Nissim Kanekar
Jansky-Max Planck Fellow
National Radio Astronomy Observatory, Socorro, USA

Probing fundamental constant evolution with radio spectroscopy

Astrophysical studies of redshifted spectral lines provide a powerful
probe of putative changes in fundamental constants across a large
lookback time. After reviewing the current status of this field, I
will describe a new technique to measure such changes, using
``conjugate satellite'' radio OH lines. Here, the sum of the OH 1720
MHz and 1620 MHz optical depths are consistent with noise, implying
that the lines arise in precisely the same gas. A comparison between
the line redshifts then allows a measurement of changes in a
combination of the fine structure constant alpha, the proton g-factor
g_p and the electron-proton mass ratio m_e/m_p, over a large fraction
of the age of the Universe. In addition, unlike optical approaches,
the conjugate OH technique does not appear to be affected by any known
systematic effects and also provides a measurement of fractional
changes in the constants from a single space-time location (rather
than averaged over many space-time points). I will discuss the best
present results from this technique, using the 18cm OH satellite lines
from the z ~ 0.25 source PKS 1413+135. Finally, I will describe other
radio techniques to probe changes in fundamental constants and
summarize the improvements that are likely to be possible with the
advent of new telescopes over the next decade.