252 research outputs found
Marginal Fermi Liquid with a Two-Dimensional Patched Fermi Surface
We consider a model composed of Landau quasiparticle states with patched
Fermi surfaces (FS) sandwiched by states with flat FS to simulate the ``cold''
spot regions in cuprates. We calculate the one particle irreducible function
and the self-energy up to two-loop order. Using renormalization group arguments
we show that in the forward scattering channel the renormalized coupling
constant is never infrared stable due to the flat FS sectors. Furthemore we
show that the self-energy scales with energy as as , and thus the Fermi liquid state within each FS
patch is turned into a marginal Fermi liquid.Comment: 5 pages, 3 ps figure
Stellar cooling anomalies and variant axion models
A number of observations of stellar systems show a mild preference for
anomalously fast cooling compared with what predicted in the standard theory,
which leads to a speculation that there exists an additional energy loss
mechanism originated from the emission of axions in stars. We revisit the
global analysis of the stellar cooling anomalies by adopting conservative
assessments on several systematic uncertainties and find that the significance
of the cooling hints becomes weaker but still indicates a non-vanishing
axion-electron coupling at around 2.4. With the revised analysis
results, we explore the possibility that such excessive energy losses are
interpreted in the framework of variant axion models, which require two Higgs
doublets and flavor-dependent Peccei-Quinn charge assignments. These models
resolve two fundamental issues faced in the traditional KSVZ/DFSZ models by
predicting a sizable axion coupling to electrons required to explain the
cooling anomalies and at the same time providing a solution to the cosmological
domain wall problem. We also find that a specific structure of the axion
couplings to electrons and nucleons slightly relaxes the constraint from
supernova 1987A and enlarges viable parameter regions compared with the DFSZ
models. It is shown that good global fits to the observational data are
obtained for axion mass ranges of , and that the predicted parameter regions can be probed in
the forthcoming helioscope searches.Comment: 38 pages, 7 figures; revised version of the manuscript, accepted for
publication in JCA
Study of gravitational radiation from cosmic domain walls
In this paper, following the previous study, we evaluate the spectrum of
gravitational wave background generated by domain walls which are produced if
some discrete symmetry is spontaneously broken in the early universe. We apply
two different methods to calculate the gravitational wave spectrum: One is to
calculate the gravitational wave spectrum directly from numerical simulations,
and another is to calculate it indirectly by estimating the unequal time
anisotropic stress power spectrum of the scalar field. Both analysises indicate
that the slope of the spectrum changes at two characteristic frequencies
corresponding to the Hubble radius at the decay of domain walls and the width
of domain walls, and that the spectrum between these two characteristic
frequencies becomes flat or slightly red tilted. The second method enables us
to evaluate the GW spectrum semi-analytically for the frequencies which can not
be resolved in the finite box lattice simulations, but relies on the
assumptions for the unequal time correlations of the source.Comment: 17 pages, 9 figures; revised version of the manuscript, accepted for
publication in JCA
Evolution of String-Wall Networks and Axionic Domain Wall Problem
We study the cosmological evolution of domain walls bounded by strings which
arise naturally in axion models. If we introduce a bias in the potential, walls
become metastable and finally disappear. We perform two dimensional lattice
simulations of domain wall networks and estimate the decay rate of domain
walls. By using the numerical results, we give a constraint for the bias
parameter and the Peccei-Quinn scale. We also discuss the possibility to probe
axion models by direct detection of gravitational waves produced by domain
walls.Comment: 19 pages, 7 figures; revised version of the manuscript, accepted for
publication in JCA
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The impact of China's vehicle emissions on regional air quality in 2000 and 2020: a scenario analysis
The number of vehicles in China has been increasing rapidly. We evaluate the impact of current and possible future vehicle emissions from China on Asian air quality. We modify the Regional Emission Inventory in Asia (REAS) for China's road transport sector in 2000 using updated Chinese data for the number of vehicles, annual mileage, and emission factors. We develop two scenarios for 2020: a scenario where emission factors remain the same as they were in 2000 (No-Policy, NoPol), and a scenario where Euro 3 vehicle emission standards are applied to all vehicles (except motorcycles and rural vehicles). The Euro 3 scenario is an approximation of what may be the case in 2020 as, starting in 2008, all new vehicles in China (except motorcycles) were required to meet the Euro 3 emission standards. Using the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem), we examine the regional air quality response to China's vehicle emissions in 2000 and in 2020 for the NoPol and Euro 3 scenarios. We evaluate the 2000 model results with observations in Japan, China, Korea, and Russia. Under NoPol in 2020, emissions of carbon monoxide (CO), nitrogen oxides (NO<sub>x</sub>), non-methane volatile organic compounds (NMVOCs), black carbon (BC), and organic carbon (OC) from China's vehicles more than double compared to the 2000 baseline. If all vehicles meet the Euro 3 regulations in 2020, however, these emissions are reduced by more than 50% relative to NoPol. The implementation of stringent vehicle emission standards leads to a large, simultaneous reduction of the surface ozone (O<sub>3</sub>) mixing ratios and particulate matter (PM<sub>2.5</sub>) concentrations. In the Euro 3 scenario, surface O<sub>3</sub> is reduced by more than 10 ppbv and surface PM<sub>2.5</sub> is reduced by more than 10 μg m<sup>−3</sup> relative to NoPol in Northeast China in all seasons. In spring, surface O<sub>3</sub> mixing ratios and PM<sub>2.5</sub> concentrations in neighboring countries are also reduced by more than 3 ppbv and 1 μg m<sup>−3</sup>, respectively. We find that effective regulation of China's road transport sector will be of significant benefit for air quality both within China and across East Asia as well
TransCom N2O model inter-comparison - Part 2:Atmospheric inversion estimates of N2O emissions
This study examines N2O emission estimates from five different atmospheric inversion frameworks based on chemistry transport models (CTMs). The five frameworks differ in the choice of CTM, meteorological data, prior uncertainties and inversion method but use the same prior emissions and observation data set. The posterior modelled atmospheric N2O mole fractions are compared to observations to assess the performance of the inversions and to help diagnose problems in the modelled transport. Additionally, the mean emissions for 2006 to 2008 are compared in terms of the spatial distribution and seasonality. Overall, there is a good agreement among the inversions for the mean global total emission, which ranges from 16.1 to 18.7 TgN yr(-1) and is consistent with previous estimates. Ocean emissions represent between 31 and 38% of the global total compared to widely varying previous estimates of 24 to 38%. Emissions from the northern mid- to high latitudes are likely to be more important, with a consistent shift in emissions from the tropics and subtropics to the mid- to high latitudes in the Northern Hemisphere; the emission ratio for 0-30A degrees N to 30-90A degrees N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The largest discrepancies across inversions are seen for the regions of South and East Asia and for tropical and South America owing to the poor observational constraint for these areas and to considerable differences in the modelled transport, especially inter-hemispheric exchange rates and tropical convective mixing. Estimates of the seasonal cycle in N2O emissions are also sensitive to errors in modelled stratosphere-to-troposphere transport in the tropics and southern extratropics. Overall, the results show a convergence in the global and regional emissions compared to previous independent studies
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