arXiv subjects

Anže Slosar

Publications and source records attributed to Anže Slosar.

At least 91 records · Page 5Linked to original sources

arXiv2019

Probing the Fundamental Nature of Dark Matter with the Large Synoptic Survey Telescope

Astrophysical and cosmological observations currently provide the only robust, empirical measurements of dark matter. Future observations with Large Synoptic Survey Telescope (LSST) will provide necessary guidance for the experimental dark matter program. This white paper represents a community effort to summarize the science case for studying the fundamental physics of dark matter with LSST. We discuss how LSST will inform our understanding of the fundamental properties of dark matter, such as particle mass, self-interaction strength, non-gravitational couplings to the Standard Model, and compact object abundances. Additionally, we discuss the ways that LSST will complement other experiments to strengthen our understanding of the fundamental characteristics of dark matter. More information on the LSST dark matter effort can be found at https://lsstdarkmatter.github.io/ .

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arXiv2019

Dark Energy and Modified Gravity

Despite two decades of tremendous experimental and theoretical progress, the riddle of the accelerated expansion of the Universe remains to be solved. On the experimental side, our understanding of the possibilities and limitations of the major dark energy probes has evolved; here we summarize the major probes and their crucial challenges. On the theoretical side, the taxonomy of explanations for the accelerated expansion rate is better understood, providing clear guidance to the relevant observables. We argue that: i) improving statistical precision and systematic control by taking more data, supporting research efforts to address crucial challenges for each probe, using complementary methods, and relying on cross-correlations is well motivated; ii) blinding of analyses is difficult but ever more important; iii) studies of dark energy and modified gravity are related; and iv) it is crucial that R&D for a vibrant dark energy program in the 2030s be started now by supporting studies and technical R&D that will allow embryonic proposals to mature. Understanding dark energy, arguably the biggest unsolved mystery in both fundamental particle physics and cosmology, will remain one of the focal points of cosmology in the forthcoming decade.

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arXiv2019

Scratches from the Past: Inflationary Archaeology through Features in the Power Spectrum of Primordial Fluctuations

Inflation may provide unique insight into the physics at the highest available energy scales that cannot be replicated in any realistic terrestrial experiment. Features in the primordial power spectrum are generically predicted in a wide class of models of inflation and its alternatives, and are observationally one of the most overlooked channels for finding evidence for non-minimal inflationary models. Constraints from observations of the cosmic microwave background cover the widest range of feature frequencies, but the most sensitive constraints will come from future large-scale structure surveys that can measure the largest number of linear and quasi-linear modes.

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arXiv2019

Science from an Ultra-Deep, High-Resolution Millimeter-Wave Survey

Opening up a new window of millimeter-wave observations that span frequency bands in the range of 30 to 500 GHz, survey half the sky, and are both an order of magnitude deeper (about 0.5 uK-arcmin) and of higher-resolution (about 10 arcseconds) than currently funded surveys would yield an enormous gain in understanding of both fundamental physics and astrophysics. In particular, such a survey would allow for major advances in measuring the distribution of dark matter and gas on small-scales, and yield needed insight on 1.) dark matter particle properties, 2.) the evolution of gas and galaxies, 3.) new light particle species, 4.) the epoch of inflation, and 5.) the census of bodies orbiting in the outer Solar System.

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arXiv2019

Neutrino Mass from Cosmology: Probing Physics Beyond the Standard Model

Recent advances in cosmic observations have brought us to the verge of discovery of the absolute scale of neutrino masses. Nonzero neutrino masses are known evidence of new physics beyond the Standard Model. Our understanding of the clustering of matter in the presence of massive neutrinos has significantly improved over the past decade, yielding cosmological constraints that are tighter than any laboratory experiment, and which will improve significantly over the next decade, resulting in a guaranteed detection of the absolute neutrino mass scale.

