4,217 research outputs found
Duality Theory for Portfolio Optimisation under Transaction Costs
For portfolio optimisation under proportional transaction costs, we provide a
duality theory for general cadlag price processes. In this setting, we prove
the existence of a dual optimiser as well as a shadow price process in a
generalised sense. This shadow price is defined via a "sandwiched" process
consisting of a predictable and an optional strong supermartingale and pertains
to all strategies which remain solvent under transaction costs. We provide
examples showing that in the present general setting the shadow price process
has to be of this generalised form
Strong supermartingales and limits of nonnegative martingales
Given a sequence of nonnegative martingales starting
at , we find a sequence of convex combinations
and a limiting process such that
converges in probability to
, for all finite stopping times . The limiting process then
is an optional strong supermartingale. A counterexample reveals that the
convergence in probability cannot be replaced by almost sure convergence in
this statement. We also give similar convergence results for sequences of
optional strong supermartingales , their left limits
and their stochastic integrals and explain the relation to the notion of the Fatou
limit.Comment: Published at http://dx.doi.org/10.1214/14-AOP970 in the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Portfolio optimisation beyond semimartingales: shadow prices and fractional Brownian motion
While absence of arbitrage in frictionless financial markets requires price
processes to be semimartingales, non-semimartingales can be used to model
prices in an arbitrage-free way, if proportional transaction costs are taken
into account. In this paper, we show, for a class of price processes which are
not necessarily semimartingales, the existence of an optimal trading strategy
for utility maximisation under transaction costs by establishing the existence
of a so-called shadow price. This is a semimartingale price process, taking
values in the bid ask spread, such that frictionless trading for that price
process leads to the same optimal strategy and utility as the original problem
under transaction costs. Our results combine arguments from convex duality with
the stickiness condition introduced by P. Guasoni. They apply in particular to
exponential utility and geometric fractional Brownian motion. In this case, the
shadow price is an Ito process. As a consequence we obtain a rather surprising
result on the pathwise behaviour of fractional Brownian motion: the
trajectories may touch an Ito process in a one-sided manner without reflection.Comment: To appear in Annals of Applied Probability. We would like to thank
Junjian Yang for careful reading of the manuscript and pointing out a mistake
in an earlier versio
Fermi Surface of the 2D Hubbard Model at Weak Coupling
We calculate the interaction-induced deformation of the Fermi surface in the
two-dimensional Hubbard model within second order perturbation theory. Close to
half-filling, interactions enhance anisotropies of the Fermi surface, but they
never modify the topology of the Fermi surface in the weak coupling regime.Comment: 4 pages, LaTeX2e, 5 embedded EPS figures, accepted to be published in
Z. Phys.
OLS-based estimation of the disturbance variance under spatial autocorrelation
We investigate the OLS-based estimator s2 of the disturbance variance in the standard linear regression model with cross section data when the disturbances are homoskedastic, but spatially correlated. For the most popular model of spatially autoregressive disturbances, we show that s2 can be severely biased in finite samples, but is asymptotically unbiased and consistent for most types of spatial weighting matrices as sample size increases. --regression,spatial error correlation,bias,variance
Landau-Vlasov model versus Vlasov-Uehling-Uhlenbeck-approach : different flow effects from the same theory?
Differences between the Nantes-Ganil-Grenoble (NGG) LV-model and the original VUU approach are analysed. It is found that the LV code tends to simulate - for small timesteps - a non-viscous testparticle fluid
Role of cytochrome c heme lyase in the import of cytochrome c into mitochondria
The import of cytochrome c into Neurospora crassa mitochondria was examined at distinct stages in vitro. The precursor protein, apocytochrome c, binds to mitochondria with high affinity and specificity but is not transported completely across the outer membrane in the absence of conversion to holocytochrome c. The bound apocytochrome c is accessible to externally added proteases but at the same time penetrates far enough through the outer membrane to interact with cytochrome c heme lyase. Formation of a complex in which apocytochrome c and cytochrome c heme lyase participate represents the rate-limiting step of cytochrome c import. Conversion from the bound state to holocytochrome c, on the other hand, occurs 10-30-fold faster. Association of apocytochrome c with cytochrome c heme lyase also takes place after solubilizing mitochondria with detergent. We conclude that the bound apocytochrome c, spanning the outer membrane, forms a complex with cytochrome c heme lyase from which it can react further to be converted to holocytochrome c and be translocated completely into the intermembrane space
Incommensurate nematic fluctuations in the two-dimensional Hubbard model
We analyze effective d-wave interactions in the two-dimensional extended
Hubbard model at weak coupling and small to moderate doping. The interactions
are computed from a renormalization group flow. Attractive d-wave interactions
are generated via antiferromagnetic spin fluctuations in the pairing and charge
channels. Above Van Hove filling, the d-wave charge interaction is maximal at
incommensurate diagonal wave vectors, corresponding to nematic fluctuations
with a diagonal modulation. Below Van Hove filling a modulation along the
crystal axes can be favored. The nematic fluctuations are enhanced by the
nearest-neighbor interaction in the extended Hubbard model, but they always
remain smaller than the dominant antiferromagnetic, pairing, or charge density
wave fluctuations.Comment: 8 pages, 4 figures; figures improve
Transition from binary processes to multifragmentation in quantum molecular dynamics for intermediate-energy heavy ion collisions
We study the transition from fusion-fission phenomena at about 20 MeV/nucleon multifragmentation at 100–200 MeV/nucleon in the reaction 16O+80Br employing the quantum molecular dynamics model. The time evolution of the density and mass distribution, the charged-particle multiplicity, and spectra as well as angular distributions of light particles are investigated. The results exhibit the transition of the disassembly mechanism, but no sharp change is found. The results are in good agreement with recently measured 4-Pi data
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