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Investigating the Amplitude of the Kinematic Dipole and Clustering in Cosmic Large-Scale Structure and the Effects of the Long Mode in the Early Universe

Daei Rasouli, Arefeh | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57446 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Baghram, Shant; Rahvar, Sohrab
  7. Abstract:
  8. The standard ΛCDM model is built upon the cosmological principle, which states that the universe is homogeneous and isotropic on large scales (greater than 100 Mpc). A crucial test of this principle involves analyzing the Cosmic Microwave Background (CMB) radiation, which exhibits a dipole anisotropy on the order of ΔT/T∼10^−3. This dipole is commonly interpreted as owing to our motion with respect to the CMB rest frame. A model-independent approach to validate this kinematic hypothesis is to determine the dipole moment in the angular distribution of large-scale structures. According to the cosmological principle, the rest frame of the large-scale structure distribution should align with the CMB rest frame. Thus, the ΛCDM predicts that the dipole in the distribution of large-scale structures should correspond to the CMB dipole. However, recent observations of dipole anisotropies in the distribution of radio galaxies and quasars, obtained from the NVSS and WISE catalogs, show differences in both direction and magnitude when compared to the CMB dipole. These discrepancies pose a challenge to the predictions of the ΛCDM. In this thesis, considering the kinematic, clustering and shot noise dipoles, we investigate the cosmic large-scale structure distribution dipole using the NVSS catalog. We found the amplitude of the clustering dipole to be comparable to the expected kinematic dipole. This outcome helps to reconcile previous measurements of the NVSS dipole with the predictions based on the CMB. Furthermore, we employed a probability distribution for the dipole predicted by the standard model, taking into account all dipole components. Using the non-linear power spectrum, we calculated the correlation between the clustering dipole and the kinematic dipole, which resulted in reducing the discrepancy between the predicted and observed dipoles to less than 2σ. Additionally, we explored a model in which the distribution of matter on large scales might be intrinsically anisotropic. Using the remnant discrepancy between the observed and ΛCDM predicted dipole, we derived an upper limit for the amplitude of intrinsic anisotropy, and based on that, we calculated the clustering for this model
  9. Keywords:
  10. Universe Large-Scale Structure ; Cosmology ; Cosmic Microwave Background (CMB) ; Anisotropy ; Clustering Dipole ; Early Universe

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