From what I understood of @Canadianer's answer here...
Genetic drift randomly causes negative or positive linkage disequilibria, by changing allele frequencies through random sampling. Natural selection acts on additive genetic variance in fitness and negative linkage disequilibrium also means low variance. Therefore, selection mainly reduces the additive genetic variance of loci that are in positive linkage disequilibrium and in consequence it reduces the polymorphism of loci that are in positive linkage disequilibrium. Therefore, the joint effect of genetic drift and natural selection causes a decrease in linkage disequilibrium.
Can you please demonstrates this effect with a mathematical model? Or Can you point me to an article that provides such mathematical model?
I let you free to chose the complexity of your model! It should just provide insights into the effect of genetic drift and natural selection on linkage disequilibrium.