arXiv subjects

Hao Zhang

Publications and source records attributed to Hao Zhang.

1,346 records · Page 75Linked to original sources

arXiv2010

An Adaptive Multi-channel P2P Video-on-Demand System using Plug-and-Play Helpers

We present a multi-channel P2P Video-on-Demand (VoD) system using "plug-and-play" helpers. Helpers are heterogenous "micro-servers" with limited storage, bandwidth and number of users they can serve simultaneously. Our proposed system has the following salient features: (1) it minimizes the server load; (2) it is distributed, and requires little or no maintenance overhead and which can easily adapt to system dynamics; and (3) it is adaptable to varying supply and demand patterns across multiple video channels irrespective of video popularity. Our proposed solution jointly optimizes over helper-user topology, video storage allocation and bandwidth allocation. The combinatorial nature of the problem and the system demand for distributed algorithms makes the problem uniquely challenging. By utilizing Lagrangian decomposition and Markov chain approximation based arguments, we address this challenge by designing two distributed algorithms running in tandem: a primal-dual storage and bandwidth allocation algorithm and a "soft-worst-neighbor-choking" topology-building algorithm. Our scheme provably converges to a near-optimal solution, and is easy to implement in practice. Simulation results validate that the proposed scheme achieves minimum sever load under highly heterogeneous combinations of supply and demand patterns, and is robust to system dynamics of user/helper churn, user/helper asynchrony, and random delays in the network.

cs.NI↗

arXiv2010

Color Sextet Scalars in Early LHC Experiments

We explore the potential for discovery of an exotic color sextet scalar in same-sign top quark pair production in early running at the LHC. We present the first phenomenological analysis at colliders of color sextet scalars with full top quark spin correlations included. We demonstrate that one can measure the scalar mass, the top quark polarization, and confirm the scalar resonance with 1 inverse fb of integrated luminosity. The top quark polarization can distinguish gauge triplet and singlet scalars.

hep-ph↗

arXiv2010

Color Sextet Vector Bosons and Same-Sign Top Quark Pairs at the LHC

We investigate the production of beyond-the-standard-model color-sextet vector bosons at the Large Hadron Collider and their decay into a pair of same-sign top quarks. We demonstrate that the energy of the charged lepton from the top quark semi-leptonic decay serves as a good measure of the top-quark polarization, which, in turn determines the quantum numbers of the boson and distinguishes vector bosons from scalars.

hep-ph↗

arXiv2010

Airborne Radar STAP using Sparse Recovery of Clutter Spectrum

Space-time adaptive processing (STAP) is an effective tool for detecting a moving target in spaceborne or airborne radar systems. Statistical-based STAP methods generally need sufficient statistically independent and identically distributed (IID) training data to estimate the clutter characteristics. However, most actual clutter scenarios appear only locally stationary and lack sufficient IID training data. In this paper, by exploiting the intrinsic sparsity of the clutter distribution in the angle-Doppler domain, a new STAP algorithm called SR-STAP is proposed, which uses the technique of sparse recovery to estimate the clutter space-time spectrum. Joint sparse recovery with several training samples is also used to improve the estimation performance. Finally, an effective clutter covariance matrix (CCM) estimate and the corresponding STAP filter are designed based on the estimated clutter spectrum. Both the Mountaintop data and simulated experiments have illustrated the fast convergence rate of this approach. Moreover, SR-STAP is less dependent on prior knowledge, so it is more robust to the mismatch in the prior knowledge than knowledge-based STAP methods. Due to these advantages, SR-STAP has great potential for application in actual clutter scenarios.

cs.IT↗

arXiv2009

A Dark Matter Model with Non-Abelian Gauge Symmetry

We propose a dark matter model in which the dark sector is gauged under a new SU(2) group. The dark sector consists of SU(2) dark gauge fields, two triplet dark Higgs fields, and two dark fermion doublets (dark matter candidates in this model). The dark sector interacts with the SM sector through kinetic and mass mixing operators. The model explains both PAMELA and Fermi LAT data very well and also satisfies constraints from both the DM relic density and Standard Model precision observables. The phenomenology of the model at the LHC is also explored.

