arXiv subjects

L. C. Liu

Publications and source records attributed to L. C. Liu.

11 recordsLinked to original sources

arXiv2015

Eta-mesic nuclei: past, present, future

Eta-mesic nucleus or the quasibound nuclear state of an eta ($η$) meson in a nucleus is caused by strong-interaction force alone. This new type of nuclear species, which extends the landscape of nuclear physics, has been extensively studied since its prediction in 1986. In this paper, we review and analyze in great detail the models of the fundamental $η$--nucleon interaction leading to the formation of an $η$--mesic nucleus, the methods used in calculating the properties of a bound $η$, and the approaches employed in the interpretation of the pertinent experimental data. In view of the successful observation of the $η$--mesic nucleus $^{25}$Mg$_η$ and other promising experimental results, future direction in searching for more $η$--mesic nuclei is suggested.

nucl-th↗

arXiv2010

Eta-Mesic Nucleus and COSY-GEM Data

The experimental data of the COSY-GEM Collaboration for the recoil-free transfer reaction p (27Al, 3He) π- p' X, leading to the formation of bound state of eta (η) meson in 25Mg nucleus, is reanalyzed in this paper. In particular, predicted values of binding energy and half-width of the η-mesic nucleus 25Mgη, given by different theoretical approaches, are compared with the ones obtained from the experimental missing mass spectrum. It is found that the spectrum can be explained reasonably well if interference effect of another process, where ηis not bound in 25Mg but is scattered by the nucleus and emerge as a pion, is taken into account. The data also indicate that the interaction between N*(1535) and a nucleus is attractive in nature.

nucl-th↗

arXiv2009

Eta-Mesic Nucleus: A New Form of Nuclear Matter

Formation of eta-mesic nucleus, a bound state of an eta meson in a nucleus, is reviewed in this paper. Three different theoretical approaches are used to calculate the binding energies and widths of such nuclei. The effect of eta-mesic nucleus in pion double-charge-exchange reaction is discussed. Experimental efforts by different groups to detect the nucleus are also discussed. The ramifications of the theoretical and experimental studies of the bound state of eta in a nucleus are pointed out.

nucl-th↗

arXiv2002

Cluster Transformation Coefficients for Structure and Dynamics Calculations in n-Particle Systems: Atoms, Nuclei, and Quarks

The structure and dynamics of an n-particle system are described with coupled nonlinear Heisenberg's commutator equations where the nonlinear terms are generated by the two-body interaction that excites the reference vacuum via particle-particle and particle-hole excitations. Nonperturbative solutions of the system are obtained with the use of dynamic linearization approximation and cluster transformation coefficients. The dynamic linearization approximation converts the commutator chain into an eigenvalue problem. The cluster coefficients factorize the matrix elements of the (n)-particles or particle-hole systems in terms of the matrix elements of the (n-1)-systems coupled to a particle-particle, particle-hole, and hole-hole boson. Group properties of the particle-particle, particle-hole, and hole-hole permutation groups simplify the calculation of these coefficients. The particle-particle vacuum-excitations generate superconductive diagrams in the dynamics of 3-quarks systems. Applications of the model to fermionic and bosonic systems are discussed.

hep-th↗

arXiv2002

Dependence of calculated binding energies and widths of $η$-mesic nuclei on treatment of subthreshold $η$-nucleon interaction

We demonstrate that the binding energies and widths of eta-mesic nuclei depend strongly on subthreshold eta-N interaction. This strong dependence is made evident from comparing three different eta-nucleus optical potentials: (1) a microscopic optical potential taking into account the full effects of off-shell eta-nucleon interactions; (2) a factorization approximation to the microscopic optical potential where a downward energy shift parameter is introduced to approximate the subthreshold eta-nucleon interaction; and (3) an optical potential using on-shell eta-nucleon scattering length as the interaction input. Our analysis indicates that the in-medium $η$N interaction for bound-state formation is about 30 MeV below the free-space $η$N threshold, which causes a substantial reduction of the attractive force between the $η$ and nucleon with respect to that implied by the scattering length. Consequently, the scattering-length approach overpredicts the binding energies and caution must be exercised when these latter predictions are used as guide in searching for $η$-nucleus bound states. We also show that final-state-interaction analysis cannot provide an unequivocal determination of the existence of $η$-nucleus bound state. More direct measurements are, therefore, necessary.

