5 Conclusion

Constraints on various cosmological parameters have been derived by using the Archeops data alone and in combination with other measurements. The measured power at low $\ell$ is in agreement with the COBE data, providing for the first time a direct link between the Sachs-Wolfe plateau and the first acoustic peak. The Archeops data give a high signal-to-noise ratio determination of the parameters of the first acoustic peak and of the power spectrum down to COBE scales ($\ell=15$), because of the large sky coverage that greatly reduces the sample variance. The measured spectrum is in good agreement with that predicted by simple inflation models of scale-free adiabatic peturbations. Archeops on its own also sets a constraint on open models, $\Omega_{\rm tot}> 0.90$ (68% CL). In combination with CBDMVC experiments, tight constraints are shown on cosmological parameters like the total density, the spectral index and the baryon content, with values of $\Omega_{\rm tot}= 1.13^{+0.12}_{-0.15}$, n = 0.96^+0.03_-0.04 and $\Omega_{\rm b}h^2= 0.021^{+0.002}_{-0.003}$respectively, all at 68% CL and assuming $\tau=0$. These results lend support to the inflationary paradigm. The addition of non-CMB constraints removes degeneracies between different parameters and allows to achieve a $10\%$ precision on $\Omega_{\rm b}h^2$ and $\Omega_{\Lambda}$and better than 5% precision on $\Omega_{\rm tot}$ and n. Flatness of the Universe is confirmed with a high degree of precision: $\Omega_{\rm tot}=1.00^{+0.03}_{-0.02}$ (Archeops + CMB + HST).

Acknowledgements

The authors would like to thank the following institutes for funding and balloon launching capabilities: CNES (French space agency), PNC (French Cosmology Program), ASI (Italian Space Agency), PPARC, NASA, the University of Minnesota, the American Astronomical Society and a CMBNet Research Fellowship from the European Commission.