Thermal Effects on Twophoton Decays of Pseudoscalars.pdfVIP

TIFR/TH/97-03 January, 1997 hep-ph/yymmdd 7 Thermal Effects on 9 Two-photon Decays of Pseudo-scalars 9 1 b e F Sourendu Gupta1 and S. N. Nayak2 1 Theory Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India. 1 v 5 0 2 Abstract 2 0 We study the effect of finite temperatures and Fermion density 7 9 on the effective pseudo-scalar-photon vertex induced by the triangle / diagram. The manifestly covariant calculations show that when the h p pseudo-scalar mass is much less than the temperature, then there is a - p large enhancement of the decay rate. Alternatively, when the temper- e ature is much higher than the Fermion mass, or the Fermion chemical h : potential is large, the lifetime is enhanced. Other related processes, v and applications of these results to cosmology and astrophysics, are i X discussed. r a 1E-mail: sgupta@theory.tifr.res.in 2E-mail: nayak@theory.tifr.res.in 1 Introduction Goldstone Bosons arise in field theories when some global symmetry is spon- taneously broken. A solution of the strong CP problem involves the breaking of Peccei-Quinn symmetry and gives rise to a pseudo-scalar called the axion (A) [1], which becomes massive through mixing with the pion. Axions have couplings to charged Fermions and are candi