Joint Dark Energy Mission Research Articles

Power law cosmology in modified theory with thermodynamics analysis

We study a model in f(R,G) gravity described as a linear combination of R and an exponential function of G. We constrain the dependent parameters H0 and the deceleration parameter q using the latest 77 points of the OHD data, 1395 points of the Pantheon, Gamma Ray Burst, Gold data (PGG) and the joint data OHD+PGG and compare the results with the ΛCDM. Also, we speculate constraints using a simulated data set for the future JDEM (Joint Dark Energy Mission)/Omega, supernovae survey. We see that our results in power law cosmology are a better fit with the PGG data than the earlier analysis (Kumar, 2012; Rani, 2015). However, the constraints obtained on H average, <H0> and q average, <q> using the simulated data set for the future JDEM/Omega, supernovae survey are found to be inconsistent with the values obtained from the OHD and the PGG data. Additionally, we discuss statefinder diagnostics and see that the power law models approach the standard ΛCDM model (q→−1). This model satisfies the Generalized Second Law of Thermodynamics. Finally, we conclude that the power law cosmology in f(R,G) gravity explains most of the distinguished attributes of evolution in cosmology.

Constraining thawing quintessence

We look at observational constraints on the thawing class of scalar field models proposed to explain the late time acceleration of the universe. Using the recently introduced `Statefinder Hierarchy', we compare these thawing class of models with other widely studied dark energy (and modified gravity) models to check the underlying parameter degeneracies. We put constraints on the deviations of these thawing models from the canonical \Lambda CDM model using a large class of observational data, e.g, the Supernova Type Ia data, the BAO data, the CMB data and data from the measurements of the Hubble parameter using red-envelope galaxies. We also forecast constraints using a simulated dataset for the future JDEM SNe survey. Our study shows that, although with current data it is difficult to distinguish different thawing models from \Lambda CDM, a future JDEM like mission would be able tell apart thawing models from \Lambda CDM for currently acceptable values of \Omega_{m0}

Probing dark energy dynamics from current and future cosmological observations

We report the constraints on the dark energy equation-of-state $w(z)$ using the latest ``Constitution'' SNe sample combined with the WMAP5 and Sloan Digital Sky Survey data. Assuming a flat Universe, and utilizing the localized principal component analysis and the model selection criteria, we find that the $\ensuremath{\Lambda}\mathrm{CDM}$ model is generally consistent with the current data, yet there exists a weak hint of the possible dynamics of dark energy. In particular, a model predicting $w(z)&lt;\ensuremath{-}1$ at $z\ensuremath{\in}[0.25,0.5)$ and $w(z)&gt;\ensuremath{-}1$ at $z\ensuremath{\in}[0.5,0.75)$, which means that $w(z)$ crosses $\ensuremath{-}1$ in the range of $z\ensuremath{\in}[0.25,0.75)$, is mildly favored at 95% confidence level. Given the best fit model for current data as a fiducial model, we make future forecast from the joint data sets of Joint Dark Energy Mission, Planck, and Large Synoptic Survey Telescope, and we find that the future surveys can reduce the error bars on the $w$ bins by roughly a factor of 10 for a 5-$w$-bin model.

No evidence for dark energy dynamics from a global analysis of cosmological data

We use a variant of principal component analysis to investigate the possible temporal evolution of the dark energy equation of state, w(z). We constrain w(z) in multiple redshift bins, utilizing the most recent data from Type Ia supernovae, the cosmic microwave background, baryon acoustic oscillations, the integrated Sachs-Wolfe effect, galaxy clustering, and weak lensing data. Unlike other recent analyses, we find no significant evidence for evolving dark energy; the data remains completely consistent with a cosmological constant. We also study the extent to which the time-evolution of the equation of state would be constrained by a combination of current- and future-generation surveys, such as Planck and the Joint Dark Energy Mission.

Constraining dark energy with clusters: Complementarity with other probes

The Figure of Merit Science Working Group recently forecast the constraints on dark energy that will be achieved prior to the Joint Dark Energy Mission by ground-based experiments that exploit baryon acoustic oscillations, type Ia supernovae, and weak gravitational lensing. We show that cluster counts from ongoing and near-future surveys should provide robust, complementary dark energy constraints. In particular, we find that optimally combined optical and Sunyaev-Zel'dovich effect cluster surveys should improve the Dark Energy Task Force figure of merit for pre-Joint Dark Energy Mission projects by a factor of 2 even without prior knowledge of the nuisance parameters in the cluster mass-observable relation. Comparable improvements are achieved in the forecast precision of parameters specifying the principal component description of the dark energy equation of state parameter, as well as in the growth index $\ensuremath{\gamma}$. These results indicate that cluster counts can play an important complementary role in constraining dark energy and modified gravity even if the associated systematic errors are not strongly controlled.

