Multipole decomposition of the general luminosity distance 'Hubble law' -- a new framework for observational cosmology

Heinesen, Asta

doi:10.48550/arxiv.2010.06534

Cited by 10 publications

(32 citation statements)

References 47 publications

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“…Interestingly, in addition to the aforementioned theoretical predictions [6,7,22], there have been reports claiming that a dipolar axis (fairly close to that of the CMB) may exist in the supernovae data [24]- [30]. In other words, our universe may indeed seem to accelerate faster towards one direction and equally slower in the opposite.…”

Section: The Local Apparent Dipolementioning

confidence: 75%

“…The emergence of such an anisotropy was first suggested in [6] and then theoretically demonstrated in [7], by taking into account apparent shear-like effects of the relative motion. More recently, a different approach that employed the null geodesics of the photon trajectories to analyse the impact of relative motion on the luminosity distance, reached an analogous conclusion [22].…”

Section: The Local Apparent Dipolementioning

confidence: 90%

“…This scenario was originally proposed in [6,7] and it was later refined in [10]. Recently, an alternative approach, involving the null geodesics of electromagnetic signals (emitted and received by observers in the universe) and introducing a multiple-moment expansion of the corresponding luminosity distance, arrived at similar results [22]. In particular, the study showed that the (effective) deceleration parameter associated with the aforementioned null rays can take negative values within an otherwise decelerating universe and in so doing create the illusion of universal acceleration to the unsuspecting observers (see [22] and also § 4.4 next).…”

Section: Surveymentioning

confidence: 92%

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The peculiar Jeans length

Tsagas¹

2021

Preprint

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Large-scale bulk flows are commonplace in the universe. This means that observers living in typical galaxies, like our Milky Way, do not follow the mean universal expansion, but have peculiar velocities relative to it. Using relativistic linear cosmological perturbation theory, we show that bulk peculiar motions introduce a characteristic length scale. The latter is analogous to the familiar Jeans length and marks the threshold below which the linear kinematics, as seen by observers living inside the bulk flow, are dominated by relative-motion effects. On these scales cosmological measurements can vary considerably between the restframe of the bulk flow and that of the smooth Hubble expansion, due to relative-motion effects alone. In this work, we look into and compare the measurements of the deceleration parameter. We find that the associated "peculiar Jeans length" has typical size of the order of few hundred Mpc. On smaller scales, the deceleration parameter measured by the bulk-flow observers can be considerably larger (or lower) than its Hubble-frame counterpart. This, in turn, depends on whether the peculiar motion is slightly expanding (or contracting) relative to the background universal expansion. Then, assuming that expanding and contracting bulk flows are randomly distributed, nearly half of the observers in the universe may be misled to think that their cosmos is over-decelerated. The rest of them, on the other hand, may come to believe that the universe is under-decelerated, or even accelerated in some cases.

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Section: The Local Apparent Dipolementioning

confidence: 75%

Section: The Local Apparent Dipolementioning

confidence: 90%

Section: Surveymentioning

confidence: 92%

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The peculiar Jeans length

Tsagas¹

2021

Preprint

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“…This illustrates the importance of accurately incorporating the existence of cosmological structures, even when light propagation over large distances is considered. This importance has also been discussed in the context of the luminosity distance-redshift relation [22]. In general the configuration of structure on small and intermediate scales enter effective large scale cosmological descriptions.…”

Section: Discussionmentioning

confidence: 99%

Multipole decomposition of redshift drift -- model independent mapping of the expansion history of the Universe

Heinesen

2020

Preprint

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We consider redshift drift in a general space-time as expressed in terms of physically interpretable multipole series. An important realisation from the derived results is that redshift drift cannot in general be thought of as a direct probe of the average expansion rate of the Universe due to the presence of structure along the light beams from the astrophysical sources to the observer. We also predict the general presence of a dipolar and a quadrupolar offset in the detection of redshift drift for observers placed in locally anisotropic environments.

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“…This implies that for cosmological purposes, the consistently calibrated cosmic distance ladder would have a reference flux determined at 1Mpc. The generalised coordinate independent expressions for the area and the luminosity distance at low redshift are (see appendix A for details of the derivation) [23,47]…”

Section: Ii1 Inhomogeneous Distances In a Realistic Model Of The Univ...mentioning

confidence: 99%

Consequences of using a smooth cosmic distance in a lumpy universe: I

Umeh¹

2022

Preprint

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How do we appropriately fit a model based on an idealised Friedmann-Lemaıtre Robertson-Walker (FLRW) spacetime to observations made from a single location in a lumpy Universe? We address this question for surveys that measure the imprints of the Baryon Acoustic Oscillation (BAO) in galaxy distribution and the peak apparent magnitude of the type 1A supernova (SN1A). These observables are related to the cosmological model through the Alcock-Paczynski parameters and the distance-redshift relation. Using the corresponding inhomogeneous spacetime expressions of these as observed data, we perform a parameter inference assuming that the background FLRW model is the correct model of the universe. This process allows us to estimate the best fit Hubble rate and the deceleration parameter. We find that the inferred Hubble rate from the monopole of the Alcock-Paczynski parameters is in tension with the Hubble rate determined using the distance-redshift relation. The latter gives the best fit Hubble rate for the cosmological expansion. The constraint on the Hubble rate from the Alcock-Paczynski parameters is contaminated by the environment. When the environmental contribution is restricted to modes in the Hubble flow, we find about (9-12)% discrepancy in the Hubble rate. Finally, we comment on the insufficiency of the method of cosmography in constraining the deceleration parameter. CONTENTS

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Multipole decomposition of the general luminosity distance 'Hubble law' -- a new framework for observational cosmology

Cited by 10 publications

References 47 publications

The peculiar Jeans length

The peculiar Jeans length

Multipole decomposition of redshift drift -- model independent mapping of the expansion history of the Universe

Consequences of using a smooth cosmic distance in a lumpy universe: I

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