20 Search Results

Here we constrain six possible extensions to the Λ cold dark matter (CDM) model using measurements from the Dark Energy Survey’s first three years of observations, alone and in combination with external cosmological probes. The DES data are the two-point correlation functions of weak gravitational lensing, galaxy clustering, and their cross-correlation. We use simulated data vectors and blind analyses of real data to validate the robustness of our results to astrophysical and modeling systematic errors. In many cases, constraining power is limited by the absence of theoretical predictions beyond the linear regime that are reliable at our required precision. Themore » Λ CDM extensions are dark energy with a time-dependent equation of state, nonzero spatial curvature, additional relativistic degrees of freedom, sterile neutrinos with eV-scale mass, modifications of gravitational physics, and a binned σ₈(z) model which serves as a phenomenological probe of structure growth. For the time-varying dark energy equation of state evaluated at the pivot redshift we find (w_p, w_a) = (-0.99$$^{+0.28}_{-0.17}$$, -0.9 ±1.2) at 68% confidence with z_p = 0.24 from the DES measurements alone, and (w_p, w_a) = (- 1.03$$^{+0.04}_{-0.03}$$, -0.4 $$^{+0.4}_{-0.3)}$$ with z_p = 0.21 for the combination of all data considered. Curvature constraints of Ω_k = 0.0009 ± 0.0017 and effective relativistic species N_eff = 3.10$$^{+0.15}_{-0.16}$$ are dominated by external data, though adding DES information to external low-redshift probes tightens the Ω_k constraints that can be made without cosmic microwave background observables by 20%. For massive sterile neutrinos, DES combined with external data improves the upper bound on the mass m_eff by a factor of 3 compared to previous analyses, giving 95% limits of (Δ N_eff, m_eff) ≤ (0.28, 0.20 eV) when using priors matching a comparable Planck analysis. For modified gravity, we constrain changes to the lensing and Poisson equations controlled by functions Σ (k ,z) = Σ₀Ω_Λ(z)/Ω _Λ,0 and μ(k, z) = μ₀Ω_Λ(z)/Ω _{Λ ,0,} respectively, to Σ₀ = 0.6$$^{+ 0.4}_{ -0.5}$$ from DES alone and (Σ₀, μ₀) = (0.04 ± 0.05, 0.08$$^{+0.21}_{-0.19}$$) for the combination of all data, both at 68% confidence. Overall, we find no significant evidence for physics beyond Λ CDM.« less

The main focus of the PI during this time was leading the effort to produce cosmological results on the data set from the first three years from the Dark Energy Survey (DES). The analysis combines weak gravitational lensing and maps of the galaxy distribution, supplemented by estimates of the redshifts of galaxies. This will ultimately lead to 33 papers, culminating in a single paper that brings all this together and provides a constraint on the clustering parameter σ₈.This will be directly compared to the constraint obtained by high-redshift experiments, such as the Planck satellite, extrapolated forward assuming the CDM model.more » If the two values disagree, as they currently seem to at the 2-sigma level, this will be an indication that the model is incorrect or incomplete. These papers are expected to be submitted in January, 2021. Leading this effort, with help from many others, has been the primary research focus of the PI during this grant.« less

Covariance matrices are among the most difficult pieces of end-to-end cosmological analyses. In principle, for two-point functions, each component involves a four-point function, and the resulting covariance often has hundreds of thousands of elements. We investigate various compression mechanisms capable of vastly reducing the size of the covariance matrix in the context of cosmic shear statistics. This helps identify which of its parts are most crucial to parameter estimation. We start with simple compression methods, by isolating and “removing” 200 modes associated with the lowest eigenvalues, then those with the lowest signal-to-noise ratio, before moving on to more sophisticated schemesmore » like compression at the tomographic level and, finally, with the massively optimized parameter estimation and data compression (MOPED). We find that, while most of these approaches prove useful for a few parameters of interest, like Ω_m, the simplest yield a loss of constraining power on the intrinsic alignment (IA) parameters as well as S₈. For the case considered—cosmic shear from the first year of data from the Dark Energy Survey—only MOPED was able to replicate the original constraints in the 16-parameter space. Finally, we apply a tolerance test to the elements of the compressed covariance matrix obtained with MOPED and confirm that the IA parameter A_IA is the most susceptible to inaccuracies in the covariance matrix.« less

