7 research outputs found
Constraining f(R) theories with cosmography
A method to set constraints on the parameters of extended theories of
gravitation is presented. It is based on the comparison of two series
expansions of any observable that depends on H(z). The first expansion is of
the cosmographical type, while the second uses the dependence of H with z
furnished by a given type of extended theory. When applied to f(R) theories
together with the redshift drift, the method yields limits on the parameters of
two examples (the theory of Hu and Sawicki (2007), and the exponential gravity
introduced by Linder (2009)) that are compatible with or more stringent than
the existing ones, as well as a limit for a previously unconstrained parameter.Comment: 9 pages, 2 figures; v2: modifications in title and presentation,
results unchange
Space-time variation of the electron-to-proton mass ratio in a Weyl model
Seeking a possible explanation for recent data indicating a space-time
variation of the electron-to-proton mass ratio within the Milky Way, we
consider a phenomenological model where the effective fermion masses depend on
the local value of the Weyl tensor. We contrast the required values of the
model's free parameters with bounds obtained from modern tests on the violation
of the Weak Equivalence Principle and we find that these quantities are
incompatible. This result indicates that the variation of nucleon and electron
masses through a coupling with the Weyl tensor is not a viable model.Comment: 24 page
J-PAS: Forecasts for dark matter - dark energy elastic couplings
We consider a cosmological model where dark matter and dark energy feature a
coupling that only affects their momentum transfer in the corresponding Euler
equations. We perform a fit to cosmological observables and confirm previous
findings within these scenarios that favour the presence of a coupling at more
than . This improvement is driven by the Sunyaev-Zeldovich data. We
subsequently perform a forecast for future J-PAS data and find that clustering
measurements will permit to clearly discern the presence of an interaction
within a few percent level with the uncoupled case at more than when
the complete survey, covering sq. deg., is considered. We found that the
inclusion of weak lensing measurements will not help to further constrain the
coupling parameter. For completeness, we compare to forecasts for DESI and
Euclid, which provide similar discriminating power.Comment: 34 pages, 17 figures, added some clarifications and discussions,
matches published versio