hep-ph↗

arXiv2009

Fixed-domain asymptotic properties of tapered maximum likelihood estimators

When the spatial sample size is extremely large, which occurs in many environmental and ecological studies, operations on the large covariance matrix are a numerical challenge. Covariance tapering is a technique to alleviate the numerical challenges. Under the assumption that data are collected along a line in a bounded region, we investigate how the tapering affects the asymptotic efficiency of the maximum likelihood estimator (MLE) for the microergodic parameter in the Matérn covariance function by establishing the fixed-domain asymptotic distribution of the exact MLE and that of the tapered MLE. Our results imply that, under some conditions on the taper, the tapered MLE is asymptotically as efficient as the true MLE for the microergodic parameter in the Matérn model.

math.ST↗

arXiv2009

An Efficient Greedy Algorithm for Sparse Recovery in Noisy Environment

Greedy algorithm are in widespread use for sparse recovery because of its efficiency. But some evident flaws exists in most popular greedy algorithms, such as CoSaMP, which includes unreasonable demands on prior knowledge of target signal and excessive sensitivity to random noise. A new greedy algorithm called AMOP is proposed in this paper to overcome these obstacles. Unlike CoSaMP, AMOP can extract necessary information of target signal from sample data adaptively and operate normally with little prior knowledge. The recovery error of AMOP is well controlled when random noise is presented and fades away along with increase of SNR. Moreover, AMOP has good robustness on detailed setting of target signal and less dependence on structure of measurement matrix. The validity of AMOP is verified by theoretical derivation. Extensive simulation experiment is performed to illustrate the advantages of AMOP over CoSaMP in many respects. AMOP is a good candidate of practical greedy algorithm in various applications of Compressed Sensing.

cs.IT↗

arXiv2009

Threshold Resummation Effects in Neutral Higgs Boson Production by Bottom Quark Fusion at the CERN Large Hadron Collider

We investigate the QCD effects in the production of neutral Higgs bosons via bottom quark fusion in both the standard model and the minimal supersymmetric standard model at the CERN Large Hadron Collider. We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. We use the soft-collinear effective theory to resum the large logarithms near threshold from soft gluon emission. Our results show that the resummation effects can enhance the total cross sections by about 5% compared with the NLO results.

hep-ph↗

arXiv2009

A Class of Novel STAP Algorithms Using Sparse Recovery Technique

A class of novel STAP algorithms based on sparse recovery technique were presented. Intrinsic sparsity of distribution of clutter and target energy on spatial-frequency plane was exploited from the viewpoint of compressed sensing. The original sample data and distribution of target and clutter energy was connected by a ill-posed linear algebraic equation and popular $L_1$ optimization method could be utilized to search for its solution with sparse characteristic. Several new filtering algorithm acting on this solution were designed to clean clutter component on spatial-frequency plane effectively for detecting invisible targets buried in clutter. The method above is called CS-STAP in general. CS-STAP showed their advantage compared with conventional STAP technique, such as SMI, in two ways: Firstly, the resolution of CS-STAP on estimation for distribution of clutter and target energy is ultra-high such that clutter energy might be annihilated almost completely by carefully tuned filter. Output SCR of CS-STAP algorithms is far superior to the requirement of detection; Secondly, a much smaller size of training sample support compared with SMI method is requested for CS-STAP method. Even with only one snapshot (from target range cell) could CS-STAP method be able to reveal the existence of target clearly. CS-STAP method display its great potential to be used in heterogeneous situation. Experimental result on dataset from mountaintop program has provided the evidence for our assertion on CS-STAP.

cs.IT↗

arXiv2009

Spin transport properties of a quantum dot coupled to ferromagnetic leads with noncollinear magnetizations

A correct general formula for the spin current through an interacting quantum dot coupled to ferromagnetic leads with magnetization at an arbitrary angle $θ$ is derived within the framework of the Keldysh formalism. Under asymmetric conditions, the spin current component J_{z} may change sign for $0<θ<π$. It is shown that the spin current and spin tunneling magnetoresistance exhibit different angle dependence in the free and Coulomb blockade regimes. In the latter case, the competition of spin precession and the spin-valve effect could lead to an anomaly in the angle dependence of the spin current.

