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On the Necessity of Phantom Fields for Solving the Horizon Problem in Scalar Cosmologies

by Davide Fermi 1,2,*,†, Massimo Gengo 1,† and Livio Pizzocchero 1,2,†
1
Dipartimento di Matematica, Università di Milano, Via C. Saldini 50, I-20133 Milano, Italy
2
Istituto Nazionale di Fisica Nucleare, Sezione di Milano, I-20133 Milano, Italy
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Universe 2019, 5(3), 76; https://doi.org/10.3390/universe5030076
Received: 31 January 2019 / Revised: 1 March 2019 / Accepted: 5 March 2019 / Published: 11 March 2019
We discuss the particle horizon problem in the framework of spatially homogeneous and isotropic scalar cosmologies. To this purpose we consider a Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime with possibly non-zero spatial sectional curvature (and arbitrary dimension), and assume that the content of the universe is a family of perfect fluids, plus a scalar field that can be a quintessence or a phantom (depending on the sign of the kinetic part in its action functional). We show that the occurrence of a particle horizon is unavoidable if the field is a quintessence, the spatial curvature is non-positive and the usual energy conditions are fulfilled by the perfect fluids. As a partial converse, we present three solvable models where a phantom is present in addition to a perfect fluid, and no particle horizon appears. View Full-Text
Keywords: scalar field cosmologies; particle horizon; phantom field; quintessence scalar field cosmologies; particle horizon; phantom field; quintessence
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Fermi, D.; Gengo, M.; Pizzocchero, L. On the Necessity of Phantom Fields for Solving the Horizon Problem in Scalar Cosmologies. Universe 2019, 5, 76.

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