39,472 research outputs found
Decoherence and entropy of primordial fluctuations. I: Formalism and interpretation
We propose an operational definition of the entropy of cosmological
perturbations based on a truncation of the hierarchy of Green functions. The
value of the entropy is unambiguous despite gauge invariance and the
renormalization procedure. At the first level of truncation, the reduced
density matrices are Gaussian and the entropy is the only intrinsic quantity.
In this case, the quantum-to-classical transition concerns the entanglement of
modes of opposite wave-vectors, and the threshold of classicality is that of
separability. The relations to other criteria of classicality are established.
We explain why, during inflation, most of these criteria are not intrinsic. We
complete our analysis by showing that all reduced density matrices can be
written as statistical mixtures of minimal states, the squeezed properties of
which are less constrained as the entropy increases. Pointer states therefore
appear not to be relevant to the discussion. The entropy is calculated for
various models in paper II.Comment: 23 page
Non Singular Origin of the Universe and the Cosmological Constant Problem (CCP)
We consider a non singular origin for the Universe starting from an Einstein
static Universe in the framework of a theory which uses two volume elements
and , where is a metric independent
density, also curvature, curvature square terms, first order formalism and for
scale invariance a dilaton field are considered in the action. In the
Einstein frame we also add a cosmological term that parametrizes the zero point
fluctuations. The resulting effective potential for the dilaton contains two
flat regions, for relevant for the non singular
origin of the Universe and , describing our present
Universe. Surprisingly, avoidance of singularities and stability as imply a positive but small vacuum energy as . Zero vacuum energy density for the present universe is
the "threshold" for universe creation.Comment: awarded an honorable mention in the Gravity Research Foundation 2011
Awards for Essays in Gravitation for 201
Exact ground states of quantum many-body systems under confinement
Knowledge of the ground state of a homogeneous quantum many-body system can
be used to find the exact ground state of a dual inhomogeneous system with a
confining potential. For the complete family of parent Hamiltonians with a
ground state of Bijl-Jastrow form in free space, the dual system is shown to
include a one-body harmonic potential and two-body long-range interactions. The
extension to anharmonic potentials and quantum solids with Nosanov-Jastrow
wavefunctions is also presented. We apply this exact mapping to construct
eigenstates of trapped systems from free-space solutions with a variety of pair
correlation functions and interparticle interactions.Comment: 6 page
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