Novel Probes of Cosmology

 

   Theories of modified gravity aim to explain cosmic acceleration without invoking dark energy. Such theories typically posit new interactions due to the presence of additional fields. In addition to their signal on large scales, these theories predict new physics on the smaller scales of individual galaxies and clusters. Models of dark matter interactions also typically lead to signatures on small scales. A common feature of these new interactions is that different components of galaxies, in particular stars, gas, dark matter and black holes, respond differently to them.

            

   Astrophysical tests of dark sector interactions are powerful, complementary probes of fundamental physics. Several types of tests, involving studies of black holes, stars, galactic structure and dynamics, and galaxy clusters have been developed in the last decade, and have proven powerful at constraining models of modified gravity as well as dark matter interactions. Astrophysical tests typically require high resolution imaging of low-redshift galaxies and clusters, while for specific tests, spectroscopy, multi-wavelength data and space-based imaging may be valuable.

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   The Novel Probes Project comprises two review articles—one covering astrophysical tests of modified gravity and the other covering dark matter self-interactions—with corresponding discussion forums hosted on Slack which researchers are invited to join. The complexity of the theories and the many theory-specific details necessary to develop tests give this field a steep learning curve for observers. Our primary goal is to present observational consequences of theoretical ideas for observers and data analysts, although we hope to provide useful synopses for theorists too. DES, KiDS and HSC have powerful datasets on multi-colour imaging of galaxies and stars, and DESI, PFS, LSST, Euclid and WFIRST are coming online shortly, along with surveys in other wavelengths. Rapid connections between theory and data analysis spanning different projects can pay big dividends at this exciting time in empirical cosmology. We hope new collaborations will arise as a result of these discussions.

        

   Our reviews will be ‘living’ in that empirical constraints will be updated and new ideas presented as they mature sufficiently to meet the data. We thus aim to give authoritative summaries of new ideas and tests with current observations, as well as reference documents for planning and exploiting future surveys.

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