1,574 research outputs found
Are Experienced Analysts More Accurate?
We examine the relationship between analyst experience and the accuracy of annual earnings forecasts using a 20-year sample (1983-2002) from the Thomson Financial First Call I/B/E/S database. We test for this relationship using three different measures of forecast accuracy employed by prior researchers, which are regressed against measures of general experience and specific experience, along with five other controls, for four independent 5-year subperiods, as well as for the full 20-year period. We find that general experience levels are positively associated with forecast accuracy (negatively associated with forecast error) in most subperiods for two of the three measures of forecast accuracy. We also find, in contrast with the extant literature, that for two of the three measures of forecast accuracy and for most subperiods, specific experience does not have an association with forecast accuracy beyond that provided by the general experience measure. Our results suggest that the relationship between forecast accuracy and analyst experience (as well as some other commonly examined analyst characteristics) is dependent on the measure of accuracy employed and the time period studied
Improved test of Lorentz Invariance in Electrodynamics using Rotating Cryogenic Sapphire Oscillators
We present new results from our test of Lorentz invariance, which compares
two orthogonal cryogenic sapphire microwave oscillators rotating in the lab. We
have now acquired over 1 year of data, allowing us to avoid the short data set
approximation (less than 1 year) that assumes no cancelation occurs between the
and parameters from the photon
sector of the standard model extension. Thus, we are able to place independent
limits on all eight and parameters.
Our results represents up to a factor of 10 improvement over previous non
rotating measurements (which independently constrained 7 parameters), and is a
slight improvement (except for ) over results from
previous rotating experiments that assumed the short data set approximation.
Also, an analysis in the Robertson-Mansouri-Sexl framework allows us to place a
new limit on the isotropy parameter of
, an improvement of a factor of 2.Comment: Accepted for publication in Phys. Rev.
Forecast Constraints on Inflation from Combined CMB and Gravitational Wave Direct Detection Experiments
We study how direct detection of the inflationary gravitational wave
background constrains inflationary parameters and complements CMB polarization
measurements. The error ellipsoids calculated using the Fisher information
matrix approach with Planck and the direct detection experiment, BBO (Big Bang
Observer), show different directions of parameter degeneracy, and the
degeneracy is broken when they are combined. For a slow-roll parameterization,
we show that BBO could significantly improve the constraints on the
tensor-to-scalar ratio compared with Planck alone. We also look at a quadratic
and a natural inflation model. In both cases, if the temperature of reheating
is also treated as a free parameter, then the addition of BBO can significantly
improve the error bars. In the case of natural inflation, we find that the
addition of BBO could even partially improve the error bars of a cosmic
variance-limited CMB experiment.Comment: 12 pages, 5 figures; matches version to appear in PRD; typos
correcte
Electrodynamics with Lorentz-violating operators of arbitrary dimension
The behavior of photons in the presence of Lorentz and CPT violation is
studied. Allowing for operators of arbitrary mass dimension, we classify all
gauge-invariant Lorentz- and CPT-violating terms in the quadratic Lagrange
density associated with the effective photon propagator. The covariant
dispersion relation is obtained, and conditions for birefringence are
discussed. We provide a complete characterization of the coefficients for
Lorentz violation for all mass dimensions via a decomposition using
spin-weighted spherical harmonics. The resulting nine independent sets of
spherical coefficients control birefringence, dispersion, and anisotropy. We
discuss the restriction of the general theory to various special models,
including among others the minimal Standard-Model Extension, the isotropic
limit, the case of vacuum propagation, the nonbirefringent limit, and the
vacuum-orthogonal model. The transformation of the spherical coefficients for
Lorentz violation between the laboratory frame and the standard Sun-centered
frame is provided. We apply the results to various astrophysical observations
and laboratory experiments. Astrophysical searches of relevance include studies
of birefringence and of dispersion. We use polarimetric and dispersive data
from gamma-ray bursts to set constraints on coefficients for Lorentz violation
involving operators of dimensions four through nine, and we describe the mixing
of polarizations induced by Lorentz and CPT violation in the cosmic-microwave
background. Laboratory searches of interest include cavity experiments. We
present the theory for searches with cavities, derive the experiment-dependent
factors for coefficients in the vacuum-orthogonal model, and predict the
corresponding frequency shift for a circular-cylindrical cavity.Comment: 58 pages two-column REVTeX, accepted in Physical Review
Matrix equations and trilinear commutation relations
In this paper we discuss a general algebraic approach to treating static
equations of matrix models with a mass-like term. In this approach the
equations of motions are considered as consequence of parafermi-like trilinear
commutation relations. In this context we consider several solutions, including
construction of noncommutative spheres. The equivalence of fuzzy spheres and
parafermions is underlined.Comment: 10 pages, an incorrect claim is removed, one reference is adde
Supersymmetric Dissipative Quantum Mechanics from Superstrings
Following the approach of Callan and Thorlacius applied to the superstring,
we derive a supersymmetric extension of the non-local dissipative action of
Caldeira and Leggett. The dissipative term turns out to be invariant under a
group of superconformal transformations. When added to the usual kinetic term,
it provides an example of supersymmetric dissipative quantum mechanics. As a
by-product of our analysis, an intriguing connection to the homeotic/hybrid
fermion model, proposed for CPT violation in neutrinos, appears.Comment: Latex, 16 page
Mechanics and Quantum Supermechanics of a Monopole Probe Including a Coulomb Potential
A supersymmetric Lagrangian used to study D-particle probes in a D6-brane
background is exactly soluble. We present an analysis of the classical and
quantum mechanics of this theory, including classical trajectories in the
bosonic theory, and the exact quantum spectrum and wavefunctions, including
both bound and unbound states.Comment: 34 pages with 4 black&white eps figures. v2: Reference corrected and
a reference added. Figure files are significantly smaller; colour figures are
included with the source (use \colorfigtrue). v3: Reference adde
General relativistic corrections to the Sagnac effect
The difference in travel time of corotating and counter-rotating light waves
in the field of a central massive and spinning body is studied. The corrections
to the special relativistic formula are worked out in a Kerr field. Estimation
of numeric values for the Earth and satellites in orbit around it show that a
direct measurement is in the order of concrete possibilities.Comment: REVTex, accepted for publication on Phys. Rev.
- …