Collisional Effects on HFS Transitions of Antiprotonic Helium

Collisions of metastable antiprotonic helium with medium atoms induce transitions between hyperfine structure sublevels as well as shift and broadening of the microwave M1 spectral lines. We consider these effects in the framework of a simple model with scalar and tensor interactions between $(\bar{p}\mathrm{He}^+)_{nL}$ and $\mathrm{He}$ atoms. $S$-matrix is obtained by solving coupled-channels equations involving 4 HFS sublevels $(F=L\pm 1/2, J=F\pm 1/2)$ of the $nL$ level and relative angular momenta up to $l=5$ at the kinetic energy $E\lesssim 10$ K. The calculated spin-flip cross sections are less than elastic ones by 4 orders of value. At the density $N=3\times 10^{20}$ cm$^{-3}$ and T=6 K we obtain the relaxation times $\tau(FJ\to F'J')\gtrsim 160$ ns, the frequency shifts of M1 spectral lines $\Delta\nu\lesssim 66$ KHz for the favored transitions ($\Delta F=\pm 1, \Delta J=\pm 1$) and frequency broadening of the M1 spectral lines $\gamma/2\lesssim 5.8$ MHz. The results are compatible with the recent experimental data obtained by a laser-microwave-laser resonance method.Comment: 4 pages, 3 figure, report on LEAP03, Japan, March 200

A Simple Empirically Motivated Template for the Unresolved Thermal Sunyaev-Zeldovich Effect

We develop a model for the power spectrum of unresolved clusters of galaxies arising from the thermal Sunyaev-Zeldovich (tSZ) effect. The model is based on a'universal' gas pressure profile constrained by X-ray observations and includes a parameter to describe departures from self-similar evolution. The model is consistent with recent Planck observations of the tSZ effect for X-ray clusters with redshifts z<1 and reproduces the low amplitude for the tSZ inferred from recent ground based observations. By adjusting two free parameters, we are able to reproduce the tSZ power spectra from recent numerical simulations to an accuracy that is well within theoretical uncertainties. Our model provides a simple, empirically motivated tSZ template that may be useful for the analysis of new experiments such as Planck.Comment: 6 pages 4 figure