3,069 research outputs found
Slow roll in simple non-canonical inflation
We consider inflation using a class of non-canonical Lagrangians for which
the modification to the kinetic term depends on the field, but not its
derivatives. We generalize the standard Hubble slow roll expansion to the
non-canonical case and derive expressions for observables in terms of the
generalized slow roll parameters. We apply the general results to the
illustrative case of ``Slinky'' inflation, which has a simple, exactly
solvable, non-canonical representation. However, when transformed into a
canonical basis, Slinky inflation consists of a field oscillating on a
multi-valued potential. We calculate the power spectrum of curvature
perturbations for Slinky inflation directly in the non-canonical basis, and
show that the spectrum is approximately a power law on large scales, with a
``blue'' power spectrum. On small scales, the power spectrum exhibits strong
oscillatory behavior. This is an example of a model in which the widely used
solution of Garriga and Mukhanov gives the wrong answer for the power spectrum.Comment: 9 pages, LaTeX, four figures. (V2: minor changes to text. Version
submitted to JCAP.
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
Cascade Failure in a Phase Model of Power Grids
We propose a phase model to study cascade failure in power grids composed of
generators and loads. If the power demand is below a critical value, the model
system of power grids maintains the standard frequency by feedback control. On
the other hand, if the power demand exceeds the critical value, an electric
failure occurs via step out (loss of synchronization) or voltage collapse. The
two failures are incorporated as two removal rules of generator nodes and load
nodes. We perform direct numerical simulation of the phase model on a
scale-free network and compare the results with a mean-field approximation.Comment: 7 pages, 2 figure
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
Projected Heat-Related Mortality in the U.S. Urban Northeast
Increased heat-related mortality is projected to be among the major impacts of climate change on human health, and the United States urban Northeast region is likely to be particularly vulnerable. In support of regional adaptation planning, quantitative information is needed on potential future health responses at the urban and regional scales. Here, we present future projections of heat-related mortality in Boston, New York and Philadelphia utilizing downscaled next-generation climate models and Representative Concentration Pathways (RCPs) developed in support of the Intergovernmental Panel on Climate Change (IPCC)’s Fifth Assessment Report (AR5). Our analyses reveal that heat-related mortality rates per 100,000 of population during the baseline period between 1985 and 2006 were highest in Philadelphia followed by New York City and Boston. However, projected heat-related mortality rates in the 2020s, 2050s and 2080s were highest in New York City followed by Philadelphia and Boston. This study may be of value in developing strategies for reducing the future impacts of heat and building climate change resilience in the urban Northeast region
The Phantom Bounce: A New Oscillating Cosmology
An oscillating universe cycles through a series of expansions and
contractions. We propose a model in which ``phantom'' energy with
grows rapidly and dominates the late-time expanding phase. The universe's
energy density is so large that the effects of quantum gravity are important at
both the beginning and the end of each expansion (or contraction). The bounce
can be caused by high energy modifications to the Friedmann equation, which
make the cosmology nonsingular. The classic black hole overproduction of
oscillating universes is resolved due to their destruction by the phantom
energy.Comment: Four pages, one figure. V3: version to appear in JCA
Particulate matter pollution in African cities
Abstract:
Rapid urban population growth, air pollution emissions, and changing patterns of disease in African cities may increase the burden of air pollution-related morbidity and mortality in coming decades. Yet, air monitoring is limited across the continent and many countries lack air quality standards. This paper focuses on particulate matter (PM) pollution, one of the most relevant and widely used indicators of urban air quality. We provide an overview of published PM monitoring studies in Africa, outline major themes, point out data gaps, and discuss strategies for addressing particulate air pollution in rapidly growing African cities. Our review reveals that, although few studies have reported annual mean levels of coarse and fine particles, collective evidence from short- and long-term air monitoring studies across urban Africa demonstrates that pollution levels often exceed international guidelines. Furthermore, pollution levels may be rising as a result of increased motor vehicle traffic building on already high background concentrations of PM in many locations due to climatic and geographic conditions. Biomass burning and industrial activities, often located in cities, further exacerbate levels of PM. Despite the health risks this situation presents, air quality programs, particularly in sub-Saharan Africa, have been stalled or discontinued in recent years. Implementation of systematic PM data collection would enable air pollution-related health impact assessments, the development of strategies to reduce the air pollution health burden, and facilitate urban planning and transportation policy as it relates to air quality and health.
Keywords
Urban air quality, Environmental health, Particulate matter, PM10, PM2.5, Afric
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