Abstract
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.
Highlights
There are many reasons for considering cosmological models where a classical scalar field is present, in addition to ordinary matter and radiation.Since the beginning of 1980s, it was suggested that a scalar field could be related the alleged inflationary behavior of the early universe [1,2,3,4]
Putting the usual energy conditions on the state equations of the fluids and assuming a non-positive spatial curvature, we prove that a quintessence with an arbitrary self-interaction potential always produces a particle horizon
We show that a phantom field with a suitable self-potential, in presence of some reasonable kind of perfect fluid, can produce a FLRW cosmology with no horizon: three examples of this kind are presented
Summary
There are many reasons for considering cosmological models where a classical scalar field is present, in addition to ordinary matter and radiation. Concerning Item (II), we are aware that phantom fields are potentially responsible for a number of pathological features, such as a Big Rip (the simultaneous divergence of the scale factor, and of the density and pressure at a finite time after the Big Bang) or a Little Rip (divergence of the same quantities in the infinitely far future) [50,51,52,53,54,55]; on top of that, it was pointed out that the thermodynamics of phantom fields may cause the appearance of negative temperatures or of a negative total entropy for the universe [56,57,58,59,60] Discussing these issues is beyond the purposes of the present work ; here, we are led to consider a phantom by purely logical arguments related to Proposition 1, which are inescapable if one wants a cosmological model with no horizon and matter fulfilling the usual energy conditions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
