2,005 research outputs found
Heavy Pseudoscalar Twist-3 Distribution Amplitudes within QCD Theory in Background Fields
In this paper, we study the properties of the twist-3 distribution amplitude
(DA) of the heavy pseudo-scalars such as , and . New sum
rules for the twist-3 DA moments \left_{\rm HP} and
\left_{\rm HP} up to sixth orders and up to dimension-six
condensates are deduced under the framework of the background field theory.
Based on the sum rules for the twist-3 DA moments, we construct a new model for
the two twist-3 DAs of the heavy pseudo-scalar with the help of the
Brodsky-Huang-Lepage prescription. Furthermore, we apply them to the
transition form factor () within the
light-cone sum rules approach, and the results are comparable with other
approaches. It has been found that the twist-3 DAs and
are important for a reliable prediction of
. For example, at the maximum recoil region, we have
, in which those two twist-3 terms
provide and contributions. Also we calculate the
branching ratio of the semi-leptonic decay as .Comment: 12 pages, 16 figure
Statistical physics of isotropic-genesis nematic elastomers: I. Structure and correlations at high temperatures
Isotropic-genesis nematic elastomers (IGNEs) are liquid crystalline polymers
(LCPs) that have been randomly, permanently cross-linked in the
high-temperature state so as to form an equilibrium random solid. Thus, instead
of being free to diffuse throughout the entire volume, as they would be in the
liquid state, the constituent LCPs in an IGNE are mobile only over a finite
length-scale controlled by the density of cross-links. We address the effects
that such network-induced localization have on the liquid-crystalline
characteristics of an IGNE, as probed via measurements made at high
temperatures. In contrast with the case of uncross-linked LCPs, for IGNEs these
characteristics are determined not only by thermal fluctuations but also by the
quenched disorder associated with the cross-link constraints. To study IGNEs,
we consider a microscopic model of dimer nematogens in which the dimers
interact via orientation-dependent excluded volume forces. The dimers are,
furthermore, randomly, permanently cross-linked via short Hookean springs, the
statistics of which we model by means of a Deam-Edwards type of distribution.
We show that at length-scales larger than the size of the nematogens this
approach leads to a recently proposed phenomenological Landau theory of IGNEs
[Lu et al., Phys. Rev. Lett. 108, 257803 (2012)], and hence predicts a regime
of short-ranged oscillatory spatial correlations in the nematic alignment, of
both thermal and glassy types. In addition, we consider two alternative
microscopic models of IGNEs: (i) a wormlike chain model of IGNEs that are
formed via the cross-linking of side-chain LCPs; and (ii) a jointed chain model
of IGNEs that are formed via the cross-linking of main-chain LCPs. At large
length-scales, both of these models give rise to liquid-crystalline
characteristics that are qualitatively in line with those predicted by the
dimer-and-springs model.Comment: 33 pages, 6 figures, 6 appendice
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