178,961 research outputs found

    Random Isotropic Structures and Possible Glass Transitions in Diblock Copolymer Melts

    Get PDF
    We study the microstructural glass transitions in diblock-copolymer melts using a thermodynamic replica approach. Our approach performs an expansion in terms of the natural smallness parameter -- the inverse of the scaled degree of polymerization, which allows us to systematically study the approach to mean-field behavior as the degree of polymerization increases. We find that in the limit of infinite long polymer chains, both the onset of glassiness and the vitrification transition (Kauzmann temperature) collapse to the mean-field spinodal, suggesting that the spinodal can be regarded as the mean-field signature for glass transitions in this class of systems. We also study the order-disorder transitions (ODT) within the same theoretical framework; in particular, we include the leading-order fluctuation corrections due to the cubic interaction in the coarse-grained Hamiltonian, which has been ignored in previous works on the ODT in block copolymers. We find that the cubic term stabilizes both the ordered (body-centered-cubic) phase and the glassy state relative to the disordered phase. While in melts of symmetric copolymers the glass transition always occurs after the order-disorder transition (below the ODT temperature), for asymmetric copolymers, it is possible that the glass transition precedes the ordering transition.Comment: An error corrected in the referenc

    Analysis of the strong coupling constant GDsβˆ—DsΟ•G_{D_{s}^{*}D_{s}\phi} and the decay width of Dsβˆ—β†’DsΞ³D_{s}^{*}\rightarrow D_{s}\gamma with QCD sum rules

    Full text link
    In this article, we calculate the form factors and the coupling constant of the vertex Dsβˆ—DsΟ•D_{s}^{*}D_{s}\phi using the three-point QCD sum rules. We consider the contributions of the vacuum condensates up to dimension 77 in the operator product expansion(OPE). And all possible off-shell cases are considered, Ο•\phi, DsD_{s} and Dsβˆ—D_{s}^{*}, resulting in three different form factors. Then we fit the form factors into analytical functions and extrapolate them into time-like regions, which giving the coupling constant for the process. Our analysis indicates that the coupling constant for this vertex is GDsβˆ—DsΟ•=4.12Β±0.70GeVβˆ’1G_{Ds*Ds\phi}=4.12\pm0.70 GeV^{-1}. The results of this work are very useful in the other phenomenological analysis. As an application, we calculate the coupling constant for the decay channel Dsβˆ—β†’DsΞ³D_{s}^{*}\rightarrow D_{s}\gamma and analyze the width of this decay with the assumption of the vector meson dominance of the intermediate Ο•(1020)\phi(1020). Our final result about the decay width of this decay channel is Ξ“=0.59Β±0.15keV\Gamma=0.59\pm0.15keV.Comment: arXiv admin note: text overlap with arXiv:1501.03088 by other author
    • …
    corecore