Mapping the inhomogeneous Universe with Standard Sirens: Degeneracy between inhomogeneity and modified gravity theories. (arXiv:2007.15020v1 [astro-ph.CO])

Mapping the inhomogeneous Universe with Standard Sirens: Degeneracy between inhomogeneity and modified gravity theories. (arXiv:2007.15020v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kalomenopoulos_M/0/1/0/all/0/1">Marios Kalomenopoulos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Khochfar_S/0/1/0/all/0/1">Sadegh Khochfar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gair_J/0/1/0/all/0/1">Jonathan Gair</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arai_S/0/1/0/all/0/1">Shun Arai</a>

The detection of gravitational waves (GWs) and an accompanying
electromagnetic (E/M) counterpart have been suggested as a future probe for
cosmology and theories of gravity. In this paper, we present calculations of
the luminosity distance of sources taking into account inhomogeneities in the
matter distribution that are predicted in numerical simulations of structure
formation. We assume mock GWs sources, with known redshift, based on binary
population synthesis models, between redshifts $z=0$ and $z=5$. We show that
present systematic limits of observations allow for a wide range of effective
inhomogeneous models to be consistent with a homogeneous and isotropic
Friedman-Lema{^i}tre-Robertson-Walker background model. Increasing the number
of standard sirens from $150$ to $350$ and up to $z=5$ helps shrink the
confidence contours $(68% rm{C.L.})$ by $sim 35 %$, but still leaving the
inhomogeneity parameters loosely constrained. In addition, we show that
inhomogeneities resulting from clustering of matter can mimic certain classes
of modified gravity theories, or other effects that dampen GW amplitudes, and
deviations larger than $delta nu sim mathcal{O}(0.1) (99% rm{C.L.})$ to
the extra friction term $nu$, from zero, would be necessary to distinguish
them. This limit is determined by observational errors (signal-to-noise ratio)
and to improve on this constraint by an order of magnitude, one would need to
reduce systematic observational errors to about one-fifth of their current
values.

The detection of gravitational waves (GWs) and an accompanying
electromagnetic (E/M) counterpart have been suggested as a future probe for
cosmology and theories of gravity. In this paper, we present calculations of
the luminosity distance of sources taking into account inhomogeneities in the
matter distribution that are predicted in numerical simulations of structure
formation. We assume mock GWs sources, with known redshift, based on binary
population synthesis models, between redshifts $z=0$ and $z=5$. We show that
present systematic limits of observations allow for a wide range of effective
inhomogeneous models to be consistent with a homogeneous and isotropic
Friedman-Lema{^i}tre-Robertson-Walker background model. Increasing the number
of standard sirens from $150$ to $350$ and up to $z=5$ helps shrink the
confidence contours $(68% rm{C.L.})$ by $sim 35 %$, but still leaving the
inhomogeneity parameters loosely constrained. In addition, we show that
inhomogeneities resulting from clustering of matter can mimic certain classes
of modified gravity theories, or other effects that dampen GW amplitudes, and
deviations larger than $delta nu sim mathcal{O}(0.1) (99% rm{C.L.})$ to
the extra friction term $nu$, from zero, would be necessary to distinguish
them. This limit is determined by observational errors (signal-to-noise ratio)
and to improve on this constraint by an order of magnitude, one would need to
reduce systematic observational errors to about one-fifth of their current
values.

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