3,152 research outputs found
Restoring the sting to metric preheating
The relative growth of field and metric perturbations during preheating is
sensitive to initial conditions set in the preceding inflationary phase. Recent
work suggests this may protect super-Hubble metric perturbations from resonant
amplification during preheating. We show that this possibility is fragile and
sensitive to the specific form of the interactions between the inflaton and
other fields. The suppression is naturally absent in two classes of preheating
in which either (1) the vacua of the non-inflaton fields during inflation are
deformed away from the origin, or (2) the effective masses of non-inflaton
fields during inflation are small but during preheating are large. Unlike the
simple toy model of a coupling, most realistic particle
physics models contain these other features. Moreover, they generically lead to
both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble
scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and
new figure. To appear Phys. Rev. D (Rapid Communication
AN IRRIGATION MODEL FOR MANAGEMENT OF LIMITED WATER SUPPLIES
A two-stage simulation/mathematical programming model is presented for determining the optimal intraseasonal allocation of irrigation water under conditions of limited water supply. The model is applied to a series of water shortage scenarios under both surface and center pivot irrigation. Economically efficient irrigation management is shown to involve the coordination of a number of managerial decisions, including irrigation scheduling, crop substitution, the adoption of improved irrigation labor practices, and idling land. The results indicate that significant opportunities exist for conserving water in the study area under both surface and center pivot irrigation.Crop Production/Industries, Resource /Energy Economics and Policy,
A new twist to preheating
Metric perturbations typically strengthen field resonances during preheating.
In contrast we present a model in which the super-Hubble field resonances are
completely {\em suppressed} when metric perturbations are included. The model
is the nonminimal Fakir-Unruh scenario which is exactly solvable in the
long-wavelength limit when metric perturbations are included, but exhibits
exponential growth of super-Hubble modes in their absence. This gravitationally
enhanced integrability is exceptional, both for its rarity and for the power
with which it illustrates the importance of including metric perturbations in
consistent studies of preheating. We conjecture a no-go result - there exists
no {\em single-field} model with growth of cosmologically-relevant metric
perturbations during preheating.Comment: 6 pages, 3 figures, Version to appear in Physical Review
Classification of Multiwavelength Transients with Machine Learning
With the advent of powerful telescopes such as the Square Kilometer Array and
the Vera C. Rubin Observatory, we are entering an era of multiwavelength
transient astronomy that will lead to a dramatic increase in data volume.
Machine learning techniques are well suited to address this data challenge and
rapidly classify newly detected transients. We present a multiwavelength
classification algorithm consisting of three steps: (1) interpolation and
augmentation of the data using Gaussian processes; (2) feature extraction using
wavelets; and (3) classification with random forests. Augmentation provides
improved performance at test time by balancing the classes and adding diversity
into the training set. In the first application of machine learning to the
classification of real radio transient data, we apply our technique to the
Green Bank Interferometer and other radio light curves. We find we are able to
accurately classify most of the 11 classes of radio variables and transients
after just eight hours of observations, achieving an overall test accuracy of
78 percent. We fully investigate the impact of the small sample size of 82
publicly available light curves and use data augmentation techniques to
mitigate the effect. We also show that on a significantly larger simulated
representative training set that the algorithm achieves an overall accuracy of
97 percent, illustrating that the method is likely to provide excellent
performance on future surveys. Finally, we demonstrate the effectiveness of
simultaneous multiwavelength observations by showing how incorporating just one
optical data point into the analysis improves the accuracy of the worst
performing class by 19 percent.Comment: 16 pages, 12 figure
Massless Metric Preheating
Can super-Hubble metric perturbations be amplified exponentially during
preheating ? Yes. An analytical existence proof is provided by exploiting the
conformal properties of massless inflationary models. The traditional conserved
quantity \zeta is non-conserved in many regions of parameter space. We include
backreaction through the homogeneous parts of the inflaton and preheating
fields and discuss the role of initial conditions on the post-preheating
power-spectrum. Maximum field variances are strongly underestimated if metric
perturbations are ignored. We illustrate this in the case of strong
self-interaction of the decay products. Without metric perturbations,
preheating in this case is very inefficient. However, metric perturbations
increase the maximum field variances and give alternative channels for the
resonance to proceed. This implies that metric perturbations can have a large
impact on calculations of relic abundances of particles produced during
preheating.Comment: 8 pages, 4 colour figures. Version to appear in Phys. Rev. D.
