arXiv subjects

Donghui Jeong

Publications and source records attributed to Donghui Jeong.

116 records · Page 7Linked to original sources

arXiv2009

Galaxy-CMB and galaxy-galaxy lensing on large scales: sensitivity to primordial non-Gaussianity

A convincing detection of primordial non-Gaussianity in the local form of the bispectrum, whose amplitude is given by the fNL parameter, offers a powerful test of inflation. In this paper we calculate the modification of two-point cross-correlation statistics of weak lensing - galaxy-galaxy lensing and galaxy-Cosmic Microwave Background (CMB) cross-correlation - due to fNL. We derive and calculate the covariance matrix of galaxy-galaxy lensing including cosmic variance terms. We focus on large scales (l<100) for which the shape noise of the shear measurement becomes irrelevant and cosmic variance dominates the error budget. For a modest degree of non-Gaussianity, fNL=+/-50, modifications of the galaxy-galaxy lensing signal at the 10% level are seen on scales R~300 Mpc, and grow rapidly toward larger scales as \propto R^2. We also see a clear signature of the baryonic acoustic oscillation feature in the matter power spectrum at ~150 Mpc, which can be measured by next-generation lensing experiments. In addition we can probe the local-form primordial non-Gaussianity in the galaxy-CMB lensing signal by correlating the lensing potential reconstructed from CMB with high-z galaxies. For example, for fNL=+/-50, we find that the galaxy-CMB lensing cross power spectrum is modified by ~10% at l~40, and by a factor of two at l~10, for a population of galaxies at z=2 with a bias of 2. The effect is greater for more highly biased populations at larger z; thus, high-z galaxy surveys cross-correlated with CMB offer a yet another probe of primordial non-Gaussianity.

astro-ph.CO↗

arXiv2009

Infrared divergence of pure Einstein gravity contributions to cosmological density power spectrum

We probe the pure Einstein's gravity contributions to the second-order density power spectrum. In the small-scale, we discover that the Einstein's gravity contribution is negligibly small. This guarantees that Newton's gravity is sufficient to handle the baryon acoustic oscillation scale. In the large scale, however, we discover that the Einstein's gravity contribution to the second-order power spectrum dominates the linear-order power spectrum. Thus, pure Einstein gravity contribution appearing in the third-order perturbation leads to an infrared divergence in the power spectrum.

astro-ph.CO↗

arXiv2009

Primordial non-Gaussianity, scale-dependent bias, and the bispectrum of galaxies

We calculate the bispectrum, B_g(k_1,k_2,k_3), Fourier transform of the three-point function of density peaks (e.g., galaxies), using two different methods: the Matarrese-Lucchin-Bonometto formula and the locality of galaxy bias. The bispectrum of peaks is not only sensitive to that of the underlying matter density fluctuations, but also to the four-point function. For a physically-motivated, local form of primordial non-Gaussianity in the curvature perturbation, we show that the galaxy bispectrum contains five physically distinct pieces: (i) non-linear gravitational evolution, (ii) non-linear galaxy bias, (iii) f_nl, (iv) f_nl^2, and (v) \gnl. While (i), (ii), and a part of (iii) have been derived in the literature, (iv) and (v) are derived in this paper for the first time. Our finding suggests that the galaxy bispectrum is more sensitive to f_nl than previously recognized, and is also sensitive to a new term, g_nl. For a more general form of local-type non-Gaussianity, the coefficient \fnl^2 can be interpreted as τ_nl, which allows us to test multi-field inflation models. The usual terms from Gaussian initial conditions, have the smallest signals in the squeezed configurations, while the others have the largest signals; thus, we can distinguish them easily. We cannot interpret the effects of f_nl on B_g(k_1,k_2,k_3) as a scale-dependent bias, and thus replacing the linear bias in the galaxy bispectrum with the scale-dependent bias known for the power spectrum results in an incorrect prediction. As the importance of primordial non-Gaussianity relative to the non-linear gravity evolution and galaxy bias increases toward higher redshifts, galaxy surveys probing a high-redshift universe are particularly useful for probing the primordial non-Gaussianity.

astro-ph.CO↗

arXiv2009

Evolution of the curvature perturbation during and after multi-field inflation

We study the evolution of the curvature perturbation on the super-horizon scales starting from the inflationary epoch until there remains only a single dynamical degree of freedom, presureless matter, in the universe. We consider the cosmic inflation driven by a multiple number of the inflaton fields, which decay into both radiation and pressureless matter components. We present a complete set of the exact background and perturbation equations which describe the evolution of the universe throughout its history. By applying these equations to the simple but reasonable model of multi-field chaotic inflation, we explicitly show that the total curvature perturbation is continuously varying because of the non-adiabatic components of the curvature perturbation generated by the multiple inflaton fields throughout the whole evolution of the universe. We also provide an useful analytic estimation of the total as well as matter and radiation curvature perturbations, assuming that matter is completely decoupled from radiation from the beginning. The resulting isocurvature perturbation between matter and radiation is at most sub-percent level when the masses of the inflaton fields are distributed between $10^{-6}m_{pl}$ and $10^{-5}m_{pl}$. We find that this result is robust unless we use non-trivial decay rates, and that thus, in general, it is hard to obtain large matter-radiation isocurvature perturbation. Also, by using the $δ{N}$ formalism, we point out that the inflationary calculation, especially when involving multiple inflaton fields, is likely to lose the potentially important post-inflationary evolution which can modify the resulting curvature perturbation.

