Ratios of heavy hadron semileptonic decay rates

Ratios of charmed meson and baryon semileptonic decay rates appear to be satisfactorily described by considering only the lowest-lying (S-wave) hadronic final states and assuming the kinematic factor describing phase space suppression is the same as that for free quarks. For example, the rate for $D_s$ semileptonic decay is known to be $(17.0 \pm 5.3)$ lower than those for $D^0$ or $D^+$, and the model accounts for this difference. When applied to hadrons containing $b$ quarks, this method implies that the $B_s$ semileptonic decay rate is about 1% higher than that of the nonstrange $B$ mesons. This small difference thus suggests surprisingly good local quark-hadron duality for $B$ semileptonic decays, complementing the expectation based on inclusive quark-hadron duality that these differences in rates should not exceed a few tenths of a percent. For $\Lambda_b$ semileptonic decay, however, the inclusive rate is predicted to be about 13% greater than that of the nonstrange $B$ mesons. This value, representing a considerable departure from a calculation using a heavy quark expansion, is close to the corresponding experimental ratio $\Gamma(\Lambda_b)/ \bar \Gamma(B) = 1.13 \pm 0.03$ of total decay rates.Comment: 12 pages, no figures. References adde

Multiple transonic solutions and a new class of shock transitions in solar and stellar winds

The steady isothermal solar wind equations are shown to admit, under certain circumstances, mutliple transonic solutions when, for example, momentum deposition gives rise to multiplee critical points in the flow. These multiple solutions consist of a continuous solution and solutions which involve shock transitions between critical solutions. The ambiguity arising from the multiplicity of the solutions can be resolved by following the time evolution of a wind profile with one critical point. Results of the numerical integration of the time-dependent equations with momentum addition show that each of these multiple solutions is physically accessible and depends on the rate of change of momentum deposition. These results suggest that standing shocks are likely to be present in the inner solar wind flow

A note on spectator effects and quark-hadron duality in inclusive beauty decays

In this paper, we evaluate the expectation values of four-quark operators for the inclusive beauty decays from the differences in the inclusive total decay rates, assuming that the heavy quark expansion converges at $O(1/m^3)$. The obtained expectation values yeilds the ratio $\tau(\Lambda_b)/\tau(B)$ close to the experimental onee. We further point out that the quark-hadron duality violation would be rather small allowing predictions of inclusive quantities.Comment: 5 pages, typos corrected, version to be published in PL

Formation of standing shocks in stellar winds and related astrophysical flows

Stellar winds and other analogous astrophysical flows can be described, to lowest order, by the familiar one dimensional hydrodynamic equations which, being nonlinear, admit in some instances discontinuous as well as continuous transonic solutions for identical inner boundary conditions. The characteristics of the time dependent differential equations of motion are described to show how a perturbation changes profile in time and, under well defined conditions, develops into a stationary shock discontinuity. The formation of standing shocks in wind type astrophysical flows depends on the fulfillment of appropriate necessary conditions, which are determined by the conservation of mass, momentum and energy across the discontinuity, and certain sufficient conditions, which are determined by the flow's history

Comparisons of rational engineering correlations of thermophoretically-augmented particle mass transfer with STAN5-predictions for developing boundary layers

Modification of the code STAN5 to properly include thermophoretic mass transport, and examination of selected test cases developing boundary layers which include variable properties, viscous dissipation, transition to turbulence and transpiration cooling. Under conditions representative of current and projected GT operation, local application of St(M)/St(M),o correlations evidently provides accurate and economical engineering design predictions, especially for suspended particles characterized by Schmidt numbers outside of the heavy vapor range

Engineering correlations of variable-property effects on laminar forced convection mass transfer for dilute vapor species and small particles in air

A simple engineering correlation scheme is developed to predict the variable property effects on dilute species laminar forced convection mass transfer applicable to all vapor molecules or Brownian diffusing small particle, covering the surface to mainstream temperature ratio of 0.25 T sub W/T sub e 4. The accuracy of the correlation is checked against rigorous numerical forced convection laminar boundary layer calculations of flat plate and stagnation point flows of air containing trace species of Na, NaCl, NaOH, Na2SO4, K, KCl, KOH, or K2SO4 vapor species or their clusters. For the cases reported here the correlation had an average absolute error of only 1 percent (maximum 13 percent) as compared to an average absolute error of 18 percent (maximum 54 percent) one would have made by using the constant-property results

Constraints on the total coupling strength to bosons in iron based superconductors

At present, there is still no consistent interpretation of the normal and superconducting properties of Fe-based superconductors (FeSCs). The strength of the el-el interaction and the role of correlation effects are under debate. Here, we examine several common materials and illustrate various problems and concepts that are generic for all FeSCs. Based on empirical observations and qualitative insight from density functional theory, we show that the superconducting and low-energy thermodynamic properties of the FeSCs can be described semi-quantitively within multiband Eliashberg theory. We account for an important high-energy mass renormalization phenomenologically,and in agreement with constraints provided by thermodynamic, optical, and angle-resolved photoemission data. When seen in this way, all FeSCs with $T_\mathrm{c} <$ 40~K studied so far are found to belong to an {\it intermediate} coupling regime. This finding is in contrast to the strong coupling scenarios proposed in the early period of the FeSC history.We also discuss several related issues, including the role of band shifts as measured by the positions of van Hove singularities, and the nature of a recently suggested quantum critical point in the strongly hole-doped systems AFe$_2$As$_2$ (A = K, Rb, Cs). Using high-precision full relativistic GGA-band structure calculations, we arrive at a somewhat milder mass renormalization in comparison with previous studies. From the calculated mass anisotropies of all Fermi surface sheets, only the $\varepsilon$-pocket near the corner of the BZ is compatible with the experimentally observed anisotropy of the upper critical field. pointing to its dominant role in the superconductivity of these three compounds.Comment: 19 pages, 9 figure

Properties of the Charmed P-wave Mesons

Two broad charmed mesons, the D_0^* and D_1', have recently been observed. We examine the quark model predictions for the D_0^* and D_1' properties and discuss experimental measurements that can shed light on them. We find that these states are well described as the broad, j=1/2 non-strange charmed P-wave mesons. Understanding the D_0^* and D_1' states can provide important insights into the D_{sJ}^*(2317), D_{sJ}(2460) states whose unexpected properties have led to renewed interest in hadron spectroscopy.Comment: 7 pages. Some additional discussion and reference

Interplay of antiferromagnetism, ferromagnetism and superconductivity in EuFe_2(As_1-xP_x)_2 single crystals

We report a systematic study on the influence of antiferromagnetic and ferromagnetic phases of Eu^2+ moments on the superconducting phase upon doping the As site by isovalent P, which acts as chemical pressure on EuFe_2As_2. Bulk superconductivity with transition temperatures of 22 K and 28 K are observed for x=0.16 and 0.20 samples respectively. The Eu ions order antiferromagnetically for x=0.22 whereupon the Eu ions order ferromagnetically. Density functional theory based calculations reproduce the observed experimental findings consistently. We discuss in detail the coexistence of superconductivity and magnetism in a tiny region of the phase space and comment on the competition of ferromagnetism and superconductivity in the title compound.Comment: 6 pages, 5 figures, 1 tabl