Do correlations create an energy gap in electronic bilayers? Critical analysis of different approaches

This paper investigates the effect of correlations in electronic bilayers on the longitudinal collective mode structure. We employ the dielectric permeability constructed by means of the classical theory of moments. It is shown that the neglection of damping processes overestimates the role of correlations. We conclude that the correct account of damping processes leads to an absence of an energy gap.Comment: 4 page

Dielectric matrix and plasmon dispersion in strongly coupled electronic bilayer liquids

We develop a dielectric matrix and analyze plasmon dispersion in strongly coupled charged-particle bilayers in the quantum domain. The formulation is based on the classical quasi-localized charge approximation (QLCA) and extends the QLCA formalism into the quantum domain. Its development, which parallels that of 2D companion paper [Phys. Rev. E 70, 026406 (2004)] by three of the authors, generalizes the single-layer scalar formalism therein to a bilayer matrix formalism. Using pair correlation function data generated from diffusion Monte Carlo simulations, we calculate the dispersion of the in-phase and out-of-phase plasmon modes over a wide range of in-layer coupling values and layer spacings. The out-of-phase spectrum exhibits an exchange-correlation induced long-wavelength energy gap in contrast to earlier predictions of acoustic dispersion softened by exchange-correlations. The energy gap is similar to what has been previously predicted for classical charged-particle bilayers and subsequently confirmed by recent molecular dynamics computer simulations.Comment: 53 pages including 15 Figures with their captions. Submitted to Physical Review

Factorization of 3-point static structure functions in 3D Yukawa liquids

In many-body systems the convolution approximation states that the 3-point static structure function, $S^{(3)}(\textbf{k}_{1},\textbf{k}_{2})$, can approximately be "factorized" in terms of the 2-point counterpart, $S^{(2)}(\textbf{k}_{1})$. We investigate the validity of this approximation in 3-dimensional strongly-coupled Yukawa liquids: the factorization is tested for specific arrangements of the wave vectors $\textbf{k}_{1}$ and $\textbf{k}_{2}$, with molecular dynamics simulations. With the increase of the coupling parameter we find a breakdown of factorization, of which a notable example is the appearance of negative values of $S^{(3)}(\textbf{k}_{1},\textbf{k}_{2})$, whereas the approximate factorized form is restricted to positive values. These negative values -- based on the quadratic Fluctuation-Dissipation Theorem -- imply that the quadratic part of the density response of the system changes sign with wave number. Our simulations that incorporate an external potential energy perturbation clearly confirm this behavior

The Kalman-Tran-D'Souza Model and the Semileptonic Decay Rates of Heavy Baryons

We present an investigation of the inclusive semileptonic decay widths of the heavy baryons Lambda_Q and Xi_Q, (Q=b,c) performed within a relativistic constituent quark model, formulated on the light-front. In a way conceptually similar to the deep-inelastic scattering case, the H_Q baryon inclusive width is expressed as the integral of the free Q-quark partial width multiplied by a bound-state factor related to the Q-quark distribution function in the H_Q. The non-perturbative meson structure is described through the quark-model wave functions, constructed via the Hamiltonian light-front formalism using as input the Kalman-Tran-D'Souza equal time wave functions. A link between spectroscopic quark models and the H_Q decay physics is obtained in this way. It is shown that the bound-state effects and the Fermi motion of the b-quark remarkably reduce the decay rate with respect to the free-quark result. Our predictions for the BR(Lambda_c ->X_s e nu_e) and BR(Lambda_b->X_c e nu_e) decays are in good agreement with existing data.Comment: 6 pages, latex, espcrc2.sty (included), 3 figures. The invited talk presented by C.S.K. at the 4-th International Conference on Hyperons, Charm and Beauty Hadrons, Valencia, June 27-30, 200

Is the Vlasov equation valid for Yukawa plasmas?

We analyze the Vlasov dispersion relation for Yukawa plasmas in three dimensions for the purpose of identifying coupling parameter domains where the Vlasov approach is justified and the existence of a well-developed RPA type collective excitation is allowed. We establish a rigorous lower bound for the coupling parameter, below which there can be no real solution to the Vlasov dispersion relation. In the coupling domain, where weakly damped solutions do exist, we have focused on the long-wavelength acoustic regime where we establish more restrictive estimates for the lower bound of the coupling parameter. We also derive a general formula for the corresponding acoustic phase velocity, valid over a wide range of coupling parameter/screening parameter ratios above the lower bound. We conclude that the Vlasov approach is tenable only above a critical coupling value. Comparison with Molecular Dynamics simulation results further highlights the limitations of the Vlasov approximation for weakly coupled Yukawa plasmas