1,060 research outputs found
Inflationary cosmology in modified gravity theories
We review inflationary cosmology in modified gravity such as gravity
with its extensions in order to generalize the Starobinsky inflation model. In
particular, we explore inflation realized by three kinds of effects:
modification of gravity, the quantum anomaly, and the term in loop
quantum cosmology. It is explicitly demonstrated that in these inflationary
models, the spectral index of scalar modes of the density perturbations and the
tensor-to-scalar ratio can be consistent with the Planck results. Bounce
cosmology in gravity is also explained.Comment: 24 pages, no figure, invited review to appear in Symmetr
Trace-anomaly driven inflation in gravity and in minimal massive bigravity
We explore trace-anomaly driven inflation in modified gravity. It is
explicitly shown that in teleparallel gravity, the de Sitter inflation
can occur, although quasi de Sitter inflation happens in gravity.
Furthermore, we investigate the influence of the trace anomaly on inflation. It
is found that in gravity, the de Sitter inflation can end because it
becomes unstable due to the trace anomaly, whereas also in higher derivative
gravity, the de Sitter inflation can be realized and it will be over thanks to
the trace anomaly for smaller parameter regions in comparison with those in
teleparallelism. The instability of the de Sitter inflation in gravity
and gravity (both with taking account of the trace anomaly) is examined.
In addition, we study trace-anomaly driven inflation in minimal massive
bigravity, where the contribution from the massive graviton acts as negative
cosmological constant. It is demonstrated that the de Sitter inflation can
occur and continue for long enough duration.Comment: 13 pages, no figure, version accepted for publication in Physics
Letters
Time-dependent matter instability and star singularity in gravity
We investigate a curvature singularity appearing in the star collapse process
in gravity. In particular, we propose an understanding of the mechanism
to produce the curvature singularity. Moreover, we explicitly demonstrate that
() term addition could cure the curvature
singularity and viable gravity models could become free of such a
singularity. Furthermore, we discuss the realization process of the curvature
singularity and estimate the time scale of its appearance. For exponential
gravity, it is shown that in case of the star collapse, the time scale is much
shorter than the age of the universe, whereas in cosmological circumstances, it
is as long as the cosmological time.Comment: 15 pages, 2 figures, version accepted for publication in Physics
Letters
Reconstruction of scalar field theories realizing inflation consistent with the Planck and BICEP2 results
We reconstruct scalar field theories to realize inflation compatible with the
BICEP2 result as well as the Planck. In particular, we examine the chaotic
inflation model, natural (or axion) inflation model, and an inflationary model
with a hyperbolic inflaton potential. We perform an explicit approach to find
out a scalar field model of inflation in which any observations can be
explained in principle.Comment: 7 pages, no figure, version accepted for publication in Physics
Letters
- …