content_image/415030.jpg content_image/415031.jpg content_image/415032.jpg content_image/415034.jpg content_image/415029.jpg content_image/415033.jpg content_image/415026.jpg content_image/415027.jpg content_image/415028.jpg
with B arbitrary. Employing the relation [33] 

<img src='content_image/415030.jpg'>

where γ = 0 , 5772 ... is the Euler-Mascheroni con- stant and ζ is the zeta Riemann function, and ex- panding ( − B $^{2}$x$^{2}$) a as a power series 

one can compare both sides of (52). After some algebra one gets 

<img src='content_image/415031.jpg'>

<img src='content_image/415032.jpg'>

Expanding the exponential in power series and equating the coefficients of equal powers of a one obtains 

<img src='content_image/415034.jpg'>

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<img src='content_image/415029.jpg'>

<img src='content_image/415033.jpg'>

<img src='content_image/415026.jpg'>

<img src='content_image/415027.jpg'>

<img src='content_image/415028.jpg'>

with ¯ B 2 ≡ 4 e 2 $_{γ}$B $^{2}$. 

This work was supported by CAPES and CNPq, by grants of FCT, FEDER, OE, POCI 2010, CERN/FP/83510/2008, and by HadronPhysics2, Grant Agreement n. 227431 under the Seventh Framework Programme of EU. 

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## ACKNOWLEDGMENTS 