The influence of galaxy formation physics on weak lensing tests of general relativity

Forthcoming projects such as the Dark Energy Survey, Joint Dark Energy Mission, and the Large Synoptic Survey Telescope, aim to measure weak lensing shear correlations with unprecedented accuracy. Weak lensing observables are sensitive to both the distance-redshift relation and the growth of structure in the Universe. If the cause of accelerated cosmic expansion is dark energy within general relativity, both cosmic distances and structure growth are governed by the properties of dark energy. Consequently, one may use lensing to check for this consistency and test general relativity. After reviewing the phenomenology of such tests, we address a major challenge to such a program. The evolution of the baryonic component of the Universe is highly uncertain and can influence lensing observables, manifesting as modified structure growth for a fixed cosmic distance scale. Using two proposed methods, we show that one could be led to reject the null hypothesis of general relativity when it is the true theory if this uncertainty in baryonic processes is neglected. Recent simulations suggest that we can correct for baryonic effects using a parameterized model in which the halo mass-concentration relation is modified. The correction suffices to render biases small compared to statistical uncertainties. We study the ability of future weak lensing surveys to constrain the internal structures of halos and test the null hypothesis of general relativity simultaneously. Compared to alternative methods which null information from small-scales to mitigate sensitivity to baryonic physics, this internal calibration program should provide limits on deviations from general relativity that are several times more constraining. Specifically, we find that limits on general relativity in the case of internal calibration are degraded by only ∼ 30% or less compared to the case of perfect knowledge of nonlinear structure.

Inference for the dark energy equation of state using Type IA supernova data

The surprising discovery of an accelerating universe led cosmologists to posit the existence of energy--a mysterious energy field that permeates the universe. Understanding dark energy has become the central problem of modern cosmology. After describing the scientific background in depth, we formulate the task as a nonlinear inverse problem that expresses the comoving distance function in terms of the dark-energy equation of state. We present two classes of methods for making sharp statistical inferences about the equation of state from observations of Type Ia Supernovae (SNe). First, we derive a technique for testing hypotheses about the equation of state that requires no assumptions about its form and can distinguish among competing theories. Second, we present a framework for computing parametric and nonparametric estimators of the equation of state, with an associated assessment of uncertainty. Using our approach, we evaluate the strength of statistical evidence for various competing models of dark energy. Consistent with current studies, we find that with the available Type Ia SNe data, it is not possible to distinguish statistically among popular dark-energy models, and that, in particular, there is no support in the data for rejecting a cosmological constant. With much more supernova data likely to be available in coming years (e.g., from the DOE/NASA Joint Dark Energy Mission), we address the more interesting question of whether future data sets will have sufficient resolution to distinguish among competing theories.

Beyond Einstein Should Start With Dark Energy Probe, Says Panel

SPACE PHYSICSLast week, a panel of U.S. physicists and astronomers recommended that NASA and the Department of Energy begin work next year on the $1-billion-plus Joint Dark Energy Mission.

Dynamical behavior of generic quintessence potentials: Constraints on key dark energy observables

We perform a comprehensive study of a class of dark energy models---scalar field models where the effective potential can be described by a polynomial series---exploring their dynamical behavior using the method of flow equations that has previously been applied to inflationary models. Using supernova, baryon oscillation, cosmic microwave background (CMB) and Hubble constant data, and an implicit theoretical prior imposed by the scalar field dynamics, we find that the $\ensuremath{\Lambda}\mathrm{CDM}$ model provides an excellent fit to the data. Constraints on the generic scalar field potential parameters are presented, along with the reconstructed $w(z)$ histories consistent with the data and the theoretical prior. We propose and pursue computationally feasible algorithms to obtain estimates of the principal components of the equation of state, as well as parameters ${w}_{0}$ and ${w}_{a}$. Further, we use the Monte Carlo Markov chain machinery to simulate future data based on the Joint Dark Energy Mission, Planck, and baryon acoustic oscillation surveys and find that the inverse area figure of merit improves nearly by an order of magnitude. Therefore, most scalar field models that are currently consistent with data can be potentially ruled out by future experiments. We also comment on the classification of dark energy models into thawing and freezing in light of the more diverse evolution histories allowed by this general class of potentials.