Contains substantial new analysis of the ranges of parameter space for which
large changes to the inflation-produced power spectrum are expecte
Automatic Quantification of Epidermis Curvature in H&E Stained Microscopic Skin Image of Mice
Changes in the curvature of the epidermis layer is often associated with many skin disorders, such as ichthyoses and generic effects of ageing. Therefore, methods to quantify changes in the curvature are of a scientific and clinical interest. Manual methods to determine curvature are both laborious and intractable to large scale investigations. This paper proposes an automatic algorithm to quantify curvature of microscope images of H&E-stained murine skin. The algorithm can be divided into three key stages. First, skin layers segmentation based on colour deconvolution to separate the original image into three channels of different representations to facilitate segmenting the image into multiple layers, namely epidermis, dermis and subcutaneous layers. The algorithm then further segments the epidermis layer into cornified and basal sub-layers. Secondly, it quantifies the curvature of the epidermis layer by measuring the difference between the epidermis edge and a straight line (theoretical reference line) connecting the two far sides of the epidermis edge. Finally, the curvature measurements extracted from a large number of images of mutant mice are used to identify a list of genes responsible for changes in the epidermis curvature. A dataset of 5714 H&E microscopic images of mutant and wild type mice were used to evaluate the effectiveness of the algorithm
Primordial black hole production due to preheating
During the preheating process at the end of inflation the amplification of
field fluctuations can lead to the amplification of curvature perturbations. If
the curvature perturbations on small scales are sufficiently large, primordial
black holes (PBHs) will be overproduced. In this paper we study PBH production
in the two-field preheating model with quadratic inflaton potential. We show
that for many values of the inflaton mass m, and coupling g, small scale
perturbations will be amplified sufficiently, before backreaction can shut off
preheating, so that PBHs will be overproduced during the subsequent radiation
dominated era.Comment: 5 pages, 3 eps figures. Minor changes to match version to appear in
PRD as a rapid communicatio
Post-Inflationary Reheating
We study a model for reheating that has been much investigated for parametric
resonance, having a quartic interaction of the scalar inflaton with another
scalar field. Attention is particularly on the quantum excitations of the
inflaton field and the metric perturbation with a smooth transition from
quantum to classical stochastic states, followed through from a specific
inflation model to a state including a relativistic fluid. The scalar fields
enter non-perturbatively but the metric enters perturbatively, and the validity
of this latter is assessed. In this model our work seems to point the large
scale curvature parameter changing.Comment: 25 pages, 6 figures. Coding error(misprint) corrected:figures and
some conclusions change
New constraints on multi-field inflation with nonminimal coupling
We study the dynamics and perturbations during inflation and reheating in a
multi-field model where a second scalar field is nonminimally coupled to
the scalar curvature ). When is positive, the usual
inflationary prediction for large-scale anisotropies is hardly altered while
the fluctuation in sub-Hubble modes can be amplified during preheating
for large . For negative values of , however, long-wave modes of the
fluctuation exhibit exponential increase during inflation, leading to
the strong enhancement of super-Hubble metric perturbations even when
is less than unity. This is because the effective mass becomes negative
during inflation. We constrain the strength of and the initial by
the amplitude of produced density perturbations. One way to avoid nonadiabatic
growth of super-Hubble curvature perturbations is to stabilize the mass
through a coupling to the inflaton. Preheating may thus be necessary in these
models to protect the stability of the inflationary phase.Comment: 20 pages, 8 figures, submitted to Physical Review
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