I have a simple Gaussian copula to generate returns on a number of assets. Then, I also have a stochastic interest rate process. After the copula generates "fundamental" returns, I reprice the assets with the new risk-free rate. So the actual return is the "fundamental" one plus a (negative) derivative to interest rate.Question: what would be the best way to get the variance of returns given repricing?Followup: if I were to set every asset against some capital structure with debt and equity and priced those according to Merton model (equity as an option on assets with debt as strike), would that mean that debt would have positive convexity and equity - negative. If so, under Brownian Motion of interest rates, would equity returns be on average smaller than under constant interest rates?Thanks!PS this is definitely not an assignment - I don't even study anything like that