arXiv subjects

Cora Dvorkin

Publications and source records attributed to Cora Dvorkin.

At least 91 records · Page 5Linked to original sources

arXiv2018

21-cm Fluctuations from Charged Dark Matter

The epoch of the formation of the first stars, known as the cosmic dawn, has emerged as a new arena in the search for dark matter. In particular, the first claimed 21-cm detection exhibits a deeper global absorption feature than expected, which could be caused by a low baryonic temperature, and has been interpreted as a sign for electromagnetic interactions between baryons and dark matter. This hypothesis has a striking prediction: large temperature anisotropies sourced by the velocity-dependent cooling of the baryons. However, in order to remain consistent with the rest of cosmological observations, only part of the dark matter is allowed to be charged, and thus interactive. Here we compute, for the first time, the 21-cm fluctuations caused by a charged subcomponent of the dark matter, including both the pre- and post-recombination evolution of all fluids. We find that, for the same parameters that can explain the anomalous 21-cm absorption signal, any percent-level fraction of charged dark matter would source novel 21-cm fluctuations with a unique acoustic spectrum, and with an amplitude above any other known effects. These fluctuations are uncorrelated with the usual adiabatic anisotropies, and would be observable at high significance with interferometers such as LOFAR and HERA, thus providing a novel probe of dark matter at cosmic dawn.

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arXiv2018

Gravitational Lensing and the Power Spectrum of Dark Matter Substructure: Insights from the ETHOS N-body Simulations

Strong gravitational lensing has been identified as a promising astrophysical probe to study the particle nature of dark matter. In this paper we present a detailed study of the power spectrum of the projected mass density (convergence) field of substructure in a Milky Way-sized halo. This power spectrum has been suggested as a key observable that can be extracted from strongly lensed images and yield important clues about the matter distribution within the lens galaxy. We use two different $N$-body simulations from the ETHOS framework: one with cold dark matter and another with self-interacting dark matter and a cutoff in the initial power spectrum. Despite earlier works that identified $ k \gtrsim 100$ kpc$^{-1}$ as the most promising scales to learn about the particle nature of dark matter we find that even at lower wavenumbers - which are actually within reach of observations in the near future - we can gain important information about dark matter. Comparing the amplitude and slope of the power spectrum on scales $0.1 \lesssim k/$kpc$^{-1} \lesssim 10$ from lenses at different redshifts can help us distinguish between cold dark matter and other exotic dark matter scenarios that alter the abundance and central densities of subhalos. Furthermore, by considering the contribution of different mass bins to the power spectrum we find that subhalos in the mass range $10^7 - 10^8$ M$_{\odot}$ are on average the largest contributors to the power spectrum signal on scales $2 \lesssim k/$kpc$^{-1} \lesssim 15$, despite the numerous subhalos with masses $> 10^8$ M$_{\odot}$ in a typical lens galaxy. Finally, by comparing the power spectra obtained from the subhalo catalogs to those from the particle data in the simulation snapshots we find that the seemingly-too-simple halo model is in fact a fairly good approximation to the much more complex array of substructure in the lens.

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arXiv2018

Inflationary vs. Reionization Features from Planck 2015 Data

Features during inflation and reionization leave corresponding features in the temperature and polarization power spectra that could potentially explain anomalies in the Planck 2015 data but require a joint analysis to disentangle. We study the interplay between these two effects using a model-independent parametrization of the inflationary power spectrum and the ionization history. Preference for a sharp suppression of large scale power is driven by a feature in the temperature power spectrum at multipoles $\ell \sim 20$, whereas preference for a component of high redshift ionization is driven by a sharp excess of polarization power at $\ell \sim 10$ when compared with the lowest multipoles. Marginalizing inflationary freedom does not weaken the preference for $z \gtrsim 10$ ionization, whereas marginalizing reionization freedom slightly enhances the preference for an inflationary feature but can also mask its direct signature in polarization. The inflation and reionization interpretation of these features makes predictions for the polarization spectrum which can be tested in future precision measurements especially at $10\lesssim \ell \lesssim 40$.

