ON BREAKING COSMIC DEGENERACY

It has been argued that the power spectrum of the anisotropies in the cosmic microwave background may be effectively degenerate, namely, tha t the observable spectrum does not determine a unique set of cosmologi cal parameters. We describe the physical origin of this degeneracy and show that at small angular scales it is broken by gravitational lensi ng: effectively degenerate spectra become distinguishable at I similar to 3000 because lensing causes their damping tails to fall at differe nt rates with increasing l. This effect also helps in distinguishing n early degenerate power spectra such as those of mixed dark matter mode ls. Forthcoming interferometer experiments should provide the means of measuring otherwise degenerate parameters at the 5%-25% level.