1. Akhundzadeh, A., Huber, T., Hyatt, M., & Schneider, E. (2020). eSSVI Implied Volatility Surface. Factset White Paper.
https://advantage.factset.com/essvi-implied-volatility-surface-white-paper
2. Robust calibration and arbitrage-free interpolation of SSVI slices
3. Gatheral, J. (2004). A Parsimonious Arbitrage-Free Implied Volatility Parameterization with Application to the Valuation of Volatility Derivatives. Global Derivatives & Risk Management. https://api.semanticscholar.org/CorpusID:156076635
4. Arbitrage-free SVI volatility surfaces
5. Convergence of Heston to SVI