Rough multifactor volatility for SPX and VIX options

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Rough multifactor volatility for SPX and VIX options

Antoine Jacquier
Aitor Muguruza
Alexandre Pannier
Published on 12/28/2021
Options
Equities
Derivatives
United States (US)
Volatility effect
Volatility premium
Factor investing
Machine learning

This paper develops a comprehensive asymptotic theory for implied volatility in multifactor rough volatility models, with applications to SPX and VIX options. The authors extend previous single-factor results to a general multifactor setting using Malliavin calculus, deriving explicit small-time limits for the ATM implied volatility level, skew, and curvature. The key technical innovation is the use of the Clark-Ocone formula to represent the underlying asset as an exponential martingale, enabling the application of asymptotic expansions even in non-Markovian rough volatility models. The results are applied to the two-factor rough Bergomi model, yielding closed-form expressions that reveal how parameters control the skew and curvature of both SPX and VIX smiles. This provides a theoretical foundation for joint calibration, showing that multifactor models can capture the different short-time behaviors of SPX and VIX implied volatilities, which single-factor models fail to do. The paper also includes detailed proofs and numerical examples demonstrating the effectiveness of the approach.

Highlights

  • 1Provides explicit small-time asymptotics for ATM implied volatility level, skew, and curvature in a general class of multifactor rough volatility models.
  • 2Extends previous single-factor rough volatility results to multifactor settings, enabling joint calibration of SPX and VIX options.
  • 3Derives closed-form expressions for the two-factor rough Bergomi model, highlighting parameter interplay for skew and curvature.
  • 4Uses Malliavin calculus and Clark-Ocone formula to handle non-Markovian rough volatility dynamics.

Methods

  • M
    Malliavin calculus for Gaussian processes to derive Clark-Ocone representations.
  • M
    Small-time asymptotic expansions for implied volatility level, skew, and curvature.
  • M
    Multifactor rough volatility modeling with fractional Brownian motion kernels.
  • M
    Numerical analysis of the two-factor rough Bergomi model for joint SPX-VIX calibration.

Results

  • R
    The short-time ATM implied volatility level equals the limit of the forward volatility.
  • R
    The ATM skew scales as T^{H-1/2} in rough volatility models, matching empirical observations.
  • R
    The ATM curvature is expressed in terms of integrals of Malliavin derivatives, providing a second criterion for model selection.
  • R
    Closed-form formulas for the two-factor rough Bergomi model show that curvature can be positive or negative depending on parameters.
  • R
    The multifactor framework allows decoupling of SPX and VIX smile features, improving joint calibration.
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