Variational Study of<ΨΨ> in 1+1 Dimensional Lattice QCD

The Wilson fermion Condensates in 1+1 dimensional Lattice QCD are calculated by using the improved Hamiltonian and the variational method.The results are consistant with the predictions from continuum theory,and are almost independent of the Wilson parameter r. The three-links terms give important contribution to<ψψ> in the improved Hamiltonian theory.     

Fermion Condensates in Lower Dimensional Gauge Theories

Combining a unitary transformation,the variational method and the exact ground state of pure gauge Hamiltonian.we investigate syst matically the vacumm structure and spintaneous chiral-symmetry breaking in (1+1) and (2+1) dimensional Hamiltonian lattice gauge theories with fermions,and obtain nice scaling behaviors for 〈ψψ〉 extending to the weak coupling regime.This paper not only reproduces well the exact value in the continuum Schwinger model,but also predicts the values for the fermion condensates in QCD₂,QED₃ and QCD₃.     

Measurement of J/ψ decays into ΛΛ π+π-

Based on 58 million J/ψ events collected by the BESⅡ detector at the BEPC, J/ψ→ΛΛ π⁺π^- is observed for the first time. The branching fraction is measured to be Br(J/ψ→ΛΛ π⁺π^-)=(4.30±0.13±0.99)×10^-3, excluding the decays to intermediate states, namely J/ψ→Ξ^-Ξ⁺, J/ψ→Σ(1385)^-Σ(1385)⁺, and J/ψ→Σ(1385)⁺Σ(1385)^-. The branching fractions for these intermediate resonance channels are measured to be:Br(J/ψ→Ξ^-Ξ⁺)=（0.90±0.03±0.18）×10^-3, Br(J/ψ→Σ(1385)^-Σ(1385)⁺)=(1.23±0.07±0.30)×10^-3,and Br(J/ψ→Σ(1385)⁺Σ(1385)^-)=(1.50±0.08±0.38)×10^-3, respectively. The angular distribution is of the form dN/d(cosθ)α(1+αcos²θ) with α=(0.35±0.29±0.06) for J/ψ→Ξ^-Ξ⁺, α=(-0.54±0.22±0.10) for J/ψ→Σ(1385)^-Σ(1385)⁺, and α=(-0.35±0.29±0.06) for J/ψ→Σ(1385)⁺Σ(1385)^-.     

Cosmological imprints of Dirac neutrinos in a keV-vacuum 2HDM

The Dirac neutrino masses could be simply generated by a neutrinophilic scalar doublet with a vacuum being dramatically different from the electroweak one. While the case with an eV-scale vacuum has been widely explored previously, we exploit in this work the desert where the scalar vacuum is of \begin{document}$\mathcal{O}(\mathrm{keV})$\end{document} scale. In this regime, there would be rare hope to probe the keV-vacuum neutrinophilic scalar model via the lepton-flavor-violating processes, which makes it distinguishable from the widely considered eV-scale vacuum. Although such a keV-vacuum scenario is inert in the low-energy flavor physics, we show that the baryogenesis realized via the lightest Dirac neutrino can be a natural candidate in explaining the baryon asymmetry of the Universe. Furthermore, the Dirac neutrinos with a keV-vacuum scalar can generate a shift of the effective neutrino number within the range \begin{document}$0.097\leqslant \Delta N_{\rm eff}\leqslant 0.112$\end{document}, which can be probed by the future Simons Observatory experiments. In particular, the model with a minimal value \begin{document}$\Delta N_{\rm eff}=0.097$\end{document} can already be falsified by the future CMB Stage-IV and Large Scale Structure surveys, providing consequently striking exploratory avenues in the cosmological regime for such a keV-vacuum scenario.     

THE BEHAVIOURS OF F2ep(X,Q2)-F2en(X,Q2) AND THE SCALE-BREAKING PARAMETER

The scale-breaking parameter F₂^ep(x, Q²) of non-singlet component F₂^ep-F₂^en and some other quantities in the electro-production process are discussed by usinb the analytic expression for the distribution function of valence quarks in ha.drons up to leading log approximation given by a, previous paper^[1]. Comparisons with data are also given.

