Which mathematical symbol is commonly associated with the volatility at time t=0 in term structure models?

In term structure models, particularly those that deal with the dynamics of interest rates or asset prices, the symbol commonly associated with volatility is σ. This symbol represents the standard deviation of returns, which is a crucial component in financial modeling, particularly when quantifying the risk associated with prices over time.

At time t=0, σ captures the immediate level of uncertainty or variability in the price or rate, which is foundational for understanding how prices evolve over time. This volatility is essential in the pricing of options, the assessment of risks in portfolios, and in the application of various financial theories that rely on stochastic processes.

In contrast, while the other symbols may appear in financial contexts—such as α often representing a drift parameter or return factor, λ commonly associated with risk aversion or intensity in certain models, and k typically relating to mean reversion or decay rates—σ specifically denotes volatility and is the standard notation used across most models to illustrate this critical concept.