426,273 research outputs found

    Automated One-loop Computation in Quarkonium Process within NRQCD Framework

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    In last decades, it has been realized that the next-to-leading order corrections may become very important, and sometimes requisite, for some processes involving quarkoinum production or decay, e.g., e+eβˆ’β†’J/ψ+Ξ·ce^+e^- \to J/\psi + \eta_c and J/Οˆβ†’3Ξ³J/\psi \to 3\gamma. In this article, we review some basic steps to perform automated one-loop computations in quarkonium process within the Non-relativistic Quantum Chromodynamics (NRQCD) factorization framework, and we give an introduction to some related public tools or packages and their usages in each step. We start from generating Feynman diagrams and amplitudes with \textsc{FeynArts} for the quarkonium process, performing Dirac- and Color- algebras simplifications using \textsc{FeynCalc} and \textsc{FeynCalcFormLink}, and then to doing partial fractions on the linear-dependent propagators by \textsc{APart}, and finally to reducing the Tensor Integrals (TI) into Scalar Integrals (SI) or Master Integrals (MI) using Integration-By-Parts (IBP) method with the help of \textsc{Fire}. We will use a simple concrete example to demonstrate the basic usages of the corresponding packages or tools in each step.Comment: 8 pages, conference proceedings for ACAT 201

    Effective mass splitting of neutron and proton and isospin emission in heavy-ion collisions

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    Within the framework of an isospin and momentum dependent transport model, the emissions of isospin particles (nucleons and light clusters) squeezed out in heavy-ion collisions are investigated as probes of the poorly known symmetry energy at high baryon density. Two different mass splittings of neutrons and protons in nuclear medium as mnβˆ—>mpβˆ—m_{n}^{\ast}>m_{p}^{\ast} and mnβˆ—<mpβˆ—m_{n}^{\ast}<m_{p}^{\ast} are used in the model and their influence on the isospin emission in heavy-ion collisions is discussed thoroughly. The competition between the stiffness and the momentum dependence of the symmetry potential on reaction dynamics are compared and systematically analyzed. It is found that the difference of the neutron and proton directed flows and the transverse momentum distribution of the neutron/proton ratio are sensitive to the stiffness of the symmetry energy, which can not be changed with the controversial effective mass splitting. The elliptic flows of free nucleons at high transverse momentum within mid-rapidity emission are a promising observable as distinguishing the nucleon effective mass splitting.Comment: 16 pages, 7 figure

    Further studies of dothistromin toxin genes in the fungal forest pathogen Dothistroma septosporum : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Biochemistry at Massey University, Palmerston North, New Zealand

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    The fungal pathogen Dothistroma septosporum is the main causal agent of Dothistroma (red-hand) needle blight, which is a devastating foliar disease of a wide range of pine species. Dothistromin is a difuranoanthraquinone toxin produced by D. septosporum and is considered as a possible virulence factor for the disease. Based on the similarity of chemical structure between dothistromin and aflatoxin (AF) /sterigmatocystin (ST) precursors, nine putative dothistromin biosynthetic genes have been identified, which are homologous to their corresponding genes in the AF/ST gene clusters. However, in contrast to all 25 AF biosynthetic genes tightly clustered in one region (70-Kb) of the genome, the dothistromin gene clusters are located on a 1.3-Mb chromosome and separated into three mini-clusters along with non-dothistromin genes. The dotC gene, located in the mini-cluster 1, is predicted to encode a major facilitator superfamily (MFS) membrane transporter involved in secretion of dothistromin. In this work, by constructing DotC-eGFP fusion protein containing mutants, the subcellular localization of the DotC protein was determined to be mainly targeted to the plasma membrane. The biological function of the dotC gene was characterized by targeted gene disruption. The dotC gene disrupted mutants showed a significant reduction of dothistromin production in both the medium and mycelium. In addition, the exponential growth of dotC null mutants was inhibited when exogenous dothistromin was presented and these mutants also displayed more sensitivity than the wild type strain to exogenous dothistromin. The results indicated that the DotC protein is a membrane associated protein and might have a role in dothistromin production and be involved in secretion of exogenously supplied dothistromin toxin. Two novel dothistromin biosynthetic genes, norA/B and verB (partial sequence), were identified by using degenerate PCR and D. septosporum genomic library screening. The putative NorA/B and VerB are postulated to encode a dehydrogenase and a desaturase, respectively and are similar to AF/ST genes. These findings further confirmed that the dothistromin shares biosynthetic pathway steps with AF/ST

    Transverse emission of isospin ratios as a probe of high-density symmetry energy in isotopic nuclear reactions

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    Transverse emission of preequilibrium nucleons, light clusters (complex particles) and charged pions from the isotopic 112,124^{112,124}Sn+112,124^{112,124}Sn reactions at a beam energy of 400\emph{A} MeV, to extract the high-density behavior of nuclear symmetry energy, are investigated within an isospin and momentum dependent transport model. Specifically, the double ratios of neutron/proton, triton/helium-3 and Ο€βˆ’/Ο€+\pi^{-}/\pi^{+} in the squeeze-out domain are analyzed systematically, which have the advantage of reducing the influence of the Coulomb force and less systematic errors. It is found that the transverse momentum distribution of isospin ratios strongly depend on the stiffness of nuclear symmetry energy, which would be a nice observable to extract the high-density symmetry energy. The collision centrality and the mass splitting of neutron and proton in nuclear medium play a significant role on the distribution structure of the ratios, but does not change the influence of symmetry energy on the spectrum.Comment: 5 figures, 13 page

    The fundamental role of superconducting quasiparticle coherence in cuprate superconductors

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    Within the kinetic energy driven superconducting mechanism, we study the interplay between superconductivity and the nodal and antinodal superconducting quasiparticle coherences in cuprate superconductors, and find the s-wave superconducting transition temperature is heavily suppressed by the antinodal superconducting quasiparticle coherence, while the d-wave superconducting transition temperature is enhanced, therefore the antinodal superconducting quasiparticle coherence plays a more crucial role in superconductivity of cuprate superconductors.Comment: 4 pages, 2 figures, typos correcte

    Next-to-leading-order QCD corrections to gluon fragmentation into 1S0(1,8){}^1S_0^{(1,8)} quarkonia

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    Within the NRQCD factorization framework, we compute the next-to-leading-order QCD corrections to the gluon fragmentation into the 1S0(1,8){}^1S_0^{(1,8)} Fock components of a quarkonium, at the lowest order in velocity expansion. We follow the operator definition of the fragmentation function advanced by Collins and Soper. The key technique underpinning our calculation is the sector decomposition method widely used in the area of multi-loop computation. It is found that the NLO QCD corrections have significant effects, and qualitatively modify the profiles of the corresponding leading-order fragmentation functions.Comment: 10 pages, 2 figures, 2 table
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