Rough differential equations for volatility
Rough differential equations for volatility
This paper introduces a novel framework for rough volatility using rough differential equations (RDEs). The key innovation is a canonical joint lift of a Brownian motion and a low-regularity adapted stochastic rough path, such as fractional Brownian motion with Hurst parameter less than 1/2. This lift, defined via Itô integrals and shuffle relations, yields a geometric rough path that allows the price and volatility processes to be modeled as the solution to a single RDE. The framework offers significant flexibility: correlation between price and volatility can be introduced either through correlated drivers or directly in the dynamics, and path-dependent volatility models are naturally accommodated. The authors extend lead-lag approximations to the fractional setting, proving convergence rates for piecewise linear, hybrid, and mollifier approximations, which serve as numerical schemes. The paper validates the approach with numerical experiments and calibrates a simple new RDE-based rough volatility model to market data, demonstrating good fit. This work provides a versatile alternative to stochastic Volterra equations for rough volatility, leveraging the well-developed theory of rough paths and enabling efficient simulation and calibration.
Highlights
- 1Introduces a canonical joint lift of a Brownian motion and a low-regularity adapted stochastic rough path, extending previous work to handle rough volatility.
- 2Proposes a new class of rough volatility models based on rough differential equations (RDEs), offering flexibility in correlation and path-dependency.
- 3Extends lead-lag approximations to fractional settings, providing convergence rates for numerical schemes.
- 4Validates the framework numerically and calibrates a novel RDE-based rough volatility model to market data.
Methods
- MItô lift of an adapted rough path: defines joint rough path via Itô integrals and shuffle relations.
- MRough differential equations (RDEs): models price and volatility as solution to a single RDE driven by the joint rough path.
- MLead-lag approximations: piecewise linear, hybrid, and mollifier approximations for numerical simulation.
- MStochastic sewing and Kolmogorov continuity theorem for regularity estimates.
Results
- RThe joint lift yields a geometric rough path with inhomogeneous Hölder regularity, enabling RDE formulation.
- RLead-lag approximations converge in rough path topology with explicit rates, supporting numerical schemes.
- RThe RDE framework encompasses classical and rough volatility models (e.g., rBergomi, rHeston) as special cases.
- RNumerical tests confirm convergence and calibration to market data shows good fit with few parameters.
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