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arXiv2018

Efficient Computation of Galaxy Bias with Neutrinos and Other Relics

Cosmological data can be used to search for---and characterize---light particles in the standard model, if these populate our Universe. In addition to the well-known effect of these light relics in the background cosmology, usually parametrized through a change in the effective number $N_{\rm eff}$ of neutrino species, these particles can become nonrelativistic at later times, affecting the growth of matter fluctuations due to their thermal velocities. An extensively studied example is that of massive neutrinos, which are known to produce a suppression in the matter power spectrum due to their free streaming. Galaxies, as biased traces of matter fluctuations, can therefore provide us with a wealth of information about both known and unknown degrees of freedom in the standard model. To harness this information, however, the galaxy bias has to be determined in the presence of massive relics, which is expected to vary with scale. Here we present the code RelicFast, which efficiently computes the scale-dependent bias induced by relics of different masses, spins, and temperatures, through spherical collapse and the peak-background split. Using this code, we find that, in general, the bias induced by light relics partially compensates the suppression of power, and should be accounted for in any search for relics with galaxy data. In particular, for the case of neutrinos, we find that both the normal and inverted hierarchies present a percent-level step in the Lagrangian bias, with a size scaling linearly with the neutrino-mass sum, in agreement with recent simulations. RelicFast can compute halo bias in under a second, allowing for this effect to be properly included for different cosmologies, and light relics, at little computational cost.

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arXiv2018

Science Impacts of the SPHEREx All-Sky Optical to Near-Infrared Spectral Survey II: Report of a Community Workshop on the Scientific Synergies Between the SPHEREx Survey and Other Astronomy Observatories

SPHEREx is a proposed NASA MIDEX mission selected for Phase A study. SPHEREx would carry out the first all-sky spectral survey in the near infrared. At the end of its two-year mission, SPHEREx would obtain 0.75-to-5$μ$m spectra of every 6.2 arcsec pixel on the sky, with spectral resolution R>35 and a 5-$σ$ sensitivity AB$>$19 per spectral/spatial resolution element. More details concerning SPHEREx are available at http://spherex.caltech.edu. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light. Though these three themes are undoubtedly compelling, they are far from exhausting the scientific output of SPHEREx. Indeed, SPHEREx would create a unique all-sky spectral database including spectra of very large numbers of astronomical and solar system targets, including both extended and diffuse sources. These spectra would enable a wide variety of investigations, and the SPHEREx team is dedicated to making the data available to the community to enable these investigations, which we refer to as Legacy Science. To that end, we have sponsored two workshops for the general scientific community to identify the most interesting Legacy Science themes and to ensure that the SPHEREx data products are responsive to their needs. In February of 2016, some 50 scientists from all fields met in Pasadena to develop these themes and to understand their implications for the SPHEREx mission. The 2016 workshop highlighted many synergies between SPHEREx and other contemporaneous astronomical missions, facilities, and databases. Consequently, in January 2018 we convened a second workshop at the Center for Astrophysics in Cambridge to focus specifically on these synergies. This white paper reports on the results of the 2018 SPHEREx workshop.

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arXiv2018

Galaxy Bispectrum from Massive Spinning Particles

Massive spinning particles, if present during inflation, lead to a distinctive bispectrum of primordial perturbations, the shape and amplitude of which depend on the masses and spins of the extra particles. This signal, in turn, leaves an imprint in the statistical distribution of galaxies; in particular, as a non-vanishing galaxy bispectrum, which can be used to probe the masses and spins of these particles. In this paper, we present for the first time a new theoretical template for the bispectrum generated by massive spinning particles, valid for a general triangle configuration. We then proceed to perform a Fisher-matrix forecast to assess the potential of two next-generation spectroscopic galaxy surveys, EUCLID and DESI, to constrain the primordial non-Gaussianity sourced by these extra particles. We model the galaxy bispectrum using tree-level perturbation theory, accounting for redshift-space distortions and the Alcock-Paczynski effect, and forecast constraints on the primordial non-Gaussianity parameters marginalizing over all relevant biases and cosmological parameters. Our results suggest that these surveys would potentially be sensitive to any primordial non-Gaussianity with an amplitude larger than $f_{\rm NL}\approx 1$, for massive particles with spins 2, 3, and 4. Interestingly, if non-Gaussianities are present at that level, these surveys will be able to infer the masses of these spinning particles to within tens of percent. If detected, this would provide a very clear window into the particle content of our Universe during inflation.

