62 research outputs found
Reconstruction of the primordial fluctuation spectrum from the five-year WMAP data by the cosmic inversion method with band-power decorrelation analysis
The primordial curvature fluctuation spectrum is reconstructed by the cosmic
inversion method using the five-year WMAP data of the cosmic microwave
background temperature anisotropy. We apply the covariance matrix analysis and
decompose the reconstructed spectrum into statistically independent
band-powers. The statistically significant deviation from a simple power-law
spectrum suggested by the analysis of the first-year data is not found in the
five-year data except possibly at one point near the border of the wavenumber
domain where accurate reconstruction is possible.Comment: 9page
Metric perturbation from inflationary magnetic field and generic bound on inflation models
There is an observational indication of extragalactic magnetic fields. No
known astrophysical process can explain the origin of such large scale magnetic
fields, which motivates us to look for their origin in primordial inflation. By
solving the linearized Einstein equations, we study metric perturbations
sourced by magnetic fields that are produced during inflation. This leads to a
simple but robust bound on the inflation models by requiring that the induced
metric perturbation should not exceed the observed value 10^-5. In case of the
standard single field inflation model, the bound can be converted into a lower
bound on the Hubble parameter during inflation.Comment: 14 page
Hiding cosmic strings in supergravity D-term inflation
The influence of higher-order terms in the K\"{a}hler potential of the
supergravity D-term inflation model on the density perturbation is studied. We
show that these terms can make the inflaton potential flatter, which lowers the
energy scale of inflation under the COBE/WMAP normalization. As a result, the
mass per unit length of cosmic strings, which are produced at the end of
inflation, can be reduced to a harmless but detectable level without
introducing a tiny Yukawa coupling. Our scenario can naturally be implemented
in models with a low cut-off as in Type I or Type IIB orientifold models.Comment: 15 pages, 4 figure
Band-power reconstruction of the primordial fluctuation spectrum by the maximum likelihood reconstruction method
The primordial curvature fluctuation spectrum is reconstructed by the maximum
likelihood reconstruction method using the five-year Wilkinson Microwave
Anisotropy Probe data of the cosmic microwave background temperature
anisotropy. We apply the covariance matrix analysis and decompose the
reconstructed spectrum into statistically independent band-powers. The
prominent peak off a simple power-law spectrum found in our previous analysis
turn out to be a deviation. From the statistics of primordial
spectra reconstructed from mock observations, the probability that a primordial
spectrum including such excess is realized in a power-law model is estimated to
be about 2%.Comment: 9 page
Thermal background can solve the cosmological moduli problem
It is shown that the coherent field oscillation of moduli fields with weak or
TeV scale masses can dissipate its energy efficiently if they have a derivative
coupling to standard bosonic fields in a thermal state. This mechanism may
provide a new solution to the cosmological moduli problem in some special
situations.Comment: 4 pages. revised versio
G-inflation: inflation driven by the Galileon field
We propose a new class of inflation model, G-inflation, which has a
Galileon-like nonlinear derivative interaction of the form in the Lagrangian with the resultant equations of
motion being of second order. It is shown that (almost) scale-invariant
curvature fluctuations can be generated even in the exactly de Sitter
background and that the tensor-to-scalar ratio can take a significantly larger
value than in the standard inflation models, violating the standard consistency
relation. Furthermore, violation of the null energy condition can occur without
any instabilities. As a result, the spectral index of tensor modes can be blue,
which makes it easier to observe quantum gravitational waves from inflation by
the planned gravitational-wave experiments such as LISA and DECIGO as well as
by the upcoming CMB experiments such as Planck and CMBpol.Comment: 5 pages, 1 figure; v2: major clarification; v3: original version of
the article published in Phys. Rev. Lett. 105, 231302 (2010
Primordial non-Gaussianity from G-inflation
We present a comprehensive study of primordial fluctuations generated from
G-inflation, in which the inflaton Lagrangian is of the form with . The Lagrangian still gives
rise to second-order gravitational and scalar field equations, and thus offers
a more generic class of single-field inflation than ever studied, with a richer
phenomenology. We compute the power spectrum and the bispectrum, and clarify
how the non-Gaussian amplitude depends upon parameters such as the sound speed.
In so doing we try to keep as great generality as possible, allowing for non
slow-roll and deviation from the exact scale-invariance.Comment: 12 pages; v2: Minor changes, added 4 figures, matches the published
versio
Density fluctuations in one-field inflation
Any one-field inflation is actually realized in a multifield configuration
because the inflaton must have couplings with other fields to reheat the
universe and is coupled to all other fields at least gravitationally. In all
single inflaton models, it is explicitly or implicitly assumed that the heavier
fields are stuck to their potential minima during inflation, which are
time-dependent in general. We present a formalism to calculate curvature
perturbations in such a time-dependent background and show that the proper
expression can be obtained using a single-field analysis with a reduced
potential in which all these heavy fields are situated at their respective,
time-dependent minima. Our results provide a firm ground on the conventional
calculation.Comment: 9 pages, to appear in Phys. Rev.
Neutralino Dark Matter from Heavy Gravitino Decay
We propose a new scenario of non-thermal production of neutralino cold dark
matter, in which the overproduction problem of lightest supersymmetric
particles (LSPs) in the standard thermal history is naturally solved. The
mechanism requires a heavy modulus field which decays mainly to ordinary
particles releasing large entropy to dilute gravitinos produced just after
inflation and thermal relics of LSPs. Significant amount of gravitinos are also
pair-produced at the decay, which subsequently decay into the neutralinos. We
identify the regions of the parameter space in which the requisite abundance of
the neutralino dark matter is obtained without spoiling the big-bang
nucleosynthesis by injection of hadronic showers from gravitino decay. The
neutralino abundance obtained in this mechanism is insensitive to the details
of the superparticle mass spectrum, unlike the standard thermal abundance. We
also briefly mention the testability of the scenario in future experiments.Comment: 19 pages, 5 figures, to appear in Phys. Rev.
Space laser interferometers can determine the thermal history of the early Universe
It is shown that space-based gravitational wave detectors such as DECIGO
and/or Big Bang Observer (BBO) will provide us with invaluable information on
the cosmic thermal history after inflation and they will be able to determine
the reheat temperature provided that it lies in the range preferred by
the cosmological gravitino problem, GeV. Therefore it is
strongly desired that they will be put into practice as soon as possible.Comment: 5 page
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