arXiv subjects

Eric V. Linder

Publications and source records attributed to Eric V. Linder.

At least 163 records · Page 9Linked to original sources

arXiv2009

Testing Standard Cosmology with Large Scale Structure

The galaxy power spectrum contains information on the growth of structure, the growth rate through redshift space distortions, and the cosmic expansion through baryon acoustic oscillation features. We study the ability of two proposed experiments, BigBOSS and JDEM-PS, to test the cosmological model and general relativity. We quantify the latter result in terms of the gravitational growth index γ, whose value in general relativity is γ\approx 0.55. Significant deviations from this value could indicate new physics beyond the standard model of cosmology. The results show that BigBOSS (JDEM-PS) would be capable of measuring γwith an uncertainty σ(γ) = 0.043 (0.054), which tightens to σ(γ) = 0.031 (0.038) if we include Stage III data priors, marginalizing over neutrino mass, time varying dark energy equation of state, and other parameters. For all dark energy parameters and related figures of merit the two experiments give comparable results. We also carry out some studies of the influence of redshift range, resolution, treatment of nonlinearities, and bias evolution to enable further improvement.

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arXiv2009

Dark Energy Properties in DBI Theory

The Dirac-Born-Infeld (DBI) action from string theory provides several new classes of dark energy behavior beyond quintessence due to its relativistic kinematics. We constrain parameters of natural potentials and brane tensions with cosmological observations as well as showing how to design these functions for a desired expansion history. We enlarge the attractor solutions, including new ways of obtaining cosmological constant behavior, to the case of generalized DBI theory with multiple branes. An interesting novel signature of DBI attractors is that the sound speed is driven to zero, unlike for quintessence where it is the speed of light.

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arXiv2009

Aetherizing Lambda: Barotropic Fluids as Dark Energy

We examine the class of barotropic fluid models of dark energy, in which the pressure is an explicit function of the density, p = f(ρ). Through general physical considerations we constrain the asymptotic past and future behaviors and show that this class is equivalent to the sum of a cosmological constant and a decelerating perfect fluid, or "aether", with w_{AE}\ge0. Barotropic models give substantially disjoint predictions from quintessence, except in the limit of \LambdaCDM. They are also interesting in that they simultaneously can ameliorate the coincidence problem and yet "predict" a value of w\approx-1.

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arXiv2009

Cosmological Constant Behavior in DBI Theory

Cosmological constant behavior can be realized as solutions of the Dirac-Born-Infeld (DBI) action within Type IIB string theory and the AdS/CFT correspondence. We derive a family of attractor solutions to the cosmological constant that arise purely from the "relativistic" nature of the DBI action without an explicit false vacuum energy. We also find attractor solutions with values of the equation of state near but with $w\ne-1$; the forms for the potential arising from flux interactions are renormalizable and natural, and the D3-brane tension can be given by the standard throat form. We discuss present and future observational constraints on the theory.

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arXiv2009

CMB Lensing Constraints on Neutrinos and Dark Energy

Signatures of lensing of the cosmic microwave background radiation by gravitational potentials along the line of sight carry with them information on the matter distribution, neutrino masses, and dark energy properties. We examine the constraints that Planck, PolarBear, and CMBpol future data, including from the B-mode polarization or the lensing potential, will be able to place on these quantities. We simultaneously fit for neutrino mass and dark energy equation of state including time variation and early dark energy density, and compare the use of polarization power spectra with an optimal quadratic estimator of the lensing. Results are given as a function of systematics level from residual foreground contamination. A realistic CMBpol experiment can effectively constrain the sum of neutrino masses to within 0.05 eV and the fraction of early dark energy to 0.002. We also present a surprisingly simple prescription for calculating dark energy equation of state constraints in combination with supernova distances from JDEM.

