Precision spectroscopy of H2 and a possible variation of m p/me over cosmological time

A novel and highly accurate (at the level of Δλ/λ = 5 × 10^-8) database of 233 spectral lines in the Lyman and Werner bands of H₂ is determined via laboratory spectroscopy employing a narrowband and tunable extreme ultraviolet laser system. Furthermore an updated set of so-called K_i coefficients, representing the sensitivity of each spectral line on a variation of the proton-to-electron mass ratio μ = m_p/m_e are derived for all lines in the H₂ spectrum. The laboratory wavelengths and K_i's are used in a comparison with a recent set of highly accurate H₂ spectral lines observed in the Q 0347-383 and Q 0405-443 quasars yielding a fractional change in the mass-ratio of Δμ/μ, = 2.4 ± 0.6 × 10 ^-5 (1σ). This result indicates, at a 4σ confidence level, that μ may have decreased in the past 12 billion years.