     

HADRONIC PRODUCTION OF J/ψ、ψ′(3684) AND THE CONTENT OF THE CHARMED STRATONS IN THE SEA OF THE STRATONS

Hadronic production of J/ψ、ψ′(3684) particles is discussed in this paper on thebasis of reference [1] after considering the massive effects of the charmed straton.The results of [1] are improved.With the aid of the decay of ψ″→DD and the effective coupling constant between ψ″(3772) and the charmed straton we estimate that the content of the charmed stratonin the sea of the stratons is 0.41% of the ordinary stratons at most.     

1－－QQqq STATES,THEIR MIXING WITH QQ STATES,AND HADRONIC TRANSITIONS

In the framework of the MIT bag model and under Born-Oppenheimer approximation, the 1^－－QQqq states and their mixing with QQ states are discussed, where Q=c, b; q=u, d, and both QQ and qq are colour singlets. The mixing is introduced through a coupling, constant. An approximate scaling law for hadronic transitions (QQ)′→(QQ)ππ could be obtained and the ratio of Γ(ψ′→4ππ) to Γ(Υ′→Υππ) could be compatible with the data if the coupling constant is flavour-independent. The mixing is dominated by QQqq states in which qq is a P-wave 0⁺⁺ state and therefore the observed isotropic angular distribution of the pion in ψ′→ψππ and γ′→γππ can be well explained.     

Pions as spin waves: Chiral symmetry breaking in lattice gauge theory

In hamiltonian lattice gauge theory, the fermion vacuum at lowest order in 1/g² can be determined from degenerate perturbation theory plus mean field-spin wave techniques. Using compact QED as an example, we show that: (i) chiral symmetry is spontaneously broken; and (ii) $\text{m}{}_{\mathrm{<mtext>pseudoGoldstone</mtext>}}{}^2\text{∝ m}{}_{\mathrm{<mtext>fermion</mtext>}}\text{〈}\text{ψ}\text{ψ〉}$. The pseudoscalar pseudoGoldstone particles—the “pions” of this abelian theory—correspond to antiferromagnetic spin wave excitations of the fermion vacuum.     

The quenched approximation in some two-dimensional field theories

We investigate the effect of suppressing closed fermion loops (the quenched approximation) in some (1 + 1)-dimensional field theories. In the Schwinger and Thirring models we find that effects of fermion loops on bound state masses can be absorbed in a rescaling of the coupling constant. In the Schwinger model an extra (decoupled) massless ghost appears and the order parameter $\text{〈}\text{ψ}\text{ψ〉}$ becomes infrared divergent. In an extension of the Schwinger model we compute effective lagrangians for the bound state spectrum in the quenched and unquenched case that look rather different.     

THE SPECTRA OF THE NEW PARTICLES

Considering ψ (4030) as a semi stable bound state of D^*D* instead of exitedstate of J/ψ, the spectra of the J/ψ family can de described by the wave equation of har-monic oscillator with mass squared eigen values. The case is similar with that of the or-dinary mesons. The only difference is that the gap of energy level squared for J/ψfamily is as twice large as the ordinary hadrons. The similar conclusion is also valid tothe γ family with energy level gap 5.6 times larger than the ordinary hadrons. In edition, the mixing of S and D wave induced by tensor force is calculated and the energylevel of ψ(3770) with D wave dominance is obtained.     

