Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>We study optional projections of <jats:inline-formula><jats:alternatives><jats:tex-math>${\mathbb{G}}$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mi>G</mml:mi>
</mml:math></jats:alternatives></jats:inline-formula>-adapted strict local martingales on a smaller filtration <jats:inline-formula><jats:alternatives><jats:tex-math>${\mathbb{F}}$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML">
<mml:mi>F</mml:mi>
</mml:math></jats:alternatives></jats:inline-formula> under changes of equivalent martingale measures. General results are provided as well as a detailed analysis of two specific examples given by the inverse Bessel process and a class of stochastic volatility models. This analysis contributes to clarify the absence of arbitrage opportunities of market models under restricted information.</jats:p>