2,101 research outputs found
Multi-disformal invariance of nonlinear primordial perturbations
We study disformal transformations of the metric in the cosmological context.
We first consider the disformal transformation generated by a scalar field
and show that the curvature and tensor perturbations on the uniform
slicing, on which the scalar field is homogeneous, are non-linearly
invariant under the disformal transformation. Then we discuss the
transformation properties of the evolution equations for the curvature and
tensor perturbations at full non-linear order in the context of spatial
gradient expansion as well as at linear order. In particular, we show that the
transformation can be described in two typically different ways: one that
clearly shows the physical invariance and the other that shows an apparent
change of the causal structure. Finally we consider a new type of disformal
transformation in which a multi-component scalar field comes into play, which
we call a "multi-disformal transformation". We show that the curvature and
tensor perturbations are invariant at linear order, and also at non-linear
order provided that the system has reached the adiabatic limit.Comment: 8 page
Self-unitarization of New Higgs Inflation and compatibility with Planck and BICEP2 data
In this paper we show that the Germani-Kehagias model of Higgs inflation (or
New Higgs Inflation), where the Higgs boson is kinetically non-minimally
coupled to the Einstein tensor is in perfect compatibility with the latest
Planck and BICEP2 data. Moreover, we show that the tension between the Planck
and BICEP2 data can be relieved within the New Higgs inflation scenario by a
negative running of the spectral index. Regarding the unitarity of the model,
we argue that it is unitary throughout the evolution of the Universe. Weak
couplings in the Higgs-Higgs and Higgs-graviton sectors are provided by a large
background dependent cut-off scale during inflation. In the same regime, the W
and Z gauge bosons acquire a very large mass, thus decouple. On the other hand,
if they are also non-minimally coupled to the Higgs boson, their effective
masses can be enormously reduced. In this case, the W and Z bosons are no
longer decoupled. After inflation, the New Higgs model is well approximated by
a quartic Galileon with a renormalizable potential. We argue that this can
unitarily create the right conditions for inflation to eventually start.Comment: 14 pages, 1 figure. [v2]: Explanations added, minor changes, results
unchanged. Version published in JCA
\delta N versus covariant perturbative approach to non-Gaussianity outside the horizon in multifield inflation
We compute the super-Hubble evolution of non-Gaussianity of primordial
curvature perturbations in two-field inflation models by employing two
formalisms: delta N and covariant formalisms. Although two formalisms treat the
evolution of fluctuations radically different, we show that the formulas of
f_{NL} parameter agree quantitatively with each other within 1 % accuracy. We
analytically find that the amplitude of f_{NL} decays no faster than a^{-3} as
the inflationary trajectory reaches to the adiabatic limit for generic
potentials.Comment: v4: minor changes, version accepted for PRD; v3: 10 pages, 14
figures, added two examples that produce relatively large non-Gaussianity in
Appendix to support the results; v2: 8 pages, 10 figures, added reference
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