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SUMMARY:Fifth Force Constraints from Galaxy-Scale Tests - Aneesh Naik (IoA
 )
DTSTART:20200710T103000Z
DTEND:20200710T113000Z
UID:TALK143860@talks.cam.ac.uk
CONTACT:Martin Haehnelt
DESCRIPTION:In recent years\, 'scalar-tensor' theories of gravity\, in whi
 ch a new scalar field couples to gravity\, have been subject to increased 
 attention. In these theories\, the scalar field mediates 'fifth forces'\, 
 which can be rendered undetectable in the laboratory or Solar System by sc
 reening mechanisms\, which act to suppress the fifth force in regions of h
 igh density. Nonetheless\, interesting signatures arise elsewhere\, such a
 s on galactic scales. This talk will divide roughly into two halves\, desc
 ribing two such astrophysical signatures: upturns in galaxy rotation curve
 s\, and asymmetries in stellar streams. In the first half\, I will describ
 e the results of a recent investigation\, searching for the upturn signatu
 re in the high-quality rotation curves of the SPARC sample. This investiga
 tion was primarily limited by uncertainty about dark matter halo shapes: a
  fifth force in the outer regions of a galaxy with a cuspy halo can resemb
 le the rotation curve of a galaxy with a cored halo and no fifth force\, l
 eading to a degeneracy. In the second half\, I will turn to the stellar st
 ream investigation\, which remains in its 'proof of concept' stage. In par
 ticular\, I will show results from restricted N-body simulations of stream
  formation\, and discuss constraints obtainable from upcoming Gaia data re
 leases.
LOCATION:via zoom 
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