18 research outputs found
Natural inflation at the GUT scale
Natural inflation driven by Pseudo-Nambu-Goldstone bosons have a problem that
the nearly scale invariant spectrum of density perturbations is attained only
when the symmetry breaking scale is of the order of Planck scale. We show here
that if one couples the PNGB to a thermal bath as in warm inflation models, the
amplitude and spectral index which agrees with the WMAP data is obtained with
the symmetry breaking in the GUT scale. We give a GUT model of PNGB arising out
of spontaneously broken lepton number at the GUT scale which gives rise to
heavy Majorana masses for the right handed neutrinos which is needed in see-saw
models. This model also generates a lepton asymmetry because of the derivative
coupling of the PNGB to the lepton current. A characteristic feature of this
model is the prediction of large non-gaussianity which may be observed in the
forthcoming PLANCK experiment.Comment: Final version, published in Physical Review
Enhanced polarization of CMB from thermal gravitational waves
If inflation was preceded by a radiation era then at the time of inflation
there will exist a decoupled thermal distribution of gravitons. Gravitational
waves generated during inflation will be amplified by the process of stimulated
emission into the existing thermal distribution of gravitons. Consequently the
usual zero temperature scale invariant tensor spectrum is modified by a
temperature dependent factor. This thermal correction factor amplify the
-mode polarization of the CMB by an order of magnitude at large angles,
which may now be in the range of observability of WMAP.Comment: 5 pages, 1 figure, Revtex file. Some minor corrections included, some
new references introduced. Accepted for publication in Physical Review
Letter
Non-canonical Higgs inflation
The large value of non-minimal coupling constant required to satisfy
CMB observations in Higgs inflation violates unitarity. In this work we study
Higgs-inflation with non-canonical kinetic term of DBI form to find whether
can be reduced. To study the inflationary dynamics, we transform the
action to the Einstein frame, in which the Higgs is minimally coupled to
gravity with a non-canonical kinetic term and modified potential. We choose the
Higgs self coupling constant for our analysis. We find that the
value of can be reduced from to to
satisfy Planck constraints on amplitude of scalar power spectrum. However, this
model produces a larger tensor-to-scalar ratio , in comparison to the Higgs
inflation with canonical kinetic term. We also find that, to satisfy joint
constraints on scalar spectral index and tensor-to-scalar ratio from
Planck-2018 and bounds on from Planck and BICEP3, the value of should
be of the order of .Comment: 14 pages, 5 figure
Observational constraints on power law Starobinsky inflation
In this work we revisit power law, , inflation to find
the deviations from inflation allowed by current CMB and LSS
observations. We compute the power spectra for scalar and tensor perturbations
numerically and perform MCMC analysis to put constraints on parameters and
from Planck-2018, BICEP3 and other LSS observations. We consider
general reheating scenario and also vary the number of e-foldings during
inflation, , along with the other parameters. We find , and
with . This indicates that the
current observations allow deviation from Starobinsky inflation. The scalar
spectral index, , and tensor-to-scalar ratio, , derived from these
parameters, are consistent with the Planck and BICEP3 observations.Comment: Referee's comments incorporated, New references added, Accepted for
publication in Phys. Rev.
Imprint of spatial curvature on inflation power spectrum
If the universe had a large curvature before inflation there is a deviation
from the scale invariant perturbations of the inflaton at the beginning of
inflation. This may have some effect on the CMB anisotropy at large angular
scales. We calculate the density perturbations for both open and closed
universe cases using the Bunch-Davies vacuum condition on the initial state. We
use our power spectrum to calculate the temperature anisotropy spectrum and
compare the results with the WMAP three year data. We find that our power
spectrum gives a lower quadrupole anisotropy when , but matches
the temperature anisotropy calculated from the standard Ratra-Peebles power
spectrum at large . The determination of spatial curvature from temperature
anisotropy data is not much affected by the different power spectra which arise
from the choice of different boundary conditions for the inflaton perturbation.Comment: 17 pages, 4 figures, revtex4; section on comparison with WMAP3 data
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WMAP Constraints On K-Inflation
We study the K-Inflation models where the inflaton field has non-canonical
kinetic term. In particular, we consider the Dirac-Born-Infeld (DBI) form for
the kinetic energy of the inflaton field. We consider quadratic and quartic
potentials as well as the potential for the natural inflation. We use a
modified version of the MODECODE (proposed by Mortonson et al.) to calculate
the power spectrum of the primordial perturbations generated by the inflaton
field and subsequently use the WMAP7 results to constrain the models.
Interestingly with DBI type kinetic term, lesser gravity waves are produced as
one approaches more towards scale invariance. This is true for all the
potentials considered. Unlike the canonical case, this feature, in particular,
helps the quartic () potential with DBI type kinetic term to be
consistent with WMAP data.Comment: 9 pages, 4 eps figures, 2 Tables, Latex Styl