286 research outputs found
Cosmologically allowed regions for the axion decay constant
If the Peccei-Quinn symmetry is already broken during inflation, the decay
constant of the axion can be in a wide region from GeV to
GeV for the axion being the dominant dark matter. In this case,
however, the axion causes the serious cosmological problem, isocurvature
perturbation problem, which severely constrains the Hubble parameter during
inflation. The constraint is relaxed when Peccei-Quinn scalar field takes a
large value (Planck scale) during inflation. In this letter, we
point out that the allowed region of the decay constant is reduced to a
rather narrow region for a given tensor-to-scalar ratio when Peccei-Quinn
scalar field takes during inflation. For example, if the ratio
is determined as in future measurements, we can predict
GeV for domain wall number
.Comment: 9 pages, 1 figure, LaTeX; some explanations and references adde
Cosmologically safe QCD axion as a present from extra dimension
We propose a QCD axion model where the origin of PQ symmetry and suppression
of axion isocurvature perturbations are explained by introducing an extra
dimension. Each extra quark-antiquark pair lives on branes separately to
suppress PQ breaking operators. The size of the extra dimension changes after
inflation due to an interaction between inflaton and a bulk scalar field, which
implies that the PQ symmetry can be drastically broken during inflation to
suppress undesirable axion isocurvature fluctuations.Comment: 6 page
Lower bound of the tensor-to-scalar ratio in a nearly quadratic chaotic inflation model in supergravity
We consider an initial condition problem in a nearly quadratic chaotic
inflation model in supergravity. We introduce shift symmetry breaking not only
in the superpotential but also in the Kahler potential. In this model the
inflaton potential is nearly quadratic for inflaton field values around the
Planck scale, but deviates from the quadratic one for larger field values. As a
result, the prediction on the tensor-to-scalar ratio can be smaller than that
of a purely quadratic model. Due to the shift symmetry breaking in the Kahler
potential, the inflaton potential becomes steep for large inflaton field
values, which may prevent inflation from naturally taking place in a closed
universe. We estimate an upper bound on the magnitude of the shift symmetry
breaking so that inflation takes place before a closed universe with a Planck
length size collapses, which yields a lower bound on the tensor-to-scalar
ratio, .Comment: 11 pages, 6 figure
Revisiting the Minimal Chaotic Inflation Model
We point out that the prediction of the minimal chaotic inflation model is
altered if a scalar field takes a large field value close to the Planck scale
during inflation due to a negative Hubble induced mass. In particular, we show
that the inflaton potential is effectively suppressed at a large inflaton field
value in the presence of such a scalar field. The scalar field may be
identified with the standard model Higgs field or flat directions in
supersymmetric theory. With such spontaneous suppression, we find that the
minimal chaotic inflation model, especially the model with a quadratic
potential, is consistent with recent observations of the cosmic microwave
background fluctuation without modifying the inflation model itself.Comment: 5 pages, 3 figure
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