18,683 research outputs found
K-Inflation in Noncommutative Space-Time
The power spectra of the scalar and tensor perturbations in the
noncommutative k-inflation model are calculated in this paper. In this model,
all the modes created when the stringy space-time uncertainty relation is
satisfied are generated inside the sound/Hubble horizon during inflation for
the scalar/tensor perturbations. It turns out that a linear term describing the
noncommutative space-time effect contributes to the power spectra of the scalar
and tensor perturbations. Confronting the general noncommutative k-inflation
model with latest results from \textit{Planck} and BICEP2, and taking and
as free parameters, we find that it is well consistent with
observations. However, for the two specific models, i.e. the tachyon and DBI
inflation models, it is found that the DBI model is not favored, while the
tachyon model lies inside the contour, if the e-folds number is
assumed to be around .Comment: 9 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1404.016
Is Cosmological Constant Needed in Higgs Inflation?
The detection of B-mode shows a very powerful constraint to theoretical
inflation models through the measurement of the tensor-to-scalar ratio .
Higgs boson is the most likely candidate of the inflaton field. But usually,
Higgs inflation models predict a small value of , which is not quite
consistent with the recent results from BICEP2. In this paper, we explored
whether a cosmological constant energy component is needed to improve the
situation. And we found the answer is yes. For the so-called Higgs chaotic
inflation model with a quadratic potential, it predicts ,
with e-folds number , which is large enough to
overcome the problems such as the horizon problem in the Big Bang cosmology.
The required energy scale of the cosmological constant is roughly , which means a mechanism is still needed to solve the
fine-tuning problem in the later time evolution of the universe, e.g. by
introducing some dark energy component.Comment: 4 pages, 2 figure
Quasi-two-body decays in the perturbative QCD approach
In this paper, we calculated the branching ratios of the quasi-two-body
decays
by employing the perturbative QCD (PQCD) approach. The contributions from the
-wave resonances , and were taken into
account. The two-pion distribution amplitude is
parameterized by the vector current time-like form factor to study
the considered decay modes. We found that (a) the PQCD predictions for the
branching ratios of the considered quasi-two-body decays are in the order of
, while the two-body decay rates are extracted from those for the
corresponding quasi-two-body decays; (b) the whole pattern of the pion form
factor-squared measured by the BABAR Collaboration could be
understood based on our theoretical results; (c) the general expectation based
on the similarity between and
decays are confirmed: is consistent with the measured
within errors; and (d) new ratios
and among the branching ratios of the
considered decay modes are defined and could be tested by future experiments.Comment: 10 pages, 3 figure
- β¦