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 $k=0.05{\textstyle \phantom{\rule{0.167em}{0ex}}}{\mathrm{M}\mathrm{p}\mathrm{c}}^{-1}$ 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.