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

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

Optimal measurements for nonlocal correlations

A problem in quantum information theory is to find the experimental setup that maximizes the nonlocality of correlations with respect to some suitable measure such as the violation of Bell inequalities. The latter has however some drawbacks. First and foremost it is unfeasible to determine the whole set of Bell inequalities already for a few measurements and thus unfeasible to find the experimental setup maximizing their violation. Second, the Bell violation suffers from an ambiguity stemming from the choice of the normalization of the Bell coefficients. An alternative measure of nonlocality with a direct information-theoretic interpretation is the minimal amount of classical communication required for simulating nonlocal correlations. In the case of many instances simulated in parallel, the minimal communication cost per instance is called nonlocal capacity, and its computation can be reduced to a convex-optimization problem. This quantity can be computed for a higher number of measurements and turns out to be useful for finding the optimal experimental setup. Focusing on the bipartite case, in this paper, we present a simple method for maximizing the nonlocal capacity over a given configuration space and, in particular, over a set of possible measurements, yielding the corresponding optimal setup. Furthermore, we show that there is a functional relationship between Bell violation and nonlocal capacity. The method is illustrated with numerical tests and compared with the maximization of the violation of CGLMP-type Bell inequalities on the basis of entangled two-qubit as well as two-qutrit states. Remarkably, the anomaly of nonlocality displayed by qutrits turns out to be even stronger if the nonlocal capacity is employed as a measure of nonlocality.Comment: Some typos and errors have been corrected, especially in the section concerning the relation between Bell violation and communication complexit

Regulatory T Cells

Immunologic self-tolerance is critically dependent on the induction but also on the downregulation of immune responses. Though ignored and neglected for many years, suppressor T cells, now renamed regulatory T cells (Tregs), play an important role in the negative regulation of immune responses. Several subsets of Tregs have been described. Naturally occurring CD4+CD25+ Tregs are important in the prevention of autoimmune diseases. Type 1 Tregs, another subtype of Treg that is inducible, exert their suppressive activity primarily via the release of IL-10. Detailed knowledge about the phenotype and mode of action of these cells will significantly increase our understanding of the pathogenesis of autoimmune diseases and will also help to identify new therapeutic strategies