Robust Dark Energy Constraints from Supernovae, Galaxy Clustering, and 3 yrWilkinson Microwave Anisotropy ProbeObservations

Type Ia supernova (SN Ia), galaxy clustering, and cosmic microwave background anisotropy (CMB) data provide complementary constraints on the nature of the dark energy in the universe. We find that the three-year Wilkinson Microwave Anisotropy Probe (WMAP) observations give a CMB shift parameter of R = (\Omega_m H_0^2)^{1/2} \int_0^{z_{CMB}} dz'/H(z')= 1.70 \pm 0.03. Using this new measured value of the CMB shift parameter, together with the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS), and SN Ia data from the HST/GOODS program and the first year Supernova Legacy Survey, we derive model-independent constraints on the dark energy density rho_X(z) and the cosmic expansion rate H(z). We also derive constraints on the dark energy equation of state w_X(z)=w_0+w'z (with cutoff at z=2) and w_X(a)=w_0+(1-a)w_a. We find that current data provide slightly tighter constraints on rho_X(z) and H(z) as free functions in redshift, and roughly a factor of two improvement in constraining w_X(z). A cosmological constant remains consistent with data, however, uncertainties remain large for model-independent constraints of dark energy. Significant increase in the number of observed SNe Ia between redshifts of 1 and 2, complemented by improved BAO and weak lensing cosmography measurements (as expected from the JEDI mission concept for the Joint Dark Energy Mission), will be required to dramatically tighten model-independent dark energy constraints.

Ideal Bandpasses for Type Ia Supernova Cosmology

ABSTRACTTo use Type Ia supernovae as standard candles for cosmology, we need accurate broadband magnitudes. In practice the observed magnitude may differ from the ideal magnitude‐redshift relationship either through intrinsic inhomogeneities in the Type Ia supernova population, or through observational error. Here we investigate how we can choose filter bandpasses to reduce the error caused by both these effects. We find that bandpasses with large integral fluxes and sloping wings are best able to minimize several sources of observational error, and are also least sensitive to intrinsic differences in Type Ia supernovae. The most important feature of a complete filter set for Type Ia supernova cosmology is that each bandpass be a redshifted copy of the first. We design practical sets of redshifted bandpasses that are matched to typical high‐resistivity CCD and HgCdTe infrared detector sensitivities. These are designed to minimize systematic error in well‐observed supernovae; final designs for specific missions should also consider signal‐to‐noise ratio requirements and observing strategy. In addition, we calculate how accurately filters need to be calibrated in order to achieve the required photometric accuracy of future supernova cosmology experiments, such as the Supernova /Acceleration Probe (SNAP), which is one possible realization of the Joint Dark Energy Mission (JDEM). We consider the effect of possible periodic miscalibrations that may arise from the construction of an interference filter.

The Detectability of Pair‐Production Supernovae atz≲ 6

Nonrotating, zero metallicity stars with initial masses 140 < M < 260 solar masses are expected to end their lives as pair-production supernovae (PPSNe), in which an electron-positron pair-production instability triggers explosive nuclear burning. Interest in such stars has been rekindled by recent theoretical studies that suggest primordial molecular clouds preferentially form stars with these masses. Since metal enrichment is a local process, the resulting PPSNe could occur over a broad range of redshifts, in pockets of metal-free gas. Using the implicit hydrodynamics code KEPLER, we have calculated a set of PPSN light curves that addresses the theoretical uncertainties and allows us to assess observational strategies for finding these objects at intermediate redshifts. The peak luminosities of typical PPSNe are only slightly greater than those of Type Ia, but they remain bright much longer (~ 1 year) and have hydrogen lines. Ongoing supernova searches may soon be able to limit the contribution of these very massive stars to < 1% of the total star formation rate density out to z=2 which already provides useful constraints for theoretical models. The planned Joint Dark Energy Mission satellite will be able to extend these limits out to z=6.

Cosmology with weak lensing surveys

Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy.

Uncorrelated measurements of the cosmic expansion history and dark energy from supernovae

We present a method for measuring the cosmic expansion history $H(z)$ in uncorrelated redshift bins, and apply it to current and simulated type Ia supernova data assuming spatial flatness. If the matter density parameter ${\ensuremath{\Omega}}_{m}$ can be accurately measured from other data, then the dark-energy density history $X(z)={\ensuremath{\rho}}_{X}(z)/{\ensuremath{\rho}}_{X}(0)$ can trivially be derived from this expansion history $H(z)$. In contrast to customary ``black box'' parameter fitting, our method is transparent and easy to interpret: the measurement of $H(z{)}^{\ensuremath{-}1}$ in a redshift bin is simply a linear combination of the measured comoving distances for supernovae in that bin, making it obvious how systematic errors propagate from input to output. We find the Riess et al. (2004) gold sample to be consistent with the vanilla concordance model where the dark energy is a cosmological constant. We compare two mission concepts for the NASA/DOE Joint Dark-Energy Mission (JDEM), the Joint Efficient Dark-energy Investigation (JEDI), and the Supernova Accelaration Probe (SNAP), using simulated data including the effect of weak lensing (based on numerical simulations) and a systematic bias from K corrections. Estimating $H(z)$ in seven uncorrelated redshift bins, we find that both provide dramatic improvements over current data: JEDI can measure $H(z)$ to about 10% accuracy and SNAP to 30%--40% accuracy.