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Alizadeh E.,University of Illinois at Urbana - Champaign | Hirata C.M.,Caltech M C 350 17
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The advent of precise measurements of the CMB anisotropies has motivated correspondingly precise calculations of the cosmic recombination history. Cosmic recombination proceeds far out of equilibrium because of a " bottleneck" at the n=2 level of hydrogen: atoms can only reach the ground state via slow processes-two-photon decay or Lyman-α resonance escape. However, even a small primordial abundance of molecules could have a large effect on the interline opacity in the recombination epoch and lead to an additional route for hydrogen recombination. Therefore, this paper computes the abundance of the H2 molecule during the cosmic recombination epoch. Hydrogen molecules in the ground electronic levels X1Σg+ can either form from the excited H2 electronic levels B1Σu+ and C1Πu or through the charged particles H2+, HeH+, and H-. We follow the transitions among all of these species, resolving the rotational and vibrational sublevels. Since the energies of the X1Σg+-B1Σu+ (Lyman band) and X1Σg+-C1Πu (Werner band) transitions are near the Lyman-α energy, the distortion of the CMB spectrum caused by escaped H Lyman-line photons accelerates both the formation and the destruction of H2 due to this channel relative to the thermal rates. This causes the populations of H2 molecules in X1Σg+ energy levels to deviate from their thermal equilibrium abundances. We find that the resulting H2 abundance is 10-17 at z=1200 and 10 -13 at z=800, which is too small to have any significant influence on the recombination history. © 2011 American Physical Society.


Tseliakhovich D.,Caltech M C 350 17 | Hirata C.,Caltech M C 350 17 | Slosar A.,Brookhaven National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Single-field inflationary models predict nearly Gaussian initial conditions, and hence a detection of non-Gaussianity would be a signature of the more complex inflationary scenarios. In this paper we study the effect on the cosmic microwave background and on large-scale structure from primordial non-Gaussianity in a two-field inflationary model in which both the inflaton and curvaton contribute to the density perturbations. We show that in addition to the previously described enhancement of the galaxy bias on large scales, this setup results in large-scale stochasticity. We provide joint constraints on the local non-Gaussianity parameter f∼NL and the ratio ξ of the amplitude of primordial perturbations due to the inflaton and curvaton using WMAP and Sloan Digital Sky Survey data. © 2010 The American Physical Society.


Cohn J.D.,University of California at Berkeley | White M.,University of California at Berkeley | White M.,Lawrence Berkeley National Laboratory | Chang T.-C.,Academia Sinica, Taiwan | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Acoustic waves travelling through the early Universe imprint a characteristic scale in the clustering of galaxies, QSOs and intergalactic gas. This scale can be used as a standard ruler to map the expansion history of the Universe, a technique known as baryon acoustic oscillations (BAO). BAO offer a high-precision, low-systematics means of constraining our cosmological model. The statistical power of BAO measurements can be improved if the 'smearing' of the acoustic feature by non-linear structure formation is undone in a process known as reconstruction. In this paper, we use low-order Lagrangian perturbation theory to study the ability of 21-cm experiments to perform reconstruction and how augmenting these surveys with galaxy redshift surveys at relatively low number densities can improve performance. We find that the critical number density which must be achieved in order to benefit 21-cm surveys is set by the linear theory power spectrum near its peak, and corresponds to densities achievable by upcoming surveys of emission line galaxies such as eBOSS and DESI. As part of this work, we analyse reconstruction within the framework of Lagrangian perturbation theory with local Lagrangian bias, redshift-space distortions, k-dependent noise and anisotropic filtering schemes. © 2016 The Authors.


Krause E.,Caltech M C 350 17 | Hirata C.M.,Caltech M C 350 17
Astronomy and Astrophysics | Year: 2010

It is usually assumed that the ellipticity power spectrum measured in weak lensing observations can be expressed as an integral over the underlying matter power spectrum. This is true at order O(Φ2) in the gravitational potential. We extend the standard calculation, constructing all corrections to order (Φ4). There are four types of corrections: corrections to the lensing shear due to multiple-deflections; corrections due to the fact that shape distortions probe the reduced shear γ/(1-κ) rather than the shear itself; corrections associated with the non-linear conversion of reduced shear to mean ellipticity; and corrections due to the fact that observational galaxy selection and shear measurement is based on galaxy brightnesses and sizes which have been (de)magnified by lensing. We show how the previously considered corrections to the shear power spectrum correspond to terms in our analysis, and highlight new terms that were not previously identified. All correction terms are given explicitly as integrals over the matter power spectrum, bispectrum, and trispectrum, and are numerically evaluated for the case of sources at z = 1. We find agreement with previous works for the O(Φ3) terms. We find that for ambitious future surveys, the OΦ4) terms affect the power spectrum at the ∼ 1-5σ level; they will thus need to be accounted for, but are unlikely to represent a serious difficulty for weak lensing as a cosmological probe. © 2010 ESO.