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arXiv2009

Tainted Evidence: Cosmological Model Selection vs. Fitting

Interpretation of cosmological data to determine the number and values of parameters describing the universe must not rely solely on statistics but involve physical insight. When statistical techniques such as "model selection" or "integrated survey optimization" blindly apply Occam's Razor, this can lead to painful results. We emphasize that the sensitivity to prior probabilities and to the number of models compared can lead to "prior selection" rather than robust model selection. A concrete example demonstrates that Information Criteria can in fact misinform over a large region of parameter space.

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arXiv2009

Extending the Gravitational Growth Framework

The gravitational growth index formalism provides a model independent way to look for deviations from general relativity by testing dark energy physics distinct from its effects on the cosmic expansion history. Here we extend the approach to incorporate an early time parameter g_star in addition to the growth index in describing the growth of large scale structure. We illustrate its utility for models with modified gravity at high redshift, early acceleration, or early dark energy. Future data will have the capability to constrain the dark energy equation of state, the growth index gamma, and g_star simultaneously, with no degradation in the equation of state determination.

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arXiv2008

Being PC: Principal Components and Dark Energy

Principal component analysis is considered as an addition to the well-tested parametrization w(a)=w_0+w_a(1-a) for the dark energy equation of state. This brief note cautions against some unjustified assumptions in interpretation of PCA calculations, giving quantified examples.

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arXiv2008

Like vs. Like: Strategy and Improvements in Supernova Cosmology Systematics

Control of systematic uncertainties in the use of Type Ia supernovae as standardized distance indicators can be achieved through contrasting subsets of observationally-characterized, like supernovae. Essentially, like supernovae at different redshifts reveal the cosmology, and differing supernovae at the same redshift reveal systematics, including evolution not already corrected for by the standardization. Here we examine the strategy for use of empirically defined subsets to minimize the cosmological parameter risk, the quadratic sum of the parameter uncertainty and systematic bias. We investigate the optimal recognition of subsets within the sample and discuss some issues of observational requirements on accurately measuring subset properties. Neglecting like vs. like comparison (i.e. creating only a single Hubble diagram) can cause cosmological constraints on dark energy to be biased by 1σor degraded by a factor 1.6 for a total drift of 0.02 mag. Recognition of subsets at the 0.016 mag level (relative differences) erases bias and reduces the degradation to 2%.

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arXiv2008

Can Early Dark Energy be Detected in Non-Linear Structure?

We present the first study of early dark energy cosmologies using N-body simulations to investigate the formation of non-linear structure. In contrast to expectations from semi-analytic approaches, we find that early dark energy does not imprint a unique signature on the statistics of non-linear structures. Investigating the non-linear power spectra and halo mass functions, we show that universal mass functions hold for early dark energy, making its presence difficult to distinguish from $Λ$CDM. Since early dark energy biases the baryon acoustic oscillation scale, the lack of discriminating power is problematic.

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arXiv2008

Halo Mass Functions in Early Dark Energy Cosmologies

We examine the linear density contrast at collapse time, $δ_c$ for large-scale structure in dynamical dark energy cosmologies, including models with early dark energy. Contrary to previous results, we find that as long as dark energy is homogeneous on small scales, $δ_c$ is insensitive to dark energy properties for parameter values fitting current data, including the case of early dark energy. This is significant since using the correct $δ_c$ is crucial for accurate Press-Schechter prediction of the halo mass function. Previous results have found an apparent failing of the extended Press-Schechter approach (Sheth-Tormen) for early dark energy. Our calculations demonstrate that with the correct $δ_c$ the accuracy of this approach is restored. We discuss the significance of this result for the halo mass function and examine what dark energy physics would be needed to cause significant change in $δ_c$, and the observational signatures this would leave.

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arXiv2008

A Cosmic Vision Beyond Einstein

The acceleration of the cosmic expansion is a fundamental challenge to standard models of particle physics and cosmology. The new physics of dark energy may lie in the nature of gravity, the quantum vacuum, or extra dimensions. I give a brief overview of the puzzles and possibilities of dark energy, and discuss the confrontation of a wide variety of "beyond Einstein" models with the latest data, showing what we currently know and what we must seek to learn. Next generation experiments using a variety of cosmological probes will deeply explore dark energy, dark matter, and gravitation.

