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SUMMARY:Measuring the galaxy bias\, gravity and sigma8 using the bispectru
 m - Hector Gil-Marin (ICG Portsmouth)
DTSTART:20150216T130000Z
DTEND:20150216T140000Z
UID:TALK56787@talks.cam.ac.uk
CONTACT:Tommaso Giannantonio
DESCRIPTION:Observations of Type Ia supernovae suggest that the Universe h
 as been accelerating since redshift z ∼ 0.5. Today the physical mechanis
 m responsible for this process is still a mystery. The simplest model to e
 xplain the acceleration of the Universe is the ΛCDM model. This model ass
 umes that the acceleration is driven by an exotic form of energy with nega
 tive pressure that might be related to the vacuum energy of quantum field 
 theories. This theory is equivalent to adding an integration constant to t
 he Einstein equations. Alternative theories to the vacuum energy\, such as
  f(R) class of models propose a modification of gravity in the infrared th
 at would produce an accelerated expansion. These models produce accelerate
 d expansion through a modification of the Einstein-Hilbert action by an ar
 bitrary function of the Ricci scalar R. As a consequence\, an extra propag
 ating scalar field appears that mediates a fifth force on all forms of mat
 ter.  In case the expansion of the Universe is driven by some of these alt
 ernative models\, we expect that the growth of structure\, namely f\, to b
 e different to the predictions from General Relativity. In order to detect
  such potential deviations in the growth of structure of the Universe\, th
 e redshift space power spectrum multipoles have been measured from galaxy 
 spectroscopic surveys such as BOSS. One of the caveats of this technique i
 s that at large scales the growth factor is fully degenerate with the ampl
 itude of the linear dark matter power spectrum\, and therefore only the qu
 antity sigma8 times f can be constrained. Measuring the bispectrum allows 
 to break this degeneracy\, and therefore to obtain an isolated measurement
  of the growth of structure (and also sigma8) from galaxy surveys.\nHoweve
 r\, measuring the bispectrum from galaxy surveys and more importantly mode
 lling its behaviour in redshift space for biased objects present several c
 hallenges that must be addressed if one wants to use this technique. The a
 im of this talk is to talk about these challenges and limitations and pres
 ent some possible solutions\, focusing in the applicability of the method 
 to galaxy surveys\, with especial attention to BOSS.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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