Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.Comment: 24 pp, uses JHEP styl

On the near-threshold pˉp\bar pp invariant mass spectrum measured in J/ψJ/\psi and ψ′\psi' decays

A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/\psi \to x \bar pp$ and $\psi (3686) \to x \bar pp$ $(x = \gamma,\, \omega,\, \rho,\, \pi,\, \eta)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered and, in addition, an older phenomenological model constructed by the J\"ulich group. It is shown that the near-threshold spectrum observed in various decay reactions can be reproduced simultaneously and consistently by our treatment of the $\bar pp$ FSI. It turns out that the interaction in the isospin-1 $^1S_0$ channel required for the description of the $J/\psi \to \gamma \bar pp$ decay predicts a $\bar NN$ bound state.Comment: 13 pages, 12 figure

Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.Comment: 24 pp, uses JHEP styl

Test of semi-local duality in a large NCN_C framework

In this paper we test the semi-local duality based on the method of Ref.[1] for calculating final-state interactions at varying number of colors ($N_C$). We compute the amplitudes by dispersion relations that respect analyticity and coupled channel unitarity, as well as accurately describing experiment. The $N_C$ dependence of the $\pi\pi\to\pi\pi$ scattering amplitudes is obtained by comparing these amplitudes to the one of chiral perturbation theory. The semi-local duality is investigated by varying $N_C$. Our results show that the semi-local duality is not violated when $N_C$ is large. At large $N_C$, the contributions of the $f_2(1270)$, the $f_0(980)$ and the $f_0(1370)$ cancel that of the $\rho(770)$ in the finite energy sum rules, while the $f_0(500)$ has almost no effect. This gives further credit to the method developed in Ref.[1] for investigating the $N_C$ dependence of hadron-hadron scattering with final-state interactions. This study is also helpful to understand the structure of the scalar mesons.Comment: 8 pages, 5 figures, several comments are adde

Two-dimensional Poisson Trees converge to the Brownian web

The Brownian web can be roughly described as a family of coalescing one-dimensional Brownian motions starting at all times in $\R$ and at all points of $\R$. It was introduced by Arratia; a variant was then studied by Toth and Werner; another variant was analyzed recently by Fontes, Isopi, Newman and Ravishankar. The two-dimensional \emph{Poisson tree} is a family of continuous time one-dimensional random walks with uniform jumps in a bounded interval. The walks start at the space-time points of a homogeneous Poisson process in $\R^2$ and are in fact constructed as a function of the point process. This tree was introduced by Ferrari, Landim and Thorisson. By verifying criteria derived by Fontes, Isopi, Newman and Ravishankar, we show that, when properly rescaled, and under the topology introduced by those authors, Poisson trees converge weakly to the Brownian web.Comment: 22 pages, 1 figure. This version corrects an error in the previous proof. The results are the sam

B_l4 decays and the extraction of |V_ub|

The Cabibbo-Kobayashi-Maskawa matrix element |V_ub| is not well determined yet. It can be extracted from both inclusive or exclusive decays, like B --> pi (rho) l nu-bar_l. However, the exclusive determination from B --> rho l nu-bar_l, in particular, suffers from a large model dependence. In this paper, we propose to extract |V_ub| from the four-body semileptonic decay B --> pi pi l nu-bar_l, where the form factors for the pion-pion system are treated in dispersion theory. This is a model-independent approach that takes into account the pi-pi rescattering effects, as well as the effect of the rho meson. We demonstrate that both finite-width effects of the rho meson as well as scalar pi-pi contributions can be considered completely in this way.Comment: 12 pages, 4 figures; v2: Appendix C removed, version published in Phys. Rev.

The significance of self-annealing in two-phase alloys processed by high-pressure torsion

The Zn-22% Al eutectoid alloy and the Pb-62% Sn eutectic alloy were processed by high-pressure torsion (HPT) over a range of experimental conditions. Both alloys exhibit similar characteristics with significant grain refinement after processing by HPT but with a reduction in the hardness values by comparison with the initial unprocessed conditions. After storage at room temperature for a period of time, it is shown that the microhardness of both alloys gradually recovers to close to the initial unprocessed values. Electron backscatter diffraction (EBSD) measurements on the Pb-Sn alloy suggest that the self-recovery behaviour is correlated with the fraction of high-angle grain boundaries (HAGBs) after HPT processing. Thus, high fractions of HAGBs occur immediately after processing and this favours grain boundary migration and sliding which is important in the self-annealing and recovery process. Conversely, the relatively lower fractions of HAGBs occurring after annealing at room temperature are not so conducive to easy migration and slidin

Microstructures and mechanical properties of pure tantalum processed by high-pressure torsion

A body-centred cubic (BCC) structure metal, tantalum, was processed by high- pressure torsion (HPT) at room temperature with different numbers of rotations. The microstructural evolution was studied by electron backscatter diffraction (EBSD). The grain sizes were significantly refined at the disk edge area in the early stages of deformation (N = 0.5) but tended to attain saturation after the numbers of rotations was increased to N = 5. As the deformation continued, some coarse grains appeared in the disk edge areas and it appeared that there was structural recovery at the expense of grain boundary migration in the tantalum during HPT processing. Microhardness measurements showed the hardness gradually evolved towards a more homogenized level across the disk surfaces as the numbers of rotations increased. The hardness level after N = 10 turns was slightly lower than after N = 5 turns, thereby indicating the occurrence of a recovery process after 5 turn

Non-Markov dynamics and phonon decoherence of a double quantum dot charge qubit

In this paper we investigate decoherence times of a double quantum dot (DQD) charge qubit due to it coupling with acoustic phonon baths. We individually consider the acoustic piezoelectric as well as deformation coupling phonon baths in the qubit environment. The decoherence times are calculated with two kinds of methods. One of them is based on the qusiadiabatic propagator path integral (QUAPI) and the other is based on Bloch equations, and two kinds of results are compared. It is shown that the theoretical decoherence times of the DQD charge qubit are shorter than the experimental reported results. It implies that the phonon couplings to the qubit play a subordinate role, resulting in the decoherence of the qubit.Comment: 5 pages, 4 figure

Excitation energy transfer: Study with non-Markovian dynamics

In this paper, we investigate the non-Markovian dynamics of a model to mimic the excitation energy transfer (EET) between chromophores in photosynthesis systems. The numerical path integral method is used. This method includes the non-Markovian effects of the environmental affects and it does not need the perturbation approximation in solving the dynamics of systems of interest. It implies that the coherence helps the EET between chromophores through lasting the transfer time rather than enhances the transfer rate of the EET. In particular, the non-Markovian environment greatly increase the efficiency of the EET in the photosynthesis systems.Comment: 5 pages, 5 figure