BCS-BEC crossover in nuclear matter with the relativistic Hartree-Bogoliubov theory

Based on the relativistic Hartree-Bogoliubov theory, the influence of the pairing interaction strength on the di-neutron correlations and the crossover from superfluidity of neutron Cooper pairs in the $^{1}S_{0}$ channel to Bose-Einstein condensation of di-neutron pairs is systematically investigated in the nuclear matter. The bare nucleon-nucleon interaction Bonn-B is taken in the particle-particle channel with an effective factor to simulate the medium effects and take into account the possible ambiguity of pairing force, and the effective interaction PK1 is used in the particle-hole channel. If the effective factor is larger than 1.10, a di-neutron BEC state appears in the low-density limit, and if it is smaller than 0.85, the neutron Cooper pairs are found totally in the weak coupling BCS region. The reference values of several characteristic quantities which characterize the BCS-BEC crossover are obtained respectively from the dimensionless parameter $1/(k_{\rm Fn}a)$ with $a$ the scattering length and $k_{\rm{Fn}}$ the neutron Fermi momentum, the zero-momentum transfer density correlation function D(0) and the effective chemical potential $\nu_{\rm n}$.Comment: 8 pages, 4 figures, 2 tables, Accepted Thursday Jun 14, 2012 for Physical Review

Informal payments in developing countries' public health sector

In China and some other developing countries' public health sectors, many patients give their doctors a payment outside the official channel before a major treatment. This secret payment has been documented as informal payment in the literature. We argue that the fundamental cause for informal payments is that patients have more information about doctors' skill than the government does. The price, set by the government, for services offered by doctors cannot fully differentiate patients' various needs. As a consequence, informal payment rises as a tool for patients to compete for the skillful doctor. We study the welfare implications of different policies that can potentially be used to regulate such payments. Patient heterogeneity plays a central role in welfare implications of different policies: when patients' willingness-to-pay differs a lot, informal payments should be allowed and when it differs little, informal payments should be banned. Also we show that selling the right to choose physicians publicly always improves social welfare.informal payments; public health sector; welfare; efficiency