New Microwave Background Constraints on the Cosmic Matter Budget: Trouble for Nucleosynthesis?

We compute the joint constraints on ten cosmological parameters from the latest cosmic microwave background measurements. The lack of a significant second acoustic peak in the new BOOMERANG and MAXIMA data favors models with more baryons than big bang nucleosynthesis predicts, almost independently of what prior information is included. The simplest flat inflation models with purely scalar scale-invariant fluctuations prefer a baryon density $0.022<\mathrm{}{h}^2{\Omega }_b<0.040\mathrm{}$ and a total nonbaryonic ( $\mathrm{hot}+\mathrm{cold}$) dark matter density $0.14<\mathrm{}{h}^2{\Omega }_{\mathrm{dm}}<0.32\mathrm{}$ at $95\%$ confidence and allow reionization no earlier than $z\sim 30$.