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 ${\rm Re} \Sigma \sim \omega \ln \omega$ as $\omega \to 0$, and thus the Fermi liquid state within each FS patch is turned into a marginal Fermi liquid.Comment: 5 pages, 3 ps figure

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

Global and regional emissions estimates for N2O

We present a comprehensive estimate of nitrous oxide (N2O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N2O are available from measurements at Cape Grim, Tasmania; Cape Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and at Trinidad Head, California using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. The Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected discrete air samples in flasks and in situ measurements from remote sites across the globe and analyzed them for a suite of species including N2O. In addition to these major networks, we include in situ and aircraft measurements from the National Institute of Environmental Studies (NIES) and flask measurements from the Tohoku University and Commonwealth Scientific and Industrial Research Organization (CSIRO) networks. All measurements show increasing atmospheric mole fractions of N2O, with a varying growth rate of 0.1-0.7% per year, resulting in a 7.4% increase in the background atmospheric mole fraction between 1979 and 2011. Using existing emission inventories as well as bottom-up process modeling results, we first create globally gridded a priori N2O emissions over the 37 years since 1975. We then use the three-dimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions for five source sectors from 13 regions in the world. This is the first time that all of these measurements from multiple networks have been combined to determine emissions. Our inversion indicates that global and regional N2O emissions have an increasing trend between 1995 and 2008. Despite large uncertainties, a significant increase is seen from the Asian agricultural sector in recent years, most likely due to an increase in the use of nitrogenous fertilizers, as has been suggested by previous studies.</p

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&lt;sub&gt;x&lt;/sub&gt;), 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&lt;sub&gt;3&lt;/sub&gt;) mixing ratios and particulate matter (PM&lt;sub&gt;2.5&lt;/sub&gt;) concentrations. In the Euro 3 scenario, surface O&lt;sub&gt;3&lt;/sub&gt; is reduced by more than 10 ppbv and surface PM&lt;sub&gt;2.5&lt;/sub&gt; is reduced by more than 10 μg m&lt;sup&gt;−3&lt;/sup&gt; relative to NoPol in Northeast China in all seasons. In spring, surface O&lt;sub&gt;3&lt;/sub&gt; mixing ratios and PM&lt;sub&gt;2.5&lt;/sub&gt; concentrations in neighboring countries are also reduced by more than 3 ppbv and 1 μg m&lt;sup&gt;−3&lt;/sup&gt;, 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

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$\,\sigma$. 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 $0.45\,\mathrm{meV} \lesssim m_a \lesssim 30\,\mathrm{meV}$, 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

Two-Particle-Self-Consistent Approach for the Hubbard Model

Even at weak to intermediate coupling, the Hubbard model poses a formidable challenge. In two dimensions in particular, standard methods such as the Random Phase Approximation are no longer valid since they predict a finite temperature antiferromagnetic phase transition prohibited by the Mermin-Wagner theorem. The Two-Particle-Self-Consistent (TPSC) approach satisfies that theorem as well as particle conservation, the Pauli principle, the local moment and local charge sum rules. The self-energy formula does not assume a Migdal theorem. There is consistency between one- and two-particle quantities. Internal accuracy checks allow one to test the limits of validity of TPSC. Here I present a pedagogical review of TPSC along with a short summary of existing results and two case studies: a) the opening of a pseudogap in two dimensions when the correlation length is larger than the thermal de Broglie wavelength, and b) the conditions for the appearance of d-wave superconductivity in the two-dimensional Hubbard model.Comment: Chapter in "Theoretical methods for Strongly Correlated Systems", Edited by A. Avella and F. Mancini, Springer Verlag, (2011) 55 pages. Misprint in Eq.(23) corrected (thanks D. Bergeron

A multi-model intercomparison of halogenated very short-lived substances (TransCom-VSLS): Linking oceanic emissions and tropospheric transport for a reconciled estimate of the stratospheric source gas injection of bromine

Abstract. The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated (nine chemical transport models and two chemistry–climate models) by simulating the major natural bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2), over a 20-year period (1993–2012). Except for three model simulations, all others were driven offline by (or nudged to) reanalysed meteorology. The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences due to emissions and transport processes. Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA's long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements – including high-altitude observations from the NASA Global Hawk platform. The models generally capture the observed seasonal cycle of surface CHBr3 and CH2Br2 well, with a strong model–measurement correlation (r  ≥  0.7) at most sites. In a given model, the absolute model–measurement agreement at the surface is highly sensitive to the choice of emissions. Large inter-model differences are apparent when using the same emission inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve best agreement to surface CHBr3 observations using the lowest of the three CHBr3 emission inventories tested (similarly, 8 out of 11 models for CH2Br2). In general, the models reproduce observations of CHBr3 and CH2Br2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific well. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr3 (and to a lesser extent CH2Br2) most elevated over the tropical western Pacific during boreal winter. The models also indicate the Asian monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models. We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr3 and CH2Br2 of 2.0 (1.2–2.5) ppt,  ∼  57 % larger than the best estimate from the most recent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. The transport-driven interannual variability in the annual mean bromine SGI is of the order of ±5 %, with SGI exhibiting a strong positive correlation with the El Niño–Southern Oscillation (ENSO) in the eastern Pacific. Overall, our results do not show systematic differences between models specific to the choice of reanalysis meteorology, rather clear differences are seen related to differences in the implementation of transport processes in the models. </jats:p