arXiv subjects

Gang Li

Publications and source records attributed to Gang Li.

At least 739 records · Page 41Linked to original sources

arXiv2010

A Quenched Study of SU(3) Glueballs at Finite Temperature

Thermal properties of glueballs in SU(3) Yang-Mills theory are investigated in a large temperature range from $0.3T_c$ to $1.9T_c$ on anisotropic lattices. The glueball operators are optimized for the projection of the ground states by the variational method with a smearing scheme. Their thermal correlators are calculated in all 20 symmetry channels. It is found in all channels that the pole masses $M_G$ of glueballs remain almost constant when the temperature is approaching the critical temperature $T_c$ from below, and start to reduce gradually with the temperature going above $T_c$. The correlators in the $0^{++}$, $0^{-+}$, and $2^{++}$ channels are also analyzed based on the Breit-Wigner $\emph{Ansatz}$ by assuming a thermal width $Γ$ to the pole mass $ω_0$ of each thermal glueball ground state. While the values of $ω_0$ are insensitive to $T$ in the whole temperature range, the thermal widths $Γ$ exhibit distinct behaviors at temperatures below and above $T_c$. The widths are very small (approximately few percent of $ω_0$ or even smaller) when $T T_c$ and reach values of roughly $Γ\sim ω_0/2$ at $T\approx 1.9T_c$.

hep-lat↗

arXiv2009

Accessing thermodynamics from dynamical cluster-embedding approaches

Dynamical quantum-cluster approaches, such as different cluster extensions of the dynamical mean-field theory (cluster DMFT) or the variational cluster approximation (VCA), combined with efficient cluster solvers, such as the quantum Monte-Carlo (QMC) method, provide controlled approximations of the single-particle Green's function for lattice models of strongly correlated electrons. To access the thermodynamics, however, a thermodynamical potential is needed. We present an efficient numerical algorithm to compute the grand potential within cluster-embedding approaches that are based on novel continuous-time QMC schemes: It is shown that the numerically exact cluster grand potential can be obtained from a quantum Wang-Landau technique to reweight the coefficients in the expansion of the partition function. The lattice contributions to the grand potential are computed by a proper infinite summation over Matsubara frequencies. A proof of principle is given by applying the VCA to antiferromagnetic (short-range) order in the two-dimensional Hubbard model at finite temperatures.

cond-mat.str-el↗

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

Study of isospin violating $ϕ$ excitation in $e^+e^- \to ωπ^0$

We study the reaction $e^+ e^-\to ωπ^0$ in the vicinity of $ϕ$ mass region. The isospin-violating $ϕ$ excitation is accounted for by two major mechanisms. One is electromagnetic (EM) transition and the other is strong isospin violations. For the latter, we consider contributions from the intermediate hadronic meson loops and $ϕ$-$ρ^0$ mixing as the major mechanisms via the $t$ and s-channel transitions, respectively. By fitting the recent KLOE data, we succeed in constraining the model parameters and extracting the $ϕ\toωπ^0$ branching ratio. It shows that the branching ratio is sensitive to the $ϕ$ excitation line shape and background contributions. Some crucial insights into the correlation between isospin violation and Okubo-Zweig-Iizuka (OZI) rule evading transitions are also learned.

hep-ph↗

arXiv2009

Low-energy $D^{*+}D^0_1$ Scattering and the Resonance-like Structure $Z^+(4430)$

Low-energy scattering of $D^*$ and $D_1$ meson are studied using quenched lattice QCD with improved lattice actions on anisotropic lattices. The calculation is performed within Lüscher's finite-size formalism which establishes the relation between the scattering phase in the infinite volume and the exact energy level in the finite volume. The threshold scattering parameters, namely the scattering length $a_0$ and the effective range $r_0$, for the s-wave scattering in $J^P=0^-$ channel are extracted. After the chiral and continuum extrapolations, we obtain: $a_0=2.52(47)$fm and $r_0=0.7(1)$fm where the errors are purely statistical. Based on these results, we discuss the possibility of a shallow bound state for the two charmed mesons within the non-relativistic potential scattering model. It is argued that, albeit the interaction between the two charmed mesons being attractive, it is unlikely that they can form a shallow bound state in this channel. This calculation provides some useful information on the nature of the newly discovered resonance-like structure $Z^+(4430)$ by the Belle Collaboration.

