Scaling Evolution of Universal Dark-Matter Halo Density Profiles

Dark-matter halos show a universal density profile with a scaling such that less massive systems are typically denser. This mass-density relation is well described by a proportionality between the characteristic density of halos and the mean cosmic density at halo formation time. It has recently been shown that this proportionality could be the result of the following simple evolutionary picture. Halos form in major mergers with essentially the same, cosmogony-dependent, dimensionless profile, and then grow inside-outside, as a consequence of accretion. Here we verify the consistency of this picture and show that it predicts the correct zero point of the mass-density relation.Comment: 9 pages, 1 Table and 1 postscript figure, latex uses aaspp4.sty, accepted for publication in The Astrophysical Journal Letter

The Effects of the Peak-Peak Correlation on the Peak Model of Hierarchical Clustering

In two previous papers a semi-analytical model was presented for the hierarchical clustering of halos via gravitational instability from peaks in a random Gaussian field of density fluctuations. This model is better founded than the extended Press-Schechter model, which is known to agree with numerical simulations and to make similar predictions. The specific merger rate, however, shows a significant departure at intermediate captured masses. The origin of this was suspected as being the rather crude approximation used for the density of nested peaks. Here, we seek to verify this suspicion by implementing a more accurate expression for the latter quantity which accounts for the correlation among peaks. We confirm that the inclusion of the peak-peak correlation improves the specific merger rate, while the good behavior of the remaining quantities is preserved.Comment: ApJ accepted. 15 pages, including 4 figures. Also available at ftp://pcess1.am.ub.es/pub/ApJ/effectpp.ps.g

Extended Press-Schechter theory and the density profiles of dark matter haloes

An inside-out model for the formation of haloes in a hierarchical clustering scenario is studied. The method combines the picture of the spherical infall model and a modification of the extended Press-Schechter theory. The mass accretion rate of a halo is defined to be the rate of its mass increase due to minor mergers. The accreted mass is deposited at the outer shells without changing the density profile of the halo inside its current virial radius. We applied the method to a flat $\Lambda CDM$ Universe. The resulting density profiles are compared to analytical models proposed in the literature, and a very good agreement is found. A trend is found of the inner density profile becoming steeper for larger halo mass, that also results from recent N-body simulations. Additionally, present-day concentrations as well as their time evolution are derived and it is shown that they reproduce the results of large cosmological N-body simulations.Comment: 9 pages, 7 figures, accepted for publication in MNRA

Determinants of Effective Tax Investigations in Malaysia

Whilst most tax authorities throughout the world publish their organisation’s objectives and policies, hitherto, there is very little research investigating the attitudes of those at the “front line”, namely tax investigation officers. This qualitative study investigates the attitudes of 16 senior investigation officers from the Inland Revenue Board Malaysia (IRBM) who are also the directors of investigation branches and divisions throughout the country. The sensitive area of criminal tax investigations as opposed to civil investigations is also examined in this article. An individual semi-structured interview method was used for this research. It is found that the effectiveness of tax investigations is strongly influenced by the professional proficiency of the officers, which incorporates their knowledge and skills, ability to work independently, high integrity as well as their capacity for being a good team worker. In addition, the other factors that were found to be influential include tax penalties and the enforcement strategies of the IRBM. The degree of tax law complexity, whilst important, was found to be relatively less important than the foregoing factors. Although this research was based on Malaysian officers’ experience, the study is placed in the context of international research, and uses Australian and Organisation for Economic Co-operation and Development (OECD) policies and recommendations as comparative reference points wherever possible