183 research outputs found

### A General Analytic Formula for the Spectral Index of the Density Perturbations produced during Inflation

The standard calculation of the spectrum of density perturbations produced
during inflation assumes that there is only one real dynamical degree of
freedom during inflation. However, there is no reason to believe that this is
actually the case. In this paper we derive general analytic formulae for the
spectrum and spectral index of the density perturbations produced during
inflation.Comment: 10 pages, more explanation and references added, version to be
published in Progress of Theoretical Physic

### Inflation on Moduli Space and Cosmic Perturbations

We show that a moduli space of the form predicted by string theory, lifted by
supersymmetry breaking, gives rise to successful inflation for large regions of
parameter space without any modification or fine tuning. This natural
realization of inflation relies crucially on the complex nature of the moduli
fields and the multiple points of enhanced symmetry, which are generic features
of moduli space but not usually considered in inflationary model building.
Our scenario predicts cosmic perturbations with an almost exactly flat
spectrum for a wide range of scales with running on smaller, possibly
observable, scales. The running takes the form of either an increasingly steep
drop off of the spectrum, or a rise to a bump in the spectrum before an
increasingly steep drop off.Comment: 23 pages, 4 figures; Added Fig. 1 and re-emphasis on dynamical
selection of desirable initial angles for inflaton modulus. To be published
in JHE

### Inflation model building in moduli space

A self-consistent modular cosmology scenario and its testability in view of
future CMB experiments are discussed. Particular attention is drawn to the
enhanced symmetric points in moduli space which play crucial roles in our
scenario. The running and moreover the running of running for the cosmic
perturbation spectrum are also analyzed.Comment: 5 pages, to appear in PASCOS04 proceeding

### Damping of an oscillating scalar field indirectly coupled to a thermal bath

The damping process of a homogeneous oscillating scalar field that indirectly
interacts with a thermal bath through a mediator field is investigated over a
wide range of model parameters. We consider two types of mediator fields, those
that can decay to the thermal bath and those that are individually stable but
pair annihilate. The former case has been extensively studied in the literature
by treating the damping as a local effect after integrating out the assumed
close-to-equilibrium mediator field. The same approach does not apply if the
mediator field is stable and freezes out of equilibrium. To account for the
latter case, we adopt a non-local description of damping that is only
meaningful when we consider full half-oscillations of the field being damped.
The damping rates of the oscillating scalar field and the corresponding heating
rate of the thermal bath in all bulk parameter regions are calculated in both
cases, corroborating previous results in the direct decay case. Using the
obtained results, the time it takes for the amplitude of the scalar field to be
substantially damped is estimated.Comment: 39 pages, 9 figures, 1 table; typos corrected, references adde

### Couplings and spectra in modular inflation

We analyze how the spectrum of perturbations produced in a multi-component
modular inflation model proposed by Kadota and Stewart depends on couplings
between the two moduli. Although some simple direct couplings give essentially
the same results as the original model, $dn/d\ln k \propto n-1$, simple
indirect couplings produce a power law spectrum, $n-1 = \textrm{constant}$,
which can naturally be close to scale invariant.Comment: 11 pages, format changed, some corrections of formula

### CMB Spectral Distortion Constraints on Thermal Inflation

Thermal inflation is a second epoch of exponential expansion at typical
energy scales $V^{1/4} \sim 10^{6 \sim 8} \mathrm{GeV}$. If the usual
primordial inflation is followed by thermal inflation, the primordial power
spectrum is only modestly redshifted on large scales, but strongly suppressed
on scales smaller than the horizon size at the beginning of thermal inflation,
$k > k_{\rm b} = a_{\rm b} H_{\rm b}$. We calculate the spectral distortion of
the cosmic microwave background generated by the dissipation of acoustic waves
in this context. For $k_{\rm b} \ll 10^3 \mathrm{Mpc}^{-1}$, thermal inflation
results in a large suppression of the $\mu$-distortion amplitude, predicting
that it falls well below the standard value of $\mu \simeq 2\times 10^{-8}$.
Thus, future spectral distortion experiments, similar to PIXIE, can place new
limits on the thermal inflation scenario, constraining $k_{\rm b} \gtrsim 10^3
\mathrm{Mpc}^{-1}$ if $\mu \simeq 2\times 10^{-8}$ were found.Comment: 18 pages, 7 figure

- …