Ribbons on the Cosmic Background Radiation Sky: A Powerful Test of a Baryon Symmetric Universe

If the Universe consists of domains of matter and antimatter, annihilations at domain interfaces leave a distinctive imprint on the cosmic background radiation (CBR) sky. The signature is anisotropies in the form of long, thin ribbons of width ${\theta }_W\sim {0.1}^{\circ }$, separated by angle ${\theta }_L\simeq 1^{\circ }\left(L/{100h}^{-1\mathrm{}}\mathrm{Mpc}\right)$ ( $L$ is the characteristic domain size) and with distortion parameter $y\approx {10}^{-6\mathrm{}}$. Such a pattern could potentially be detected by the high-resolution CBR anisotropy experiments planned for the next decade, and such experiments may finally settle the question of whether or not our Hubble volume is baryon symmetric.