Connected formulas for amplitudes in standard model

Witten's twistor string theory has led to new representations of S-matrix in massless QFT as a single object, including Cachazo-He-Yuan formulas in general and connected formulas in four dimensions. As a first step towards more realistic processes of the standard model, we extend the construction to QCD tree amplitudes with massless quarks and those with a Higgs boson. For both cases, we find connected formulas in four dimensions for all multiplicities which are very similar to the one for Yang-Mills amplitudes. The formula for quark-gluon color-ordered amplitudes differs from the pure-gluon case only by a Jacobian factor that depends on flavors and orderings of the quarks. In the formula for Higgs plus multi-parton amplitudes, the massive Higgs boson is effectively described by two additional massless legs which do not appear in the Parke-Taylor factor. The latter also represents the first twistor-string/connected formula for form factors.Comment: 18 pages, 3 figure

Estimating Chinese Interprovincial OutPut Spillovers with Provincial Input-Output Tables

This paper aims at estimating productivity improvement of Chinese 17 relatively backward provinces in manufactures through importing manufactured intermediates from advanced provinces on the basis of just published 2002 national and provincial input-output tables. As Chinese regional inequality remains large, North-South spillover models of trade are appropriate to guide this study. Applying reliable methods to approximate net interprovincial imports by province and sector and the allocation of imported manufactured inputs among sectors within each province, we use a Cob-Douglas production function incorporating Dixit-Stiglitz type increasing returns to variety to deal with the manufactured inputs, and treat the output spillovers as one part of total factor productivity. According to our estimations, as expected, interprovincial imports of manufactured inputs have significant impacts on industrial sectors as well on all sectors of these provinces.Chinese interprovincial trade;North-South spillovers;input-output tables;regional inequality;imported intermediates

New BCJ representations for one-loop amplitudes in gauge theories and gravity

We explain a procedure to manifest the Bern-Carrasco-Johansson duality between color and kinematics in $n$-point one-loop amplitudes of a variety of supersymmetric gauge theories. Explicit amplitude representations are constructed through a systematic reorganization of the integrands in the Cachazo-He-Yuan formalism. Our construction holds for any nonzero number of supersymmetries and does not depend on the number of spacetime dimensions. The cancellations from supersymmetry multiplets in the loop as well as the resulting power counting of loop momenta is manifested along the lines of the corresponding superstring computations. The setup is used to derive the one-loop version of the Kawai-Lewellen-Tye formula for the loop integrands of gravitational amplitudes.Comment: 58 + 15 page

Does China's Trade Expansion Help African Development? - A South-South Trade Model Approach

With the aim to explain the explosive growth of trade between China and Africa, especially the impacts of China's exportation on African countries, a simple South-South trade model is constructed to formulate the idea that for a technologically backward country to improve its production capability, when there exists nontrivial substitution effects, it is better to import from a South country which has superior technology, than from a North country with enormous technological advance. Then the Comtrade panel data are used to assess the impacts of imports from China (in comparison with those from the USA and France) on Sub-Saharan African manufactured exports (as proxies of their production performances). The results confirm the inference drawn from the model.South-South trade;impact of Chinese exportation on Africa;technology spillover effects;intermediate goods;substitution effects.