15 Advanced Asymptotic Methods 15.1 Bifurcation Methods 15.2 Portfolio Choices for Small Risks 15.3 Gauge Functions and Asymptotic Expansions 15.4 Method of Undetermined Gauges 15.5 Asympotic Expansions of Integrals 15.6 Hybrid Perturbation-Projection Methods 15.7 Further Reading and Summary 15.8 Exercises