Hot+Open+Questions

Below is a list of open questions and hot topics for studies of the high-redshift background//__. Feel free to add more or comment on those we have.__// If any particularly interest you, speak up and let us know so that we can best design the workshop, discussions, and focus group sessions. In particular, if you are interested in leading or organizing a breakout session or focus group, please start a thread in the discussion section here, and/or edit the text directly below. =Observations and Experiments: Today=
 * What have we learned so far about RFI mitigation? How do the sites appear? What obstacles has LOFAR in particular encountered and/or overcome?
 * What are the best observing strategies to extract EoR information optimally?
 * What have we learned so far about correlator hardware and design?
 * What have we learned so far about point source subtraction?
 * What have we learned about the ionosphere?
 * What have learned from the existing intensity mapping experiments (i.e., low-redshift 21 cm maps)? How can the high-redshift experiments inform their design and implementation?

=Data Analysis: Today=
 * What does the polarized low-frequency sky look like?
 * What foreground strategies have been developed? Which work best? Can we combine strategies to do an even better job?
 * What are the challenges and benefits of cross-correlation? What do we need to do to enable it, both in our own experiments and through lobbying others? What lessons can we learn from the low-redshift correlation attempts?
 * What statistics should we be considering other than the power spectrum?

=Theoretical Issues: Today=
 * Do our simulations agree with each other adequately? Do the semi-numeric models agree with the simulations? At what point in analyzing the data will we need to turn from analytic to semi-numeric to full simulation models?
 * How do recombinations in the intergalactic medium affect reionization, especially the tail end? How do we best model them?
 * How robust are our models of reionization?
 * How (if at all) can we use existing information from other techniques - galaxy surveys, quasars, the CMB - to inform our models of high-redshift structure formation?
 * What should the theoretical community be doing to best prepare for the arrival of actual data?

=**Experiments and Analysis: The Future**=
 * What should we be working on to best revolutionize the field? Does the future lie in better correlators? In innovative telescope designs?
 * What will it really take to pull out redshift-space distortions from the 21 cm signal? Is it worth it?
 * What are the next steps in building bigger and better telescopes?
 * When do we take the leap toward the moon? Jack Burns suggests: //"   This group might be a good one to help us think through all of the facets that might need to go into an Explorer proposal as well as advance the EDGES experiment. We can talk through arguments about the ground vs. the Moon at <100 MHz. We can discuss new algorithms for foreground subtraction. We can discuss the range of theory predictions of the spectral signatures including X-ray heating, Pop II vs Pop III star formation impact, dark matter decay in the Dark Ages, etc"   //

=Theoretical Issues: The Future=
 * What kinds of signatures are of most interest to particle physicists? What should we really be going after to answer these kinds of questions?
 * How robust are our models of the pre-reionization era, where the first galaxies establish the spin temperature field and subsequently heat the IGM? What are the next steps to develop these models?
 * What should the theoretical community be doing to help design and inform the next generation of 21 cm experiments?
 * When will we be able to model reionization "from first principles"? That is, a simulation that includes dark matter, hydrodynamics (and resolving well all relevant galaxies), and radiative transfer (without post-processing), in a representative cosmological volume.