Fermion Propagator in Quenched QED3 in the light of the Landau-Khalatnikov-Fradkin transformation

We study the gauge dependence of the fermion propagator in quenched QED3 with and without dynamical symmetry breaking in the light of its Landau-Khalatnikov-Fradkin Transformation (LKFT). In the former case, starting with the massive bare propagator in the Landau gauge, we obtain non perturbative propagator in an arbitrary covariant gauge. At the one-loop level it yields exact wavefunction renormalization and correct $(\alpha \xi)$ terms for the mass fuction. Also, we obtain valuable information for the higher order perturbative expansion of the propagator. As for the case of dynamical chiral symmetry breaking, we start by approximating the numerical solution to the Schwinger-Dyson equation in Landau gauge in the rainbow approximation in terms of analytic functions. We then LKF transform this result to obtain the dynamically generated fermion propagator in an arbitrary covariant gauge. We find that the results obtained have nice qualitative features. We also extend this exercise to the cases involving more reliable ans\"atze for the vertex and encounter similar (and improved) qualitative features.Comment: 6 pages, 6 figures. Contribution to the Proceedings of QCD Downunder 2004 Workshop, held at the Special Centre for the Subatomic Structure of Matter, University of Adelaide, March, 2004. Uses espcrc2.st

Non-perturbative Fermion Propagator for the Massless Quenched QED3

For massless quenched QED in three dimensions, we evaluate a non-perturbative expression for the fermion propagator which agrees with its two loop perturbative expansion in the weak coupling regime. This calculation is carried out by making use of the Landau-Khalatnikov-Fradkin transformations. Any improved construction of the fermion-boson vertex must make sure that the solution of the Schwinger-Dyson equation for the fermion propagator reproduces this result. For two different gauges, we plot the fermion propagator against momentum. We then make a comparison with a similar plot, using the earlier expression for the fermion propagator, which takes into account only the one loop result.Comment: 11 pages, 3 figures, to appear in Phys. Lett.

Truncated Schwinger-Dyson Equations and Gauge Covariance in QED3

We study the Landau-Khalatnikov-Fradkin transformations (LKFT) in momentum space for the dynamically generated mass function in QED3. Starting from the Landau gauge results in the rainbow approximation, we construct solutions in other covariant gauges. We confirm that the chiral condensate is gauge invariant as the structure of the LKFT predicts. We also check that the gauge dependence of the constituent fermion mass is considerably reduced as compared to the one obtained directly by solving SDE.Comment: 17 pages, 11 figures. v3. Improved and Expanded. To appear in Few Body System

Non-perturbative Aspects of Schwinger-Dyson Equations

Schwinger-Dyson equations (SDEs) provide a natural staring point to study non-perturbative phenomena such as dynamical chiral symmetry breaking in gauge field theories. We briefly review this research in the context of quenched quantum electrodynamics (QED) and discuss the advances made in the gradual improvement of the assumptions employed to solve these equations. We argue that these attempts render the corresponding studies more and more reliable and suitable for their future use in the more realistic cases of unquenched QED, quantum chromodynamics (QCD) and models alternative to the standard model of particle physics.Comment: 8 pages, 1 figure, Talk given at the X Mexican School of Particles and Fields, Playa del Carmen, Mexico, 2002 (uses AIP style files

Conceptual design and multidisciplinary optimisation of power device for solar powered aircraft

