Analysis of the strong coupling constant GDs∗DsϕG_{D_{s}^{*}D_{s}\phi} and the decay width of Ds∗→DsγD_{s}^{*}\rightarrow D_{s}\gamma with QCD sum rules

In this article, we calculate the form factors and the coupling constant of the vertex $D_{s}^{*}D_{s}\phi$ using the three-point QCD sum rules. We consider the contributions of the vacuum condensates up to dimension $7$ in the operator product expansion(OPE). And all possible off-shell cases are considered, $\phi$, $D_{s}$ and $D_{s}^{*}$, 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 $G_{Ds*Ds\phi}=4.12\pm0.70 GeV^{-1}$. 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 $D_{s}^{*}\rightarrow D_{s}\gamma$ and analyze the width of this decay with the assumption of the vector meson dominance of the intermediate $\phi(1020)$. Our final result about the decay width of this decay channel is $\Gamma=0.59\pm0.15keV$.Comment: arXiv admin note: text overlap with arXiv:1501.03088 by other author

Temporal variability in early afterglows of short gamma-ray bursts

The shock model has successfully explained the observed behaviors of afterglows from long gamma-ray bursts (GRBs). Here we use it to investigate the so-called early afterglows from short GRBs, which arises from blast waves that are not decelerated considerably by their surrounding medium. We consider a nearby medium loaded with $e^{\pm}$ pairs (Beloborodov 2002). The temporal behaviors show first a soft-to-hard spectral evolution, from the optical to hard X-ray, and then a usual hard-to-soft evolution after the blast waves begin to decelerate. The light curves show variability, and consist of two peaks. The first peak, due to the pair effect, can be observed in the X-ray, though too faint and too short in the optical. The second peak will be easily detected by {\it Swift}. We show that detections of the double-peak structure in the light curves of early afterglows are very helpful to determine all the shock parameters of short GRBs, including both the parameters of the relativistic source and the surroundings. Besides, from the requirement that the forward-shock emission in short GRBs should be below the BATSE detection threshold, we give a strong constraint on the shock model parameters. In particular, the initial Lorentz factor of the source is limited to be no more than $\sim 10^3$, and the ambient medium density is inferred to be low, n\la 10^{-1} cm$^{-3}$.Comment: 5 pages, 1 figure, minor changes to match the publish in MNRA