hep-lat↗

arXiv2009

Towards a dynamical understanding of the non-$D \bar D$ decay of $ψ(3770)$

We investigate the $ψ(3770)$ non-$D\bar{D}$ decays into $VP$, where $V$ and $P$ denote vector and pseudoscalar mesons, respectively, via OZI-rule-evading intermediate meson rescatterings in an effective Lagrangian theory. By identifying the leading meson loop transitions and constraining the model parameters with the available experimental data for $ψ(3770)\to J/ψη$, $ϕη$ and $ρπ$, we succeed in making a quantitative prediction for all $ψ(3770)\to VP$ with $BR_{VP}$ from 0.41% to 0.64%. It indicates that the OZI-rule-evading long-range interactions are still playing a role in $ψ(3770)$ strong decays, and could be a key towards a full understanding of the mysterious $ψ(3770)$ non-$D\bar{D}$ decay mechanism.

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

Parton Distributions

We provide an assessment of the state of the art in various issues related to experimental measurements, phenomenological methods and theoretical results relevant for the determination of parton distribution functions (PDFs) and their uncertainties, with the specific aim of providing benchmarks of different existing approaches and results in view of their application to physics at the LHC. We discuss higher order corrections, we review and compare different approaches to small x resummation, and we assess the possible relevance of parton saturation in the determination of PDFS at HERA and its possible study in LHC processes. We provide various benchmarks of PDF fits, with the specific aim of studying issues of error propagation, non-gaussian uncertainties, choice of functional forms of PDFs, and combination of data from different experiments and different processes. We study the impact of combined HERA (ZEUS-H1) structure function data, their impact on PDF uncertainties, and their implications for the computation of standard candle processes, and we review the recent F_L determination at HERA. Finally, we compare and assess methods for luminosity measurements at the LHC and the impact of PDFs on them.

hep-ph↗

arXiv2008

Further insights into the "$ρπ$ puzzle"

Based on a systematic investigation of $J/ψ(ψ^\prime)\to VP$, where $V$ and $P$ stand for light vector and pseudoscalar mesons, we identify the role played by the electromagnetic (EM) transitions and intermediate meson loop transitions, which are essential ingredients for understanding the $J/ψ$ and $ψ^\prime$ couplings to $VP$. We show that on the one hand, the EM transitions have relatively larger interferences in $ψ^\prime\to ρπ$ and $K^*\bar{K}+c.c.$ as explicitly shown by vector meson dominance (VMD). On the other hand, the strong decay of $ψ^\prime$ receives relatively larger destructive interferences from the intermediate meson loop transitions. By identifying these mechanisms in an overall study of $J/ψ(ψ^\prime)\to VP$, we provide a coherent understanding of the so-called "$ρπ$ puzzle".

hep-ph↗

arXiv2008

Hadronic loop contributions to $J/ψ$ and $ψ^\prime$ radiative decays into $γη_c$ or $γη_c^\prime$

Intermediate hadronic meson loop contributions to $J/ψ$, $ψ^\prime \to γη_c$ ($γη_c^\prime$) are studied apart from the dominant M1 transitions in an effective Lagrangian approach. Due to the property of the unique antisymmetric tensor coupling in $V\to VP$, the hadronic loop transitions provide explicit corrections to the M1 transition amplitudes derived from the naive "quenched" $c\bar{c}$ transitions via the coupling form factors. This mechanism interfering with the M1 transition amplitudes naturally accounts for the deviations from the Godfrey-Isgur model predictions in $J/ψ$ and $ψ^\prime\to γη_c$. It also predicts a small branching ratio of $ψ^\prime\to γη_c^\prime$, which can be examined by experimental measurements at BES and CLEO-c.

hep-ph↗

arXiv2008

Study of the Hubbard model on the triangular lattice using dynamical cluster approximation and dual fermion methods

