1,359 research outputs found
Precision cosmology with redshift-space bispectrum: a perturbation theory based model at one-loop order
The large-scale matter distribution in the late-time Universe exhibits
gravity-induced non-Gaussianity, and the bispectrum, three-point cumulant is
expected to contain significant cosmological information. In particular, the
measurement of the bispectrum helps to tighten the constraints on dark energy
and modified gravity through the redshift-space distortions (RSD). In this
paper, extending the work by Taruya, Nishimichi & Saito (2010, Phys.Rev.D 82,
063522), we present a perturbation theory (PT) based model of redshift-space
matter bispectrum that can keep the non-perturbative damping effect under
control. Characterizing this non-perturbative damping by a univariate function
with single free parameter, the PT model of the redshift-space bispectrum is
tested against a large set of cosmological -body simulations, finding that
the predicted monopole and quadrupole moments are in a good agreement with
simulations at the scales of baryon acoustic oscillations (well beyond the
range of agreement of standard PT). The validity of the univariate ansatz of
the damping effect is also examined, and with the PT calculation at
next-to-leading order, the fitted values of the free parameter is shown to
consistently match those obtained from the PT model of power spectrum by
Taruya, Nishimichi & Saito (2010).Comment: 21 pages, 13 figure
Ab initio Study of Valley Line on a Total-Energy Surface for Zone-Center Distortions of Ferroelectric Perovskite Oxides BaTiO3 and PbTiO3
An ab initio structure optimization technique is newly developed to determine
the valley line on a total-energy surface for zone-center distortions of
ferroelectric perovskite oxides and is applied to barium titanate BaTiO3 and
lead titanate PbTiO3. The proposed technique is an improvement over King-Smith
and Vanderbilt's scheme [Phys. Rev. B 49, p.5828 (1994)] of evaluating total
energy as a function of the amplitude of atomic displacements. The results of
numerical calculations show that total energy can be expressed as a
fourth-order function of the amplitude of atomic displacements in BaTiO3 but
not in PbTiO3.Comment: 4 pages, 5 figure
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