Solar-powered aircraft is propelled by a photovoltaic cell that converts solar energy into electrical energy. The extra energy is stored in a rechargeable battery for later use when solar energy is not available. The performance of solar-powered aircraft is limited to solar radiation availability, low efficiency of the photovoltaic cell, and low energy density of the rechargeable battery. The research aims to improve the power device sizing, reduce the aircraft's mass, and improve the flight duration for sustainable flight operations for solar-powered aircraft (CLOUD 1). This was achieved using a multidisciplinary optimisation tool, a commercial package ModeFrontier software. Photovoltaic Geographic information system (PVGIS) software was used to obtain a solar radiation model for Malaysia. The model was used to develop both the energy balance and mission path for Malaysia to facilitate the availability and utilisation of solar energy for successful flight operations. Airfoil analysis was conducted. WE.3.55.9.3 airfoil was the best-chosen airfoil used for the wing design, while the empennage design, NACA 0008, was the most suitable. Hence, the latter was used for horizontal and vertical tail design with XFLR5 v6 software's aid. A novel methodology for the power device sizing was developed on MS Excel with 435.48Wh, 540.96Wh, 32, and 70 as the total required electrical energy, available solar energy, number of solar cells required, and the number of batteries required, respectively. The optimisation strategy embraced ModeFrontier software with the goal set to; minimise total electrical energy required, minimise the total mass, and maximise the available solar energy. The optimisation results show that available solar energy was 283.56Wh, the total electrical power required was 228.32Wh, the number of solar cells was 16, and the number of batteries was 36. The total mass of the aircraft was 2.05 Kg, respectively. The optimisation results achieved 53%, 51%, and 26% reductions in the number of solar cells, the number of batteries, and the aircraft's mass. Also, the flight duration was improved by 33%. The optimal configuration was used to design the solar-powered aircraft (CLOUD I)

The Role of Agricultural Growth in South Asian Countries and the Affordability of Food: An Inter-country Analysis

Agriculture is the mainstay of the most developing countries, which supplies food and employment to the majority of the population. Because of the dominance of the agricultural sector, a sufficient supply of domestic food is indispensable to support stable socio-economic and political systems in these countries. To attain a sustained growth of agricultural productivity, sufficient investment in the agricultural sector is crucial, particularly in the initial stages of economic development. This increases agricultural production and as a result, there is a shift in (human) resources from the agricultural sector to the industrial and services sectors. According to Duranton (1998), in order to transform from agricultural sector to industrial sector a significant increase in the agricultural sector productivity is necessary. On the demand-side, the growth in agricultural production increases agricultural income which leads to increase in the demand for industrial products; whereas on the supplyside, the increase in the agricultural productivity shifts human resources from the agricultural to the industrial sector [Jorgenson (1967)]. Economists have further explained these interdependences and linkages between agricultural and industrial sectors. According to Kaldor’s (1978) two-sector model, agricultural and industrial sectors supply inputs to each other and provide market for their outputs but differ in a number of ways. The agricultural sector has disguised unemployment and produces consumer goods for competitive markets, while industrial sector produces investment goods which are sold in imperfectly competitive markets at mark-up prices.

The Impacts of Economic Reforms and Trade Liberalisation on Agricultural Export Performance in Pakistan

Economic reforms and trade liberalisation policies have been widely adopted in developing countries in recent years. Pakistan is no exception. This paper focuses on the effects of economic reform policies on the agricultural export performance. A number of studies have investigated the effects of trade liberalisation on export growth in developing countries, and have reached inconclusive results. Some studies have identified positive effects of trade liberalisation on export performance [Krueger (1997); Bleaney (1999); and Ahmed (2002)], others confirmed an insignificant or even a negative relationship [Greenaway, et al. (1994); Jenkins (1996) and Greenaway, et al. (2002)]. There are number of reasons for conflicting conclusions including different researchers have used different indicators for liberalisation and different methods to analyse the effect; difference in the extent of liberalisation studies; most studies have analysed scenarios rather than evaluating the effects, and so on. The present study analyses agricultural trade policy of Pakistan and accesses the impact of trade liberalisation on agricultural export performance, especially diversification, competitiveness, and openness. The relative importance of domestic supply related factors such as tariffs, quotas, etc. compared with external demand factors in affecting agricultural export expansion is analysed with respect to (i) relative agricultural export growth, (ii) changes in market shares of (traditional) agricultural exports, and (iii) changes in the export commodity composition.