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12.5. CMB

The baryon density can be obtained from the amplitude of the fluctuations on the sky of the temperature of the CMB. The baryons in the IGM at z appeq 1300 scattered the CMB photons. The amplitude of the fluctuations is a measure of Omegab h2, and other parameters. Published data favor large Omegab , with large errors, however dramatic improvements are imminent, and future constraints may approach or exceed the accuracy of Omegab from SBBN [192], [193].