APPROXIMATE B.S. WAVE FUNCTIONS FOR AN ELECTROMAGNETIC BOUND SYSTEM OF SPINS (1/2, 1/2) OR (1/2, 1/2) WITH UNEQUAL MASSES

The Bethe-Salpeter equation for an electromagnetic bound system of spins (1/2—1/2) or (1/2—1/2) with unequal masses are solved in this paper. The approximate B.S. wave functions for these systems are given. Utilising these wave functions, the decay rate and branching ratio for Ξ⁰→(Σ⁺μ^－)+v_μ are calculated with accuracy up to order O(α). The results are wΞ⁰→(Σ⁺μ^－)+v_μ1.12(1/sec) and R=[wΞ⁰→(Σ⁺μ^－)+v_μ]/[wΞ⁰→(Σ⁺μ^－)+v_μ]4.7×10^-7. Similarly, the process Λ→(pμ^－)+v_μ is also discussed.     

First evidence of ψ(2S)→Ω-Ω+

The decay ψ(2S)→Ω^-Ω⁺ is analyzed using 14×10⁶ ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω^-Ω⁺ to be 1.5×10⁴ at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω⁺ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω⁺ is determined to be (4.80±1.56(stat)±1.30(sys))10⁵.     

Observational constraint on dark energy from quantum uncertainty

We explore the theoretical possibility that dark energy density is derived from massless scalar bosons in vacuum and present a physical model for dark energy. By assuming massless scalar bosons fall into the horizon boundary of the cosmos with the expansion of the universe, we can deduce the uncertainty in the relative position of scalar bosons based on the quantum fluctuation of space-time and the assumption that scalar bosons satisfy P-symmetry under the parity transformation \begin{document}$ {P}\varphi ({r}) = - \varphi ({r})$\end{document}, which can be used to estimate scalar bosons and dark energy density. Furthermore, we attempt to explain the origin of negative pressure from the increasing entropy density of the Boltzmann system and derive the equation for the state parameter, which is consistent with the specific equations of state for dark energy. Finally, we employ the SNIa Pantheon sample and Planck 2018 CMB angular power spectra to constrain the models and provide statistical results for the cosmology parameters.     

Properties of the P_c(4312) pentaquark and its bottom partner

We present an analysis of the newly observed pentaquark P_c(4312)~+ to shed light on its quantum numbers.To do that,the QCD sum rules approach is used.The measured mass of this particle is close to the ∑_c~(++)D~-threshold and has a small width,which supports the possibility of its being a molecular state.We consider an interpolating current in a molecular form and analyze both the positive and negative parity states with spin-1/2.We also consider the bottom counterpart of the state with similar molecular form.Our mass result for the charm pentaquark state supports that the quantum numbers of the observed state are consistent with J~P=1/2~-.     

Explanation of Y(4630) as a hadronic resonant state

Theorists have given various explanations for the discovery of Y(4630). We find that if Y(4630) is interpreted as the D-wave resonant state of the \begin{document}$ \Lambda_c \bar {\Lambda}_c $\end{document} system, the particle mass, decay width, and all quantum numbers are consistent with experimental observations. We use the Bonn approximation to obtain the interaction potential of the one boson exchange model. Then, we extend the complex scaling method to calculate the bound and resonant states. The results indicate that the \begin{document}$ \Lambda_c \bar{\Lambda}_c $\end{document} system can form not only the bound state of the S wave but also the resonant state of the high angular momentum, and the \begin{document}$ ^3D_1 $\end{document} wave resonant state can explain the structure of Y(4630) very well.     

A coupled-channel lattice study of the resonance-like structure Zc(3900)

In this exploratory study, near-threshold scattering of D and \begin{document}$\bar{D}^*$\end{document} meson is investigated using lattice QCD with \begin{document}$N_f=2+1+1$\end{document} twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with \begin{document}$I^G(J^{PC})=1^+(1^{+-})$\end{document} where the resonance-like structure \begin{document}$Z_c(3900)$\end{document} was discovered. We first identify the two most relevant channels and the lattice study is performed in the two-channel scattering model. Combined with the two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results for the scattering length parameters suggest that for the particular lattice parameters that we studied, the best fit parameters do not correspond to the peak in the elastic scattering cross-section near the threshold. Furthermore, in the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond the 3\begin{document}$\sigma$\end{document} level.     

