arXiv subjects

Xi-Guo Lee

Publications and source records attributed to Xi-Guo Lee.

14 recordsLinked to original sources

arXiv2016

Chandrasekhar's Dynamical Friction and non-extensive statistics

The motion of a point like object of mass $M$ passing through the background potential of massive collisionless particles ($m << M$) suffers a steady deceleration named dynamical friction. In his classical work, Chandrasekhar assumed a Maxwellian velocity distribution in the halo and neglected the self gravity of the wake induced by the gravitational focusing of the mass $M$. In this paper, by relaxing the validity of the Maxwellian distribution due to the presence of long range forces, we derive an analytical formula for the dynamical friction in the context of the $q$-nonextensive kinetic theory. In the extensive limiting case ($q = 1$), the classical Gaussian Chandrasekhar result is recovered. As an application, the dynamical friction timescale for Globular Clusters spiraling to the galactic center is explicitly obtained. Our results suggest that the problem concerning the large timescale as derived by numerical $N$-body simulations or semi-analytical models can be understood as a departure from the standard extensive Maxwellian regime as measured by the Tsallis nonextensive $q$-parameter.

astro-ph.GA↗

arXiv2008

Angular Momentum of a Brane-world Model

In this paper we discuss the properties of the general covariant angular momentum of a five-dimensional brane-world model. Through calculating the total angular momentum of this model, we are able to analyze the properties of the total angular momentum in the inflationary RS model. We show that the space-like components of the total angular momentum of are all zero while the others are non-zero, which agrees with the results from ordinary RS model.

hep-th↗

arXiv2008

Energy-momentum of a Cosmological Brane Model and the Gauge Hierarchy

We analyze the general covariant energy-momentum tensor of the gravitational system in genreal five-dimensional cosmological brane-world models. Then through calculating this energy-momentum for the cosmological generalization of the Randall-Sundrum model, which includes the original RS model as the static limit, we are able to show that the weakness of the gravitation on the "visible" brane is a general feature of this model. This is the origin of the gauge hierarchy from a gravitational point of view. Our results are also consistent with the fact that a gravitational system has vanishing total energy.

hep-th↗

arXiv2008

Strangeness Production Process $pp \to nK^ + Σ^ +$ within Resonance Model

We explore production mechanism and final state interaction in the $pp \to nK^ + Σ^ +$ channel based on the inconsistent experimental data published respectively by COSY-11 and COSY-ANKE. The scattering parameter $a> 0$ for $nΣ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $nΣ^ +$ interaction comparable to $pp$ interaction is also indicated. Based on this analysis we calculate the contribution from resonance $Δ^* (1920)$ through $π^ +$ exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance $Δ^*(1620)$, the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.

nucl-th↗

arXiv2008

The role of $N^{*}(1535)$ in $η'$ production

We study the near-threshold $η'$ production mechanism in nucleon-nucleon and $πN$ collisions under the assumption that sub-threshold resonance $N^{*}(1535)$ is predominant. In an effective Lagrangian approach which gives a reasonable description to the $pN \to pN η$ and $πp \to p η$ reactions, it is found that t-channel $π$ exchange make the dominate contribution to the $pN \to pN η'$ process, and a value of 6.5 for the ratio of $σ(pn \to pn η')$ to $σ(pp \to pp η')$ is predicted. A strong coupling strength of $N^{*}(1535)$ to $η' N$ ($g_{η' NN^*}^2 /4π= 1.1$) is extracted from a combined analysis to $pp \to pp η'$ and $πN \to N η'$, and the possible implication to the intrinsic component of $N^{*}(1535)$ is explored.

nucl-th↗

arXiv2007

Small Cosmological Constants from a Modified Randall-Sundrum Model

We study a mechanism, inspired from the mechanism for generating the gauge hierarchy in Randall-Sundrum model, to investigate the cosmological constant problem. First we analyze the bulk cosmological constant and brane vacuum energies in RS model. We show that the five-dimensional bulk cosmological constant and the vacuum energies of the two branes all obtain their natural values. Finally we argue how we can generate a small four-dimensional effective cosmological constant on the branes through modifying the original RS model.

