Proposal to search for a monochromatic component of solar axions using 57Fe.

The most attractive solution of the strong CP problem is to introduce the Peccei-Quinn global symmetry which is spontaneously broken at energy scale fa [1]. Although the original axion model has been experimentally excluded, variant “invisible” axion models are still viable. Such models are referred to as hadronic [2] and Dine-Fischler-Srednicki-Zhitnitskǐı [3] axions. At present, these “invisible” axions are constrained by laboratory searches and by astrophysical and cosmological arguments. The well-known window for fa which escapes all the phenomenological constraints is 10–10 GeV. This window is frequently quoted because it is cosmologically interesting. Besides this, there is another window around 10 GeV for the hadronic axions. This is usually called the hadronic axion window. A careful study [4] of the window revealed that fa in the range 3 × 10–3 × 10 GeV cannot be excluded by the existing arguments, because most of them were based on the axion-photon coupling which is the least known parameter among those describing the low energy dynamics of the hadronic axions. In addition, it is argued that fa around 10 GeV is desirable to explain the eeγγ + / ET event in the CDF experiment [5]. Furthermore, a recent paper indicates that axion might be a hot