109,876 research outputs found
Inflating with Large Effective Fields
We re-examine large scalar fields within effective field theory, in
particular focussing on the issues raised by their use in inflationary models
(as suggested by BICEP2 to obtain primordial tensor modes). We argue that when
the large-field and low-energy regimes coincide the scalar dynamics is most
effectively described in terms of an asymptotic large-field expansion whose
form can be dictated by approximate symmetries, which also help control the
size of quantum corrections. We discuss several possible symmetries that can
achieve this, including pseudo-Goldstone inflatons characterized by a coset
(based on abelian and non-abelian, compact and non-compact symmetries),
as well as symmetries that are intrinsically higher dimensional. Besides the
usual trigonometric potentials of Natural Inflation we also find in this way
simple {\em large-field} power laws (like ) and exponential
potentials, . Both of these can
describe the data well and give slow-roll inflation for large fields without
the need for a precise balancing of terms in the potential. The exponential
potentials achieve large through the limit and so
predict ; consequently gives but not much larger (and so could be ruled out as measurements on
and improve). We examine the naturalness issues for these models and
give simple examples where symmetries protect these forms, using both
pseudo-Goldstone inflatons (with non-abelian non-compact shift symmetries
following familiar techniques from chiral perturbation theory) and
extra-dimensional models.Comment: 21 pages + appendices, 3 figure
Diverse Aging and Health Inequality by Race and Ethnicity
Although gerontologists have long embraced the concept of heterogeneity in theories and models of aging, recent research reveals the importance of racial and ethnic diversity on life course processes leading to health inequality. This article examines research on health inequality by race and ethnicity and identifies theoretical and methodological innovations that are transforming the study of health disparities. Drawing from cumulative inequality theory, we propose greater use of life course analysis, more attention to variability within racial and ethnic groups, and better integration of environmental context into the study of accumulation processes leading to health disparities
Evidence of magnetic field quenching of phosphorous-doped silicon quantum dots
We present data on the electrical transport properties of highly-doped
silicon-on-insulator quantum dots under the effect of pulsed magnetic fields up
to 48 T. At low field intensities, B<7 T, we observe a strong modification of
the conductance due to the destruction of weak localization whereas at higher
fields, where the magnetic field length becomes comparable to the effective
Bohr radius of phosphorous in silicon, a strong decrease in conductance is
demonstrated. Data in the high and low electric field bias regimes are then
compared to show that close to the Coulomb blockade edge magnetically-induced
quenching to single donors in the quantum dot is achieved at about 40 T.Comment: accepted for publication at Current Applied Physic
The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter Photometry
The nature of far-infrared dust emission toward main sequence stars, whether
interstellar or circumstellar, can be deduced from submillimeter photometry. We
present JCMT/SCUBA flux measurements at 850 microns toward 8 stars with large
photospheric excesses at 60-100 microns. 5 sources were detected at 3-sigma or
greater significance and one was marginally detected at 2.5-sigma. The inferred
dust masses and temperatures range from 0.033 to 0.24 Earth masses and 43-65 K
respectively. The frequency behavior of the opacity, tau_nu ~ nu^beta, is
relatively shallow, beta < 1. These dust properties are characteristic of
circumstellar material, most likely the debris from planetesimal collisions.
The 2 non-detections have lower temperatures, 35-38 K and steeper opacity
indices, beta > 1.5, that are more typical of interstellar cirrus. The
confirmed disks all have inferred diameters > 2'', most lie near the upper
envelope of the debris disk mass distribution, and 4 are bright enough to be
feasible for high resolution imaging.Comment: accepted by Ap
Effect of external conditions on the structure of scrolled graphene edges
Characteristic dimensions of carbon nanoscrolls - "buckyrolls" - are
calculated by analyzing the competition between elastic, van der Waals, and
electrostatic energies for representative models of suspended and
substrate-deposited graphene samples. The results are consistent with both
atomistic simulations and experimental observations of scrolled graphene edges.
Electrostatic control of the wrapping is shown to be practically feasible and
its possible device applications are indicated.Comment: 4 pages, 3 figure
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