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arXiv2008

Calibrating Dark Energy

Exploring the diversity of dark energy dynamics, we discover a calibration relation, a uniform stretching of the amplitude of the equation of state time variation with scale factor. This defines homogeneous families of dark energy physics. The calibration factor has a close relation to the standard time variation parameter w_a, and we show that the new, calibrated w_a describes observables, i.e. distance and Hubble parameter as a function of redshift, typically to an accuracy level of 10^{-3}. We discuss implications for figures of merit for dark energy science programs.

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arXiv2008

Field Flows of Dark Energy

Scalar field dark energy evolving from a long radiation- or matter-dominated epoch has characteristic dynamics. While slow-roll approximations are invalid, a well defined field expansion captures the key aspects of the dark energy evolution during much of the matter-dominated epoch. Since this behavior is determined, it is not faithfully represented if priors for dynamical quantities are chosen at random. We demonstrate these features for both thawing and freezing fields, and for some modified gravity models, and unify several special cases in the literature.

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arXiv2008

Shifting the Universe: Early Dark Energy and Standard Rulers

The presence of dark energy at high redshift influences both the cosmic sound horizon and the distance to last scattering of the cosmic microwave background. We demonstrate that through the degeneracy in their ratio, early dark energy can lie hidden in the CMB temperature and polarization spectra, leading to an unrecognized shift in the sound horizon. If the sound horizon is then used as a standard ruler, as in baryon acoustic oscillations, then the derived cosmological parameters can be nontrivially biased. Fitting for the absolute ruler scale (just as supernovae must be fit for the absolute candle magnitude) removes the bias but decreases the leverage of the BAO technique by a factor 2.

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arXiv2008

Gravitational Wave Sirens as a Triple Probe of Dark Energy

Gravitational wave standard sirens have been considered as precision distance indicators to high redshift; however, at high redshift standard sirens or standard candles such as supernovae suffer from lensing noise. We investigate lensing noise as a signal instead and show how measurements of the maximum demagnification (minimum convergence) probe cosmology in a highly complementary manner to the distance itself. Revisiting the original form for minimum convergence we quantify the bias arising from the commonly used approximation. Furthermore, after presenting a new lensing probability function we discuss how the width of the lensed standard siren amplitude distribution also probes growth of structure. Thus standard sirens and candles can serve as triple probes of dark energy, measuring both the cosmic expansion history and growth history.

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arXiv2008

Mapping the Cosmological Expansion

The ability to map the cosmological expansion has developed enormously, spurred by the turning point one decade ago of the discovery of cosmic acceleration. The standard model of cosmology has shifted from a matter dominated, standard gravity, decelerating expansion to the present search for the origin of acceleration in the cosmic expansion. We present a wide ranging review of the tools, challenges, and physical interpretations. The tools include direct measures of cosmic scales through Type Ia supernova luminosity distances, and angular distance scales of baryon acoustic oscillation and cosmic microwave background density perturbations, as well as indirect probes such as the effect of cosmic expansion on the growth of matter density fluctuations. Accurate mapping of the expansion requires understanding of systematic uncertainties in both the measurements and the theoretical framework, but the result will give important clues to the nature of the physics behind accelerating expansion and to the fate of the universe.

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arXiv2007

To Bin or Not To Bin: Decorrelating the Cosmic Equation of State

The physics behind the acceleration of the cosmic expansion can be elucidated through comparison of the predictions of dark energy equations of state to observational data. In seeking to optimize this, we investigate the advantages and disadvantages of using principal component analysis, uncorrelated bandpowers, and the equation of state within redshift bins. We demonstrate that no one technique is a panacea, with tension between clear physical interpretation from localization and from decorrelated errors, as well as model dependence and form dependence. Specific lessons include the critical role of proper treatment of the high redshift expansion history and the lack of a unique, well defined signal-to-noise or figure of merit.

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