We investigate the Hubbard model on the triangular lattice at half-filling using the dynamical cluster approximation (DCA) and dual fermion (DF) methods in combination with continuous-time quantum Monte carlo (CT QMC) and semiclassical approximation (SCA) methods. We study the one-particle properties and nearest-neighbor spin correlations using the DCA method. We calculate the spectral functions using the CT QMC and SCA methods. The spectral function in the SCA and obtained by analytic continuation of the Pade approximation in CT QMC are in good agreement. We determine the metal-insulator transition (MIT) and the hysteresis associated with a first-order transition in the double occupancy and nearest-neighbor spin correlation functions as a function of temperature. As a further check, we employ the DF method and discuss the advantages and limitation of the dynamical mean field theory (DMFT), DCA and recently developed DF methods by comparing Green's functions. We find an enhancement of antiferromagnetic (AF) correlations and provide evidence for magnetically ordered phases by calculating the spin susceptibility.

cond-mat.str-el↗

arXiv2008

Lattice susceptibility for 2D Hubbard Model within dual fermion method

In this paper, we present details of the dual fermion (DF) method to study the non-local correction to single site DMFT. The DMFT two-particle Green's function is calculated using continuous time quantum monte carlo (CT-QMC) method. The momentum dependence of the vertex function is analyzed and its renormalization based on the Bethe-Salpeter equation is performed in particle-hole channel. We found a magnetic instability in both the dual and the lattice fermions. The lattice fermion susceptibility is calculated at finite temperature in this method and also in another recently proposed method, namely dynamical vertex approximation (D$Γ$A). The comparison between these two methods are presented in both weak and strong coupling region. Compared to the susceptibility from quantum monte carlo (QMC) simulation, both of them gave satisfied results.

cond-mat.str-el↗

arXiv2008

Decays of $J/ψ$ and $ψ^\prime$ into vector and pseudoscalar meson and the pseudoscalar glueball-$q\bar{q}$ mixing

We introduce a parametrization scheme for $J/ψ(ψ^\prime)\to VP$ where the effects of SU(3) flavor symmetry breaking and doubly OZI-rule violation (DOZI) can be parametrized by certain parameters with explicit physical interpretations. This scheme can be used to clarify the glueball-$q\bar{q}$ mixing within the pseudoscalar mesons. We also include the contributions from the electromagnetic (EM) decays of $J/ψ$ and $ψ^\prime$ via $J/ψ(ψ^\prime)\to γ^*\to VP$. Via study of the isospin violated channels, such as $J/ψ(ψ^\prime)\to ρη$, $ρη^\prime$, $ωπ^0$ and $ϕπ^0$, reasonable constraints on the EM decay contributions are obtained. With the up-to-date experimental data for $J/ψ(ψ^\prime)\to VP$, $J/ψ(ψ^\prime)\to γP$ and $P\to γγ$, etc, we arrive at a consistent description of the mentioned processes with a minimal set of parameters. As a consequence, we find that there exists an overall suppression of the $ψ^\prime\to 3g$ form factors, which sheds some light on the long-standing "$ρπ$ puzzle". By determining the glueball components inside the pseudoscalar $η$ and $η^\prime$ in three different glueball-$q\bar{q}$ mixing schemes, we deduce that the lowest pseudoscalar glueball, if exists, has rather small $q\bar{q}$ component, and it makes the $η(1405)$ a preferable candidate for $0^{-+}$ glueball.