Possible strange hidden-charm pentaquarks from ∑c(*)Ds* and Ξc(',*)* interactions

Using the one-boson-exchange model, we investigate the Λ_cD_s^*, ∑_cD_s^*, ∑_c^*D_s^*, Ξ_cD^*, Ξ'_cD^*, and Ξ_c^*D^* interactions by considering the one-eta-exchange and/or one-pion-exchange contributions. We further predict the existence of hidden-charm molecular pentaquarks. Promising candidates for hidden-charm molecular pentaquarks include a Ξ'_cD^* state with 0((1/2)^-) and the Ξ_c^*D^* states with 0((1/2)^-) and 0((3/2)^-). Experimental searches for these predicted hidden-charm molecular pentaquarks are an interesting future research topic for experiments like LHCb.     

THE TEST OF SLAC METHOD USING LEE MODEL

Treating Lee Model by Slac method,we find that,to state ||V> of one particle and state ||VN> of two particles,there corresponds a solution of Slac bag type re-spectively.The latter bears resemblance to the former in energy especially for ||V> state with the replacement of the interaction constants g by g/√e only.In addition,the“bag”corresponds precisely to the scalar field in ||V> and ||VN> states.However,for ψ_N^- and ψ_V^- field,we get δ-function type solutions by Slac method.They deviate greatly from the rigorous solutions.The“skin confinement”as statedby Bardeen et al.,and Rafelski is closely related to the δ-confinment in the one par-tiele state found here by coherent state approximation.Thus it may not representthe physical picture in the rigorous solution of a quantum field theory.     

Effect of dark energy models on the energy content of charged and rotating black holes

The energy content of the charged-Kerr(CK)spacetime surrounded by dark energy(DE)is investigated using approximate Lie symmetry methods for the differential equations.For this,we consider three different DE scenarios:cosmological constant with an equation of state parameter$ω_q=-2/3,quintessence DE with an equation of state parameterω_c=-1,and a frustrated network of cosmic strings with an equation of state parameterω_n=-1/3.To study the gravitational energy of the CK black hole surrounded by the DE,we explore the symmetries of the 2nd-order perturbed geodesic equations.It is noticed,for all the values ofω,the exact symmetries are recovered as 2nd-order approximate trivial symmetries.These trivial approximate symmetries give the rescaling of arc length parameter s in this spacetime which indicates that the energy in the underlying spacetime has to be rescaled by a factor that depends on the black hole parameters and the DE parameter.This rescaling factor is compared with the factor of the CK spacetime found in[Hussain et al.Gen.Relativ.Gravit.(2009)]and the effects of the DE on it are discussed.It is observed that for all the three values of the equation of state parameterω,the effect of DE results in decreased energy content of the black hole spacetime,regardless of values of the charge Q,spin a and the DE parameterα.This reduction in the energy content due to the involvement of the DE favours the idea of mass reduction of black holes by accretion of DE given by[Babichev et al.Phys.Rev.Lett.(2004)].     

Anisotropic evolution of 4-brane in a 6D generalized Randall-Sundrum model

We investigate a 6 D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant.Each stress-energy tensor T_(ab)~i on the brane is shown to be similar to a constant vacuum energy.This is consistent with the Randall-Sundrum model,in which each 3-brane Lagrangian yielded a constant vacuum energy.By adopting an anisotropic metric ansatz,we obtain the 5 D Friedmann-Robertson-Walker field equations.In a slightly later period,the expansion of the universe is proportional to the square root of time,t~(1/2),which is similar to the period of the radiation-dominated regime.Moreover,we investigate the case with two a(t) and two b(t).In a large range of t,we obtain the 3 D effective cosmological constant Λ_(eff)=-2Ω/30,which is independent of the integral constant.Here,the scale factor is an exponential expansion,which is consistent with our present observation of the universe.Our results demonstrate that it is possible to construct a model that solves the dark energy problem,while guaranteeing a positive brane tension.