Hemispherical asymmetry from an isotropy violating stochastic
  gravitational wave background
  Measurement of Cosmic Microwave Background (CMB) temperature by Planck has
resulted in extremely tight constraints on the $\Lambda$CDM model. However the
data indicates a evidence of dipole modulated temperature fluctuations at large
angular scale which is beyond the standard Statistically Isotropic (SI)
$\Lambda$CDM model. The signal measured by Planck requires a scale dependent
modulation amplitude that is beyond the scope of the phenomenological model
considered by Planck. We propose a phenomenological model with mixed modulation
field for scalar and tensor perturbations which affect the temperature
fluctuations at large angular scales. Hence this model is a possible route to
explain the scale dependent nature of the modulation field. The salient
prediction of this model is the direction dependent tensor to scalar ratio
which results in anisotropic Stochastic Gravitational Wave Background (SGWB).
This feature is potentially measurable from the $B$-mode polarization map of
Planck and BICEP-2 and leads to determination of the modulation strength.
Measurability of SI violated polarization field due to this model is estimated
for Planck and PRISM. Absence of the signal in the polarization field can
restrict the viability of the model.
