Model calculations of the Sivers function satisfying the Burkardt Sum   Rule
  It is shown that, at variance with previous analyses, the MIT bag model can explain the available data of the Sivers function and satisfies the Burkardt Sum Rule to a few percent accuracy. The agreement is similar to the one recently found in the constituent quark model. Therefore, these two model calculations of the Sivers function are in agreement with the present experimental and theoretical wisdom. 
A. Courtoy, S. Scopetta, V. Vento