content_image/436006.jpg content_image/436000.jpg content_image/436002.jpg content_image/436005.jpg content_image/436001.jpg content_image/436003.jpg content_image/436004.jpg
<img src='content_image/436006.jpg'>

deformation l can be made collinear to the minus direc- tion, and a vector n µ 2 = (1 , 0 , 0$_{t}$ ) is used instead of n µ $_{1}$. The eikonal factors are, 

<img src='content_image/436000.jpg'>

for Fig. 3(c) and 

<img src='content_image/436002.jpg'>

for Fig. 3(d). 

In our calculation of the SSA, p$_{2}$ is unpolarized so there is no factor of i coming from the attachment to the up- per spectator. Therefore, it is only the real principal value contributions that are kept in Eqs. (12,13). Note that there can be no double Sivers effect at the level of one extra gluon because there must be at least one extra gluon from each of the hadrons for their PDFs to have spin dependence. 

The t $^{a}$s in Eqs. (8,10) combine with the t $^{a}$s in Eq. (9,11) to produce an overall color factor equal to 

Exactly the same color factor also arises when l is collinear to p$_{2}$ as in Figs. 3(c,d). 

<img src='content_image/436005.jpg'>

The remaining type of single-gluon graphs are those in Fig. 4. For the lines collinear to H$_{1}$ the eikonal propaga- tors are 

<img src='content_image/436001.jpg'>

from Fig. 4(a) and 

<img src='content_image/436003.jpg'>

from Fig. 4(b). The sum of these graphs gives a contri- bution equal to 

If the color factor in Eq. (17) did not vanish, then it would contribute to an SSA when the factor of i combines with the factor of i in Eq. (9). The same result is obtained from the Hermitian conjugate graphs. In a totally un- polarized cross section, there would be no contribution 

<img src='content_image/436004.jpg'>

