Production of a gluon with the exchange of three reggeized gluons in the Lipatov effective action approach

In the Regge kinematics the amplitude for gluon production off three scattering centers is found in the Lipatov effective action technique. The vertex for gluon emission with the reggeon splitting in three reggeons is calculated and its transversality is demonstrated. It is shown that in the sum of all contributions terms containing principal value singularities are cancelled and substituted by the standard Feynman poles. These results may be used for calculation of the inclusive cross-section for gluon production on two nucleons in the nucleus.Comment: 22 pages, 9 figures; submitted to Eur.Phys.Jour.

Production of Strange Clusters and Strange Matter in Nucleus-Nucleus Collisions at the AGS

Production probabilities for strange clusters and strange matter in Au+Au collisions at AGS energy are obtained in the thermal fireball model. The only parameters of the model, the baryon chemical potential and temperature, were determined from a description of the rather complete set of hadron yields from Si+nucleus collisions at the AGS. For the production of light nuclear fragments and strange clusters the results are similar to recent coalescence model calculations. Strange matter production with baryon number larger than 10 is predicted to be much smaller than any current experimental sensitivities.Comment: 9 Pages (no figures

Transverse momentum distributions and their forward- backward correlations in the percolating colour string approach

The forward-backward correlations in the $p_T$ distributions, which present a clear signature of non-linear effects in particle production, are studied in the model of percolating colour strings. Quantitative predictions are given for these correlations at SPS, RHIC and LHC energies. Interaction of strings also naturally explains the flattening of $p_T$ distributions and increase of $$ with energy and atomic number for nuclear collisionsComment: 6 pages in LaTex, 3 figures in Postscrip

An Extinction Map and Color Magnitude Diagram for the Globular Cluster NGC 3201

Differential $E_{V-I}$ variations of up to $\sim 0.2$ mag on a scale of arcminutes across NGC 3201 are presented in the form of an extinction map. This map, created by calculating average $E_{V-I}$ values for stars in small subregions of the field with respect to a fiducial region, greatly improves the appearance of the CMD of the cluster. We describe how we implemented this technique in detail with our data for NGC 3201. A comparison between our map and that of the same region extracted from the COBE/DIRBE reddening maps published by Schlegel, Finkbeiner, & Davis (1998) (SFD) displays larger-scale similarities between the two maps as well as smaller-scale features which show up in our map but not in the SFD map. Several methods of determining an $E_{V-I}$ zeropoint to add to our differential extinction map are presented. Isochrone fitting proved to be the most successful one, but it produces an average $E_{V-I}$ for the cluster which is smaller than previously published values by $\sim 1.5\sigma$. Finally, our results seem to support the statement by Arce & Goodman (1999) that the SFD maps overestimate the reddening in regions of high extinction.Comment: 19 pages, 12 figures, 1 table, accepted for publication in AJ (March 2001). Full resolution version may be obtained at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.pdf (PDF) and at http://www.astro.lsa.umich.edu/users/kaspar/html/ngc3201.ps.gz (PS

Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-Emergence Signatures of Active Regions

We use a publicly available numerical wave-propagation simulation of Hartlep et al. 2011 to test the ability of helioseismic holography to detect signatures of a compact, fully submerged, 5% sound-speed perturbation placed at a depth of 50 Mm within a solar model. We find that helioseismic holography as employed in a nominal "lateral-vantage" or "deep-focus" geometry employing quadrants of an annular pupil is capable of detecting and characterizing the perturbation. A number of tests of the methodology, including the use of a plane-parallel approximation, the definition of travel-time shifts, the use of different phase-speed filters, and changes to the pupils, are also performed. It is found that travel-time shifts made using Gabor-wavelet fitting are essentially identical to those derived from the phase of the Fourier transform of the cross-covariance functions. The errors in travel-time shifts caused by the plane-parallel approximation can be minimized to less than a second for the depths and fields of view considered here. Based on the measured strength of the mean travel-time signal of the perturbation, no substantial improvement in sensitivity is produced by varying the analysis procedure from the nominal methodology in conformance with expectations. The measured travel-time shifts are essentially unchanged by varying the profile of the phase-speed filter or omitting the filter entirely. The method remains maximally sensitive when applied with pupils that are wide quadrants, as opposed to narrower quadrants or with pupils composed of smaller arcs. We discuss the significance of these results for the recent controversy regarding suspected pre-emergence signatures of active regions