Search

The effective theory of isoscalar dark matter-nucleon interactions mediated by heavy spin-one or spin-zero particles depends on 10 coupling constants besides the dark matter particle mass. Here we compare this 11-dimensional effective theory to current observations in a comprehensive statistical analysis of several direct detection experiments, including the recent LUX, SuperCDMS and CDMSlite results. From a multidimensional scan with about 3 million likelihood evaluations, we extract the marginalized posterior probability density functions (a Bayesian approach) and the profile likelihoods (a frequentist approach), as well as the associated credible regions and confidence levels, for each coupling constant vs dark matter mass and for each pair of coupling constants. We compare the Bayesian and frequentist approach in the light of the currently limited amount of data. We find that current direct detection data contain sufficient information to simultaneously constrain not only the familiar spin-independent and spin-dependent interactions, but also the remaining velocity and momentum dependent couplings predicted by the dark matter-nucleon effective theory. For current experiments associated with a null result, we find strong correlations between some pairs of coupling constants. For experiments that claim a signal (i.e., CoGeNT and DAMA), we find that pairs of coupling constants produce degenerate results., Comment: 32 pages, 11 figures, replaced to match the published version

The exact formation scenarios and evolutionary processes that led to the existence of the class of low surface brightness galaxies (LSBs) have not yet been understood completely. Since the environment of LSBs has been studied before only on small scales (below 2 Mpc), a study of the galaxy content in the vicinity of LSB galaxies on larger scales could add a lot to our understanding of the origin of this galaxy class. We used the spectroscopic main galaxy sample of the SDSS DR4 to investigate the environmental galaxy density of LSB galaxies compared to the galaxy density in the vicinity of high surface brightness galaxies (HSBs). The environment studies, divided into two redshift bins, show that both the low mass, and the more massive LSBs possess an environment with a lower galaxy density than HSBs. The differences in the galaxy density between LSBs and HSBs are significant on scales between 2 and 5 Mpc, the scales of groups and filaments. To quantify this, we have introduced for the first time the LSB-HSB Antibias. The obtained LSB-HSB Antibias parameter has a value of 10%-15%. From these results we conclude that LSBs formed in low-density regions of the initial universe and have drifted until now to the outer parts of the filaments and walls of the large-scale structure. Furthermore, our results, together with actual cosmological simulations, show that LSBs are caused by a mixture of nature and nurture., Astronomy & Astrophysics in press