nucl-th↗

arXiv2002

The width of the ξ(2230) meson

A lower bound of 135 MeV for the width of the ξmeson is obtained from analyzing the pp and pbar-p interactions by use of Regge theory. The pp data exclude a narrow ξas the latter would lead to total pbar-p cross sections far exceeding the measured ones. The broad width explains why the ξmay not be seen in pbarp-p experiments.

hep-ph↗

arXiv2000

The Xi(2230) Meson and The Pomeron Trajectory

We examine the possibility that the xi(2230) meson is a member of the Pomeron trajectory. A method of connecting the xi --> p pbar decay width and the pp cross sections through the Pomeron residue function is presented. We have used a relativistic, singularity-free form factor to make the analytic continuation of the residue function between crossed channels. We predict that if the xi(2230) meson is a Pomeron, then it should have a xi --> p pbar decay width of about 2 MeV.

hep-ph↗

arXiv1999

Collectivity in the Brain Sensory Response

A question of cooperative effects in auditory brain processing on various space- and time-scales is addressed. The experimental part of our study is based on Multichannel Magnetoencephalography recordings in normal human subjects. Left, right and binaural stimulations were used, in separate runs, for each subject. The resulting time-series representing left and right auditory cortex activity provide a clear evidence for two levels of neuronal cooperation. One is the local hemispheric collective response, termed M100 for its maximum at around 100ms after a stimulus onset. Its only global characteristics turn out to be time-locked to a stimulus, however, which means that the detailed neuronal evolution is largely stochastic. This, together with the $1/f$ character of the corresponding power spectrum indicates self-organized criticality as an underlying mechanism. The second level is communication between the two hemispheres with clear laterality effects: as a rule, the contralateral hemisphere leads by $\sim$10ms. Mutual information analysis points to a direct information transport as a way of this communication.

cond-mat↗

arXiv1998

Cooperative dynamics in auditory brain response

Simultaneous estimates of the activity in the left and right auditory cortex of five normal human subjects were extracted from Multichannel Magnetoencephalography recordings. Left, right and binaural stimulation were used, in separate runs, for each subject. The resulting time-series of left and right auditory cortex activity were analysed using the concept of mutual information. The analysis constitutes an objective method to address the nature of inter-hemispheric correlations in response to auditory stimulations. The results provide a clear evidence for the occurrence of such correlations mediated by a direct information transport, with clear laterality effects: as a rule, the contralateral hemisphere leads by 10-20ms, as can be seen in the average signal. The strength of the inter-hemispheric coupling, which cannot be extracted from the average data, is found to be highly variable from subject to subject, but remarkably stable for each subject.

physics.bio-ph↗

arXiv1995

Composite vertices that lead to soft form factors

The momentum-space cut-off parameter $Λ$ of hadronic vertex functions is studied in this paper. We use a composite model where we can measure the contributions of intermediate particle propagations to $Λ$. We show that in many cases a composite vertex function has a much smaller cut-off than its constituent vertices, particularly when light constituents such as pions are present in the intermediate state. This suggests that composite meson-baryon-baryon vertex functions are rather soft, i.e., they have Λconsiderably less than 1 GeV. We discuss the origin of this softening of form factors as well as the implications of our findings on the modeling of nuclear reactions.

nucl-th↗

arXiv1994

Pionic Content of Rho-N-N and Rho-N-Delta Vertex Functions

The dynamical content of rho-N-N and rho-N-Delta vertex functions is studied with a mesonic model. A set of coupled integral equations satisfied by these vertex functions were solved self-consistently. These soulutions indicate that the dominant mesonic content arises from di-pion dynamics. With the experimentally determined pion-baryon-baryon coupling constants and ranges as input, the model predicts a g_{ρNN} that agrees with the meson-exchange-potential results. On the other hand, it predicts a smaller f_{ρNΔ} and much softer form factors. Implications of the findings on the use of phenomenological coupling constants in nuclear reaction studies are discussed.

nucl-th↗