cond-mat.mes-hall↗

arXiv2009

Next-to-leading order QCD corrections to the top quark decay via model-independent FCNC couplings

D0 and CDF collaborations at the Fermilab Tevatron have searched for non-standard-model single top-quark production and set upper limits on the anomalous top quark flavor-changing neutral current (FCNC) couplings $κ^g_{tc}/Λ$ and $κ^g_{tu}/Λ$ using the measurement of total cross section calculated at the next-to-leading order (NLO) in QCD. In this Letter, we report on the effect of anomalous FCNC couplings to various decay branching ratios of the top quark, calculated at the NLO. This result is not only mandatory for a consistent treatment of both the top quark production and decay via FCNC couplings by D0 and CDF at the Tevatron but is also important for the study of ATLAS and CMS sensitivity to these anomalous couplings at the CERN LHC. We find that the NLO corrections to the partial decay widths of the three decay channels $ t\to q + g$, $ t\to q + γ$ and $ t\to q + Z$ are at the order of 10% in magnitude and modify their branching ratios by about 20%, 0.4% and 2%, respectively, as compared to their leading order predictions.

hep-ph↗

arXiv2008

Grain Boundary Motion Exhibits the Dynamics of Glass-Forming Liquids

Polycrystalline materials can be viewed as composites of crystalline particles or grains separated from one another by thin amorphous grain boundary (GB) regions. While GB have been exhaustively investigated at low temperatures, where these regions resolve into complex ordered structures accessible to measurement, much less is known about them at higher temperatures where the GB can exhibit significant mobility, structural disorder, and where experimental characterization methods are limited. The time and spatial scales accessible to molecular dynamics (MD) simulation make this method appropriate for investigating both the dynamical and structural properties of grain boundaries at elevated temperatures. In the present study, we use MD simulations to determine how the GB dynamics changes with temperature and applied stress. It has long been hypothesized that GB have features in common with glass-forming liquids based on the processing characteristics of polycrystalline materials. We find remarkable support for this suggestion, as evidenced by string-like collective motion, transient caging of atom motion, and non-Arrhenius (Vogel-Fulcher) temperature dependence of GB mobility. Evidently, the frustration caused by the inability of atoms in GB region to simultaneously order with respect to competing grains is responsible for this striking similarity. The paradigm that grains in a polycrystalline material are encapsulated by a frustrated fluid provides a powerful conceptual model of polycrystalline materials, pointing the way to improved control over their material properties.

cond-mat.mtrl-sci↗

arXiv2007

Contributions from SUSY-FCNC couplings to the interpretation of the HyperCP events for the decay Σ^+ \to p μ^+ μ^-

The observation of three events for the decay $Σ^+ \to p μ^+ μ^-$ with a dimuon invariant mass of $214.3\pm0.5$MeV by the HyperCP collaboration imply that a new particle X may be needed to explain the observed dimuon invariant mass distribution. We show that there are regions in the SUSY-FCNC parameter space where the $A^0_1$ in the NMSSM can be used to explain the HyperCP events without contradicting all the existing constraints from the measurements of the kaon decays, and the constraints from the $K^0-\bar{K}^0$ mixing are automatically satisfied once the constraints from kaon decays are satisfied.

hep-ph↗

arXiv2007

Unparticle Physics and Supersymmetry Phenomenology

We show a natural form of the interaction between unparticle and supersymmetry. Using the couplings of unparticle to supersymmetry presented, as examples, we calculate the differential decay rates for the processes ${\it {\tilde f}}\to {\it f}+{\cal U}_{3/2}$, ${\it {\tilde χ}}^0\to{\it γ}+{\cal U}_{3/2}$, ${\it {\tilde χ}}^\pm\to W^\pm+{\cal U}_{3/2}$ and ${\it {\tilde χ}}^0\to Z^0+{\cal U}_{3/2}$. Finally, we discuss the phenomenological implication of our results and give some comments.

hep-ph↗