The hemispherical power asymmetry is a large-scale CMB anomaly where one hemisphere (in a roughly fixed sky direction) shows systematically higher temperature fluctuation power than the opposite hemisphere, with a dipole-like modulation A ≈ 0.07 detected at ?3s in WMAP and Planck temperature maps, particularly for low multipoles l ? 60 (Eriksen et al. 2004; Akrami et al. 2014). In ΛCDM the primordial perturbations are assumed statistically isotropic and Gaussian, so such a coherent, directional modulation is highly unlikely as a random fluctuation and typically requires additional ingredients—such as a space-dependent primordial power spectrum, special curvaton fields, or inhomogeneous inflation—whose construction is non-trivial and often constrained by the absence of comparable asymmetry on smaller angular scales (Gordon et al. 2005; McDonald 2014).