New limit on pseudoscalar-photon mixing from WMAP Observations
  The pseudoscalar-photon mixing in presence of large scale magnetic field induces polarization in light from distant cosmological sources. We study the effect of these pseudoscalars or axion like particles (ALPs) on Cosmic Microwave Background Radiation (CMBR) and constrain the product of mixing strength $g_{\phi}$ times background magnetic field $B$. The background magnetic field has been assumed to be primordial and we assume large scale correlations with the correlation length of 1Mpc. We use WMAP seven year foreground reduced polarization and temperature data to constrain pseudoscalar-photon mixing parameter. We look for different mass limits of the pseudoscalars and find $g_{\phi}B\le 1.6\times10^{-13} GeV^{-1} nG$ with ALPs of mass $10^{-10} eV$ and $g_{\phi}B\le3.4\times10^{-15} GeV^{-1} nG$ for ultra light ALPs of mass $10^{-15} eV$. 
Prabhakar Tiwari
hep-ph astro-ph.CO