hep-th↗

arXiv2007

General $SU(2)_L\times SU(2)_R \times U(1)_{EM}$ Sigma Model With External Sources, Dynamical Breaking And Spontaneous Vacuum Symmetry Breaking

We give a general $SU(2)_L\times SU(2)_R$ $\times U(1)_{EM}$ sigma model with external sources, dynamical breaking and spontaneous vacuum symmetry breaking, and present the general formulation of the model. It is found that $σ$ and $π^0$ without electric charges have electromagnetic interaction effects coming from their internal structure. A general Lorentz transformation relative to external sources $J_{gauge}$ $=(J_{A_μ},J_{A_μ^κ})$ is derived, using the general Lorentz transformation and the four-dimensional current of nuclear matter of the ground state with $J_{gauge}$ = 0, we give the four-dimensional general relations between the different currents of nuclear matter systems with $J_{gauge}\neq 0$ and those with $J_{gauge}=0$. The relation of the density's coupling with external magnetic field is derived, which conforms well to dense nuclear matter in a strong magnetic field. We show different condensed effects in strong interaction about fermions and antifermions, and give the concrete scalar and pseudoscalar condensed expressions of $σ_0$ and $π_0$ bosons. About different dynamical breaking and spontaneous vacuum symmetry breaking, the concrete expressions of different mass spectra are obtained in field theory. This paper acquires the running spontaneous vacuum breaking value $σ_0^{\prime},$ and obtains the spontaneous vacuum breaking in terms of the running $σ_0^{\prime}$, which make nucleon, $σ$ and $π$ particles gain effective masses. We achieve both the effect of external sources and nonvanishing value of the condensed scalar and pseudoscalar paticles. It is deduced that the masses of nucleons, $σ$ and $π$ generally depend on different external sources.

hep-th↗

arXiv2007

BRST Invariant Theory Of A Generalized 1+1 Dimensional Nonlinear Sigma Model With Topological Term

We give a generalized Lagrangian density of 1+1 Dimensional O(3) nonlinear sigma model with subsidiary constraints, different Lagrange multiplier fields and topological term, find a lost intrinsic constraint condition, convert the subsidiary constraints into inner constraints in the nonlinear sigma model, give the example of not introducing the lost constraint, by comparing the example with the case of introducing the lost constraint, we obtain that when not introducing the lost constraint, one has to obtain a lot of various non-intrinsic constraints. We further deduce the gauge generator, give general BRST transformation of the model under the general conditions. It is discovered that there exists a gauge parameter originating from the freedom degree of BRST transformation in a general O(3) nonlinear sigma model, and we gain the general commutation relations of ghost field.

hep-th↗

arXiv2007

Topological structure of the many vortices solution in Jackiw-Pi model

We construct an M-solitons solutions in Jackiw-Pi model depends on 5M parameters(two positions, one scale, one phase per solition and one charge of each solution). By using ϕ-mapping method, we discuss the topological structure of the self-duality solution in Jackiw-Pi model in terms of gauge potential decomposition. We set up relationship between Chern-Simons vortices solution and topological number which is determined by Hopf indices and and Brouwer degrees. We also give the quantization of flux in this case.

hep-th↗

arXiv2006

Unified Expressions Of All Integral Variational Principles

In terms of the quantitative causal principle, this paper obtains a general variational principle, gives unified expressions of the general, Hamilton, Voss, Hölder, Maupertuis-Lagrange variational principles of integral style, the invariant quantities of the general, Voss, Hölder, Maupertuis-Lagrange variational principles are given, finally the Noether conservation charges of the general, Voss, Hölder, Maupertuis-Lagrange variational principles are deduced, and the intrinsic relations among the invariant quantities and the Noether conservation charges of the all integral variational principles are achieved.

