B polarization of cosmic background radiation from second-order scattering sources

B-mode polarization of the cosmic background radiation is induced from purely scalar primordial sources at second order in perturbations of the homogeneous, isotropic universe. We calculate the B-mode angular power spectrum C_l^{BB} sourced by the second-order scattering term in the full second-order Boltzmann equations for the polarized radiation phase-space density, which have recently become available. We find that at l\approx 200 the second-order effect is comparable to the first-order effect for a tensor-to-scalar ratio of r=10^{-6}, and to about 2\cdot 10^{-4} at l\approx 1000. It is always negligible relative to the weak-lensing induced contribution.Comment: 32 page

Geothermal Casimir Phenomena

We present first worldline analytical and numerical results for the nontrivial interplay between geometry and temperature dependencies of the Casimir effect. We show that the temperature dependence of the Casimir force can be significantly larger for open geometries (e.g., perpendicular plates) than for closed geometries (e.g., parallel plates). For surface separations in the experimentally relevant range, the thermal correction for the perpendicular-plates configuration exhibits a stronger parameter dependence and exceeds that for parallel plates by an order of magnitude at room temperature. This effect can be attributed to the fact that the fluctuation spectrum for closed geometries is gapped, inhibiting the thermal excitation of modes at low temperatures. By contrast, open geometries support a thermal excitation of the low-lying modes in the gapless spectrum already at low temperatures.Comment: 8 pages, 3 figures, contribution to QFEXT07 proceedings, v2: discussion switched from Casimir energy to Casimir force, new analytical results included, matches JPhysA versio

Worldline Monte Carlo for fermion models at large N_f

Strongly-coupled fermionic systems can support a variety of low-energy phenomena, giving rise to collective condensation, symmetry breaking and a rich phase structure. We explore the potential of worldline Monte Carlo methods for analyzing the effective action of fermionic systems at large flavor number N_f, using the Gross-Neveu model as an example. Since the worldline Monte Carlo approach does not require a discretized spacetime, fermion doubling problems are absent, and chiral symmetry can manifestly be maintained. As a particular advantage, fluctuations in general inhomogeneous condensates can conveniently be dealt with analytically or numerically, while the renormalization can always be uniquely performed analytically. We also critically examine the limitations of a straightforward implementation of the algorithms, identifying potential convergence problems in the presence of fermionic zero modes as well as in the high-density region.Comment: 40 pages, 13 figure

Snapshots of Protein Dynamics and Post-translational Modifications In One Experiment—β-Catenin and Its Functions*

β-catenin plays multiple roles in the canonical Wnt signaling pathway and in cell-cell adhesion complexes. In addition, β-catenin is a proto-oncogene and activating β-catenin mutations are relevant in the genesis of colorectal, hepatocellular and other common cancers. Different functions of β-catenin as transcriptional co-activator or cell adhesion molecule are orchestrated by changes in concentration and phosphorylation as well as its ability to complex with proteins such as cadherins or transcription factors. Detailed quantitative and time-resolved analysis of β-catenin, based on the evaluation of the changes in the Wnt pathway, enable greater insights into health- and disease-related β-catenin function. The present paper describes a novel suspension bead array assay panel for β-catenin, which requires minimal amounts of sample and is able to relatively quantify total β-catenin, the extent of phosphorylation at multiple sites and the ratio of complexed and free β-catenin. This is the first study to combine three biochemical methods—sandwich immunoassay, co-immunoprecipitation, and protein-protein interaction assay—in one suspension bead assay panel. The assay was used to measure changes in the concentration of eight different β-catenin forms in HEK293 cells in a time-resolved manner. In contrast to the general consensus, our study demonstrates an increase in β-catenin phosphorylated at Ser-45 upon treatment of cells with rWnt3a or a GSK3 inhibition; we also link C-terminal phosphorylation of β-catenin on Ser-552 and Ser-675 with canonical Wnt signaling