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arXiv2019

A unified pseudo-$C_\ell$ framework

The pseudo-$C_\ell$ is an algorithm for estimating the angular power and cross-power spectra that is very fast and, in realistic cases, also nearly optimal. The algorithm can be extended to deal with contaminant deprojection and $E/B$ purification, and can therefore be applied in a wide variety of scenarios of interest for current and future cosmological observations. This paper presents NaMaster, a public, validated, accurate and easy-to-use software package that, for the first time, provides a unified framework to compute angular cross-power spectra of any pair of spin-0 or spin-2 fields, contaminated by an arbitrary number of linear systematics and requiring $B$- or $E$-mode purification, both on the sphere or in the flat-sky approximation. We describe the mathematical background of the estimator, including all the features above, and its software implementation in NaMaster. We construct a validation suite that aims to resemble the types of observations that next-generation large-scale structure and ground-based CMB experiments will face, and use it to show that the code is able to recover the input power spectra in the most complex scenarios with no detectable bias. NaMaster can be found at https://github.com/LSSTDESC/NaMaster, and is provided with comprehensive documentation and a number of code examples.

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arXiv2019

LSST Target of Opportunity proposal for locating a core collapse supernova in our galaxy triggered by a neutrino supernova alert

A few times a century, a core collapse supernova (CCSN) occurs in our galaxy. When such galactic CCSNe happen, over 99\% of its gravitational binding energy is released in the form of neutrinos. Over a period of tens of seconds, a powerful neutrino flux is emitted from the collapsing star. When the exploding shock wave finally reaches the surface of the star, optical photons escaping the expanding stellar envelope leave the star and eventually arrive at Earth as a visible brightening. Crucially, although the neutrino signal is prompt, the time to the shock wave breakout can be minutes to many hours later. This means that the neutrino signal will serve as an alert, warning the optical astronomy community the light from the explosion is coming. Quickly identifying the location of the supernova on the sky and disseminating it to the all available ground and spaced-based instruments will be critical to learn as much as possible about the event. Some neutrino experiments can report pointing information for these galactic CCSNe. In particular, the Super-Kamiokande experiment can point to a few degrees for CCSNe near the center of our galaxy. A CCSN located 10 kpc from Earth is expected to result in a pointing resolution on the order of 3 degrees. LSST's field of view (FOV) is well matched to this initial search box. LSSTs depth is also uniquely suited for identifying CCSNe even if they fail or are obscured by the dust of the galactic plane. This is a proposal to, upon receipt of such an alert, prioritize the use of LSST for a full day of observing to continuously monitor a pre-identified region of sky and, by using difference imaging, identify and announce the location of the supernova.

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arXiv2018

Optimizing the LSST Observing Strategy for Dark Energy Science: DESC Recommendations for the Wide-Fast-Deep Survey

Cosmology is one of the four science pillars of LSST, which promises to be transformative for our understanding of dark energy and dark matter. The LSST Dark Energy Science Collaboration (DESC) has been tasked with deriving constraints on cosmological parameters from LSST data. Each of the cosmological probes for LSST is heavily impacted by the choice of observing strategy. This white paper is written by the LSST DESC Observing Strategy Task Force (OSTF), which represents the entire collaboration, and aims to make recommendations on observing strategy that will benefit all cosmological analyses with LSST. It is accompanied by the DESC DDF (Deep Drilling Fields) white paper (Scolnic et al.). We use a variety of metrics to understand the effects of the observing strategy on measurements of weak lensing, large-scale structure, clusters, photometric redshifts, supernovae, strong lensing and kilonovae. In order to reduce systematic uncertainties, we conclude that the current baseline observing strategy needs to be significantly modified to result in the best possible cosmological constraints. We provide some key recommendations: moving the WFD (Wide-Fast-Deep) footprint to avoid regions of high extinction, taking visit pairs in different filters, changing the 2x15s snaps to a single exposure to improve efficiency, focusing on strategies that reduce long gaps (>15 days) between observations, and prioritizing spatial uniformity at several intervals during the 10-year survey.

