Scaling and data collapse for the mean exit time of asset prices

We study theoretical and empirical aspects of the mean exit time of financial time series. The theoretical modeling is done within the framework of continuous time random walk. We empirically verify that the mean exit time follows a quadratic scaling law and it has associated a pre-factor which is specific to the analyzed stock. We perform a series of statistical tests to determine which kind of correlation are responsible for this specificity. The main contribution is associated with the autocorrelation property of stock returns. We introduce and solve analytically both a two-state and a three-state Markov chain models. The analytical results obtained with the two-state Markov chain model allows us to obtain a data collapse of the 20 measured MET profiles in a single master curve.Comment: REVTeX 4, 11 pages, 8 figures, 1 table, submitted for publicatio

Fighting Decoherence by Feedback-controlled Dissipation

Repeated closed-loop control operations acting as piecewise-constant Liouville superoperators conditioned on the outcomes of regularly performed measurements may effectively be described by a fixed-point iteration for the density matrix. Even when all Liouville superoperators point to the completely mixed state, feedback of the measurement result may lead to a pure state, which can be interpreted as selective dampening of undesired states. Using a microscopic model, we exemplify this for a single qubit, which can be purified in an arbitrary single-qubit state by tuning the measurement direction and two qubits that may be purified towards a Bell state by applying a special continuous two-local measurement. The method does not require precise knowledge of decoherence channels and works for large reservoir temperatures provided measurement, processing, and control can be implemented in a continuous fashion.Comment: to appear in PR

Mercury in the environs of the north slope of Alaska

The analysis of Greenland ice suggests that the flux of mercury from the continents to the atmosphere has increased in recent times, perhaps partly as a result of the many of man’s activities that effect an alteration of terrestrial surfaces. Upon the exposure of fresh crustal matter, the natural outgassing of mercury vapor from the earth’s surface could be enhanced. Accordingly, mercury was measured in a variety of environmental materials gathered from the North Slope of Alaska to provide background data prior to the anticipated increase of activity in this environment. The materials were collected during the U. S. Coast Guard WEBSEC 72-73 cruises as well as through the facilities provided by Naval Arctic Research Laboratory in the spring of 1973. The method of measurement depended upon radioactivation of mercury with neutrons and the subsequent quantification of characteristic gamma radiations after radiochemical purification. Mercury concentrations in seawater at several locations in the vicinity of 151°W, 71°N averaged 20 parts per trillion. The waters from all stations east of this location showed a significantly smaller concentration. This difference may relate to penetration o f Bering- Chukchi Sea water into the southern Beaufort Sea to 151°W. Marine sediments on the shelf and slope between 143°W and 153°W contained about 100 parts per billion mercury, except for those on the continental shelf between Barter Island and the Canning River, where the concentration was less than half this value. These results are consistent with sediment input from the respective rivers when their mercury content and mineralogy are considered. The mercury content of river waters was 18 ppt and in reasonable agreement with the average of snow samples (13 ppt). The burden of mercury in plankton was 37 ppb.This work was supported by the office of Naval Research under grant N R 083-290

Ground state energy of a homogeneous Bose-Einstein condensate beyond Bogoliubov

The standard calculations of the ground-state energy of a homogeneous Bose gas rely on approximations which are physically reasonable but difficult to control. Lieb and Yngvason [Phys. Rev. Lett. 80, 2504 (1998)] have proved rigorously that the commonly accepted leading order term of the ground state energy is correct in the zero-density-limit. Here, strong indications are given that also the next to leading term is correct. It is shown that the first terms obtained in a perturbative treatment provide contributions which are lost in the Bogoliubov approach.Comment: 6 pages, accepted for publication in Europhys. Lett. http://www.epletters.ch

Integrability of a Generalized Ito System: the Painleve Test

It is shown that a generalized Ito system of four coupled nonlinear evolution equations passes the Painleve test for integrability in five distinct cases, of which two were introduced recently by Tam, Hu and Wang. A conjecture is formulated on integrability of a vector generalization of the Ito system.Comment: LaTeX, 5 page

Pulsation models for the roAp star HD 134214

Precise time-series photometry with the MOST satellite has led to identification of 10 pulsation frequencies in the rapidly oscillating Ap (roAp) star HD 134214. We have fitted the observed frequencies with theoretical frequencies of axisymmetric modes in a grid of stellar models with dipole magnetic fields. We find that, among models with a standard composition of $(X,Z) = (0.70,0.02)$ and with suppressed convection, eigenfrequencies of a $1.65\,{\rm M}_\odot$ model with $\log T_{\rm eff} = 3.858$ and a polar magnetic field strength of 4.1kG agree best with the observed frequencies. We identify the observed pulsation frequency with the largest amplitude as a deformed dipole ($\ell = 1$) mode, and the four next-largest-amplitude frequencies as deformed $\ell = 2$ modes. These modes have a radial quasi-node in the outermost atmospheric layers ($\tau \sim 10^{-3}$). Although the model frequencies agree roughly with observed ones, they are all above the acoustic cut-off frequency for the model atmosphere and hence are predicted to be damped. The excitation mechanism for the pulsations of HD 134214 is not clear, but further investigation of these modes may be a probe of the atmospheric structure in this magnetic chemically peculiar star.Comment: 9 pages, 6 figures; accepted for publication in MNRA

Non-Markovian incoherent quantum dynamics of a two-state system

We present a detailed study of the non-Markovian two-state system dynamics for the regime of incoherent quantum tunneling. Using perturbation theory in the system tunneling amplitude $\Delta$, and in the limit of strong system-bath coupling, we determine the short time evolution of the reduced density matrix and thereby find a general equation of motion for the non-Markovian evolution at longer times. We relate the nonlocality in time due to the non-Markovian effects with the environment characteristic response time. In addition, we study the incoherent evolution of a system with a double-well potential, where each well consists several quantized energy levels. We determine the crossover temperature to a regime where many energy levels in the wells participate in the tunneling process, and observe that the required temperature can be much smaller than the one associated with the system plasma frequency. We also discuss experimental implications of our theoretical analysis.Comment: 10 pages, published versio

Escape of a Uniform Random Walk from an Interval

We study the first-passage properties of a random walk in the unit interval in which the length of a single step is uniformly distributed over the finite range [-a,a]. For a of the order of one, the exit probabilities to each edge of the interval and the exit time from the interval exhibit anomalous properties stemming from the change in the minimum number of steps to escape the interval as a function of the starting point. As a decreases, first-passage properties approach those of continuum diffusion, but non-diffusive effects remain because of residual discreteness effectsComment: 8 pages, 8 figures, 2 column revtex4 forma

Beam spin asymmetry in deeply virtual π\pi production

An interpretation of the beam spin azimuthal asymmetries measured at JLAB in deep exclusive electroproduction of charged and neutral pions is presented. The model combines a Regge pole approach with the effect of nucleon resonances. The $s$- and $u$-channel contributions are described using a dual Bloom-Gilman connection between the exclusive form factors and inclusive deep inelastic structure functions. The results are in agreement with data provided the excitations of nucleon resonances are taken into account.Comment: 5 pages, 3 figures. Talk at the 19th International Spin Physics Symposium (SPIN2010), Sept.27-Oct.2, 2010, Juelich, German