Constraining Thawing Dark Energy using Galaxy Cluster Number Counts
  We study the formation of galaxy clusters in the presence of thawing class of scalar field dark energy. We consider cases where the scalar field has canonical as well non canonical kinetic term in its action. We also consider various form for the potential of the scalar field e.g, linear, quadratic, inverse quadratic, exponential as well as Pseudo-Nambu-Goldstone Boson (PNGB) type. Moreover we investigate situation where dark energy is homogeneous as well as the situation where dark energy takes part in virialization process. We use the Sheth-Tormen formalism while calculating the number density of galaxy clusters. Our results show that cluster number density for different dark energy models have significant deviation from the corresponding value for the $\Lambda$CDM case. The deviation is more for higher redshifts. Moreover the tachyon type scalar field with linear potential has the highest deviation from the $\Lambda$CDM case. For the total cluster number counts, different dark energy models can have substantial deviation from $\Lambda$CDM and this deviation is most significant around $z \sim 0.5$ for all the models we considered. We also constrain thawing class of models using the presently available data for number counts of massive X-ray clusters. The results show that current cluster data is not suitable enough for constraining potentials for the thawing scalar fields as well as for other cosmological parameters like $n_{s}$. But one can get significant constraint for the parameter $\sigma_{8}$ and a lower bound on $\Omega_{m0}$. 
N. Chandrachani Devi, T. Roy Choudhury and Anjan A. Sen
astro-ph.CO gr-qc