated by 4 minutes, and the second peak reaches up to 25-50 keV; in addition, at energy bands above 3 keV the X-ray fluxes decline significantly between the two peaks. This, together with other available imaging and spectral data, manifest a two-stage energy release process. A comprehensive analysis is carried out to investigate the nature of this two-stage process. We conclude that the second stage with the hot and super-hot sources mainly involves direct heating through loop-loop reconnection at a relatively high altitude in the corona. The uniqueness of the event characteristics and complete data set make the study a nice addition to present literature on solar flares.

astro-ph.SR↗

arXiv2018

Measurement of complete and continuous Wigner functions for discrete atomic systems

We measure complete and continuous Wigner functions of a two-level cesium atom in both a nearly pure state and highly mixed states. We apply the method [T. Tilma et al., Phys. Rev. Lett. 117, 180401 (2016)] of strictly constructing continuous Wigner functions for qubit or spin systems. We find that the Wigner function of all pure states of a qubit has negative regions and the negativity completely vanishes when the purity of an arbitrary mixed state is less than $\frac{2}{3}$. We experimentally demonstrate these findings using a single cesium atom confined in an optical dipole trap, which undergoes a nearly pure dephasing process. Our method can be applied straightforwardly to multi-atom systems for measuring the Wigner function of their collective spin state.

quant-ph↗

arXiv2018

Exploring the $Υ(4S,5S,6S) \to h_b(1P)η$ hidden-bottom hadronic transitions

Recently, Belle Collaboration has reported the measurement of the spin-flipping transition $Υ(4S) \to h_b(1P)η$ with an unexpectedly large branching ratio: $\mathcal{B}(Υ(4S) \to h_b(1P)η) =(2.18\pm 0.11\pm 0.18)\times 10^{-3}$. Such a large branching fraction contradicts with the anticipated suppression for the spin flip. In this work, we examine the effects induced by intermediate bottomed meson loops and point out that these effects are significantly important. Using the effective Lagrangian approach (ELA), we find the experimental data on $Υ(4S) \to h_b(1P)η$ can be accommodated with the reasonable inputs. We then explore the decays $Υ(5S,6S)\to h_b(1P)η$ and find that these two channels also have sizable branching fractions. We also calculate these these processes in the framework of nonrelativistic effective field theory (NREFT). For the decays $Υ(4S) \to h_b(1P) η$, the NREFT results are at the same order of magnitude but smaller than the ELA results by a factor of $2$ to $5$. For the decays $Υ(5S, 6S) \to h_b(1P) η$ the NREFT results are smaller than the ELA results by approximately one order of magnitude. We suggest future experiment Belle-II to search for the $Υ(5S, 6S)\to h_b(1P) η$ decays which will be helpful to understand the transition mechanism.

hep-ph↗

arXiv2018

$\bar{B}^0$, $\bar{B}^0_s$ and $B^-$ decays into $η_c$ plus a scalar meson

We investigate the decays of $\bar{B}^0_s$, $\bar{B}^0$ and $B^-$ into $η_c$ plus a scalar meson in a theoretical framework by taking into account the dominant process for the weak decay of $\bar{B}$ meson into $η_c$ and a $q\bar{q}$ pair. After hadronization of this $q\bar{q}$ component into pairs of pseudoscalar mesons we obtain certain weights for the pseudoscalar meson-pseudoscalar meson components. The calculation is based on the postulation that the scalar mesons $f_0(500)$, $f_0(980)$ and $a_0(980)$ are dynamically generated states from the pseudoscalar meson-pseudoscalar meson interactions in $S$-wave. Up to a global normalization factor, the $ππ$, $K \bar{K}$ and $πη$ invariant mass distributions for the decays of $\bar B^0_s \to η_c π^+ π^-$, $\bar{B}^0_s \to η_c K^+ K^-$, $\bar B^0 \to η_c π^+ π^-$, $\bar{B}^0 \to η_c K^+ K^-$, $\bar{B}^0 \to η_c π^0 η$, $B^- \to η_c K^0 K^-$ and $B^- \to η_c π^- η$ are predicted. Comparison is made with the limited experimental information available and other theoretical calcualtions. Further comparison of these results with coming LHCb measurements will be very valuable to make progress in our understanding of the nature of the low lying scalar mesons, $f_0(500), f_0(980)$ and $a_0(980)$.

