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Below we provide some examples of abstracts that were submitted very early. A google spread sheet of all abstracts can be found here. New abstract submissions will be added on a regular basis. If you plan to submit an abstract, please consider to add a line about the required resources to make the proposed effort a success. Also, we are looking for abstracts describing efforts that will enhance P5 priorities.

21 cm

Intensity mapping of galaxies in 21-cm emission at redshifts z=1-6 can fulfill many scientific goals set out in the P5 report in a cost effective way while utilizing expertise currently existing in the DOE national laboratory complex. After DESI, it will complete the program of BAO mapping of the observable universe by measuring the expansion history deep into the pre-acceleration era. The two main science cases are constraints on the dark radiation from precision determination of BAO phases and constraints on modified gravity and early dark energy models. Additional topics worth exploring include non-Gaussianity and weak lensing. The roadmap from ideation to project must proceed in several parallel tracks: i) fully determining and forecasting the science case ii) demonstrating technology, scalability and cost efficiency iii) campaigning and educating the community iv) establishing collaboration with other agencies to help secure funding and widen the science base. At the workshop we will discuss these topics and organize further work.

Southern Spectroscopic Roadmap

A southern spectroscopic survey facility would improve the scientific capabilities of all dark energy probes. Such a survey would greatly reduce the uncertainties associated with photometric redshifts and therefore deliver important information for surveys such as LSST. It would also enable the measurements of spectroscopic redshifts of tens of thousands of Type Ia supernovae. Cluster science would benefit from accurate cluster velocities and velocity dispersions. A possible roadmap in the south could include a near term (~2026) Southern Spectroscopic Survey Instrument which would be on the sky at the same time as LSST and therefore lead to important observations to enhance LSST science. During a second phase, this southern survey could be upgraded to lead to the ultimate spectroscopic survey. A Billion Object Apparatus would be capable of surveying galaxy clustering to non-linear scales for redshifts z<1.5 and all linear modes to z=3.5. Such a roadmap will need to address several challenges, from telescope availability, to new instrumentation work, to theory challenges. (This abstract is based in part on https://arxiv.org/pdf/1604.07626.pdf and discussions at earlier meetings.)

New Technology Developments for the Future

Research on technologies that will be required for the next big project, whatever that will be, is essential. Given that there is no current consensus on the next step, significant progress can be made on developing and assessing the DOE technology portfolio with relatively modest investments. We have outlined our priorities in the technology document (arXiv:1604.07821): development and characterization of Si and Ge CCDs and CMOS sensors, MKID sensor work, 21-cm instrumentation pathfinders, ring resonators, adaptive optics and fiber positioner technology improvements. Some of this work can directly inform planning for future experiments, for example if fiber positioners can be made mechanically smaller and collect more light through adaptive optics, it would be possible to reach next stage in DE with smaller fields of view, considerably relaxing requirements on telescope optics. If Ge CCDs can be made efficient and low noise it would open new possibilities in deep infrared spectroscopy. MKIDS, and other forms of cryogenic sensor arrays, could, in principle, provide intrinsic photon energy sensitivity, which might eliminate the need for observations in distinct filter bands. Similarly, small 21-cm path-finders can asses the limitations and opportunities of this technique.

New observational windows to enhance LSST and DESI

Joint Pixel Analysis: There is broad agreement that DOE science will benefit by combining information from different experiments. At the lowest level this can be achieved by combining information at the catalog-level. However, these merges are considerably more potent if data are jointly analyzed at the pixel level (arXiv:1501.07897). For example, WFIRST and Euclid data would help attack the deblending challenge in LSST. Putting the hooks into Data Management software now for the different experiments might greatly ease the cross-correlation analyses in the coming decade.

Coordinated observing, and joint SN effort: Potential coordination of the observing schedules can have significant beneficial implications for the scientific optimization of all three facilities. Of particular interest would be a coordinated supernova search-and-follow-up effort between LSST and WFIRST, since LSST’s wide field finds sufficient numbers of z < 1 supernovae, while WFIRST’s optical-to-NIR integral-field spectrograph provides the host-subtracted spectroscopy for >1000 SNe that can ensure the cosmology results (as well as train LSST’s photometry-only SN studies).

Coordinated ground/space photo-z calibration: For the calibration of photometric redshifts, it would also be important to put effort into joint planning of the WFIRST galaxy spectroscopic survey, based on the parallel use of the integral-field spectrograph to observe ~70,000 galaxies during the imaging surveys; these can provide spectra with near-IR depth that cannot be reached from the ground and thus calibrate the higher redshift range.

Spectroscopy on Subaru: There is broad agreement that Southern spectroscopy will greatly enhance LSST science. At a cost of order $5-10M, the community could buy time on Subaru to obtain of order 5 million spectra of galaxies over an unprecedented volume.

Low Resolution Spectroscopy: LSST is critically dependent upon photometric redshifts - estimates of the redshifts of objects based on flux information obtained through broad filters - for all probes of dark energy. High quality photometric redshifts can transform an inherently two dimensional map into a full 3D map of the universe, thereby harvesting much more of the information in the sky. Adding additional information using narrow band filters or low resolution spectroscopy has the potential to reduce scatter in photometric redshift estimates and reduce contamination from catastrophic outliers.

Theory, Analysis and Computing

Research: DOE has invested significant funds to create a broad-based successful cosmic surveys program. The number of scientists working on these is relatively small, so many of them work on multiple projects. The community is already seeing the burden that this places on current analyses. Increasing the research budget is one of the most powerful ways of extracting science from cosmic surveys. Developing analysis tools that cut across multiple experiments is a particularly effective way to leverage lessons learned in one project for others. A similarly crucial part of the research budget is an investment in theoretical work that has helped initiate and shape the cosmic program, and which is needed to interpret and guide future missions.

Simulations: Cosmological simulations are needed for all future surveys. Even in current surveys like DES, they are among the most challenging deliverables. Generating simulations and sophisticated analysis tools for the different probes that could be used for multiple surveys is a way to reduce the cost in dollars and (wo)manpower to the experiments in the 2020’s. In addition, building infrastructure to enable easy sharing of the simulations is important.

Novel Probes: Theories that go beyond general relativity in order to explain the current epoch of acceleration inevitably introduce new degrees of freedom, and these leave their imprint on a variety of scales. The most robust signature of modified gravity models is screening: the notion that since tests have established the validity of Einstein’s theory in the laboratory and in the Solar System, there must be a mechanism that renders the additional degrees of freedom ineffective in such regions. Novel probes search for the differences between the behavior of gravity in screened and unscreened regions using observations of galaxies, clusters or voids. Models of dark matter interactions also typically lead to signatures on small scales. A common feature of many of these probes is a kind of equivalence principle violation, namely that different components of galaxies -- stars, gas, dark matter and black holes -- respond differently to external forces. These tests thus operate on smaller scales than the cosmological tests using information that is not used in the large scale tests. Therefore, typical large-scale surveys are usually not optimal for these kind of analyses. Successful tests carried out so far have relied on archival data. The next advances could come from mini-surveys designed for such tests (the SDSS IV MANGA survey is currently being used for such an analysis) or an analysis of small scale measurements from ongoing and planned surveys. Such advances require rigorous new analysis methodology and the use of simulations or mock catalogs that represent new theories or capture the qualitative features of a class of theories.

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