In this paper, we study stochastic volatility models in regimes where the
maturity is small but large compared to the mean-reversion time of the
stochastic volatility factor. The problem falls in the class of
averaging/homogenization problems for nonlinear HJB type equations where the
"fast variable" lives in a non-compact space. We develop a general argument
based on viscosity solutions which we apply to the two regimes studied in the
paper.
We propose a multi-scale stochastic volatility model in which a fast
mean-reverting factor of volatility is built on top of the Heston stochastic
volatility model. A singular pertubative expansion is then used to obtain an
approximation for European option prices.
Using spectral decomposition techniques and singular perturbation theory, we
develop a systematic method to approximate the prices of a variety of options
in a fast mean-reverting stochastic volatility setting. Four examples are
provided in order to demonstrate the versatility of our method. These include:
European options, up-and-out options, double-barrier knock-out options, and
options which pay a rebate upon hitting a boundary. For European options, our
method is shown to produce option price approximations which are equivalent to
those developed in [5].
In 1999 Robert Fernholz observed an inconsistency between the normative
assumption of existence of an equivalent martingale measure (EMM) and the
empirical reality of diversity in equity markets. We explore a method of
imposing diversity on market models by a type of antitrust regulation that is
compatible with EMMs. The regulatory procedure breaks up companies that become
too large, while holding the total number of companies constant by imposing a
simultaneous merge of other companies.
Gaussian copulas are widely used in the industry to correlate two random
variables when there is no prior knowledge about the co-dependence between
them. The perturbed Gaussian copula approach allows introducing the skew
information of both random variables into the co-dependence structure. The
analytical expression of this copula is derived through an asymptotic expansion
under the assumption of a common fast mean reverting stochastic volatility
factor.