physics.class-ph↗

arXiv2005

Density dependent relativistic hadron theory for hadron matter with inclusion of pentaquark $Θ^+$

The density dependent relativistic hadron field theory(DDRH) is extended to inclusions of pentaquark $Θ^+$. We investigate In-medium properties of $Θ^+$ and nucleons. As well as the neutron and proton,the effective $Θ^+$ mass decreases as the baryon density increases,and remains larger than nucleons'. The effective mass of $Θ^+$ is calculated,$M^*_{Θ^+}\simeq0.71M_{Θ^+}$ at normal nuclear density with the fraction of $Θ^+$ 0.2. The effective masses of all baryon increase with the increasing fraction of $Θ^+$. The binding energy is also studied. We find the binding energy is much larger than it in nuclear matter without $Θ^+$,and then discuss the stability of the system with conclusions of pentaquark $Θ^+$. It is shown that the system becomes bounder added small fraction of $Θ^+$. Finally we discuss the condition when the system is the most stable and calculate the minimum of binding energy and the fractions of all baryons as functions of baryon density.

nucl-th↗

arXiv2003

Total Nuclear Reaction Cross Section Induced by Halo Nuclei and Stable Nuclei

We develop the method for the calculation of the total reaction cross sections induced by the halo nuclei and stable nuclei. This approach is based on the Glauber theory, which is valid for nuclear reactions at high energy. It is extended for nuclear reactions at low energy and intermediate energy by including both the quantum correction and Coulomb correction under the assumption of the effective nuclear density distribution. The calculated results of the total reaction cross section induced by stable nuclei agree well with the 30 experimental data within 10 percent accuracy.The comparison between the numerical results and the 20 experimental data for the total nuclear reaction cross section induced by the neutron halo nuclei and the proton halo nuclei indicates a satisfactory agreement after considering the halo structure of these nuclei, which implies the quite different mean fields for the nuclear reactions induced by halo nuclei and stable nuclei. The halo nucleon distributions and the root mean square radii of these nuclei can be extracted from above comparison based on the improved Glauber model, which indicate clearly the halo structures of these nuclei. Especially, it is clear to see that the medium correction of the nucleon-nucleon collision has little effect on the total reaction cross sections induced by the halo nuclei due to the very weak binding and the very extended density distribution.

nucl-th↗

arXiv2003

Influence of a momentum dependent interaction on the isospin dependence of fragmentation and dissipation in intermediate energy heavy ion collisions

We studied the influence of a momentum dependent interaction in the context of isopspin effects on fragmentation and dissipation in intermediate energy heavy ion collisions by using an isospin dependent quantum molecular dynamics model. It is shown that the nuclear stopping, the number of nucleons emitted ,and the multiplicity of intermediate mass fragments are larger with a momentum dependent interaction than without. In particular, the differences for these observables, when using an isospin dependent in-medium nucleon nucleon cross section versus an isospin independent one, are also larger at high energies for a momentum dependent interaction than without one. Therefore,momentum dependence enhances the sensitivities of those observables to the isospin effect of the in-medium nucleon nucleon cross section towards high beam energies

nucl-th↗

arXiv2002

Probing the Isospin Dependent In-Medium Nucleon-Nucleon Cross Section by Nucleon Emissions

The effects of the symmetry potential and the isospin dependent in-medium nucleon-nucleon (NN) cross section on the number of proton(neutron) emissions N$_p(N_n$) are studied respectively within an isospin-dependent quantum molecular dynamics (IQMD) model. The isospin dependent in-medium NN cross section is found to have a strong influence on N$_p(N_n$) but N$_p(N_n$) is not sensitive to the symmetry potential for the neutron-deficient colliding system at relatively high energies.We propose to make use of the N$_p(N_n$) as a probe to extract information on the isospin dependent in-medium NN cross section.

nucl-th↗