D Mesons in Nuclear Matter: A DN Coupled-Channel Equations Approach

A set of coupled two-body scattering equations is solved for the DN system embedded in an iso-symmetric nuclear matter. The in-medium behavior of charmed D mesons: (D^+,D^0), is investigated from the self-consistent solution within this scheme. The effective meson-baryon Lagrangian in charm quantum number one sector, the key ingredient in the present study, is adopted from a recent model by Hofmann and Lutz which has aimed at combining the charmed meson degree of freedom in a consistent manner with chiral unitary models. After a critical examination, the original model is modified in several important aspects, such as the method of regularization, in order to be more consistent and practical for our objective. The resultant interaction is used to reproduce the position and width of the s-wave \Lambda_c(2593) resonance in the isospin zero DN channel. In the isospin one channel, it generates a rather wide resonance at \~2770 MeV. The corresponding in-medium solution is then sought by incorporating Pauli blocking and the D- and \pi-meson dressing self-consistently. At normal nuclear matter density, the resultant \Lambda_c (2593) is found to stay narrow and shifted at a lower energy, while the I=1 resonance is lowered in position as well and broadened considerably. The possible implication of our findings on the J/\Psi suppression, etc. in relativistic heavy ion collisions is briefly discussed.Comment: 30 pages, 8 eps figures, some typos and coefficients corrected, published in Phys. Rev.

D mesons and charmonium states in asymmetric nuclear matter at finite temperatures

We investigate the in-medium masses of $D$ and $\bar{D}$ mesons in the isospin-asymmetric nuclear matter at finite temperatures arising due to the interactions with the nucleons, the scalar isoscalar meson $\sigma$, and the scalar iso-vector meson $\delta$ within a SU(4) model. The in-medium masses of $J/\psi$ and the excited charmonium states ($\psi(3686)$ and $\psi(3770)$) are also calculated in the hot isospin asymmetric nuclear matter in the present investigation. These mass modifications arise due to the interaction of the charmonium states with the gluon condensates of QCD, simulated by a scalar dilaton field introduced to incorporate the broken scale invariance of QCD within the effective chiral model. The change in the mass of $J/\psi$ in the nuclear matter with the density is seen to be rather small, as has been shown in the literature by using various approaches, whereas, the masses of the excited states of charmonium ($\psi(3686)$ and $\psi(3770)$) are seen to have considerable drop at high densities. The present study of the in-medium masses of $D$ ($\bar{D}$) mesons as well as of the charmonium states will be of relevance for the observables from the compressed baryonic matter, like the production and collective flow of the $D$ ($\bar D$) mesons, resulting from the asymmetric heavy ion collision experiments planned at the future facility of the FAIR, GSI. The mass modifications of $D$ and $\bar{D}$ mesons as well as of the charmonium states in hot nuclear medium can modify the decay of the charmonium states ($\Psi^{'}, \chi_{c}, J/\Psi$) to $D\bar{D}$ pairs in the hot dense hadronic matter. The small attractive potentials observed for the $\bar{D}$ mesons may lead to formation of the $\bar{D}$ mesic nuclei.Comment: 61 pages, 19 figues, to be published in Phys. Rev.

Coulomb Drag in the Exciton Regime in Electron-Hole Bilayers

We report electrical transport measurements on GaAs/AlGaAs based electron-hole bilayers. These systems are expected to make a transition from a pair of weakly coupled two-dimensional systems to a strongly coupled exciton system as the barrier between the layers is reduced. Once excitons form, phenomena such as Bose-Einstein condensation of excitons could be observed. In our devices, electrons and holes are confined in double quantum wells, and carriers in the devices are induced with top and bottom gates leading to variable density in each layer. Separate contact to each layer allows Coulomb drag transport measurements where current is driven in one layer while voltage is measured in the other. Coulomb drag is sensitive to interlayer coupling and has been predicted to provide a strong signature of exciton condensation. Drag measurement on EHBLs with a 30 nm barrier are consistent with drag between two weakly coupled 2D Fermi systems where the drag decreases as the temperature is reduced. When the barrier is reduced to 20 nm, we observe a consistent increase in the drag resistance as the temperature is reduced. These results indicate the onset of a much stronger coupling between the electrons and holes which leads to exciton formation and possibly phenomena related to exciton condensation.Comment: 12 pages, 3 figure

Charmonium-hadron interactions from QCD

The heavy quark system is an excellent probe to learn about the QCD dynamics at finite density. First, we discuss the properties of the $J/\psi$ and $D$ meson at finite nucleon density. We discuss why their properties should change at finite density and then introduce an exact QCD relation among these hadron properties and the energy momentum tensor of the medium. Second, we discuss attempts to calculate charmonium-hadron total cross section using effective hadronic models and perturbative QCD. We emphasize a recent calculation, where the cross section is derived using QCD factorization theorem. We conclude by discussing some challenges for SIS 200.Comment: 8 pages, Presented at 6th International Conference on Strange Quarks in Matter: 2001: A Flavorspace Odyssey (SQM2001), Frankfurt, Germany, 25-29 Sep 2001, submitted to J. Phys.

