886 research outputs found
Primordial Black Holes, Eternal Inflation, and the Inflationary Parameter Space after WMAP5
We consider constraints on inflation driven by a single, minimally coupled
scalar field in the light of the WMAP5 dataset, as well as ACBAR and the
SuperNova Legacy Survey. We use the Slow Roll Reconstruction algorithm to
derive optimal constraints on the inflationary parameter space. The scale
dependence in the slope of the scalar spectrum permitted by WMAP5 is large
enough to lead to viable models where the small scale perturbations have a
substantial amplitude when extrapolated to the end of inflation. We find that
excluding parameter values which would cause the overproduction of primordial
black holes or even the onset of eternal inflation leads to potentially
significant constraints on the slow roll parameters. Finally, we present a more
sophisticated approach to including priors based on the total duration of
inflation, and discuss the resulting restrictions on the inflationary parameter
space.Comment: v2: version published in JCAP. Minor clarifications and references
adde
New Solutions of the Inflationary Flow Equations
The inflationary flow equations are a frequently used method of surveying the
space of inflationary models. In these applications the infinite hierarchy of
differential equations is truncated in a way which has been shown to be
equivalent to restricting the set of models considered to those characterized
by polynomial inflaton potentials. This paper explores a different method of
solving the flow equations, which does not truncate the hierarchy and in
consequence covers a much wider class of models while retaining the practical
usability of the standard approach.Comment: References added, and a couple of comment
Cascading on extragalactic background light
High-energy gamma-rays propagating in the intergalactic medium can interact
with background infrared photons to produce e+e- pairs, resulting in the
absorption of the intrinsic gamma-ray spectrum. TeV observations of the distant
blazar 1ES 1101-232 were thus recently used to put an upper limit on the
infrared extragalactic background light density. The created pairs can
upscatter background photons to high energies, which in turn may pair produce,
thereby initiating a cascade. The pairs diffuse on the extragalactic magnetic
field (EMF) and cascade emission has been suggested as a means for measuring
its intensity. Limits on the IR background and EMF are reconsidered taking into
account cascade emissions. The cascade equations are solved numerically.
Assuming a power-law intrinsic spectrum, the observed 100 MeV - 100 TeV
spectrum is found as a function of the intrinsic spectral index and the
intensity of the EMF. Cascades emit mainly at or below 100 GeV. The observed
TeV spectrum appears softer than for pure absorption when cascade emission is
taken into account. The upper limit on the IR photon background is found to be
robust. Inversely, the intrinsic spectra needed to fit the TeV data are
uncomfortably hard when cascade emission makes a significant contribution to
the observed spectrum. An EMF intensity around 1e-8 nG leads to a
characteristic spectral hump in the GLAST band. Higher EMF intensities divert
the pairs away from the line-of-sight and the cascade contribution to the
spectrum becomes negligible.Comment: 5 pages, to be published as a research note in A&
Constraining Inflation
Slow roll reconstruction is derived from the Hamilton-Jacobi formulation of
inflationary dynamics. It automatically includes information from sub-leading
terms in slow roll, and facilitatesthe inclusion of priors based on the
duration on inflation. We show that at low inflationary scales the
Hamilton-Jacobi equations simplify considerably. We provide a new
classification scheme for inflationary models, based solely on the number of
parameters needed to specify the potential, and provide forecasts for likely
bounds on the slow roll parameters from future datasets. A minimal running of
the spectral index, induced solely by the first two slow roll parameters
(\epsilon and \eta) appears to be effectively undetectable by realistic Cosmic
Microwave Background experiments. However, we show that the ability to detect
this signal increases with the lever arm in comoving wavenumber, and we
conjecture that high redshift 21 cm data may allow tests of second order
consistency conditions on inflation. Finally, we point out that the second
order corrections to the spectral index are correlated with the inflationary
scale, and thus the amplitude of the CMB B-mode.Comment: 32 pages. v
Boundary Effective Field Theory and Trans-Planckian Perturbations: Astrophysical Implications
We contrast two approaches to calculating trans-Planckian corrections to the
inflationary perturbation spectrum: the New Physics Hypersurface [NPH] model,
in which modes are normalized when their physical wavelength first exceeds a
critical value, and the Boundary Effective Field Theory [BEFT] approach, where
the initial conditions for all modes are set at the same time, and modified by
higher dimensional operators enumerated via an effective field theory
calculation. We show that these two approaches -- as currently implemented --
lead to radically different expectations for the trans-Planckian corrections to
the CMB and emphasize that in the BEFT formalism we expect the perturbation
spectrum to be dominated by quantum gravity corrections for all scales shorter
than some critical value. Conversely, in the NPH case the quantum effects only
dominate the longest modes that are typically much larger than the present
horizon size. Furthermore, the onset of the breakdown in the standard
