PREPRINT
7EC53822-1C9D-4C63-A08E-E9D4888BDF76

# Hemispherical asymmetry of primordial power spectra

K. Sravan Kumar and João Marto

Submitted on 8 September 2022

## Abstract

Although the cosmic microwave background (CMB) is largely understood to be homogeneous and isotropic, the hemispherical asymmetry anomaly seems to breakdown the isotropy, since the difference between the power spectrum in the two hemispheres of the CMB is of the order of ${10}^{-2}$ at large angular scales. We argue that the existence of an anisotropic power spectrum can simply be explained by considering the existence of two distinct power spectra in the two hemispheres of the CMB. We achieve this by proposing a double vacuum structure for (single field) inflationary quantum fluctuations based on discrete spacetime transformations ($\mathcal{P}\mathcal{T}$) in a gravitational context, first in de Sitter and finally in quasi de Sitter. As a result we obtain inflationary quantum fluctuations that are produced in pairs with which we are able to reproduce the amplitude of the observed dipolar asymmetry at different scales of ${10}^{-4}\mathrm{M}\mathrm{p}{\mathrm{c}}^{-1}\lesssim k\lesssim 1\mathrm{M}\mathrm{p}{\mathrm{c}}^{-1}$ fixing the pivot scale $k=0.05\phantom{\rule{0.167em}{0ex}}{\mathrm{M}\mathrm{p}\mathrm{c}}^{-1}$ for $N=55$ e-foldings of inflation. We also predict that a similar hemispherical asymmetry should arise for the primordial gravitational waves (PGWs) as well and we compute the power asymmetry of PGW spectra at various wave numbers. In our framework we do not introduce any new parameters.

## Preprint

Comment: 11 pages, 2 figures. Any comments are welcome

Subjects: General Relativity and Quantum Cosmology; Astrophysics - Cosmology and Nongalactic Astrophysics; High Energy Physics - Theory