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RESEARCH PRODUCT

ESTIMATING SMALL ANGULAR SCALE COSMIC MICROWAVE BACKGROUND ANISOTROPY WITH HIGH-RESOLUTIONN-BODY SIMULATIONS: WEAK LENSING

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We estimate the impact of weak lensing by strongly nonlinear cosmological structures on the cosmic microwave background. Accurate calculation of large l multipoles requires N-body simulations and ray-tracing schemes with both high spatial and temporal resolution. To this end, we have developed a new code that combines a gravitational Adaptive Particle-Particle, Particle-Mesh solver with a weak-lensing evaluation routine. The lensing deviations are evaluated while structure evolves during the simulation so that all evolution steps—rather than just a few outputs—are used in the lensing computations. The new code also includes a ray-tracing procedure that avoids periodicity effects in a universe that is modeled as a three-dimensional torus in the standard way. Results from our new simulations are compared with previous ones based on Particle-Mesh simulations. We also systematically investigate the impact of box volume, resolution, and ray-tracing directions on the variance of the computed power spectra. We find that a box size of 512 h –1 Mpc is sufficient to provide a robust estimate of the weak-lensing angular power spectrum in the l-interval (2000-7000). For a reaslistic cosmological model, the power [l(l + 1)C l/2π]1/2 takes on values of a few μK in this interval, which suggests that a future detection is feasible and may explain the excess power at high l in the Berkeley-Illinois-Maryland Association and Cosmic Background Imager observations.