Abstract
In the framework of scalar-tensor theories of gravity, we construct a new kind of cosmological model that conflates inflation and ekpyrosis. During a phase of conflation, the universe undergoes accelerated expansion, but with crucial differences compared to ordinary inflation. In particular, the potential energy is negative, which is of interest for supergravity and string theory where both negative potentials and the required scalar-tensor couplings are rather natural. A distinguishing feature of the model is that, for a large parameter range, it does not significantly amplify adiabatic scalar and tensor fluctuations, and in particular does not lead to eternal inflation and the associated infinities. We also show how density fluctuations in accord with current observations may be generated by adding a second scalar field to the model. Conflation may be viewed as complementary to the recently proposed anamorphic universe of Ijjas and Steinhardt.
Highlights
EKPYROTIC PHASE IN EINSTEIN FRAMEDuring an ekpyrotic phase the universe undergoes slow contraction with high pressure p
In the framework of scalar-tensor theories of gravity, we construct a new kind of cosmological model that conflates inflation and ekpyrosis
We have introduced the idea of conflation, which corresponds to a phase of accelerated expansion in a scalar-tensor theory of gravity
Summary
During an ekpyrotic phase the universe undergoes slow contraction with high pressure p. The equation of state is assumed to be large, w = p/ρ > 1, where ρ denotes the energy density of the universe. Under these circumstances both homogeneous curvature and curvature anisotropies are suppressed, and the flatness problem can be resolved if this phase lasts long enough. The ekpyrotic phase can be modelled by a scalar field with a steep and negative potential, with action (in natural units 8πG = MP−l2 = 1). − 1, while the condition that an ekpyrotic phase has to satisfy, w > 1, is equivalent to > 3
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