1,964 research outputs found
Two centuries of trend following
We establish the existence of anomalous excess returns based on trend
following strategies across four asset classes (commodities, currencies, stock
indices, bonds) and over very long time scales. We use for our studies both
futures time series, that exist since 1960, and spot time series that allow us
to go back to 1800 on commodities and indices. The overall t-stat of the excess
returns is since 1960 and since 1800, after accounting
for the overall upward drift of these markets. The effect is very stable, both
across time and asset classes. It makes the existence of trends one of the most
statistically significant anomalies in financial markets. When analyzing the
trend following signal further, we find a clear saturation effect for large
signals, suggesting that fundamentalist traders do not attempt to resist "weak
trends", but step in when their own signal becomes strong enough. Finally, we
study the performance of trend following in the recent period. We find no sign
of a statistical degradation of long trends, whereas shorter trends have
significantly withered.Comment: 17 pages, 9 figures, 9 table
Mass-Radius Relationships for Solid Exoplanets
We use new interior models of cold planets to investigate the mass-radius
relationships of solid exoplanets, considering planets made primarily of iron,
silicates, water, and carbon compounds. We find that the mass-radius
relationships for cold terrestrial-mass planets of all compositions we
considered follow a generic functional form that is not a simple power law:
for up to , where and are scaled mass and radius
values. This functional form arises because the common building blocks of solid
planets all have equations of state that are well approximated by a modified
polytrope of the form .
We find that highly detailed planet interior models, including temperature
structure and phase changes, are not necessary to derive solid exoplanet bulk
composition from mass and radius measurements. For solid exoplanets with no
substantial atmosphere we have also found that: with 5% fractional uncertainty
in planet mass and radius it is possible to distinguish among planets composed
predominantly of iron or silicates or water ice but not more detailed
compositions; with ~5% uncertainty water ice planets with
water by mass may be identified; the minimum plausible planet size for a given
mass is that of a pure iron planet; and carbon planet mass-radius relationships
overlap with those of silicate and water planets due to similar zero-pressure
densities and equations of state. We propose a definition of "super Earths''
based on the clear distinction in radii between planets with significant gas
envelopes and those without.Comment: ApJ, in press, 33 pages including 16 figure
Extrasolar Giant Planets under Strong Stellar Irradiation
We investigate the effects on extrasolar giant planets [EGPs] of intense
irradiation by their parent stars, describing the issues involved in treating
the model atmosphere problem correctly. We treat the radiative transfer in
detail, allowing the flux from the parent star to interact with all relevant
depths of the planetary atmosphere, with no need for a pre-assumed albedo. We
present a low-resolution optical and near-IR spectrum of a close-in EGP,
focusing on the differences from an isolated planet.
In our dust-free planetary atmospheres we find that Rayleigh scattering
increases the EGP's flux by orders of magnitude shortward of the CaII H&K
doublet (393 nm), and the spectral features of the parent star are exactly
reflected. In the optical and near-IR the thermal absorption of the planet
takes over, but the absorption features are changed by the irradiation. The
inclusion of dust increases the reflected flux in the blue; the stellar
spectral lines can be seen blueward of H-beta (486 nm).Comment: 14 pages, 4 figures, LaTex, accepted in ApJ
Extreme events in multilayer, interdependent complex networks and control
This work was supported by NSF under Grant No. 1441352.Peer reviewedPublisher PD
The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets
(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar
PLanet Occultation REsearch) project, a series of transiting planet searches
using 4-m-class telescopes to continuously monitor a single field of stars in
the Galactic Plane in each ~2 week observing campaign. We discuss the general
factors which determine the efficiency and the number of planets found by a
transit search, including time sampling strategy and field selection. The
primary goal is to select the most promising planet candidates for radial
velocity follow-up observations. We show that with very high photometric
precision light curves that have frequent time sampling and at least two
detected transits, it is possible to uniquely solve for the main parameters of
the eclipsing system (including planet radius) based on several important
assumptions about the central star. Together with a measured spectral type for
the star, this unique solution for orbital parameters provides a powerful
method for ruling out most contaminants to transiting planet candidates. For
the EXPLORE project, radial velocity follow-up observations for companion mass
determination of the best candidates are done on 8-m-class telescopes within
two or three months of the photometric campaigns. This same-season follow-up is
made possible by the use of efficient pipelines to produce high quality light
curves within weeks of the observations. We conclude by presenting early
results from our first search, EXPLORE I, in which we reached <1% rms
photometric precision (measured over a full night) on ~37,000 stars to I <=
18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion
of some issues. 36 pages, including 14 figure
Photometric Light Curves and Polarization of Close-in Extrasolar Giant Planets
The close-in extrasolar giant planets [CEGPs], \ltorder 0.05 AU from their
parent stars, may have a large component of optically reflected light. We
present theoretical optical photometric light curves and polarization curves
for the CEGP systems, from reflected planetary light. Different particle sizes
of three condensates are considered. In the most reflective case, the
variability is micromagnitudes, which will be easily detectable
by the upcoming satellite missions MOST, COROT, and MONS, and possibly from the
ground in the near future. The least reflective case is caused by small, highly
absorbing grains such as solid Fe, with variation of much less than one
micromagnitude. Polarization for all cases is lower than current detectability
limits. We also discuss the temperature-pressure profiles and resulting
emergent spectra of the CEGP atmospheres. We discuss the observational results
of Tau Boo b by Cameron et al. (1999) and Charbonneau et al. (1999) in context
of our model results. The predictions - the shape and magnitude of the light
curves and polarization curves - are highly dependent on the size and type of
condensates present in the planetary atmosphere.Comment: 33 pages, accepted by Ap
The 21 cm Signature of Cosmic String Wakes
We discuss the signature of a cosmic string wake in 21cm redshift surveys.
Since 21cm surveys probe higher redshifts than optical large-scale structure
surveys, the signatures of cosmic strings are more manifest in 21cm maps than
they are in optical galaxy surveys. We find that, provided the tension of the
cosmic string exceeds a critical value (which depends on both the redshift when
the string wake is created and the redshift of observation), a cosmic string
wake will generate an emission signal with a brightness temperature which
approaches a limiting value which at a redshift of is close to 400
mK in the limit of large string tension. The signal will have a specific
signature in position space: the excess 21cm radiation will be confined to a
wedge-shaped region whose tip corresponds to the position of the string, whose
planar dimensions are set by the planar dimensions of the string wake, and
whose thickness (in redshift direction) depends on the string tension. For
wakes created at , then at a redshift of the
critical value of the string tension is , and
it decreases linearly with redshift (for wakes created at the time of equal
matter and radiation, the critical value is a factor of two lower at the same
redshift). For smaller tensions, cosmic strings lead to an observable
absorption signal with the same wedge geometry.Comment: 11 pages, 4 figures; a couple of comments added in the discussion
sectio
Looking for a varying in the Cosmic Microwave Background
We perform a likelihood analysis of the recently released BOOMERanG and
MAXIMA data, allowing for the possibility of a time-varying fine-structure
constant. We find that in general this data prefers a value of that
was smaller in the past (which is in agreement with measurements of
from quasar observations). However, there are some interesting degeneracies in
the problem which imply that strong statements about can not be made
using this method until independent accurate determinations of
and are available.
We also show that a preferred lower value of comes mainly from the
data points around the first Doppler peak, whereas the main effect of the
high- data points is to increase the preferred value for
(while also tightening the constraints on and ). We comment on
some implications of our results.Comment: 15 pages; submitted to Phys. Rev.
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