D-mesons in asymmetric nuclear matter

We calculate the in-medium $D$ and $\bar D$-meson masses in isospin asymmetric nuclear matter in an effective chiral model. The $D$ and $\bar D$ - mass modifications arising from their interactions with the nucleons and the scalar mesons in the effective hadronic model are seen to be appreciable at high densities and have a strong isospin dependence. These mass modifications can open the channels of the decay of the charmonium states ($\Psi^\prime$, $\chi_c$, $J/\Psi$) to $D \bar D$ pairs in the dense hadronic matter. The isospin asymmetry in the doublet $D=(D^0,D^+)$ is seen to be particularly appreciable at high densities and should show in observables like their production and flow in asymmetric heavy ion collisions in the compressed baryonic matter experiments in the future facility of FAIR, GSI. The results of the present work are compared to calculations of the $D(\bar D$) in-medium masses in the literature using the QCD sum rule approach, quark meson coupling model, coupled channel approach as well as from the studies of quarkonium dissociation using heavy quark potentials from lattice QCD at finite temperatures.Comment: 24 pages, 7 figures, to appear in Phys. Rev.

Properties of D-mesons in nuclear matter within a self-consistent coupled-channel approach

The spectral density of the $D$-meson in the nuclear environment is studied within a self-consistent coupled-channel approach assuming a separable potential for the bare meson-baryon interaction. The $DN$ interaction, described through a G-matrix, generates dynamically the $\Lambda_c$ (2593) resonance. This resonance is the charm counterpart of the $\Lambda$ (1405) resonance generated from the s-wave $\bar{K}N$ interaction in the I=0 channel. The medium modification of the D-meson spectral density due to the Pauli blocking of intermediate states as well as due to the dressing of the D-mesons, nucleons and pions is investigated. We observe that the inclusion of coupled-channel effects and the self-consistent dressing of the $D$-meson results in an overall reduction of the in-medium $D$-meson changes compared to previous work which neglect those effects.Comment: 23 pages, 10 figures, submitted for publicatio

Mass modification of D-meson in hot hadronic matter

We evaluate the in-medium $D$ and $\bar D$-meson masses in hot hadronic matter induced by interactions with the light hadron sector described in a chiral SU(3) model. The effective Lagrangian approach is generalized to SU(4) to include charmed mesons. We find that the D-mass drops substantially at finite temperatures and densities, which open the channels of the decay of the charmonium states ($\Psi^\prime$, $\chi_c$, $J/\Psi$) to $D \bar D$ pairs in the thermal medium. The effects of vacuum polarisations from the baryon sector on the medium modification of the $D$-meson mass relative to those obtained in the mean field approximation are investigated. The results of the present work are compared to calculations based on the QCD sum-rule approach, the quark-meson coupling model, chiral perturbation theory, as well as to studies of quarkonium dissociation using heavy quark potential from lattice QCD.Comment: 18 pages including 7 figures, minor revision of the text, figure styles modified, to appear in Phys. Rev.

Challenges in the delivery of e-government through kiosks

Kiosks are increasingly being heralded as a technology through which governments, government departments and local authorities or municipalities can engage with citizens. In particular, they have attractions in their potential to bridge the digital divide. There is some evidence to suggest that the citizen uptake of kiosks and indeed other channels for e-government, such as web sites, is slow, although studies on the use of kiosks for health information provision offer some interesting perspectives on user behaviour with kiosk technology. This article argues that the delivery of e-government through kiosks presents a number of strategic challenges, which will need to be negotiated over the next few years in order that kiosk applications are successful in enhancing accessibility to and engagement with e-government. The article suggests that this involves consideration of: the applications to be delivered through a kiosk; one stop shop service and knowledge architectures; mechanisms for citizen identification; and, the integration of kiosks within the total interface between public bodies and their communities. The article concludes by outlining development and research agendas in each of these areas.</p

Layer interdependence of transport in an undoped electron-hole bilayer

The layer interdependence of transport in an undoped electron-hole bilayer (uEHBL) device was studied as a function of carrier density, interlayer electric field, and temperature. The uEHBL device consisted of a density tunable, independently contacted two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) induced via field effect in distinct GaAs quantum wells separated by a 30 nm Al$_{0.9}$Ga$_{0.1}$As barrier. Transport measurements were made simultaneously on each layer using the van der Pauw method. An increase in 2DHG mobility with increasing 2DEG density was observed, while the 2DEG mobility showed negligible dependence on the 2DHG density. Decreasing the interlayer electric-field and thereby increasing interlayer separation also increased the 2DHG mobility with negligible effects on the 2DEG mobility. The change in interlayer separation as interlayer electric-field changed was estimated using 2DHG Coulomb drag measurements. The results were consistent with mobility of each layer being only indirectly dependent on the adjacent layer density and dominated by background impurity scattering. Temperature dependencies were also determined for the resistivity of each layer.Comment: 8 pages, 6 figures, submitted to Phys. Rev.

Theory of sound attenuation in glasses: The role of thermal vibrations

Sound attenuation and internal friction coefficients are calculated for a realistic model of amorphous silicon. It is found that, contrary to previous views, thermal vibrations can induce sound attenuation at ultrasonic and hypersonic frequencies that is of the same order or even larger than in crystals. The reason is the internal-strain induced anomalously large Gr\"uneisen parameters of the low-frequency resonant modes.Comment: 8 pages, 3 figures; to appear in PR