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The amplitudes with all positive helicity gluons are zero. The amplitudes for gluons with one negative helicity and others positive helicity are zero. The amplitude for N gluons with two negative and N − 2 positive(MHV) helicities can be given[6] 

<img src='content_image/320448.jpg'>

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[4] H. Kawai, D. C. Lewellen and S. -H. H. Tye, “A relation between tree amplitudes of closed and open strings,” Nucl. Phys. B 269 , (1986)1. 

[5] Y. X. Chen, Y. J. Du and Q. Ma, “ Relations Between Closed String Amplitudes at Higher- order Tree Level and Open String Amplitudes, ” Nucl. Phys. B 824 ,(2010)314 [arXiv: 0901. 1163]. 

[6] S. Stieberger, “Open & Closed vs. Pure Open String Disk Amplitudes,” [arXiv: 0907.2211]. 

[7] D. Lancaster and P. Mansfield, “Relations between disc diagrams,” Phys. Lett. B 217 , (1989)416. 

[8] M. R. Garousi, R. C. Myers, “Superstring Scattering from D-Branes,” Nucl.Phys. B 475 , (1996)193[arXiv: hep-th/9603194 ]. 

[9] A. Hashimoto, I. R. Klebanov, “Decay of Excited D-branes,” Phys.Lett. B 381 (1996)437 

