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#### Separate universes in loop quantum cosmology: framework and applications

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1512.05743.pdf

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##### Citation

Wilson-Ewing, E. (2016). Separate universes in loop quantum cosmology: framework and
applications.* International Journal of Modern Physics D,* *25*(8):
1642002. doi:10.1142/S0218271816420025.

Cite as: https://hdl.handle.net/11858/00-001M-0000-002A-70FF-9

##### Abstract

I present a streamlined review of how the separate universe approach to
cosmological perturbation theory can be used to study the dynamics of
long-wavelength scalar perturbations in loop quantum cosmology, and then use it
to calculate how long-wavelength curvature perturbations evolve across the loop
quantum cosmology bounce assuming a constant equation of state. A similar
calculation is possible for tensor modes using results from a complementary
approach to cosmological perturbation theory in loop quantum cosmology based on
an effective Hamiltonian constraint. An interesting result is that the
tensor-to-scalar ratio can be suppressed or amplified by quantum gravity
effects during the bounce, depending on the equation of state of the matter
field dominating the dynamics. In particular, if the equation of state lies
between -1/3 and 1, the value of the tensor-to-scalar ratio will be suppressed
during the bounce, in some cases significantly.