1,154 research outputs found
Genetically modified haloes: towards controlled experiments in ÎCDM galaxy formation
We propose a method to generate âgenetically modifiedâ (GM) initial conditions for high-resolution simulations of galaxy formation in a cosmological context. Building on the HoffmanâRibak algorithm, we start from a reference simulation with fully random initial conditions, then make controlled changes to specific properties of a single halo (such as its mass and merger history). The algorithm demonstrably makes minimal changes to other properties of the halo and its environment, allowing us to isolate the impact of a given modification. As a significant improvement over previous work, we are able to calculate the abundance of the resulting objects relative to the reference simulation. Our approach can be applied to a wide range of cosmic structures and epochs; here we study two problems as a proof of concept. First, we investigate the change in density profile and concentration as the collapse times of three individual haloes are varied at fixed final mass, showing good agreement with previous statistical studies using large simulation suites. Secondly, we modify the z = 0 mass of haloes to show that our theoretical abundance calculations correctly recover the halo mass function. The results demonstrate that the technique is robust, opening the way to controlled experiments in galaxy formation using hydrodynamic zoom simulations
Inverted initial conditions: Exploring the growth of cosmic structure and voids
We introduce and explore "paired" cosmological simulations. A pair consists of an A and B simulation
with initial conditions related by the inversion ÎŽAĂ°x; tinitialĂ ÂŒ âÎŽBĂ°x; tinitialĂ (underdensities substituted for overdensities and vice versa). We argue that the technique is valuable for improving our understanding of
cosmic structure formation. The A and B fields are by definition equally likely draws from ÎCDM initial
conditions, and in the linear regime evolve identically up to the overall sign. As nonlinear evolution takes
hold, a region that collapses to form a halo in simulation A will tend to expand to create a void in simulation
B. Applications include (i) contrasting the growth of A-halos and B-voids to test excursion-set theories of
structure formation, (ii) cross-correlating the density field of the A and B universes as a novel test for
perturbation theory, and (iii) canceling error terms by averaging power spectra between the two boxes.
Generalizations of the method to more elaborate field transformations are suggested
Cosmological Constraints on Dissipative Models of Inflation
(Abridged) We study dissipative inflation in the regime where the dissipative
term takes a specific form, \Gamma=\Gamma(\phi), analyzing two models in the
weak and strong dissipative regimes with a SUSY breaking potential. After
developing intuition about the predictions from these models through analytic
approximations, we compute the predicted cosmological observables through full
numerical evolution of the equations of motion, relating the mass scale and
scale of dissipation to the characteristic amplitude and shape of the
primordial power spectrum. We then use Markov Chain Monte Carlo techniques to
constrain a subset of the models with cosmological data from the cosmic
microwave background (WMAP three-year data) and large scale structure (SDSS
Luminous Red Galaxy power spectrum). We find that the posterior distributions
of the dissipative parameters are highly non-Gaussian and their allowed ranges
agree well with the expectations obtained using analytic approximations. In the
weak regime, only the mass scale is tightly constrained; conversely, in the
strong regime, only the dissipative coefficient is tightly constrained. A lower
limit is seen on the inflation scale: a sub-Planckian inflaton is disfavoured
by the data. In both weak and strong regimes, we reconstruct the limits on the
primordial power spectrum and show that these models prefer a {\it red}
spectrum, with no significant running of the index. We calculate the reheat
temperature and show that the gravitino problem can be overcome with large
dissipation, which in turn leads to large levels of non-Gaussianity: if
dissipative inflation is to evade the gravitino problem, the predicted level of
non-Gaussianity might be seen by the Planck satellite.Comment: 14 pages, 9 figures, Accepted by JCAP without text changes,
References adde
Tachyon warm inflationary universe models
Warm inflationary universe models in a tachyon field theory are studied.
General conditions required for these models to be realizable are derived and
discussed. We describe scalar perturbations (in the longitudinal gauge) and
tensor perturbations for these scenarios. We develop our models for a constant
dissipation parameter in one case and one dependent on in the
other case. We have been successful in describing such of inflationary universe
models. We use recent astronomical observations for constraining the parameters
appearing in our model. Also, our results are compared with their analogous
found in the cool inflationary case.Comment: 21 pages, Accepted by JCA
Quantum corrections to the inflaton potential and the power spectra from superhorizon modes and trace anomalies
We obtain the effective inflaton potential during slow roll inflation by
including the one loop quantum corrections to the energy momentum tensor from
scalar curvature and tensor perturbations as well as quantum fluctuations from
light scalars and light Dirac fermions generically coupled to the inflaton.
