2,296 research outputs found
New Solutions of the Inflationary Flow Equations
The inflationary flow equations are a frequently used method of surveying the
space of inflationary models. In these applications the infinite hierarchy of
differential equations is truncated in a way which has been shown to be
equivalent to restricting the set of models considered to those characterized
by polynomial inflaton potentials. This paper explores a different method of
solving the flow equations, which does not truncate the hierarchy and in
consequence covers a much wider class of models while retaining the practical
usability of the standard approach.Comment: References added, and a couple of comment
Boundary Effective Field Theory and Trans-Planckian Perturbations: Astrophysical Implications
We contrast two approaches to calculating trans-Planckian corrections to the
inflationary perturbation spectrum: the New Physics Hypersurface [NPH] model,
in which modes are normalized when their physical wavelength first exceeds a
critical value, and the Boundary Effective Field Theory [BEFT] approach, where
the initial conditions for all modes are set at the same time, and modified by
higher dimensional operators enumerated via an effective field theory
calculation. We show that these two approaches -- as currently implemented --
lead to radically different expectations for the trans-Planckian corrections to
the CMB and emphasize that in the BEFT formalism we expect the perturbation
spectrum to be dominated by quantum gravity corrections for all scales shorter
than some critical value. Conversely, in the NPH case the quantum effects only
dominate the longest modes that are typically much larger than the present
horizon size. Furthermore, the onset of the breakdown in the standard
inflationary perturbation calculation predicted by the BEFT formalism is likely
to be associated with a feature in the perturbation spectrum, and we discuss
the observational signatures of this feature in both CMB and large scale
structure observations. Finally, we discuss possible modifications to both
calculational frameworks that would resolve the contradictions identified here.Comment: Reworded commentary, reference added (v2) References added (v3
Dark energy in hybrid inflation
The situation that a scalar field provides the source of the accelerated
expansion of the universe while rolling down its potential is common in both
the simple models of the primordial inflation and the quintessence-based dark
energy models. Motivated by this point, we address the possibility of causing
the current acceleration via the primordial inflation using a simple model
based on hybrid inflation. We trigger the onset of the motion of the
quintessence field via the transition field, and find that the fate of the
universe depends on the true vacuum energy determined by choosing the
parameters. We also briefly discuss the variation of the equation of state and
the possible implementation of our scenario in supersymmetric theories.Comment: (v1) 10 pages, 1 figure; (v2) 12 pages, considerably revised, to
appear in Physical Review
Sharing Social Network Data: Differentially Private Estimation of Exponential-Family Random Graph Models
Motivated by a real-life problem of sharing social network data that contain
sensitive personal information, we propose a novel approach to release and
analyze synthetic graphs in order to protect privacy of individual
relationships captured by the social network while maintaining the validity of
statistical results. A case study using a version of the Enron e-mail corpus
dataset demonstrates the application and usefulness of the proposed techniques
in solving the challenging problem of maintaining privacy \emph{and} supporting
open access to network data to ensure reproducibility of existing studies and
discovering new scientific insights that can be obtained by analyzing such
data. We use a simple yet effective randomized response mechanism to generate
synthetic networks under -edge differential privacy, and then use
likelihood based inference for missing data and Markov chain Monte Carlo
techniques to fit exponential-family random graph models to the generated
synthetic networks.Comment: Updated, 39 page
Air Pollution Exposure Assessment for Epidemiologic Studies of Pregnant Women and Children: Lessons Learned from the Centers for Childrenâs Environmental Health and Disease Prevention Research
The National Childrenâs Study is considering a wide spectrum of airborne pollutants that are hypothesized to potentially influence pregnancy outcomes, neurodevelopment, asthma, atopy, immune development, obesity, and pubertal development. In this article we summarize six applicable exposure assessment lessons learned from the Centers for Childrenâs Environmental Health and Disease Prevention Research that may enhance the National Childrenâs Study: a) Selecting individual study subjects with a wide range of pollution exposure profiles maximizes spatial-scale exposure contrasts for key pollutants of study interest. b) In studies with large sample sizes, long duration, and diverse outcomes and exposures, exposure assessment efforts should rely on modeling to provide estimates for the entire cohort, supported by subject-derived questionnaire data. c) Assessment of some exposures of interest requires individual measurements of exposures using snapshots of personal and microenvironmental exposures over short periods and/or in selected microenvironments. d) Understanding issues of spatialâtemporal correlations of air pollutants, the surrogacy of specific pollutants for components of the complex mixture, and the exposure misclassification inherent in exposure estimates is critical in analysis and interpretation. e) âUsualâ temporal, spatial, and physical patterns of activity can be used as modifiers of the exposure/outcome relationships. f) Biomarkers of exposure are useful for evaluation of specific exposures that have multiple routes of exposure. If these lessons are applied, the National Childrenâs Study offers a unique opportunity to assess the adverse effects of air pollution on interrelated health outcomes during the critical early life period
The Lyth Bound and the End of Inflation
We derive an extended version of the well-known Lyth Bound on the total
variation of the inflaton field, incorporating higher order corrections in slow
roll. We connect the field variation to both the spectral index of
scalar perturbations and the amplitude of tensor modes. We then investigate the
implications of this bound for ``small field'' potentials, where the field
rolls off a local maximum of the potential. The total field variation during
inflation is {\em generically} of order , even for potentials with
a suppressed tensor/scalar ratio. Much of the total field excursion arises in
the last e-fold of inflation and in single field models this problem can only
be avoided via fine-tuning or the imposition of a symmetry. Finally, we discuss
the implications of this result for inflationary model building in string
theory and supergravity.Comment: 10 pages, RevTeX, 2 figures (V3: version accepted for publication by
JCAP
Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12
In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state
effective spin S' = 1/2) are situated on two interpenetrating corner sharing
triangular sublattices such that frustrated magnetic interactions are possible.
Previous specific heat measurements evidenced the development of short range
magnetic correlations below 0.5K and a lambda-transition at 54mK (Filippi et
al. J. Phys. C: Solid State Physics 13 (1980) 1277). From 170-Yb M"ossbauer
spectroscopy measurements down to 36mK, we find there is no static magnetic
order at temperatures below that of the lambda-transition. Below 0.3K, the
fluctuation frequency of the short range correlated Yb3+ moments progressively
slows down and as the temperature tends to 0, the frequency tends to a
quasi-saturated value of 3 x 10^9 s^-1. We also examined the Yb3+ paramagnetic
relaxation rates up to 300K using 172-Yb perturbed angular correlation
measurements: they evidence phonon driven processes.Comment: 6 pages, 5 figure
The Price of WMAP Inflation in Supergravity
The three-year data from WMAP are in stunning agreement with the simplest
possible quadratic potential for chaotic inflation, as well as with new or
symmetry-breaking inflation. We investigate the possibilities for incorporating
these potentials within supergravity, particularly of the no-scale type that is
motivated by string theory. Models with inflation driven by the matter sector
may be constructed in no-scale supergravity, if the moduli are assumed to be
stabilised by some higher-scale dynamics and at the expense of some
fine-tuning. We discuss specific scenarios for stabilising the moduli via
either D- or F-terms in the effective potential, and survey possible
inflationary models in the presence of D-term stabilisation.Comment: 15 pages, 6 figures, plain Late
- âŠ