hep-ph↗

arXiv2008

Extracting Angular Diameter Distance and Expansion Rate of the Universe from Two-dimensional Galaxy Power Spectrum at High Redshifts: Baryon Acoustic Oscillation Fitting versus Full Modeling

We present a method for extracting the angular diameter distances, $D_A$, and the expansion rates, $H$, of the universe from the {\it two-dimensional} Baryon Acoustic Oscillations (BAO) in the galaxy power spectrum. Our method builds upon the existing algorithm called the "fit-and-extract" (FITEX) method, which allows one to extract only $D_A^2/H$ from a spherically averaged one-dimensional power spectrum. We develop the FITEX-2d method, an extension of the FITEX method, to include the two-dimensional information, which allows us to extract $D_A$ and $H$ simultaneously. We test the FITEX-2d method using the Millennium Simulation as well as simplified Monte Carlo simulations with a bigger volume. The BAOs, however, contain only a limited amount of information. We show that the full modeling, including the overall shape of the power spectrum, yields much better determinations of $D_A$ and $H$, hence the dark energy equation of state parameters such as $w_0$ and $w_a$, than the BAO-only analysis by more than a factor of two, provided that non-linear effects are under control.

astro-ph↗

arXiv2008

Perturbation Theory Reloaded II: Non-linear Bias, Baryon Acoustic Oscillations and Millennium Simulation In Real Space

We calculate the non-linear galaxy power spectrum in real space, including non-linear distortion of the Baryon Acoustic Oscillations, using the standard 3rd-order perturbation theory (PT). The calculation is based upon the assumption that the number density of galaxies is a local function of the underlying, non-linear density field. The galaxy bias is allowed to be both non-linear and stochastic. We show that the PT calculation agrees with the galaxy power spectrum estimated from the Millennium Simulation, in the weakly non-linear regime (defined by the matter power spectrum) at high redshifts, $1\le z\le6$. We also show that, once 3 free parameters characterizing galaxy bias are marginalized over, the PT power spectrum fit to the Millennium Simulation data yields unbiased estimates of the distance scale, $D$, to within the statistical error. This distance scale corresponds to the angular diameter distance, $D_A(z)$, and the expansion rate, $H(z)$, in real galaxy surveys. Our results presented in this paper are still restricted to real space. The future work should include the effects of non-linear redshift space distortion. Nevertheless, our results indicate that non-linear galaxy bias in the weakly non-linear regime at high redshifts is reasonably under control.

astro-ph↗

arXiv2006

Perturbation Theory Reloaded: Analytical Calculation of Non-linearity in Baryonic Oscillations in the Real Space Matter Power Spectrum

We compare the non-linear matter power spectrum in real space calculated analytically from 3rd-order perturbation theory with N-body simulations at 1 1, the shape of oscillations is distorted from the linear theory prediction. Nevertheless, our results suggest that one can correct the distortion caused by non-linearity almost exactly. We also find that perturbation theory, which does not contain any free parameters, provides a significantly better fit to the simulations than the conventional approaches based on empirical fitting functions to simulations. The future work would include perturbation theory calculations of non-linearity in redshift space distortion and halo biasing in the weakly non-linear regime.

astro-ph↗

arXiv2004

Modular Cosmology, Thermal Inflation, Baryogenesis and Predictions for Particle Accelerators

Modular cosmology is plagued by overproduction of unwanted relics, gravitinos and especially moduli, at relatively low energy scales. Thermal inflation provides a compelling solution to this moduli problem, but invalidates most baryogenesis scenarios. We propose a simple model in which the MSSM plus neutrino mass term $(LH_u)^2$ is supplemented by a minimal flaton sector to drive the thermal inflation, and make two crucial assumptions: the flaton vacuum expectation value generates the $μ$-term of the MSSM and $m_L^2 + m_{H_u}^2 < 0$. The second assumption is particularly interesting in that it violates a well known constraint, implying that there exists a nearby deep non-MSSM vacuum, and provides a clear signature of our model which can be tested at future particle accelerators. We show that our model leads to thermal inflation followed by Affleck-Dine leptogenensis along the $LH_u$ flat direction. A key feature of our leptogenesis scenario is that the $H_uH_d$ flat direction is also induced to temporarily acquire a large value, playing a crucial role in the leptogenesis, as well as dynamically shielding the field configuration from the deep non-MSSM minimum, ensuring that the fields relax into our MSSM vacuum.

hep-ph↗