hep-ph↗

arXiv2017

Fast simulation of the CEPC detector with Delphes

Fast simulation tools are highly appreciated in particle physics phenomenology studies, especially in the exploration of the physics potential of future experimental facilities. The Circular Electron Positron Collider is a proposed Higgs and Z factory that can precisely measure the Higgs boson properties and the electroweak precision observables. A fast-simulation toolkit dedicated to the CEPC detector has been developed using Delphes. The comparison shows that this fast simulation tool is highly consistent with the full simulation, on a set of benchmark distributions. Therefore, we recommend this fast simulation toolkit for CEPC phenomenological investigations.

hep-ex↗

arXiv2017

Search for a heavy dark photon at future $e^+e^-$ colliders

A coupling of a dark photon $A'$ from a $U(1)_{A'}$ with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter $ε$. A non-zero $ε$ also induces a mixing between $A'$ and $Z$ if dark photon mass $m_{A'}$ is not zero. This mixing can be large when $m_{A'}$ is close to $m_Z$ even if the parameter $ε$ is small. Many efforts have been made to constrain the parameter $ε$ for a low dark photon mass $m_{A'}$ compared with the $Z$ boson mass $m_Z$. We study the search for dark photon in $e^+e^- \to γA' \to γμ^+ μ^-$ for a dark photon mass $m_{A'}$ as large as kinematically allowed at future $e^+e^-$ colliders. For large $m_{A'}$, care should be taken to properly treat possible large mixing between $A'$ and $Z$. We obtain sensitivities to the parameter $ε$ for a wide range of dark photon mass at planed $e^+\;e^-$ colliders, such as Circular Electron Positron Collider (CEPC), International Linear Collider (ILC) and Future Circular Collider (FCC-ee). For the dark photon mass $20~\text{GeV}\lesssim m_{A^{\prime}}\lesssim 330~\text{GeV}$, the $2σ$ exclusion limits on the mixing parameter are $ε\lesssim 10^{-3}-10^{-2}$. The CEPC with $\sqrt{s}=240~\text{GeV}$ and FCC-ee with $\sqrt{s}=160~\text{GeV}$ are more sensitive than the constraint from current LHCb measurement once the dark photon mass $m_{A^{\prime}}\gtrsim 50~\text{GeV}$. For $m_{A^{\prime}}\gtrsim 220~\text{GeV}$, the sensitivity at the FCC-ee with $\sqrt{s}=350~\text{GeV}$ and $1.5~\text{ab}^{-1}$ is better than that at the 13~TeV LHC with $300~\text{fb}^{-1}$, while the sensitivity at the CEPC with $\sqrt{s}=240~\text{GeV}$ and $5~\text{ab}^{-1}$ can be even better than that at 13~TeV LHC with $3~\text{ab}^{-1}$ for $m_{A^{\prime}}\gtrsim 180~\text{GeV}$.

hep-ph↗

arXiv2017

On Uniqueness And Existence of Conformally Compact Einstein Metrics with Homogeneous Conformal Infinity

In this paper we show that for a generalized Berger metric $\hat{g}$ on $S^3$ close to the round metric, the conformally compact Einstein (CCE) manifold $(M, g)$ with $(S^3, [\hat{g}])$ as its conformal infinity is unique up to isometries. For the high-dimensional case, we show that if $\hat{g}$ is an $\text{SU}(k+1)$-invariant metric on $S^{2k+1}$ for $k\geq1$, the non-positively curved CCE metric on the $(2k+1)$-ball $B_1(0)$ with $(S^{2k+1}, [\hat{g}])$ as its conformal infinity is unique up to isometries. In particular, since in \cite{LiQingShi}, we proved that if the Yamabe constant of the conformal infinity $Y(S^{2k+1}, [\hat{g}])$ is close to that of the round sphere then any CCE manifold filled in must be negatively curved and simply connected, therefore if $\hat{g}$ is an $\text{SU}(k+1)$-invariant metric on $S^{2k+1}$ which is close to the round metric, the CCE metric filled in is unique up to isometries. Using the continuity method, we prove an existence result of the non-positively curved CCE metric with prescribed conformal infinity $(S^{2k+1}, [\hat{g}])$ when the metric $\hat{g}$ is $\text{SU}(k+1)$-invariant.

math.DG↗

arXiv2017

Measurement of $\mathrm{H} \to μ^+ μ^-$ production in association with a Z boson at the CEPC

