The annihilation of virtual photons into pseudoscalar mesons

We investigate the possibility to constrain the pion distribution amplitude from the gamma* gamma* -> pi transition. For a surprisingly large range in the two photon virtualities we find that the transition form factor is essentially independent of the distribution amplitude. This in turn entails a parameter-free prediction of QCD. The gamma* gamma* -> eta, eta' form factors are also briefly discussed. We estimate that experimental studies might be feasible at the existing e+ e- experiments BaBar, Belle, and CLEO.Comment: 22 pages latex, 9 figure

Two-Photon Annihilation into Baryon-Antibaryon Pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard gamma gamma -> q qbar subprocess and form factors describing the soft q qbar -> B Bbar transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called B Bbar distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured B Bbar channels.Comment: 20 pages latex, 4 figures. v2: minor clarifications, references update

The uniqueness of the invariant polarisation-tensor field for spin-1 particles in storage rings

We argue that the invariant tensor field introduced in [1] is unique under the condition that the invariant spin field is unique, and thereby complete that part of the discussion in that paper.Comment: 8 page

[Fe XIV] and [Fe XI] reveal the forward shock in SNR 1E0102.2-7219

Aims. We study the forward shock in the oxygen-rich young supernova remnant (SNR) 1E0102.2-7219 (1E0102 in short) via optical coronal emission from [Fe XIV] and [Fe XI]: emission lines which offer an alternative method to X-rays to do so. Methods. We have used the Multi-Unit Spectroscopic Explorer (MUSE) optical integral field spectrograph at the Very Large Telescope (VLT) on Cerro Paranal to obtain deep observations of SNR 1E0102 in the Small Magellanic Cloud. Our observations cover the entire extent of the remnant with a seeing limited spatial resolution of 0.7" = 0.2 pc at the distance of 1E 0102. Results. Our MUSE observations unambiguously reveal the presence of [Fe XIV] and [Fe XI] emission in 1E0102. The emission largely arises from a thin, partial ring of filaments surrounding the fast moving O-rich ejecta in the system. The brightest [Fe XIV] and [Fe XI] emission is found along the eastern and north-western sides of 1E0102, where shocks are driven into denser ISM material, while fainter emission along the northern edge reveals the location of the forward shock in lower density gas, possibly the relic stellar wind cavity. Modeling of the eastern shocks and the photoionization precursor surrounding 1E0102, we derive a pre-shock density $n_H$ = (7.4 +-1.5) cm$^{-3}$, and a shock velocity 330 km/s < $v_s$ < 350 km/s.Comment: 4 pages, 4 figures, accepted for publications in A&A as a Letter to the Edito

Atom-molecule collisions in an optically trapped gas

Cold inelastic collisions between confined cesium (Cs) atoms and Cs$\_2$ molecules are investigated inside a CO$\_2$ laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of $\sim 2.5 \times 10^{-11}$cm$^3$ s$^{-1}$, mainly independent of the molecular ro-vibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0,3-1 s, four times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be $\sim 10^{-11}$ cm$^{3}$ s$^{-1}$

The physics and kinematics of the evolved, interacting planetary nebula PN G342.0-01.7

Here we aim to study the physical and kinematical characteristics of the unstudied old planetary nebula (PN) PN G342.0-01.7, which shows evidence of interaction with its surrounding interstellar medium. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to provide spectroscopy across the whole object covering the spectral range 3400-7000 {\AA}. We formed narrow-band images to investigate the excitation structure. The spectral analysis shows that the object is a distant Peimbert Type I PN of low excitation, formally of excitation class of 0.5. The low electron density, high dynamical age, and low surface brightness of the object confirm that it is observed fairly late in its evolution. It shows clear evidence for dredge-up of CN-processed material characteristic of its class. In addition, the low peculiar velocity of 7 km s$^{-1}$ shows it to be a member of the young disk component of our Galaxy. We built a self-consistent photoionisation model for the PNe matching the observed spectrum, the H$\beta$ luminosity, and the diameter. On the basis of this we derive an effective temperature $\log T_{\rm eff} \sim 5.05$ and luminosity $1.85 < \log L < 2.25$. The temperature is much higher than might have been expected using the excitation class, proving that this can be misleading in classifying evolved PNe. PN G342.0-01.7 is in interaction with its surrounding interstellar medium through which the object is moving in the south-west direction. This interaction drives a slow shock into the outer PN ejecta. A shock model suggests that it only accounts for about 10\% of the total luminosity, but has an important effect on the global spectrum of the PN.Comment: 15 pages, 6 figures, A&A accepted 201