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To say a curve is arbitrage-free, you need to pick an arbitrage path; a series of trades which, when followed, yield a net profit without creating exposure. We neglect counterparty exposure here, since you are presumably using market-neutral rates. One arbitrage is to buy a swap from your curve, and sell at the market price. This is a test of your curve ...


You have already answered your question. In Bjork, the $\beta$ terms represent the value in the money market, or deposit, account, while the $\beta$ terms in Andrea Pascucci represent the units in the money market account. Then, the two definitions are basically the same. More specifically, \begin{align*} \beta^{Bjork}_{t+1} = \beta^{Andrea\, ...


The option payoff is equivalent to $Z_{\tau \wedge T}-1$ where $\tau=\inf\{t | Z_t = 1\}$ provided that $Z_t$ is assumed to be continuous. Since $Z_t=S_t/P_t$ is a martingale under $Q_P$, we have $E_P[Z_{\tau \wedge T}]=Z_0$ and the option value is $P_0 (Z_0 - 1)=S_0-P_0$ regardless of the model.


I solved it the following way, just want make sure I'm not missing something obvious. Set up a portfolio $PF$ consisting of long $S$ and short $P$ at time $t = 0$. Choose arbitrary time $0 < t < T$. If $S_t > P_t$ then $PF_t = S_t - P_t$ which coincides with the value of the option. If $S_t$ hits $P_t$ from above, then dissolve the portfolio by ...


The option payoff at maturity $T$ is defined by \begin{align*} (S_T-P_T)1_{\left(\inf_{0 \le t <T}\frac{S_t}{P_t}\right) > 1}. \end{align*} Let $Q$ be the risk-neutral probability measure and $E$ be the corresponding expectation operator. Let $Q_p$ be a probability measure defined by \begin{align*} \frac{dQ_p}{dQ}\big|_t = \frac{P_t}{e^{rt} P_0}. ...


Both formulas (generalised Black Scholes) are correct. In the first one, you have the BS model with dividend. In the second, you have a non-zero cost of carry. It's really the same formula. Note that cost of carry = risk free rate - dividend. You can think cost of carry like the negative growth rate.

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