We analyze Dark Energy Survey (DES) data to constrain a cosmological model where a subset of parameters—focusing on Ω_m—are split into versions associated with structure growth (e.g., Ω$$^{grow}_m$$) and expansion history (e.g., Ω$$^{geo}_m$$). Once the parameters have been specified for the ΛCDM cosmological model, which includes general relativity as a theory of gravity, it uniquely predicts the evolution of both geometry (distances) and the growth of structure over cosmic time. Any inconsistency between measurements of geometry and growth could therefore indicate a breakdown of that model. Our growth-geometry split approach therefore serves both as a (largely) model-independent test for beyond-ΛCDMmore » physics, and as a means to characterize how DES observables provide cosmological information. We analyze the same multiprobe DES data as [Phys. Rev. Lett. 122, 171301 (2019)] : DES Year 1 (Y1) galaxy clustering and weak lensing, which are sensitive to both growth and geometry, as well as Y1 BAO and Y3 supernovae, which probe geometry. We additionally include external geometric information from BOSS DR12 BAO and a compressed Planck 2015 likelihood, and external growth information from BOSS DR12 RSD. We find no significant disagreement with Ω$$^{grow}_m$$=Ω$$^{geo}_m$$. When DES and external data are analyzed separately, degeneracies with neutrino mass and intrinsic alignments limit our ability to measure Ω$$^{grow}_m$$, but combining DES with external data allows us to constrain both growth and geometric quantities. We also consider a parametrization where we split both Ω_m and w, but find that even our most constraining data combination is unable to separately constrain Ω$$^{grow}_m$$ and w^grow. Relative to ΛCDM, splitting growth and geometry weakens bounds on σ₈ but does not alter constraints on h.« less

The population of Milky Way (MW) satellites contains the faintest known galaxies, and thus provides essential insight into galaxy formation and dark matter microphysics. Here, we combine a model of the galaxy--halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high-Galactic-latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated $$6.5\pmmore » 1.5$$ observed LMC-associated satellites, consistent with the number of LMC satellites inferred from $$\textit{Gaia}$$ proper motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last $$2\ \rm{Gyr}$$ at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $$2.2\times 10^{8}\ M_{\rm{\odot}}$$ at $$95\%$$ confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. In conclusion, we predict that the faintest detectable satellites occupy halos with peak virial masses above $$10^{6}\ M_{\rm{\odot}}$$, highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.« less

Cosmological measurements of structure are placing increasingly strong constraints on the sum of the neutrino masses, Σmν, through Bayesian inference. Because these constraints depend on the choice for the prior probability π(Σmν), we argue that this prior should be motivated by fundamental physical principles rather than the ad hoc choices that are common in the literature. The first step in this direction is to specify the prior directly at the level of the neutrino mass matrix Mν, since this is the parameter appearing in the Lagrangian of the particle physics theory. Thus by specifying a probability distribution over Mν, andmore » by including the known squared mass splittings, we predict a theoretical probability distribution over Σmν that we interpret as a Bayesian prior probability π(Σmν). We find that π(Σmν) peaks close to the smallest Σmν allowed by the measured mass splittings, roughly 0.06eV (0.1eV) for normal (inverted) ordering, due to the phenomenon of eigenvalue repulsion in random matrices. We consider three models for neutrino mass generation: Dirac, Majorana, and Majorana via the seesaw mechanism; differences in the predicted priors π(Σmν) allow for the possibility of having indications about the physical origin of neutrino masses once sufficient experimental sensitivity is achieved. We present fitting functions for π(Σmν), which provide a simple means for applying these priors to cosmological constraints on the neutrino masses or marginalizing over their impact on other cosmological parameters.« less

Galaxy surveys probe both structure formation and the expansion rate, making them promising avenues for understanding the dark universe. Photometric surveys accurately map the 2D distribution of galaxy positions and shapes in a given redshift range, while spectroscopic surveys provide sparser 3D maps of the galaxy distribution. We present a way to analyse overlapping 2D and 3D maps jointly and without loss of information. We represent 3D maps using spherical Fourier-Bessel (sFB) modes, which preserve radial coverage while accounting for the spherical sky geometry, and we decompose 2D maps in a spherical harmonic basis. In these bases, a simple expressionmore » exists for the cross-correlation of the two fields. One very powerful application is the ability to simultaneously constrain the redshift distribution of the photometric sample, the sample biases, and cosmological parameters. We use our framework to show that combined analysis of DESI and LSST can improve cosmological constraints by factors of $${\sim}1.2$$ to $${\sim}1.8$$ on the region where they overlap relative to identically sized disjoint regions. We also show that in the overlap of DES and SDSS-III in Stripe 82, cross-correlating improves photo-$$z$$ parameter constraints by factors of $${\sim}2$$ to $${\sim}12$$ over internal photo-$$z$$ reconstructions.« less

A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.

Cosmic surveys provide crucial information about high energy physics including strong evidence for dark energy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of dark energy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understandmore » the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.« less

A logarithmic transform of the convergence field improves `the information content', ie., the overall precision associated with the measurement of the amplitude of the convergence power spectrum by improving the covariance matrix properties. The translation of this improvement in the information content to that in cosmological parameters, such as those associated with dark energy, requires knowing the sensitivity of the log-transformed field to those cosmological parameters. In this paper we use N-body simulations with ray tracing to generate convergence fields at multiple source redshifts as a function of cosmology. The gain in information associated with the log-transformed field does leadmore » to tighter constraints on dark energy parameters, but only if shape noise is neglected. The presence of shape noise quickly diminishes the advantage of the log mapping, more quickly than we would expect based on the information content. With or without shape noise, using a larger pixel size allows for a more efficient log-transformation.« less