We prove the version of Joyce-Song formula for the Behrend function identities in the motivic setting. The main method we use is the proof of Kontsevich-Soibelman conjecture about the motivic Milnor fibers by Q. T. Le, who uses the method of motivic integration for formal schemes and Cluckers-Loeser's motivic constructible functions. In the Appendix the motivic formula can be used to provide a different proof that there is an algebra homomorphism of Kontsevich-Soibelman from the motivic Hall algebra of the abelian category of coherent sheaves on a Calabi-Yau threefold $Y$ to the motivic quantum torus of $Y$.
Categories: math.AG