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Kevin Ludwick
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The Viability of Phantom Dark Energy as a Quantum Field in 1st-Order FLRW Space
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In the standard cosmological framework of
the 0th-order FLRW metric and the use of
perfect fluids in the stress-energy tensor,
dark energy with an equation-of-state parameter
$w < -1$ (known as phantom dark energy) implies
negative kinetic energy and vacuum instability
when modeled as a scalar field.
However, the accepted values for present-day
$w$ from Planck and WMAP9 include a significant
range of values less than $-1$. We consider
a more accurate description of the universe
through the 1st-order perturbing of the isotropic
and homogeneous FLRW metric and the components
of the stress-energy tensor and investigate
whether a field with an apparent $w<-1$ may
still have positive kinetic energy. Treating
dark energy as a classical scalar field in
this metric, we find that it is not as obvious
as one might think that phantom
dark energy has negative kinetic energy categorically.
Analogously, we find that field models of
quintessence dark energy ($w>-1$) do not
necessarily
have positive kinetic energy categorically.
We then investigate the same question treating
dark energy as a quantum field in 1st-order
FLRW space-time and examining the expectation
value of the stress-energy tensor for $w<-1$
using adiabatic expansion.
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