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arXiv2018

Probing sub-GeV Dark Matter-Baryon Scattering with Cosmological Observables

We derive new limits on the elastic scattering cross-section between baryons and dark matter using Cosmic Microwave Background data from the Planck satellite and measurements of the Lyman-alpha forest flux power spectrum from the Sloan Digital Sky Survey. Our analysis addresses generic cross sections of the form $σ\propto v^n$, where v is the dark matter-baryon relative velocity, allowing for constraints on the cross section independent of specific particle physics models. We include high-$\ell$ polarization data from Planck in our analysis, improving over previous constraints. We apply a more careful treatment of dark matter thermal evolution than previously done, allowing us to extend our constraints down to dark matter masses of $\sim$MeV. We show in this work that cosmological probes are complementary to current direct detection and astrophysical searches.

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arXiv2018

Probing the small-scale structure in strongly lensed systems via transdimensional inference

Strong lensing is a sensitive probe of the small-scale density fluctuations in the Universe. We implement a novel approach to modeling strongly lensed systems using probabilistic cataloging, which is a transdimensional, hierarchical, and Bayesian framework to sample from a metamodel (union of models with different dimensionality) consistent with observed photon count maps. Probabilistic cataloging allows us to robustly characterize modeling covariances within and across lens models with different numbers of subhalos. Unlike traditional cataloging of subhalos, it does not require model subhalos to improve the goodness of fit above the detection threshold. Instead, it allows the exploitation of all information contained in the photon count maps, for instance, when constraining the subhalo mass function. We further show that, by not including these small subhalos in the lens model, fixed-dimensional inference methods can significantly mismodel the data. Using a simulated Hubble Space Telescope (HST) dataset, we show that the subhalo mass function can be probed even when many subhalos in the sample catalogs are individually below the detection threshold and would be absent in a traditional catalog. With the planned Wide Field Infrared Space Telescope (WFIRST), simultaneous probabilistic cataloging of dark subhalos in high-resolution, deep strong lens images has the potential to constrain the subhalo mass function at even lower masses.

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arXiv2018

Scale-Dependent Galaxy Bias from Massive Particles with Spin during Inflation

The presence of additional particles during inflation leads to non-Gaussianity in late-time correlators of primordial curvature perturbations. The shape and amplitude of this signal depend on the mass and spin of the extra particles. Constraints on this distinct form of primordial non-Gaussianity, therefore, provide a wealth of information on the particle content during inflation. We investigate the potential of upcoming galaxy surveys in constraining such a signature through its impact on the observed galaxy power spectrum. Primordial non-Gaussianity of various shapes induces a scale-dependent bias on tracers of large-scale structure, such as galaxies. Using this signature we obtain constraints on massive particles during inflation, which can have non-zero spins. In particular, we show that the prospects for constraining particles with spins 0 and 1 are promising, while constraining particles with spin 2 from power spectrum alone seems challenging. We show that the multi-tracer technique can significantly improve the constraints from the power spectrum by at least an order of magnitude. Furthermore, we analyze the effect of non-linearities due to gravitational evolution on the forecasted constraints on the masses of the extra particles and the amplitudes of the imprinted non-Gaussian signal. We find that gravitational evolution affects the constraints by less than a factor of 2.

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arXiv2018

On the Power Spectrum of Dark Matter Substructure in Strong Gravitational Lenses

Studying the smallest self-bound dark matter structure in our Universe can yield important clues about the fundamental particle nature of dark matter. Galaxy-scale strong gravitational lensing provides a unique way to detect and characterize dark matter substructures at cosmological distances from the Milky Way. Within the cold dark matter (CDM) paradigm, the number of low-mass subhalos within lens galaxies is expected to be large, implying that their contribution to the lensing convergence field is approximately Gaussian and could thus be described by their power spectrum. We develop here a general formalism to compute from first principles the substructure convergence power spectrum for different populations of dark matter subhalos. As an example, we apply our framework to two distinct subhalo populations: a truncated Navarro-Frenk-White subhalo population motivated by standard CDM, and a truncated cored subhalo population motivated by self-interacting dark matter (SIDM). We study in detail how the subhalo abundance, mass function, internal density profile, and concentration affect the amplitude and shape of the substructure power spectrum. We determine that the power spectrum is mostly sensitive to a specific combination of the subhalo abundance and moments of the mass function, as well as to the average tidal truncation scale of the largest subhalos included in the analysis. Interestingly, we show that the asymptotic slope of the substructure power spectrum at large wave number reflects the internal density profile of the subhalos. In particular, the SIDM power spectrum exhibits a characteristic steepening at large wave number absent in the CDM power spectrum, opening the possibility of using this observable, if at all measurable, to discern between these two scenarios.

