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SUMMARY:Fast test to assess the impact of marginalization in Monte Carlo a
 nalyses and its application to cosmology
DTSTART;VALUE=DATE-TIME:20230601T095000Z
DTEND;VALUE=DATE-TIME:20230601T101500Z
DTSTAMP;VALUE=DATE-TIME:20261017T055309Z
UID:indico-contribution-978@cern.ch
DESCRIPTION:Speakers: Adrià GÓMEZ-VALENT ()\nMonte Carlo (MC) algorithms
  are commonly employed to explore high-dimensional parameter spaces constr
 ained by data. All the statistical information obtained in the output of t
 hese analyses is contained in the Markov chains\, which one needs to proce
 ss and interpret. The marginaliza- tion technique allows us to digest thes
 e chains and compute the posterior distributions for the parameter subsets
  of interest. In particular\, it lets us draw confidence regions in two-di
 mensional planes\, and get the constraints for the individual parameters. 
 It is very well known\, though\, that the marginalized results can suffer 
 from volume effects\, which can introduce a non-negligible bias into our c
 onclusions. The impact of these effects are barely studied in the literatu
 re. In this talk I first illustrate the problem through a very clear and s
 imple example in two dimensions\, and sug- gest the use of the profile dis
 tributions (PDs) as a complementary tool to detect marginalization biases 
 directly from the MC chains. I apply this method to four cosmological mode
 ls: the standard ΛCDM\, early dark energy\, coupled dark energy and the B
 rans-Dicke model with a cosmological constant. I discuss the impact of the
  volume effects on each model and the cosmological tensions\, using the fu
 ll Planck 2018 likelihood\, the Pantheon compilation of supernovae of type
  Ia and data on baryon acoustic oscillations. This test is very efficient 
 and can be easily applied to any MC study. It allows us to estimate the PD
 s at a derisory computational cost not only for the main cosmological para
 meters\, but also for the nuisance and derived ones\, and to assess the ne
 ed to perform a more in-depth analysis with the exact computation of the P
 Ds. This talk is based on Phys.Rev.D 106 (2022) 6\, 063506 [arXiv:2203.162
 85].\n\nhttps://indico.unina.it/event/70/contributions/978/
LOCATION:Lisbon
URL:https://indico.unina.it/event/70/contributions/978/
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