Cs adsorption on Si(001) surface: ab initio study

First-principles calculations using density functional theory based on norm-conserving pseudopotentials have been performed to investigate the Cs adsorption on the Si(001) surface for 0.5 and 1 ML coverages. We found that the saturation coverage corresponds to 1 ML adsorption with two Cs atoms occupying the double layer model sites. While the 0.5 ML covered surface is of metallic nature, we found that 1 ML of Cs adsorption corresponds to saturation coverage and leads to a semiconducting surface. The results for the electronic behavior and surface work function suggest that adsorption of Cs takes place via polarized covalent bonding.Comment: 8 pages, 7 figure

Phylogeny-structured carbohydrate metabolism across microbiomes collected from different units in wastewater treatment process

With respect to global priority for bioenergy production from plant biomass, understanding the fundamental genetic associations underlying carbohydrate metabolisms is crucial for the development of effective biorefinery process. Compared with gut microbiome of ruminal animals and wood-feed insects, knowledge on carbohydrate metabolisms of engineered biosystems is limited.published_or_final_versio

Radiative decays of charmonium into light mesons

We apply perturbative QCD to the radiative decays of charmonia $J/\psi$ and $\chi_{cJ}$ into light mesons. We perform a complete numerical calculation for the quark-gluon loop diagrams involved in these processes. The calculated $J/\psi$ decay branching ratios to P-wave mesons $f_2(1270)$ and $f_1(1285)$ fit the data well, while that of $f_0(980)$ (if treated as an $s\bar s$ meson) is predicted to be $1.6\times 10^{-4}$, which implies that $f_0(1710)$ can not be the $s\bar s$ or $(u\bar u+d\bar d)/\sqrt{2}$ meson. Decays of P-wave charmonia $\chi_{cJ}\to \rho(\omega, \phi)\gamma$ (J=0,1,2) are also studied, and the branching ratio of $\chi_{c1}\to \rho\gamma$ is predicted to be $1.4\times 10^{-5}$, which may be tested by CLEO-c and BESIII with future experiments

Next-to-Leading Order QCD Correction to e+e−→J/ψ+ηc\bm{e^+ e^- \to J/\psi + \eta_c} at s=10.6\sqrt {s}=10.6GeV}

One of the most challenging open problems in heavy quarkonium physics is the double charm production in $e^+e^-$ annihilation at B factories. The measured cross section of $e^+ e^- \to J/\psi + \eta_c$ is much larger than leading order (LO) theoretical predictions. With the nonrelativistic QCD factorization formalism, we calculate the next-to-leading order (NLO) QCD correction to this process. Taking all one-loop self-energy, triangle, box, and pentagon diagrams into account, and factoring the Coulomb-singular term into the $c\bar c$ bound state wave function, we get an ultraviolet and infrared finite correction to the cross section of $e^+e^-\to J/\psi + \eta_c$ at $\sqrt{s} =10.6$ GeV. We find that the NLO QCD correction can substantially enhance the cross section with a K factor (the ratio of NLO to LO) of about 1.8-2.1; hence it greatly reduces the large discrepancy between theory and experiment. With $m_c=1.4{\rm GeV}$ and $\mu=2m_c$, the NLO cross section is estimated to be 18.9 fb, which reaches to the lower bound of experiment.Comment: Version appeared in PRL, Figure 3 added showing the renormalization scale dependence of the cross section, new BaBar data adde

Higher Charmonia and X,Y,Z states with Screened Potential

We incorporate the color-screening effect due to light quark pair creation into the heavy quark-antiquark potential, and investigate the effects of screened potential on the spectrum of higher charmonium. We calculate the masses, electromagnetic decays, and E1 transitions of charmonium states in the screened potential model, and propose possible assignments for the newly discovered charmonium or charmonium-like $"X,Y,Z"$ states. We find the masses of higher charmonia with screened potential are considerably lower than those with unscreened potential. The $\chi_{c2}(2P)$ mass agrees well with that of the Z(3930), and the mass of $\psi(4415)$ is compatible with $\psi(5S)$ rather than $\psi(4S)$. In particular, the discovered four $Y$ states in the ISR process, i.e., $Y(4008), Y(4260), Y(4320/4360), Y(4660)$ may be assigned as the $\psi(3S), \psi(4S), \psi(3D), \psi(6S)$ states respectively. The X(3940) and X(4160) found in the double charmonium production in $e^+e^-$ annihilation may be assigned as the $\eta_c(3S)$ and $\chi_{c0}(3P)$ states. Based on the calculated E1 transition widths for $\chi_{c1}(2P)\to \gamma J/\psi$ and $\chi_{c1}(2P)\to \gamma \psi(2S)$ and other results, we argue that the X(3872) may be a $\chi_{c1}(2P)$ dominated charmonium state with some admixture of the $D^0\bar{D}^{*0}$ component. Possible problems encountered in these assignments and comparisons with other interpretations for these $X,Y,Z$ states are discussed in detail. We emphasize that more theoretical and experimental investigations are urgently needed to clarify these assignments and other interpretations.Comment: Total width of X(3872) reestimated, references added; 12 pages, 1 figure; published version in PR

Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections

We estimate the decay rates of $\eta_c\rightarrow 2\gamma$, $\eta_c'\rightarrow 2\gamma$, and $J/\psi\rightarrow e^+ e^-$, $\psi^\prime\rightarrow e^+e^-$, by taking into account both relativistic and QCD radiative corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired interquark potential are used to calculate the wave functions and decay widths for these $c\bar{c}$ states. We find that the relativistic correction to the ratio $R\equiv \Gamma (\eta_c \rightarrow 2\gamma)/ \Gamma (J/ \psi \rightarrow e^+ e^-)$ is negative and tends to compensate the positive contribution from the QCD radiative correction. Our estimate gives $\Gamma(\eta_c \rightarrow 2\gamma)=(6-7) ~keV$ and $\Gamma(\eta_c^\prime \rightarrow 2\gamma)=2 ~keV$, which are smaller than their nonrelativistic values. The hadronic widths $\Gamma(\eta_c \rightarrow 2g)=(17-23) ~MeV$ and $\Gamma(\eta_c^\prime \rightarrow 2g)=(5-7)~MeV$ are then indicated accordingly to the first order QCD radiative correction, if $\alpha_s(m_c)=0.26-0.29$. The decay widths for $b\bar b$ states are also estimated. We show that when making the assmption that the quarks are on their mass shells our expressions for the decay widths will become identical with that in the NRQCD theory to the next to leading order of $v^2$ and $\alpha_s$.Comment: 14 pages LaTex (2 figures included

On the theoretical and experimental uncertainties in the extraction of the J/psi absorption cross section in cold nuclear matter

We investigate the cold nuclear matter effects on $J/\psi$ production, whose understanding is fundamental to study the quark-gluon plasma. Two of these effects are of particular relevance: the shadowing of the parton distributions and the nuclear absorption of the $c\bar{c}$ pair. If $J/\psi$'s are not produced {\it via} a $2 \to 1$ process as suggested by recent theoretical works, one has to modify accordingly the way to compute the nuclear shadowing. This naturally induces differences in the absorption cross-section fit to the data. A careful analysis of these differences however requires taking into account the experimental uncertainties and their correlations, as done in this work for $d$Au collisions at \sqrtsNN=200\mathrm{GeV}, using several shadowing parametrisations.Comment: 6 pages, 1 table, 3 figures, Submitted to J. Phys. G, talk given at the International Conference on Strangeness in Quark Matter (SQM2009), Buzios, Brasil, Sep. 27 - Oct. 2, 200

Well-posedness of the Viscous Boussinesq System in Besov Spaces of Negative Order Near Index s=−1s=-1

This paper is concerned with well-posedness of the Boussinesq system. We prove that the $n$ ($n\ge2$) dimensional Boussinesq system is well-psoed for small initial data $(\vec{u}_0,\theta_0)$ ($\nabla\cdot\vec{u}_0=0$) either in $({B}^{-1}_{\infty,1}\cap{B^{-1,1}_{\infty,\infty}})\times{B}^{-1}_{p,r}$ or in ${B^{-1,1}_{\infty,\infty}}\times{B}^{-1,\epsilon}_{p,\infty}$ if $r\in[1,\infty]$, $\epsilon>0$ and $p\in(\frac{n}{2},\infty)$, where $B^{s,\epsilon}_{p,q}$ ($s\in\mathbb{R}$, $1\leq p,q\leq\infty$, $\epsilon>0$) is the logarithmically modified Besov space to the standard Besov space $B^{s}_{p,q}$. We also prove that this system is well-posed for small initial data in $({B}^{-1}_{\infty,1}\cap{B^{-1,1}_{\infty,\infty}})\times({B}^{-1}_{\frac{n}{2},1}\cap{B^{-1,1}_{\frac{n}{2},\infty}})$.Comment: 18 page