282 research outputs found
Agegraphic Chaplygin gas model of dark energy
We establish a connection between the agegraphic models of dark energy and
Chaplygin gas energy density in non-flat universe. We reconstruct the potential
of the agegraphic scalar field as well as the dynamics of the scalar field
according to the evolution of the agegraphic dark energy. We also extend our
study to the interacting agegraphic generalized Chaplygin gas dark energy
model.Comment: 8 page
CMB B-polarization to map the Large-scale Structures of the Universe
We explore the possibility of using the B-type polarization of the CMB to map
the large-scale structures of the Universe taking advantage of the lens effects
on the CMB polarization. The functional relation between the B component with
the primordial CMB polarization and the line-of-sight mass distribution is
explicited. Noting that a sizeable fraction (at least 40%) of the dark halo
population which is responsible of this effect can also be detected in galaxy
weak lensing survey, we present statistical quantities that should exhibit a
strong sensitivity to this overlapping. We stress that it would be a sound test
of the gravitational instability picture, independent on many systematic
effects that may hamper lensing detection in CMB or galaxy survey alone.
Moreover we estimate the intrinsic cosmic variance of the amplitude of this
effect to be less than 8% for a 100, deg^2 survey with a 10' CMB beam. Its
measurement would then provide us with an original mean for constraining the
cosmological parameters, more particularly, as it turns out, the cosmological
constant Lambda.Comment: Latex2e with REVTEX ; 14 pages, 8 figure
Cosmological implications of the KATRIN experiment
The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put
unprecedented constraints on the absolute mass of the electron neutrino,
\mnue. In this paper we investigate how this information on \mnue will
affect our constraints on cosmological parameters. We consider two scenarios;
one where \mnue=0 (i.e., no detection by KATRIN), and one where
\mnue=0.3eV. We find that the constraints on \mnue from KATRIN will affect
estimates of some important cosmological parameters significantly. For example,
the significance of and the inferred value of depend
on the results from the KATRIN experiment.Comment: 13 page
Measuring the cosmological lepton asymmetry through the CMB anisotropy
A large lepton asymmetry in the Universe is still a viable possibility and
leads to many interesting phenomena such as gauge symmetry nonrestoration at
high temperature. We show that a large lepton asymmetry changes the predicted
cosmic microwave background (CMB) anisotropy and that any degeneracy in the
relic neutrino sea will be measured to a precision of 1% or better when the CMB
anisotropy is measured at the accuracy expected to result from the planned
satellite missions MAP and Planck. In fact, the current measurements already
put an upper limit on the lepton asymmetry of the Universe which is stronger
than the one coming from considerations of primordial nucleosynthesis and
structure formation.Comment: 4 pagex LaTex, 1 color postscript figure, uses epsf. Version
submitted to PRL. (Bug in code fixed, new figure, conclusions unchanged
Dark Energy, scalar-curvature couplings and a critical acceleration scale
We study the effects of coupling a cosmologically rolling scalar field to
higher order curvature terms. We show that when the strong coupling scale of
the theory is on the 10^{-3}-10^{-1}eV range, the model passes all experimental
bounds on the existence of fifth forces even if the field has a mass of the
order of the Hubble scale in vacuum and non-suppressed couplings to SM fields.
The reason is that the coupling to certain curvature invariant acts as an
effective mass that grows in regions of large curvature. This prevents the
field from rolling down its potential near sources and makes its effects on
fifth-force search experiments performed in the laboratory to be observable
only at the sub-mm scale. We obtain the static spherically symmetric solutions
of the theory and show that a long-range force appears but it is turned on only
below a fixed Newtonian acceleration scale of the order of the Hubble constant.
We comment on the possibility of using this feature of the model to alleviate
the CDM small scale crisis and on its possible relation to MOND.Comment: 12 pages, 2 figure
The Tensor to Scalar Ratio of Phantom Dark Energy Models
We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.Comment: 5 pages, 4 figure
Thermal Unparticles: A New Form of Energy Density in the Universe
Unparticle \U with scaling dimension d_\U has peculiar thermal properties
due to its unique phase space structure. We find that the equation of state
parameter \omega_\U, the ratio of pressure to energy density, is given by
1/(2d_\U +1) providing a new form of energy in our universe. In an expanding
universe, the unparticle energy density \rho_\U(T) evolves dramatically
differently from that for photons. For d_\U >1, even if \rho_\U(T_D) at a
high decoupling temperature is very small, it is possible to have a large
relic density \rho_\U(T^0_\gamma) at present photon temperature ,
large enough to play the role of dark matter. We calculate and
\rho_\U(T^0_\gamma) using photon-unparticle interactions for illustration.Comment: 5 pages; v3, journal version
Fermionic Casimir effect in toroidally compactified de Sitter spacetime
We investigate the fermionic condensate and the vacuum expectation values of
the energy-momentum tensor for a massive spinor field in de Sitter spacetime
with spatial topology . Both cases
of periodicity and antiperiodicity conditions along the compactified dimensions
are considered. By using the Abel-Plana formula, the topological parts are
explicitly extracted from the vacuum expectation values. In this way the
renormalization is reduced to the renormalization procedure in uncompactified
de Sitter spacetime. It is shown that in the uncompactified subspace the
equation of state for the topological part of the energy-momentum tensor is of
the cosmological constant type. Asymptotic behavior of the topological parts in
the expectation values is investigated in the early and late stages of the
cosmological expansion. In the limit when the comoving length of a compactified
dimension is much smaller than the de Sitter curvature radius the topological
part in the expectation value of the energy-momentum tensor coincides with the
corresponding quantity for a massless field and is conformally related to the
corresponding flat spacetime result. In this limit the topological part
dominates the uncompactified de Sitter part. In the opposite limit, for a
massive field the asymptotic behavior of the topological parts is damping
oscillatory for both fermionic condensate and the energy-momentum tensor.Comment: 19 pages, 5 figure
Fast and precise map-making for massively multi-detector CMB experiments
Future cosmic microwave background (CMB) polarisation experiments aim to
measure an unprecedentedly small signal - the primordial gravity wave component
of the polarisation field B-mode. To achieve this, they will analyse huge
datasets, involving years worth of time-ordered data (TOD) from massively
multi-detector focal planes. This creates the need for fast and precise methods
to complement the M-L approach in analysis pipelines. In this paper, we
investigate fast map-making methods as applied to long duration, massively
multi-detector, ground-based experiments, in the context of the search for
B-modes. We focus on two alternative map-making approaches: destriping and TOD
filtering, comparing their performance on simulated multi-detector polarisation
data. We have written an optimised, parallel destriping code, the DEStriping
CARTographer DESCART, that is generalised for massive focal planes, including
the potential effect of cross-correlated TOD 1/f noise. We also determine the
scaling of computing time for destriping as applied to a simulated full-season
data-set for a realistic experiment. We find that destriping can out-perform
filtering in estimating both the large-scale E and B-mode angular power
spectra. In particular, filtering can produce significant spurious B-mode power
via EB mixing. Whilst this can be removed, it contributes to the variance of
B-mode bandpower estimates at scales near the primordial B-mode peak. For the
experimental configuration we simulate, this has an effect on the possible
detection significance for primordial B-modes. Destriping is a viable
alternative fast method to the full M-L approach that does not cause the
problems associated with filtering, and is flexible enough to fit into both M-L
and Monte-Carlo pseudo-Cl pipelines.Comment: 16 pages, 14 figures. MNRAS accepted. Typos corrected and computing
time/memory requirement orders-of-magnitude numbers in section 4 replaced by
precise number
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
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