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L7. Risk-Neutral Pricing

TOC

Arbitrage Opportunity

Valuation Methods
  • Discount factor (denominator)
    • Take into account the risky nature of a cash flow
  • Certainty equivalent (numerator)
    • Transform the expected risky cash flow into certainty
  • Risk neutral evaluation
    • Correct the probability
    • Free of the structure assumptions

Hedging

No arbitrage price for option. Assume the risk-free rate is 4%. There is a stock with payoff
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Assume no arbitrage, to price a European call option written on the stock with exercise price $21 in 3 months:
  • Intuition
    • Set up a portfolio to eliminate uncertainty
    • Its return must equals risk-free rate
  • Strategy: Construct a riskless portfolio
    • Long shares of the stock
    • Short one call option
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To eliminate the uncertainty:
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With NA (no arbitrage), riskless portfolios must earn the risk-free rate
Generalization: Delta Hedging
Delta of a derivative: the ratio of the change in the price of a derivative with the price of the underlying asset
Delta hedging: The price of a portfolio is insensitive to small changes in the price of the underlying asset. Delta-neutral means a portfolio with a delta of zero.
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RN Probability and AD Price
RN probability
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The first term is the EN expected value of the acquired asset if the option is exercised at T
The second term is the RN expected cost of acquiriin git at T
The difference is RN expected value of the option at T
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Asian Option is cheaper because its volatility is lower. It is aimed for consumers or producers applied where there are multiple cash flows during a period of time.
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Analyze NA:
  • construct portfolio, test cash flows
  • risk neutral pricing, test whether have solutions
  • test whether EMM exists (corresponding probability satisfies 0<p<1)
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