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arXiv2017

Fundamental Physics with the Hubble Space Telescope

Cosmology is intrinsically intertwined with questions in fundamental physics. The existence of non-baryonic dark matter requires new physics beyond the Standard Model of elemenatary-particle interactions and Einstein's general relativity, as does the accelerating expansion of the universe. Current tensions between various cosmological measurements may be harbingers of yet more new physics. Progress on understanding dark matter and cosmic acceleration requires long term, high-precision measurements and excellent control of systematics, demanding observational programs that are often outside the discovery/characterization mode that drives many areas of astronomy. We outline potential programs through which the Hubble Space Telescope (HST) could have a major impact on issues in fundamental physics in the coming years. To realize this impact, we suggest the introduction of a "HST Fundamental Physics" observational program that would be subject to a modified proposal and review process.

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arXiv2017

Model-Independent Predictions for Smooth Cosmic Acceleration Scenarios

Through likelihood analyses of both current and future data that constrain both the expansion history of the universe and the clustering of matter fluctuations, we provide falsifiable predictions for three broad classes of models that explain the accelerated expansions of the universe: $Λ$CDM, the quintessence scenario and a more general class of smooth dark energy models that can cross the phantom barrier $w(z)=-1$. Our predictions are model independent in the sense that we do not rely on a specific parametrization, but we instead use a principal component (PC) basis function constructed a priori from a noise model of supernovae and Cosmic Microwave Background observations. For the supernovae measurements, we consider two type of surveys: the current JLA and the upcoming WFIRST surveys. We show that WFIRST will be able to improve growth predictions in curved models significantly. The remaining degeneracy between spatial curvature and $w(z)$ could be overcome with improved measurements of $σ_8 Ω_m^{1/2}$, a combination that controls the amplitude of the growth of structure. We also point out that a PC-based Figure of Merit reveals that the usual two-parameter description of $w(z)$ does not exhaust the information that can be extracted from current data (JLA) or future data (WFIRST).

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arXiv2017

Wandering in the Lyman-alpha Forest: A Study of Dark Matter-Dark Radiation Interactions

The amplitude of large-scale matter fluctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focusing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we find that measurements of the Lyman-alpha flux power spectrum from the Sloan Digital Sky Survey provides no support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of $2Δ\ln\mathcal{L}=12$ with respect to the standard $Λ$ cold dark matter ($Λ$CDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to $2Δ\ln\mathcal{L}=6$ relative to $Λ$CDM. We thus conclude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We find that the constraint on the effective number of fluid-like dark radiation species, $ΔN_{\rm fluid}$, will be improved by an order of magnitude compared to current bounds.

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arXiv2017

Inflationary Features and Shifts in Cosmological Parameters from Planck 2015 Data

We explore the relationship between features in the Planck 2015 temperature and polarization data, shifts in the cosmological parameters, and features from inflation. Residuals in the temperature data at low multipole $\ell$, which are responsible for the high $H_0\approx 70$ km s$^{-1}$Mpc$^{-1}$ and low $σ_8Ω_m^{1/2}$ values from $\ell<1000$ in power-law $Λ$CDM models, are better fit to inflationary features with a $1.9σ$ preference for running of the running of the tilt or a stronger $99\%$ CL local significance preference for a sharp drop in power around $k=0.004$ Mpc$^{-1}$ in generalized slow roll and a lower $H_0\approx 67$ km s$^{-1}$Mpc$^{-1}$. The same in-phase acoustic residuals at $\ell>1000$ that drive the global $H_0$ constraints and appear as a lensing anomaly also favor running parameters which allow even lower $H_0$, but not once lensing reconstruction is considered. Polarization spectra are intrinsically highly sensitive to these parameter shifts, and even more so in the Planck 2015 TE data due to an outlier at $\ell \approx 165$, which disfavors the best fit $H_0$ $Λ$CDM solution by more than $2σ$, and high $H_0$ value at almost $3σ$. Current polarization data also slightly enhance the significance of a sharp suppression of large-scale power but leave room for large improvements in the future with cosmic variance limited $E$-mode measurements.