During slow roll inflation there is a clean and unambiguous separation between
superhorizon and subhorizon contributions to the energy momentum tensor. The
superhorizon part is determined by the curvature perturbations and scalar field
fluctuations: both feature infrared enhancements as the inverse of a
combination of slow roll parameters which measure the departure from scale
invariance in each case.Fermions and gravitons do not exhibit infrared
divergences. The subhorizon part is completely specified by the trace anomaly
of the fields with different spins and is solely determined by the space-time
geometry. The one-loop quantum corrections to the amplitude of curvature and
tensor perturbations are obtained to leading order in slow-roll and in the
(H/M_PL)^2 expansion. This study provides a complete assessment of the
backreaction problem up to one loop including bosonic and fermionic degrees of
freedom. The result validates the effective field theory description of
inflation and confirms the robustness of the inflationary paradigm to quantum
fluctuations. Quantum corrections to the power spectra are expressed in terms
of the CMB observables:n_s, r and dn_s/dln k. Trace anomalies (especially the
graviton part) dominate these quantum corrections in a definite direction: they
enhance the scalar curvature fluctuations and reduce the tensor fluctuations.Comment: 18 pages, no figure
Constraining Inflation
Slow roll reconstruction is derived from the Hamilton-Jacobi formulation of
inflationary dynamics. It automatically includes information from sub-leading
terms in slow roll, and facilitatesthe inclusion of priors based on the
duration on inflation. We show that at low inflationary scales the
Hamilton-Jacobi equations simplify considerably. We provide a new
classification scheme for inflationary models, based solely on the number of
parameters needed to specify the potential, and provide forecasts for likely
bounds on the slow roll parameters from future datasets. A minimal running of
the spectral index, induced solely by the first two slow roll parameters
(\epsilon and \eta) appears to be effectively undetectable by realistic Cosmic
Microwave Background experiments. However, we show that the ability to detect
this signal increases with the lever arm in comoving wavenumber, and we
conjecture that high redshift 21 cm data may allow tests of second order
consistency conditions on inflation. Finally, we point out that the second
order corrections to the spectral index are correlated with the inflationary
scale, and thus the amplitude of the CMB B-mode.Comment: 32 pages. v
Extended Curvaton reheating in inflationary models
The curvaton reheating in a non-oscillatory inflationary universe model is
studied in a Jordan-Brans-Dicke theory. For different scenarios, the
temperature of reheating is computed. The result tells us that the reheating
temperature becomes practically independent of the Jordan-Brans-Dicke parameter
. This reheating temperature results to be quite different when compared
with that obtained from Einstein`s theory of gravity.Comment: Accepted by JCAP, 12 pages, 1 Figur
Cross-Correlation Detection of Point Sources in WMAP First Year Data
We apply a Cross-correlation (CC) method developed previously for detecting
gamma-ray point sources to the WMAP first year data by using the Point-Spread
Function of WMAP and obtain a full sky CC coefficient map. Analyzing this map,
we find that the CC method is a powerful tool to examine the WMAP foreground
residuals which can be further cleaned accordingly. Evident foreground signals
are found in WMAP foreground cleaned maps and Tegmark cleaned map. In this
process 101 point-sources are detected, and 26 of them are new sources besides
the originally listed WMAP 208 sources. We estimate the flux of these new
sources and verify them by another method. As a result, a revised mask file
based on the WMAP first year data is produced by including these new sources.Comment: 14 pages, 10 figures; accepted for publication by ChJA
High order correlation functions for self interacting scalar field in de Sitter space
We present the expressions of the three- and four-point correlation functions
of a self interacting light scalar field in a de Sitter spacetime at tree order
respectively for a cubic and a quartic potential. Exact expressions are derived
and their limiting behaviour on super-horizon scales are presented. Their
essential features are shown to be similar to those obtained in a classical
approach.Comment: 8 pages, 4 figure
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