Hirata C.M.,Caltech M C 350 17
Monthly Notices of the Royal Astronomical Society | Year: 2011

Lindblad resonances have been suggested as an important mechanism for angular momentum transport and heating in discs in binary black hole systems. We present the basic equations for the torque and heating rate for relativistic thin discs subjected to a perturbation. The Lindblad resonance torque is written explicitly in terms of metric perturbations for an equatorial disc in a general axisymmetric, time-stationary space-time with a plane of symmetry. We show that the resulting torque formula is gauge-invariant. Computations for the Schwarzschild and Kerr space-times are presented in the companion paper (Paper II). © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Hirata C.M.,Caltech M C 350 17
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present a fully relativistic computation of the torques due to Lindblad resonances from perturbers on circular, equatorial orbits on discs around Schwarzschild and Kerr black holes. The computation proceeds by establishing a relation between the Lindblad torques and the gravitational waveforms emitted by the perturber and a test particle in a slightly eccentric orbit at the radius of the Lindblad resonance. We show that our result reduces to the usual formula when taking the non-relativistic limit. Discs around a black hole possess an m= 1 inner Lindblad resonance (ILR) with no Newtonian-Keplerian analogue; however, its strength is very weak even in the moderately relativistic regime (r/M∼ few tens), which is in part due to the partial cancellation of the two leading contributions to the resonant amplitude (the gravitoelectric octupole and gravitomagnetic quadrupole). For equatorial orbits around Kerr black holes, we find that the m= 1 ILR strength is enhanced for retrograde spins and suppressed for prograde spins. We also find that the torque associated with the m≥ 2 ILRs is enhanced relative to the non-relativistic case; the enhancement is a factor of 2 for the Schwarzschild hole even when the perturber is at a radius of 25M. © 2011 The Author Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Hirata C.M.,Caltech M C 350 17
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

The inspiral and merger of a binary black hole system generally leads to an asymmetric distribution of emitted radiation, and hence a recoil of the remnant black hole directed opposite to the net linear momentum radiated. The recoil velocity is generally largest for comparable mass black holes and particular spin configurations, and approaches zero in the extreme mass ratio limit. It is generally believed that for extreme mass ratios η1, the scaling of the recoil velocity is |V|η2, where the proportionality coefficient depends on the spin of the larger hole and the geometry of the system (e.g. orbital inclination). The small recoil velocity is due to cancellations; while the fraction of the total binary mass radiated away in gravitational waves is O(η), most of this energy is emitted during the inspiral phase where the momentum radiated integrates to zero over an orbit. Here, we show that for low but nonzero inclination prograde orbits and very rapidly spinning large holes (spin parameter a∞>0.9678) the inspiralling binary can pass through resonances where the orbit-averaged radiation-reaction force is nonzero. These resonance crossings lead to a new contribution to the kick, |V| η3/2. For these configurations and sufficiently extreme mass ratios, this resonant recoil is dominant. While it seems doubtful that the resonant recoil will be astrophysically significant, its existence suggests caution when extrapolating the results of numerical kick results to extreme mass ratios and near-maximal spins. © 2011 American Physical Society.


Hirata C.M.,Caltech M C 350 17 | Holz D.E.,Los Alamos National Laboratory | Cutler C.,Jet Propulsion Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Gravitational wave sources are a promising cosmological standard candle because their intrinsic luminosities are determined by fundamental physics (and are insensitive to dust extinction). They are, however, affected by weak lensing magnification due to the gravitational lensing from structures along the line of sight. This lensing is a source of uncertainty in the distance determination, even in the limit of perfect standard candle measurements. It is commonly believed that the uncertainty in the distance to an ensemble of gravitational wave sources is limited by the standard deviation of the lensing magnification distribution divided by the square root of the number of sources. Here we show that by exploiting the non-Gaussian nature of the lensing magnification distribution, we can improve this distance determination, typically by a factor of 2-3; we provide a fitting formula for the effective distance accuracy as a function of redshift for sources where the lensing noise dominates. © 2010 The American Physical Society.

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