Damping scales of neutralino cold dark matter

The lightest supersymmetric particle, most likely the neutralino, might account for a large fraction of dark matter in the Universe. We show that the primordial spectrum of density fluctuations in neutralino cold dark matter (CDM) has a sharp cut-off due to two damping mechanisms: collisional damping during the kinetic decoupling of the neutralinos at about 30 MeV (for typical neutralino and sfermion masses) and free streaming after last scattering of neutralinos. The last scattering temperature is lower than the kinetic decoupling temperature by one order of magnitude. The cut-off in the primordial spectrum defines a minimal mass for CDM objects in hierarchical structure formation. For typical neutralino and sfermion masses the first gravitationally bound neutralino clouds have to have masses above 10 7M . PACS numbers: 14.80.Ly, 98.35.Ce, 98.80.-k, 98.80.C

Formation of small-scale structure in SUSY CDM

The lightest supersymmetric particle, most likely the lightest neutralino, is one of the most prominent particle candidates for cold dark matter (CDM). We show that the primordial spectrum of density fluctuations in neutralino CDM has a sharp cut-off, induced by two different damping mechanisms. During the kinetic decoupling of neutralinos, non-equilibrium processes constitute viscosity effects, which damp or even absorb density perturbations in CDM. After the last scattering of neutralinos, free streaming induces neutralino flows from overdense to underdense regions of space. Both damping mechanisms together define a minimal mass scale for perturbations in neutralino CDM, before the inhomogeneities enter the non- linear epoch of structure formation. We find that the very first gravitationally bound neutralino clouds ought to have masses above 10-6M , which is six orders of magnitude above the mass of possible axion miniclusters

The first WIMPy halos

Dark matter direct and indirect detection signals depend crucially on the dark matter distribution. While the formation of large scale structure is independent of the nature of the cold dark matter (CDM), the fate of inhomogeneities on sub-galactic scales, and hence the present day CDM distribution on these scales, depends on the micro-physics of the CDM particles. We study the density contrast of Weakly Interacting Massive Particles (WIMPs) on sub-galactic scales. We calculate the damping of the primordial power spectrum due to collisional damping and free-streaming of WIMPy CDM and show that free-streaming leads to a CDM power spectrum with a sharp cut-off at about $10^{-6} M_\odot$. We also calculate the transfer function for the growth of the inhomogeneities in the linear regime, taking into account the suppression in the growth of the CDM density contrast after matter-radiation equality due to baryons and show that our analytic results are in good agreement with numerical calculations. Combining the transfer function with the damping of the primordial fluctuations we produce a WMAP normalized primordial CDM power spectrum, which can serve as an input for high resolution CDM simulations. We find that the smallest inhomogeneities typically have co-moving radius of about 1 pc and enter the non-linear regime at a redshift of $60 \pm 20$. We study the effect of scale dependence of the primordial power spectrum on these numbers and also use the spherical collapse model to make simple estimates of the properties of the first generation of WIMP halos to form. We find that the very first WIMPy halos may have a significant impact on indirect dark matter searches.Comment: 33 pages, 9 figures. Version to appear in JCAP, includes clarification of the differences with respect to Loeb and Zaldarriaga astro-ph/0504112 calculation (bottom line is that the mass cut-off scales differ by a factor of order a few

Molecular and Functional Analysis of SBP-Box Transcription Factors in Arabidopsis thaliana

In Arabidopsis thaliana, 17 plant specific transcription factors are known to be members of the SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) gene family. This family of Arabidopsis SBP-box genes can be divided into subfamilies based on their genomic organization and sequence similarities. SPL1, SPL7, SPL12, SPL14 and SPL16 form one subfamily representing the largest and most complex members. The second subfamily is formed by the mid-sized genes SPL2, SPL6, SPL8, SPL9, SPL10, SPL11, SPL13a, SPL13b and SPL15. Finally, the small genes SPL3, SPL4 and SPL5 represent the third subfamily within the Arabidopsis SPL gene family. SBP-box genes have been exclusively found in plants and hence their functions were proposed to be plant specific. However, when the work of this thesis started, SPL8 was the only SPL gene with a known mutant phenotype. Spl8 plants show defects in anther development. Thus global expression analysis was conducted in order to gain more detailed insight in the role of SPL8 within the developing anthers. The micro-array experiment revealed 28 putative SPL8 target genes. Analysis of the target gene promoter regions showed a significant overrepresentation of the known SBP-box DNA binding motif GTAC, giving additional support that the identified genes are indeed target genes of SPL8. Reverse genetics was used in order to find out more about the role of the other SPL genes in Arabidopsis development. The results of this work led to the assumption that the two paralogous genes SPL1 and SPL12 have redundant functions in controlling flowering time in long days, rosette leaf size and fertility. Furthermore it could be shown that the two evolutionary probably very closely related genes SPL9 and SPL15 have redundant function in controlling apical dominance and the initiation rate of lateral organs at the shoot apex. Based on the results gained in this study the SPL genes are very likely to be separated into functional sub-classes in which the group of large genes has a distinct function from the miRNA regulated mid-sized and small genes