相关论文: Ammonia as a Tracer of Fundamental Constants
The Standard Model of particle physics assumes that the so-called fundamental constants are universal and unchanging. Absorption lines arising in molecular clouds along quasar sightlines offer a precise test for variations in the…
(Abridged) The ammonia method, which has been proposed to explore the electron-to-proton mass ratio, mu = m_e/m_p, is applied to nearby dark clouds in the Milky Way. This ratio, which is measured in different physical environments of high…
Numerous accidental near-degeneracies exist between the $2\nu_2$ and $\nu_4$ rotation-vibration energy levels of ammonia. Transitions between these two states possess significantly enhanced sensitivity to a possible variation of the…
Spectral lines of ammonia, NH$_3$, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces,…
A limit on a possible cosmological variation of the proton-to-electron mass ratio $\mu$ is derived from methanol (CH$_3$OH) absorption lines in the benchmark PKS1830$-$211 lensing galaxy at redshift $z = 0.89$ observed with the Effelsberg…
We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level over a…
We report deep Green Bank Telescope (GBT) spectroscopy in the redshifted NH$_3$~(1,1), CS~1-0 and H$_2$CO~0$_{\rm 00}$-1$_{\rm 01}$ lines from the $z \sim 0.685$ absorber towards B0218+357. The inversion (NH$_3$) and rotational (CS,…
The ammonia method to probe variations of the electron-to-proton mass ratio, Delta_mu/mu, is applied for the first time to dense prestellar molecular clouds in the Milky Way. Carefully selected sample of 21 NH_3/CCS pairs observed in the…
Quantum mechanical tunneling inversion transition in ammonia NH3 is actively used as a sensitive tool to study possible variations of the electron-to-proton mass ratio, mu = m_e/m_p. The molecule H3O+ has the inversion barrier significantly…
Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (J,K = 1,0 - 0,0). The interpretation of this result makes use of complementary molecular line data obtained from the…
A molecular hydrogen absorber at a lookback time of 12.4 billion years, corresponding to 10$\%$ of the age of the universe today, is analyzed to put a constraint on a varying proton--electron mass ratio, $\mu$. A high resolution spectrum of…
The status of searches for possible variation in the constants of nature from astronomical observation of molecules is reviewed, focusing on the dimensionless constant representing the proton-electron mass ratio $\mu=m_p/m_e$. The optical…
We estimate the cosmological variation of the proton-to-electron mass ratio \mu=m_p/m_e by measuring the wavelengths of molecular hydrogen transitions in the early universe. The analysis is performed using high spectral resolution…
The present constraints on fundamental constant variation (\alpha and \mu) obtained in the radio range are reviewed, coming essentially from absorption lines in front of quasars of intermediate to high-z galaxies, through CO, HI, OH, HCO+,…
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…
A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of $^{14}$NH$_3$, $^{15}$NH$_3$, $^{14}$ND$_3$, and $^{15}$ND$_3$ is carried out variationally using the TROVE approach. Variational calculations…
Radio observations in the ammonia inversion lines of four comets, C/2001 A2 (LINEAR), 153P/Ikeya-Zhang, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), were performed at the Effelsberg 100-m Radio Telescope during their respective close approaches…
We estimate sensitivity coefficients Q_\mu to variation of the electron-to-proton mass ratio \mu for microwave transitions in partly deuterated ammonia NH2D and ND2H. Because of the mixing between rotational and inversion degrees of freedom…
Using the Effelsberg 100-m telescope, absorption in the (J,K) = (1,1), (2,2) and (3,3) inversion lines of ammonia (NH_3) was detected at a redshift of z = 0.6847 toward the gravitational lens system B0218+357. The lambda ~ 2cm absorption…
An overview is presented of the H$_2$ quasar absorption method to search for a possible variation of the proton--electron mass ratio $\mu=m_p/m_e$ on a cosmological time scale. Details of the analysis of astronomical spectra, obtained with…