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Quantitative Finance · Glosario

¿Qué es Arbitrage?

Definition 1.2 Derivatives and Volatility · Capítulo 1 — No Arbitrage and the Fundamental Theorems

An arbitrage is a portfolio that costs nothing or less, never pays a negative amount, and is not identically worthless: p⋅θ≤0p\cdot \theta\le0, Dθ≥0D\theta\ge0, and at least one of the inequalities strict (p⋅θ<0p\cdot \theta<0, or Dθ≠0D\theta\ne0). The market has no arbitrage when no such portfolio exists.

Ejemplos

Example 1.9 (A binomial market)

A bond costs 0.98 and pays 1; a share costs 100 and pays 120 or 90. The equations qu+qd=0.98q_u+q_d=0.98 and 120qu+90qd=100120q_u+90q_d=100 give qu=0.3933q_u=0.3933, qd=0.5867q_d=0.5867, both positive: no arbitrage. The risk-neutral probability of the up state is 0.3933/0.98=0.40140.3933/0.98=0.4014, whatever its real-world probability. A call struck at 100 pays (20,0)(20,0) and is worth 20qu=7.866720q_u=7.8667.

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