I am reading a paper that very briefly talks about some volatility arbitrage strategies. It's so brief that I do not exactly understand how it works. It says one of the strategy is based on "short spot index volatility, long on implied volatility" on the premise that IV > realized volatility. I know how one can trade implied volatility (using a delta-hedged option portfolio), but how can I trade spot volatility?
The other arbitrage strategy is supposedly based on volatility smile: "short stock smile, long stock volatility". So unless there is a way to trade spot volatility, this seems like a contradiction.
Is there any way to trade spot volatility?