inflationary perturbation calculation predicted by the BEFT formalism is likely
to be associated with a feature in the perturbation spectrum, and we discuss
the observational signatures of this feature in both CMB and large scale
structure observations. Finally, we discuss possible modifications to both
calculational frameworks that would resolve the contradictions identified here.Comment: Reworded commentary, reference added (v2) References added (v3
Cosmological quantum entanglement
We review recent literature on the connection between quantum entanglement
and cosmology, with an emphasis on the context of expanding universes. We
discuss recent theoretical results reporting on the production of entanglement
in quantum fields due to the expansion of the underlying spacetime. We explore
how these results are affected by the statistics of the field (bosonic or
fermionic), the type of expansion (de Sitter or asymptotically stationary), and
the coupling to spacetime curvature (conformal or minimal). We then consider
the extraction of entanglement from a quantum field by coupling to local
detectors and how this procedure can be used to distinguish curvature from
heating by their entanglement signature. We review the role played by quantum
fluctuations in the early universe in nucleating the formation of galaxies and
other cosmic structures through their conversion into classical density
anisotropies during and after inflation. We report on current literature
attempting to account for this transition in a rigorous way and discuss the
importance of entanglement and decoherence in this process. We conclude with
some prospects for further theoretical and experimental research in this area.
These include extensions of current theoretical efforts, possible future
observational pursuits, and experimental analogues that emulate these cosmic
effects in a laboratory setting.Comment: 23 pages, 2 figures. v2 Added journal reference and minor changes to
match the published versio
WMAP constraint on the P-term inflationary model
In light of WMAP results, we examine the observational constraint on the
P-term inflation. With the tunable parameter , P-term inflation contains
richer physics than D-term and F-term inflationary models. We find the
logarithmic derivative spectral index with on large scales and on
small scales in agreement to observation. We obtained a reasonable range for
the choice of the gauge coupling constant in order to meet the requirements
of WMAP observation and the expected number of the e-foldings. Although tuning
and we can have larger values for the logarithmic derivative of the
spectral index, it is not possible to satisfy all observational requirements
for both, the spectral index and its logarithmic derivative at the same time.Comment: 6 pages, double column, 13 figures included. Version appearing in the
Physical Review
Revisit relic gravitational waves based on the latest CMB observations
According to the CMB observations, Mielczarek (\cite{Mielczarek}) evaluated
the reheating temperature, which could help to determine the history of the
Universe. In this paper, we recalculate the reheating temperature using the new
data from WMAP 7 observations. Based on that, we list the approximate solutions
of relic gravitational waves (RGWs) for various frequency bands. With the
combination of the quantum normalization of RGWs when they are produced and the
CMB observations, we obtain the relation between the tensor-to-scalar ratio
and the inflation index for a given scalar spectral index . As a
comparison, the diagram in the slow-roll inflation model is also
given. Thus, the observational limits of from CMB lead to the constraints
on the value of . Then, we illustrate the energy density spectrum of
RGWs with the quantum normalization for different values of and the
corresponding . For comparison, the energy density spectra of RGWs with
parameters based on slow-roll inflation are also discussed. We find that the
values of affect the spectra of RGWs sensitively in the very high
frequencies. Based on the current and planed gravitational wave detectors, we
discuss the detectabilities of RGWs.Comment: 16 pages, 6 figures, accepted for publication in Class. Quantum Gra
Constraints on Brane Inflation and Cosmic Strings
By considering simple, but representative, models of brane inflation from a
single brane-antibrane pair in the slow roll regime, we provide constraints on
the parameters of the theory imposed by measurements of the CMB anisotropies by
WMAP including a cosmic string component. We find that inclusion of the string
component is critical in constraining parameters. In the most general model
studied, which includes an inflaton mass term, as well as the brane-antibrane
attraction, values n_s < 1.02 are compatible with the data at 95 % confidence
level. We are also able to constrain the volume of internal manifold (modulo
factors dependent on the warp factor) and the value of the inflaton field to be
less than 0.66M_P at horizon exit. We also investigate models with a mass term.
These observational considerations suggest that such models have r < 2*10^-5,
which can only be circumvented in the fast roll regime, or by increasing the
number of antibranes. Such a value of r would not be detectable in CMB
polarization experiment likely in the near future, but the B-mode signal from
the cosmic strings could be detectable. We present forecasts of what a similar
analysis using PLANCK data would yield and find that it should be possible to
rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.Comment: 11 pages, 3 figures, revtex4, typos corrected, references adde
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