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arXiv2017

Exploring Cosmic Origins with CORE: Cosmological Parameters

We forecast the main cosmological parameter constraints achievable with the CORE space mission which is dedicated to mapping the polarisation of the Cosmic Microwave Background (CMB). CORE was recently submitted in response to ESA's fifth call for medium-sized mission proposals (M5). Here we report the results from our pre-submission study of the impact of various instrumental options, in particular the telescope size and sensitivity level, and review the great, transformative potential of the mission as proposed. Specifically, we assess the impact on a broad range of fundamental parameters of our Universe as a function of the expected CMB characteristics, with other papers in the series focusing on controlling astrophysical and instrumental residual systematics. In this paper, we assume that only a few central CORE frequency channels are usable for our purpose, all others being devoted to the cleaning of astrophysical contaminants. On the theoretical side, we assume LCDM as our general framework and quantify the improvement provided by CORE over the current constraints from the Planck 2015 release. We also study the joint sensitivity of CORE and of future Baryon Acoustic Oscillation and Large Scale Structure experiments like DESI and Euclid. Specific constraints on the physics of inflation are presented in another paper of the series. In addition to the six parameters of the base LCDM, which describe the matter content of a spatially flat universe with adiabatic and scalar primordial fluctuations from inflation, we derive the precision achievable on parameters like those describing curvature, neutrino physics, extra light relics, primordial helium abundance, dark matter annihilation, recombination physics, variation of fundamental constants, dark energy, modified gravity, reionization and cosmic birefringence. (ABRIDGED)

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arXiv2016

Multitracing Anisotropic Non-Gaussianity with Galaxy Shapes

Correlations between intrinsic galaxy shapes on large-scales arise due to the effect of the tidal field of the large-scale structure. Anisotropic primordial non-Gaussianity induces a distinct scale-dependent imprint in these tidal alignments on large scales. Motivated by the observational finding that the alignment strength of luminous red galaxies depends on how galaxy shapes are measured, we study the use of two different shape estimators as a multi-tracer probe of intrinsic alignments. We show, by means of a Fisher analysis, that this technique promises a significant improvement on anisotropic non-Gaussianity constraints over a single-tracer method. For future weak lensing surveys, the uncertainty in the anisotropic non-Gaussianity parameter, $A_2$, is forecast to be $σ(A_2)\approx 50$, $\sim 40\%$ smaller than currently available constraints from the bispectrum of the Cosmic Microwave Background. This corresponds to an improvement of a factor of $4-5$ over the uncertainty from a single-tracer analysis.

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arXiv2016

The Future of Primordial Features with Large-Scale Structure Surveys

Primordial features are one of the most important extensions of the Standard Model of cosmology, providing a wealth of information on the primordial universe, ranging from discrimination between inflation and alternative scenarios, new particle detection, to fine structures in the inflationary potential. We study the prospects of future large-scale structure (LSS) surveys on the detection and constraints of these features. We classify primordial feature models into several classes, and for each class we present a simple template of power spectrum that encodes the essential physics. We study how well the most ambitious LSS surveys proposed to date, including both spectroscopic and photometric surveys, will be able to improve the constraints with respect to the current Planck data. We find that these LSS surveys will significantly improve the experimental sensitivity on features signals that are oscillatory in scales, due to the 3D information. For a broad range of models, these surveys will be able to reduce the errors of the amplitudes of the features by a factor of 5 or more, including several interesting candidates identified in the recent Planck data. Therefore, LSS surveys offer an impressive opportunity for primordial feature discovery in the next decade or two. We also compare the advantages of both types of surveys.

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arXiv2016

CMB-S4 Science Book, First Edition

This book lays out the scientific goals to be addressed by the next-generation ground-based cosmic microwave background experiment, CMB-S4, envisioned to consist of dedicated telescopes at the South Pole, the high Chilean Atacama plateau and possibly a northern hemisphere site, all equipped with new superconducting cameras. CMB-S4 will dramatically advance cosmological studies by crossing critical thresholds in the search for the B-mode polarization signature of primordial gravitational waves, in the determination of the number and masses of the neutrinos, in the search for evidence of new light relics, in constraining the nature of dark energy, and in testing general relativity on large scales.

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