9 research outputs found
The classical and quantum fate of the Little Sibling of the Big Rip in cosmology
The Little Sibling of the Big Rip is a cosmological abrupt event predicted by
some phantom cosmological models that could describe our Universe. When this
event is approached the observable Universe and its expansion rate grow
infinitely, but its cosmic derivative remains finite. In this work we have
obtained the group of metric theories of gravity that reproduce this
classical cosmological background evolution. Furthermore, we have considered
the quantization of some of the resulting models in the framework of quantum
geometrodynamics, showing that the DeWitt criterion can be satisfied.
Therefore, as it also happens in General Relativity, this event may be avoided
in quantum cosmology.Comment: 10 pages; title changed; 1 table added; 8 references added; no
physics changes. This version accepted for publication in Physical Review
Big rip in shift-symmetric Kinetic Gravity Braiding theories
We revise the future fate of a group of scalar-tensor theories known as
kinetic gravity braiding models. As it is well-known, these theories can safely
drive the expansion of the universe towards a future de Sitter state if the
corresponding Lagrangian is invariant under constant shifts in the scalar
field. However, this is not the only possible future state of these
shift-symmetric models as we show in this letter. In fact, future cosmic
singularities characterized by a divergence of the energy density can also
appear in this framework. We present an explicit example where a big rip
singularity is the only possible future fate of the cosmos.Comment: 6 pages, 2 figures, 1 table. v2: minor modifications in the
conclusions section, no physics changes, matches PLB published versio
Phantom attractors in Kinetic Gravity Braiding theories: A dynamical system approach
We revise the expansion history of the scalar field theories known as kinetic
gravity braiding models. These theories are well-known for the possibility of
driving the expansion of the cosmos towards a future self-tuning de Sitter
state when the corresponding Lagrangian is invariant under constant shifts in
the scalar field. Nevertheless, this is not the only possible future fate of
these shift-symmetric models. Using a dynamical system formulation we show that
future cosmological singularities can also appear in this framework. Moreover,
we present explicit examples where the future attractor in the configuration
space of the theory corresponds to a big rip singularity.Comment: v1: 22 pages, 4 tables; v2: three references added, no physics
change
The little rip in classical and quantum cosmology
The little rip is a cosmological abrupt event predicted by some phantom dark
energy models that could describe the future evolution of our Universe. This
event can be interpreted as a big rip singularity delayed indefinitely,
although in those models bounded structures will be destroyed in a finite
cosmic time in the future. In this work, we analyse the little rip cosmology
from a classical and quantum point of view within the scheme of alternative
metric theories of gravity. The quantum analysis is performed in the
framework of quantum geometrodynamics by means of the modified
Wheeler-DeWitt equation. In this context, we show that the DeWitt criterion can
be satisfied. Similar to what happens in general relativity, this result points
towards the avoidance of the little rip in quantum cosmology.Comment: 14 pages. v2: typos fixed, references added, matches published
versio
Stability in quadratic torsion theories
We revisit the definition and some of the characteristics of quadratic
theories of gravity with torsion. We start from the most general Lagrangian
density quadratic in the curvature and torsion tensors. By assuming that
General Relativity should be recovered when torsion vanishes and investigating
the behaviour of the vector and pseudovector torsion fields in the weak-gravity
regime, we present a set of necessary conditions for the stability of these
theories. Moreover, we explicitly obtain the gravitational field equations
using the Palatini variational principle with the metricity condition
implemented via a Lagrange multiplier
Classical and Quantum f(R) Cosmology: The Big Rip, the Little Rip and the Little Sibling of the Big Rip
The big rip, the little rip and the little sibling of the big rip are cosmological doomsdays predicted by some phantom dark-energy models that could describe the future evolution of our universe. When the universe evolves towards either of these future cosmic events, all bounded structures and, ultimately, space鈥搕ime itself are ripped apart. Nevertheless, it is commonly believed that quantum gravity effects may smooth or even avoid these classically predicted singularities. In this review, we discuss the classical and quantum occurrence of these riplike events in the scheme of metric f(R) theories of gravity. The quantum analysis is performed in the framework of f(R) quantum geometrodynamics. In this context, we analyze the fulfilment of the DeWitt criterion for the avoidance of these singular fates. This review contains as well new unpublished work (the analysis of the equation of state for the phantom fluid and a new quantum treatment of the big rip and the little sibling of the big rip events)
Erratum to: Stability in quadratic torsion theories
A Correction to this paper has been published: 10.1140/epjc/s10052-017-5331-