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arXiv2018

Optimizing the LSST Observing Strategy for Dark Energy Science: DESC Recommendations for the Deep Drilling Fields and other Special Programs

We review the measurements of dark energy enabled by observations of the Deep Drilling Fields and the optimization of survey design for cosmological measurements. This white paper is the result of efforts by the LSST DESC Observing Strategy Task Force (OSTF), which represents the entire collaboration, and aims to make recommendations on observing strategy for the DDFs that will benefit all cosmological analyses with LSST. It is accompanied by the DESC-WFD white paper (Lochner et al.). We argue for altering the nominal deep drilling plan to have $>6$ month seasons, interweaving $gri$ and $zy$ observations every 3 days with 2, 4, 8, 25, 4 visits in $grizy$, respectively. These recommendations are guided by metrics optimizing constraints on dark energy and mitigation of systematic uncertainties, including specific requirements on total number of visits after Y1 and Y10 for photometric redshifts (photo-$z$) and weak lensing systematics. We specify the precise locations for the previously-chosen LSST deep fields (ELAIS-S1, XMM-LSS, CDF-S, and COSMOS) and recommend Akari Deep Field South as the planned fifth deep field in order to synergize with Euclid and WFIRST. Our recommended DDF strategy uses $6.2\%$ of the LSST survey time. We briefly discuss synergy with white papers from other collaborations, as well as additional mini-surveys and Target-of-Opportunity programs that lead to better measurements of dark energy.

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arXiv2018

Inferences of $H_0$ in presence of a non-standard recombination

Measurements of the Hubble parameter from the distance ladder are in tension with indirect measurements based on the cosmic microwave background (CMB) data and the inverse distance ladder measurements at 3-4 $σ$ level. We consider phenomenological modification to the timing and width of the recombination process and show that they can significantly affect this tension. This possibility is appealing, because such modification affects both the distance to the last scattering surface and the calibration of the baryon acoustic oscillations (BAO) ruler. Moreover, because only a very small fraction of the most energetic photons keep the early universe in the plasma state, it is possible that such modification could occur without affecting the energy density budget of the universe or being incompatible with the very tight limits on the departure from the black-body spectrum of CMB. In particular, we find that under this simplified model, with a conservative subset of Planck data alone, $H_0=73.44_{-6.77}^{+5.50}~{\rm km\ s}^{-1}\ {\rm Mpc}^{-1}$ and in combination with BAO data $H_0=68.86_{-1.35}^{+1.31}~{\rm km\ s}^{-1}\ {\rm Mpc}^{-1}$, decreasing the tension to $\sim 2σ$ level. However, when combined with Planck lensing reconstruction and high-$\ell$ polarization data, the tension climbs back to $\sim 2.7σ$, despite the uncertainty on non-ladder $H_0$ measurement more than doubling.

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arXiv2018

Power spectrum in the presence of large-scale overdensity and tidal fields: breaking azimuthal symmetry

We consider the power spectrum of a biased tracer observed in a finite volume in the presence of a large-scale overdensity and tidal fields. Expanding both the observed power spectrum and the source fields (linear power spectrum, scalar overdensity and tidal field tensor) in spherical harmonics, we explicitly confirm that each $(\ell,m)$ source generates just the corresponding $(\ell,m)$ modes of power spectrum in real space. In redshift space, each $(\ell,m)$ source additionally couples only to $(\ell+2n,m)$ modes of tracer power spectra. This generalizes the Kaiser formula for monopole, quadrupole and hexadecapole of the power spectrum to all $(\ell,m)$ modes generated to the second order in perturbation theory. This formalism can find applications in constraining the super-sample covariance and in the local power spectrum based bispectrum estimators. As an example application, we forecast the ability to measure these modes a survey with BOSS-like galaxy number densities.

