Microdosimetric concepts relevant to HZE-particles

The biological effectiveness of HZE-particles i s determined by the extreme microscopic concentrations of energy transfer in the vicinity of the particle tracks. The concept of linear energy transfer fails to describe this situation adequately. The more rigorous microdosimetric concepts are presented. A simplified treatment, based on the radial distribution of energy around the track core, is then considered

Are the reactions γγ→VV′\gamma\gamma\to VV' a challenge for the factorized Pomeron at high energies?

We would like to point to the strong violation of the putative factorized Pomeron exchange model in the reactions $\gamma\gamma\to VV'$ in the high-energy region where this model works fairly well in all other cases.Comment: 4 pages, LaTex, 1 fig. in postscript, minor typos corrected, to be published in Phys. Rev. D 60, 117503 (1999

Tests for primordial non-Gaussianity

We investigate the relative sensitivities of several tests for deviations from Gaussianity in the primordial distribution of density perturbations. We consider models for non-Gaussianity that mimic that which comes from inflation as well as that which comes from topological defects. The tests we consider involve the cosmic microwave background (CMB), large-scale structure (LSS), high-redshift galaxies, and the abundances and properties of clusters. We find that the CMB is superior at finding non-Gaussianity in the primordial gravitational potential (as inflation would produce), while observations of high-redshift galaxies are much better suited to find non-Gaussianity that resembles that expected from topological defects. We derive a simple expression that relates the abundance of high-redshift objects in non-Gaussian models to the primordial skewness.Comment: 6 pages, 2 figures, MNRAS in press (minor changes to match the accepted version

The controversy in the γγ→ρρ\gamma\gamma\to\rho\rho process: potential scattering or qqqˉqˉqq\bar{q}\bar{q} resonance ?

The $\gamma\gamma\to\rho^0\rho^0\to 4 \pi$ reaction shows a broad peak at 1.5 GeV in the $(J^P,J_z)=(2^+,2)$ channel which has no counterpart in the $\rho^+\rho^-$ channel. This "resonance" is considered as a candidate for a $qq\bar q\bar q$ state in the "s-channel". We show, however, that it can also be explained by potential scattering of $\rho^0\rho^0$ via the $\sigma$- exchange in the "t-channel".Comment: 12 pages, latex, 3 postscript figures, to appear in Zeitschrift fur Physi