hep-ph↗

arXiv2007

Isospin violation in $ϕ, J/ψ, ψ^\prime \to ωπ^0$ via hadronic loops

In this work, we study the isospin-violating decay of $ϕ\to ωπ^0$ and quantify the electromagnetic (EM) transitions and intermediate meson exchanges as two major sources of the decay mechanisms. In the EM decays, the present datum status allows a good constraint on the EM decay form factor in the vector meson dominance (VMD) model, and it turns out that the EM transition can only account for about $1/4\sim 1/3$ of the branching ratio for $ϕ\to ωπ^0$. The intermediate meson exchanges, $K\bar{K}(K^*)$ (intermediate $K\bar{K}$ interaction via $K^*$ exchanges), $K\bar{K^*}(K)$ (intermediate $K\bar{K^*}$ rescattering via kaon exchanges), and $K\bar{K^*}(K^*)$ (intermediate $K\bar{K^*}$ rescattering via $K^*$ exchanges), which evade the naive Okubo-Zweig-Iizuka (OZI) rule, serve as another important contribution to the isospin violations. They are evaluated with effective Lagrangians where explicit constraints from experiment can be applied. Combining these three contributions, we obtain results in good agreement with the experimental data. This approach is also extended to $J/ψ(ψ^\prime)\to ωπ^0$, where we find contributions from the $K\bar{K}(K^*)$, $K\bar{K^*}(K)$ and $K\bar{K^*}(K^*)$ loops are negligibly small, and the isospin violation is likely to be dominated by the EM transition.

hep-ph↗

arXiv2007

Hadron Scattering in an Asymmetric Box

We propose to study hadron-hadron scattering using lattice QCD in an asymmetric box which allows one to access more non-degenerate low-momentum modes for a given volume. The conventional Lüscher's formula applicable in a symmetric box is modified accordingly. To illustrate the feasibility of this approach, pion-pion elastic scattering phase shifts in the I=2, J=0 channel are calculated within quenched approximation using improved gauge and Wilson fermion actions on anisotropic lattices in an asymmetric box. After the chiral and continuum extrapolation, we find that our quenched results for the scattering phase shifts in this channel are consistent with the experimental data when the three-momentum of the pion is below 300MeV. Agreement is also found when compared with previous theoretical results from lattice and other means. Moreover, with the usage of asymmetric volume, we are able to compute the scattering phases in the low-momentum range (pion three momentum less than about 350MeV in the center of mass frame) for over a dozen values of the pion three-momenta, much more than using the conventional symmetric box with comparable volume.

hep-lat↗

arXiv2006

Study of electromagnetic decay of $J/ψ$ and $ψ^\prime$ to vector and pseudoscalar

The electromagnetic decay contributions to $J/ψ(ψ^\prime)\to VP$, where $V$ and $P$ stand for vector and pseudoscalar meson, respectively, are investigated in a vector meson dominance (VMD) model. We show that $J/ψ(ψ^\prime)\to γ^*\to VP$ can be constrained well with the available experimental information. We find that this process has significant contributions in $ψ^\prime\to VP$ and may play a key role in understanding the deviations from the so-called "12% rule" for the branching ratio fractions between $ψ^\prime\to VP$ and $J/ψ\to VP$. We also address that the "12% rule" becomes very empirical in exclusive hadronic decay channels.

hep-ph↗

arXiv2005

Revisiting the OZI-forbidden Radiative Decays of Orthoquarkonia

It is interesting to investigate the OZI-forbidden radiative orthoquarkonium decays $J/ψ\to γπ^0, γη$ and $γη'$ in perturbative QCD. In this work without the approximations adopted in literature we carry out a full one-loop calculation which involves integrations of 4-point and 5-point loop functions. Our numerical results are in agreement with the present data. We also briefly discuss the decays of $J/ψ\to γ+ρ^0$, as well as $Υ\to π^0γ, ηγ, η'γ$.

hep-ph↗

arXiv2004

Higgs boson pair production in the little Higgs model at hadron colliders

The Higgs boson pair production process at hadron collider provides an opportunity for performing a study of the trilinear Higgs boson self-coupling. In this paper, we analyze the pair production of a neutral Higgs boson via both gluon-gluon and $b$-$\bar{b}$ fusions in the littlest Higgs (LH) model at the CERN LHC. We find that in some parameter space the relative corrections of the total cross section to the SM prediction may reach a value of 24% when $x ~ (=4 f v'/v^2)=0.95$ at the LHC. We conclude that if the parameter $x$ has a value above 0.8, the relative corrections contributed by the LH model reach values beyond 8% and can be observed at the LHC.

hep-ph↗