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arXiv2018

The triply-ionized carbon forest from eBOSS: cosmological correlations with quasars in SDSS-IV DR14

We present measurements of the cross-correlation of the triply-ionized carbon (CIV) forest with quasars using Sloan Digital Sky Survey Data Release 14. The study exploits a large sample of new quasars from the first two years of observations by the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). The CIV forest is a weaker tracer of large-scale structure than the Ly$α$ forest, but benefits from being accessible at redshifts $z<2$ where the quasar number density from eBOSS is high. Our data sample consists of 287,651 CIV forest quasars in the redshift range $1.4<z<3.5$ and 387,315 tracer quasars with $1.2<z<3.5$. We measure large-scale correlations from CIV absorption occuring in three distinct quasar rest-frame wavelength bands of the spectra referred to as the CIV forest, the SiIV forest and the Ly$α$ forest. From the combined fit to the quasar-CIV cross-correlations for the CIV forest and the SiIV forest, the CIV redshift-space distortion parameter is $β_{\rm CIV}=0.27_{\ -0.14}^{\ +0.16}$ and its combination with the CIV linear transmission bias parameter is $b_{\rm CIV}(1+β_{\rm CIV})=-0.0183_{\ -0.0014}^{\ +0.0013}$ ($1σ$ statistical error) at the mean redshift $z=2.00$. Splitting the sample at $z=2.2$ to constrain the bias evolution with redshift yields the power-law exponent $γ=0.60\pm0.63$, indicating a significantly weaker redshift-evolution than for the Ly$α$ forest linear transmission bias. We demonstrate that CIV absorption has the potential to be used as a probe of baryon acoustic oscillations (BAO). While the current data set is insufficient for a detection of the BAO peak feature, the final quasar samples for redshifts $1.4<z<2.2$ from eBOSS and the Dark Energy Spectroscopic Instrument (DESI) are expected to provide measurements of the isotropic BAO scale to $\sim7\%$ and $\sim3\%$ precision, respectively, at $z\simeq1.6$.

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arXiv2018

Cosmic Visions Dark Energy: Small Projects Portfolio

Understanding cosmic acceleration is one of the key science drivers for astrophysics and high-energy physics in the coming decade (2014 P5 Report). With the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument (DESI) and other new facilities beginning operations soon, we are entering an exciting phase during which we expect an order of magnitude improvement in constraints on dark energy and the physics of the accelerating Universe. This is a key moment for a matching Small Projects portfolio that can (1) greatly enhance the science reach of these flagship projects, (2) have immediate scientific impact, and (3) lay the groundwork for the next stages of the Cosmic Frontier Dark Energy program. In this White Paper, we outline a balanced portfolio that can accomplish these goals through a combination of observational, experimental, and theory and simulation efforts.

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arXiv2017

How to estimate the 3D power spectrum of the Lyman-$α$ forest

We derive and numerically implement an algorithm for estimating the 3D power spectrum of the Lyman-$α$ (Ly-$α$) forest flux fluctuations. The algorithm exploits the unique geometry of Ly-$α$ forest data to efficiently measure the cross-spectrum between lines of sight as a function of parallel wavenumber, transverse separation and redshift. The key to fast evaluation is to approximate the global covariance matrix as block-diagonal, where only pixels from the same spectrum are correlated. We then compute the eigenvectors of the derivative of the signal covariance with respect to cross-spectrum parameters, and project the inverse-covariance-weighted spectra onto them. This acts much like a radial Fourier transform over redshift windows. The resulting cross-spectrum inference is then converted into our final product, an approximation of the likelihood for the 3D power spectrum expressed as second order Taylor expansion around a fiducial model. We demonstrate the accuracy and scalability of the algorithm and comment on possible extensions. Our algorithm will allow efficient analysis of the upcoming Dark Energy Spectroscopic Instrument dataset.

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arXiv2017

The Lyman-$α$ power spectrum - CMB lensing convergence cross-correlation

We investigate the three-point correlation between the Lyman-$α$ forest and the CMB weak lensing ($δ_F δ_F κ$) expressed as the cross-correlation between the CMB weak lensing field and local variations in the forest power spectrum. In addition to the standard gravitational bispectrum term, we note the existence of a non-standard systematic term coming from mis-estimation of the mean flux over the finite length of Lyman-$α$ skewers. We numerically calculate the angular cross-power spectrum and discuss its features. We integrate it into zero-lag correlation function and compare our predictions with recent results by Doux et al.. We find that our predictions are statistically consistent with the measurement, and including the systematic term improves the agreement with the measurement. We comment on the implication of the response of the Lyman-$α$ forest power spectrum to the long-wavelength density perturbations.

