Renormalization group-like proof of the universality of the Tutte polynomial for matroids

In this paper we give a new proof of the universality of the Tutte polynomial for matroids. This proof uses appropriate characters of Hopf algebra of matroids, algebra introduced by Schmitt (1994). We show that these Hopf algebra characters are solutions of some differential equations which are of the same type as the differential equations used to describe the renormalization group flow in quantum field theory. This approach allows us to also prove, in a different way, a matroid Tutte polynomial convolution formula published by Kook, Reiner and Stanton (1999). This FPSAC contribution is an extended abstract.Comment: 12 pages, 3 figures, conference proceedings, 25th International Conference on Formal Power Series and Algebraic Combinatorics, Paris, France, June 201

Isospin dependence of 6He+p optical potential and the symmetry energy

A consistent folding analysis of the elastic p(6He,6He)p scattering and charge exchange p(6He,6Li*)n reaction data measured at Elab=41.6A MeV has been performed within the coupled channels formalism. We have used the isovector coupling to link the isospin dependence of 6He+p optical potential to the cross section of p(6He,6Li*)n reaction exciting the 0+ isobaric analog state (IAS) at 3.563 MeV in 6Li. Based on these results and the Hartree-Fock calculation of asymmetric nuclear matter using the same isospin-dependent effective nucleon-nucleon interaction, we were able to confirm that the most realistic value of the symmetry energy Esym is around 31 MeV. Our analysis has also shown that the measured charge exchange p(6He,6Li*)n data are quite sensitive to the halo tail of the 6He density used in the folding calculation and the IAS of 6Li is likely to have a halo structure similar to that established for the ground state of 6He.Comment: Accepted for publication in Phys. Rev.

Massive Quark Production in Electron Positron Annihilation to Order αs2\alpha_s^2

Recent analytical and numerical results for the three-loop polarization function allow to present a phenomenological analysis of the cross section for massive quark production in electron positron annihilation to order $\alpha_s^2$. Numerical predictions based on fixed order perturbation theory are presented for charm and bottom production above 5 and 11.5 GeV, respectively. The contribution from these energy regions to $\alpha(M_Z^2)$, the running QED coupling constant at scale M_Z, are given. The dominant terms close to threshold, i.e. in an expansion for small quark velocity $\beta$, are presented.Comment: 26 pages (Latex), 16 figures (Postscript

Gauge dependence and matching procedure of a nonrelativistic QED/QCD boundstate formalism

A nonrelativistic boundstate formalism used in contemporary calculations is investigated. It is known that the effective Hamiltonian of the boundstate system depends on the choice of gauge. We obtain the transformation charge Q of the Hamiltonian for an arbitrary infinitesimal change of gauge, by which gauge independence of the mass spectrum and gauge dependences of the boundstate wave functions are dictated. We give formal arguments based on the BRST symmetry supplemented by power countings of Coulomb singularities of diagrams. For illustration: (1)we calculate Q up to O(1/c), (2)we examine gauge dependences of diagrams for a decay of a qqbar boundstate up to O(1/c) and show that cumbersome gauge cancellations can be circumvented by directly calculating Q. As an application we point out that the present calculations of top quark momentum distribution in the ttbar threshold region are gauge dependent. We also show possibilities for incorrect calculations of physical quantities of boundstates when the on-shell matching procedure is employed. We give a proof of a justification for the use of the equation of motion to simplify the form of a local NRQCD Lagrangian. The formalism developed in this work will provide useful cross checks in computations involving NRQED/NRQCD boundstates.Comment: 30 pages, 15 figures (ver1); Presentations of Introduction and Conclusion were modified substantially, although none of our findings have been changed; Side remarks have been added in various parts of the paper. (ver2); Supplementary remarks and minor corrections (ver3

Top Quark Pair Production close to Threshold: Top Mass, Width and Momentum Distribution

The complete NNLO QCD corrections to the total cross section $\sigma(e^+e^- \to Z*,\gamma*\to t\bar t)$ in the kinematic region close to the top-antitop threshold are calculated by solving the corresponding Schroedinger equations exactly in momentum space in a consistent momentum cutoff regularization scheme. The corrections coming from the same NNLO QCD effects to the top quark three-momentum distribution $d\sigma/d |\vec k_t|$ are determined. We discuss the origin of the large NNLO corrections to the peak position and the normalization of the total cross section observed in previous works and propose a new top mass definition, the 1S mass M_1S, which stabilizes the peak in the total cross section. If the influence of beamstrahlung and initial state radiation on the mass determination is small, a theoretical uncertainty on the 1S top mass measurement of 200 MeV from the total cross section at the linear collider seems possible. We discuss how well the 1S mass can be related to the $\bar{MS}$ mass. We propose a consistent way to implement the top quark width at NNLO by including electroweak effects into the NRQCD matching coefficients, which then can become complex.Comment: 53 pages, latex; minor changes, a number of typos correcte

A native plant growth promoting bacterium, Bacillus sp. B55, rescues growth performance of an ethylene-insensitive plant genotype in nature

Many plants have intimate relationships with soil microbes, which improve the plant’s growth and fitness through a variety of mechanisms. Bacillus sp. isolates are natural root-associated bacteria, isolated from Nicotiana attenuata plant roots growing in native soils. A particular isolate B55, was found to have dramatic plant growth promotion (PGP) effects on wild type (WT) and transgenic plants impaired in ethylene (ET) perception (35S-etr1), the genotype from which this bacterium was first isolated. B55 not only improves N. attenuata growth under in vitro, glasshouse, and field conditions, but it also “rescues” many of the deleterious phenotypes associated with ET insensitivity. Most notably, B55 dramatically increases the growth and survival of 35S-etr1 plants under field conditions. To our knowledge, this is the first demonstration of a PGP effect in a native plant–microbe association under natural conditions. Our study demonstrates that this facultative mutualistic plant–microbe interaction should be viewed as part of the plant’s extended phenotype. Possible modalities of recruitment and mechanisms of PGP are discussed

The Single Photon Annihilation Contributions to the Positronium Hyperfine Splitting to Order meα6m_e\alpha^6

The single photon annihilation contributions for the positronium ground state hyperfine splitting are calculated analytically to order $m_e\alpha^6$ using NRQED. Based on intuitive physical arguments the same result can also be determined by a trivial calculation using results from existing literature. Our result completes the hyperfine splitting calculation to order $m_e\alpha^6$. We compare the theoretical prediction with the most recent experimental measurement.Comment: 8 pages, latex, two eps figures include

Life cycle assessment of salmon cold chains : comparison between chilling and superchilling technologies

24ième Congrès International du Froid ICR 2015, Yokohama, JPN, 16-/08/2015 - 22/08/2015International audienceThe cold chain is defined as a set of refrigeration steps that maintain the quality and safety of food product. Refrigerant leakage and the use of fossil fuels to produce electrical power for refrigeration equipment contribute greatly to ozone depletion and global warming. Thus, new and emerging refrigeration technologies are developed to provide better energy efficient and environmentally friendly alternatives to current technologies. Superchilling is a concept where the temperature is reduced 1-2 °C below the initial freezing point of the product. The small amount of ice formed within the product (10-15%) serves as a heat sink, eliminating the need for ice during storage and transport. In this work, Life Cycle Assessment (LCA) is applied to the chilling and superchilling salmon cold chains. The superchilling cold chain presents an important improvement compared to the chilled one because of the augmentation of available volume for transportation