U′⁡(12⁢μ2,μ⁢t⁢2)∼-μ2⁢g¯⁡(μ)⁢(t2+1)14⁢ⅇ-μ2⁢ξ¯⁢∑s=0∞v¯s⁡(t)(t2+1)32⁢s⁢1μ2⁢s,