The Circular Electron-Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240-250 GeV and is expected to accumulate an integrated luminosity of 5 ab$^{\rm{-1}}$ with ten years of operation. At CEPC, Higgs bosons are dominantly produced from $ZH$ associated process. Vast amount of Higgs events collected will enable precise studies of its properties including Yukawa couplings to massive particles. With {\sc GEANT4}-based simulation of detector effects, we study CEPC feasibility on measuring Higgs boson decaying into a pair of muons. The results with or without information from Z boson decay products are provided, which show a signal significance of over 10 standard deviations can be achieved and the H-$\mathrmμ$-$\mathrmμ$ coupling can be measured within $10\%$ accuracy.

hep-ex↗

arXiv2017

$H \rightarrow e^+ e^- $ at CEPC: ISR effect with MadGraph

The Circular Electron Positron Collider (CEPC) is a future Higgs factory proposed by the Chinese high energy physics community. It will operate at a center-of-mass energy of 240-250 GeV. The CEPC will accumulate an integrated luminosity of 5 ab$^{\rm{-1}}$ in ten years' operation. With GEANT4-based full simulation samples for CEPC, Higgs boson decaying into electron pair is studied at the CEPC. The upper limit of ${\cal B}(H \rightarrow e^+ e^-)$ could reach 0.024\% at 95\% confidence level. The signal process is generated by MadGraph, with Initial State Radiation (ISR) implemented, as a first step to adjust MadGraph for a electron positron Collider.

hep-ph↗

arXiv2017

An Oracle Property of The Nadaraya-Watson Kernel Estimator for High Dimensional Nonparametric Regression

The celebrated Nadaraya-Watson kernel estimator is among the most studied method for nonparametric regression. A classical result is that its rate of convergence depends on the number of covariates and deteriorates quickly as the dimension grows, which underscores the "curse of dimensionality" and has limited its use in high dimensional settings. In this article, we show that when the true regression function is single or multi-index, the effects of the curse of dimensionality may be mitigated for the Nadaraya-Watson kernel estimator. Specifically, we prove that with $K$-fold cross-validation, the Nadaraya-Watson kernel estimator indexed by a positive semidefinite bandwidth matrix has an oracle property that its rate of convergence depends on the number of indices of the regression function rather than the number of covariates. Intuitively, this oracle property is a consequence of allowing the bandwidths to diverge to infinity as opposed to restricting them all to converge to zero at certain rates as done in previous theoretical studies. Our result provides a theoretical perspective for the use of kernel estimation in high dimensional nonparametric regression and other applications such as metric learning when a low rank structure is anticipated. Numerical illustrations are given through simulations and real data examples.

math.ST↗

arXiv2017

Star-disk interactions in multi-band photometric monitoring of the classical T Tauri star GI Tau

The variability of young stellar objects is mostly driven by star-disk interactions. In long-term photometric monitoring of the accreting T Tauri star GI Tau, we detect extinction events with typical depths of $ΔV \sim 2.5$ mag that last for days-to-months and often appear to occur stochastically. In 2014 - 2015, extinctions that repeated with a quasi-period of 21 days over several months is the first empirical evidence of slow warps predicted from MHD simulations to form at a few stellar radii away from the central star. The reddening is consistent with $R_V=3.85\pm0.5$ and, along with an absence of diffuse interstellar bands, indicates that some dust processing has occurred in the disk. The 2015 -- 2016 multi-band lightcurve includes variations in spot coverage, extinction, and accretion, each of which results in different traces in color-magnitude diagrams. This lightcurve is initially dominated by a month-long extinction event and return to the unocculted brightness. The subsequent light-curve then features spot modulation with a 7.03 day period, punctuated by brief, randomly-spaced extinction events. The accretion rate measured from $U$-band photometry ranges from $1.3\times10^{-8}$ to $1.1\times10^{-10}$ M$_\odot$ yr$^{-1}$ (excluding the highest and lowest 5% of high- and low- accretion rate outliers), with an average of $4.7 \times 10^{-9}$ M$_\odot$ yr$^{-1}$. A total of 50% of the mass is accreted during bursts of $>12.8\times10^{-9}$ M$_\odot$ yr${^{-1}}$, which indicates limitations on analyses of disk evolution using single-epoch accretion rates.

astro-ph.SR↗

arXiv2017

Generalized monogamy inequalities of convex-roof extended negativity in $N$-qubit systems

In this paper, we present some generalized monogamy inequalities based on negativity and convex-roof extended negativity (CREN). These monogamy relations are satisfied by the negativity of $N$-qubit quantum systems $ABC_1\cdots C_{N-2}$, under the partitions $AB|C_1\cdots C_{N-2}$ and $ABC_1|C_2\cdots C_{N-2}$. Furthermore, the $W$-class states are used to test these generalized monogamy inequalities.

quant-ph↗