19 research outputs found
The kinematic dipole in galaxy redshift surveys
In the concordance model of the Universe, the matter distribution - as
observed in galaxy number counts or the intensity of line emission (such as the
21cm line of neutral hydrogen) - should have a kinematic dipole due to the
Sun's motion relative to the CMB rest-frame. This dipole should be aligned with
the kinematic dipole in the CMB temperature. Accurate measurement of the
direction of the matter dipole will become possible with future galaxy surveys,
and this will be a critical test of the foundations of the concordance model.
The amplitude of the matter dipole is also a potential cosmological probe. We
derive formulas for the amplitude of the kinematic dipole in galaxy redshift
and intensity mapping surveys, taking into account the Doppler, aberration and
other relativistic effects. The amplitude of the matter dipole can be
significantly larger than that of the CMB dipole. Its redshift dependence
encodes information on the evolution of the Universe and on the tracers, and we
discuss possible ways to determine the amplitude.Comment: 10 pages, 5 figures. To appear in JCA
The observed galaxy bispectrum from single-field inflation in the squeezed limit
Using the consistency relation in Fourier space, we derive the observed galaxy bispectrum from
single- eld in
ation in the squeezed limit, in which one of the three modes has a wavelength much
longer than the other two. This provides a non-trivial check of the full computation of the bispectrum
based on second-order cosmological perturbation theory in this limit. We show that gauge modes
need to be carefully removed in the second-order cosmological perturbations in order to calculate
the observed galaxy bispectrum in the squeezed limit. We then give an estimate of the e ective non-
Gaussianity due to general-relativistic lightcone e ects that could mimic a primordial non-Gaussian
signal
Variable sound speed in interacting dark energy models
We consider a self-consistent and physical approach to interacting dark
energy models described by a Lagrangian, and identify a new class of models
with variable dark energy sound speed. We show that if the interaction between
dark energy in the form of quintessence and cold dark matter is purely momentum
exchange this generally leads to a dark energy sound speed that deviates from
unity. Choosing a specific sub-case, we study its phenomenology by
investigating the effects of the interaction on the cosmic microwave background
and linear matter power spectrum. We also perform a global fitting of
cosmological parameters using CMB data, and compare our findings to
CDM.Comment: 19 pages, 8 figures, 1 tables; version accepted by JCA