15,512 research outputs found
Update on Open Universe Inflationary Models
An overview of some new results in open inflation over the past year,
including the calculation of gravity wave contributions to the Cosmic Microwave
Background. Proceedings for COSMO-97, held in Ambleside, U.K., hence very short
due to space limitations (the version for the web is more than 3 pages because
archive numbers have been added for the references).Comment: LaTeX, uses sprocl.tex, 4 pages, corrected reference typ
Open universes from bubbles: an introduction and update
An introduction to models of open universes originating from bubbles,
including a summary of recent theoretical results for the power spectrum. To
appear in the proceedings of the XXXIth Moriond meeting, "Microwave Background
Anisotropies."Comment: LaTeX file, uses epsf.tex, 3 figures, 8 pages, minor wording changes
to clarify discussion of coordinate system
Using large galaxy surveys to distinguish z~0.5 quiescent galaxy models
One of the most striking properties of galaxies is the bimodality in their
star-formation rates. A major puzzle is why any given galaxy is star-forming or
quiescent, and a wide range of physical mechanisms have been proposed as
solutions. We consider how observations, such as might be available in upcoming
large galaxy surveys, might distinguish different galaxy quenching scenarios.
To do this, we combine an N-body simulation and multiple prescriptions from the
literature to create several quiescent galaxy mock catalogues. Each
prescription uses a different set of galaxy properties (such as history,
environment, centrality) to assign individual simulation galaxies as quiescent.
We find how and how much the resulting quiescent galaxy distributions differ
from each other, both intrinsically and observationally. In addition to tracing
observational consequences of different quenching mechanisms, our results
indicate which sorts of quenching models might be most readily disentangled by
upcoming observations and which combinations of observational quantities might
provide the most discriminatory power.
Our observational measures are auto, cross, and marked correlation functions,
pro- jected density distributions, and group multiplicity functions, which rely
upon galaxy positions, stellar masses and of course quiescence. Although
degeneracies between models are present for individual observations, using
multiple observations in concert allows us to distinguish between all ten
models we consider. In addition to identifying intrinsic and observational
consequences of quiescence prescriptions and testing these quiescence models
against each other and observations, these methods can also be used to validate
colors (or other history and environment dependent properties) in simulated
mock catalogues.Comment: 20 pages, 14 figures. Version to appear in MNRAS, incorporating
helpful suggestions from referee and other
Magnetic Inhomogeneity and Magnetotransport in Electron-Doped Ca(1-x)La(x)MnO(3) (0<=x<=0.10)
The dc magnetization (M) and electrical resistivity (\rho) as functions of
magnetic field and temperature are reported for a series of lightly electron
dopedCa(1-x)La(x)MnO(3) (0<=x<=0.10) specimens for which magnetization [Phys.
Rev. B {\bf 61}, 14319 (2000)] and scattering studies [Phys. Rev. B {\bf 68},
134440 (2003)] indicate an inhomogeneous magnetic ground state composed of
ferromagnetic (FM) droplets embedded in a G-type antiferromagnetic matrix. A
change in the magnetic behavior near x=0.02 has been suggested to be the
signature of a crossover to a long-ranged spin-canted phase. The data reported
here provide further detail about this crossover in the magnetization, and
additional insight into the origin of this phenomenon through its manifestation
in the magnetotransport. In the paramagnetic phase (T>=125 K) we find a
magnetoresistance =-C(M/M_S)^2 (M_S is the low-T saturation magnetization), as
observed in many manganites in the ferromagnetic (FM), colossal
magnetoresistance (CMR) region of the phase diagram, but with a value of C that
is two orders of magnitude smaller than observed for CMR materials. The doping
behavior C(x) follows that of M_S(x), indicating that electronic inhomogeneity
associated with FM fluctuations occurs well above the magnetic ordering
transition.Comment: 7 pp., 10 Fig.s, submitted to PR
The Strength of String Nonperturbative Effects and Strong-Weak Coupling Duality
A strong-weak coupling duality symmetry of the string equations of motion has
been suggested in the literature. This symmetry implies that vacua occur in
pairs. Since the coupling constant is a dynamical variable in string theory,
tunneling solutions between strong and weak coupling vacua may exist. Such
solutions would naturally lead to nonperturbative effects with anomalous
coupling dependence. A highly simplified example is given.Comment: 7 pages, iassns-hep-93-24, fermilab 93/087-T, nsf-itp-93-45 (A simple
example of the mechanism suggested has been added.
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