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 $10^{-15} eV$.