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arXiv2017

An evaluation of cosmological models from expansion and growth of structure measurements

We compare a large suite of theoretical cosmological models to observational data from the cosmic microwave background, baryon acoustic oscillation measurements of expansion, Type Ia SNe measurements of expansion, redshift space distortion measurements of the growth of structure, and the local Hubble constant. Our theoretical models include parametrizations of dark energy as well as physical models of dark energy and modified gravity. We determine the constraints on the model parameters, incorporating the redshift space distortion data directly in the analysis. To determine whether models can be ruled out, we evaluate the $p$ value (the probability under the model of obtaining data as bad or worse than the observed data). In our comparison, we find the well known tension of H$_0$ with the other data; no model resolves this tension successfully. Among the models we consider, the large scale growth of structure data does not affect the modified gravity models as a category particularly differently than dark energy models; it matters for some modified gravity models but not others, and the same is true for dark energy models. We compute predicted observables for each model under current observational constraints, and identify models for which future observational constraints will be particularly informative.

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arXiv2017

Baryon acoustic oscillations from the complete SDSS-III Ly$α$-quasar cross-correlation function at $z=2.4$

We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Ly$α$-forest flux-transmission at a mean redshift $z=2.40$. The measurement uses the complete SDSS-III data sample: 168,889 forests and 234,367 quasars from the SDSS Data Release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level allowing a more accurate measurement of this cross-correlation. We also developed the first simulations of the cross-correlation allowing us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios $D_{H}(z=2.40)/r_{d} = 9.01 \pm 0.36$ and $D_{M}(z=2.40)/r_{d} = 35.7 \pm 1.7$, where the errors include marginalization over the non-linear velocity of quasars and the metal - quasar cross-correlation contribution, among other effects. These results are within $1.8σ$ of the prediction of the flat-$Λ$CDM model describing the observed CMB anisotropies. We combine this study with the Ly$α$-forest auto-correlation function [2017A&A...603A..12B], yielding $D_{H}(z=2.40)/r_{d} = 8.94 \pm 0.22$ and $D_{M}(z=2.40)/r_{d} = 36.6 \pm 1.2$, within $2.3σ$ of the same flat-$Λ$CDM model.

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arXiv2017

No evidence for dust B-mode decorrelation in Planck data

Constraints on inflationary $B$-modes using Cosmic Microwave Background polarization data commonly rely on either template cleaning or cross-spectra between maps at different frequencies to disentangle galactic foregrounds from the cosmological signal. Assumptions about how the foregrounds scale with frequency are therefore crucial to interpreting the data. Recent results from the Planck satellite collaboration claim significant evidence for a decorrelation in the polarization signal of the spatial pattern of galactic dust between 353 GHz and 217 GHz. Such a decorrelation would suppress power in the cross spectrum between high frequency maps, where the dust is strong, and lower frequency maps, where the sensitivity to cosmological $B$-modes is strongest. Alternatively, it would leave residuals in lower frequency maps cleaned with a template derived from the higher frequency maps. If not accounted for, both situations would result in an underestimate of the dust contribution and thus an upward bias on measurements of the tensor-to-scalar ratio, $r$. In this paper we revisit this measurement and find that the no-decorrelation hypothesis cannot be excluded with the Planck data. There are three main reasons for this: i) there is significant noise bias in cross spectra between Planck data splits that needs to be accounted for; ii) there is strong evidence for unknown instrumental systematics whose amplitude we estimate using alternative Planck data splits; iii) there are significant correlations between measurements in different sky patches that need to be taken into account when assessing the statistical significance. Between $\ell=55-90$ and over $72\%$ of the sky, the dust $BB$ correlation between 217 GHz and 353 GHz is $1.001^{+.004/.021}_{-.004/.000}$ ($68\%~stat./syst.$) and shows no significant trend with sky fraction.

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