Enhanced sensitivity to time-variation of m_p/m_e in the inversion spectrum of ammonia

Understand

We calculate the sensitivity of the inversion spectrum of ammonia to possible time-variation of the ratio of the proton mass to the electron mass, mu=m_p/m_e.

• For the inversion transition (lambda= 1.25 cm^{-1}) the relative frequency shift is significantly enhanced: delta(omega)/omega=-4.46, delta(mu)/mu.
• This enhancement allows one to increase sensitivity to the time-variation of mu using NH_3 spectra for high redshift objects.
• We use published data on microwave spectra of the object B0218+357 to place the limit delta(mu)/mu =(0.6 +/- 1.9) 10^{-6} at redshift z=0.6847; this limit is several times better than the limits obtained by different methods and may be significantly improved.