A Challenge to the Standard Cosmological Model

Secrest, Nathan J.; Hausegger, Sebastian von; Rameez, M.; Mohayaee, Roya; Sarkar, S.

doi:10.48550/arxiv.2206.05624

Cited by 3 publications

(16 citation statements)

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“…It is worth emphasizing that, isotropy aside, these tests are essentially independent of a specific cosmological model, so there is no debate about alternative models within FLRW. To first approximation, various independent groups have reported an excess in the amplitude of the cosmic dipole [111][112][113][124][125][126][127][128][129][130] (however, see [131][132][133]), while the inferred directions coincide with the expected direction of the CMB dipole. Naïvely, this excess in amplitude implies an anisotropic Universe at scales well beyond inferred isotropy scales (see, for example, reference [134]).…”

Section: Prologuementioning

confidence: 93%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

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The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

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Section: Prologuementioning

confidence: 93%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

View full text Add to dashboard Cite

show abstract

“…Our analysis can also be straightforwardly adapted to perform a targeted search for any time-and frequency-dependent stochastic signal with a known sky pattern, e.g., GW emission from the Galactic Center [70,71]. It is also straightforward to replace the Planck values we have assumed for the dipole magnitude and direction with any other desired values, which may be relevant given the claimed tension between Planck and various lower-redshift surveys [37][38][39].…”

Section: Discussionmentioning

confidence: 99%

“…This effect is well known and has been measured with high precision in other cosmological observables, particularly the cosmic microwave background (CMB) [36]. As we discuss below, a joint measurement of this dipole and of the monopole could help us unravel the physics of the sources that contribute to the GWB, as well as potentially shedding light on the existing tension between the CMB dipole and the dipole observed in source counts of quasars and radio galaxies [37][38][39] (see however [40]).…”

Section: Introductionmentioning

confidence: 88%

“…We see that our third-generation network is expected to detect this dipole extremely quickly, with less than two days of data. This shows that future gravitational-wave observatories will be capable of measuring this particular dipole with very high precision, enabling robust tests of our understanding of the source population and of cosmology more broadly (i.e., by testing whether the dipole direction and amplitude are consistent with that of the CMB or whether they exhibit anomalies similar to those discussed in [37][38][39]). 8…”

Section: Forecasts For Third-generation Interferometersmentioning

confidence: 94%

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Targeted search for the kinematic dipole of the gravitational-wave background

et al. 2022

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There is growing interest in using current and future gravitational-wave interferometers to search for anisotropies in the gravitational-wave background. One guaranteed anisotropic signal is the kinematic dipole induced by our peculiar motion with respect to the cosmic rest frame, as measured in other full-sky observables such as the cosmic microwave background. Our prior knowledge of the amplitude and direction of this dipole is not explicitly accounted for in existing searches by LIGO/Virgo/KAGRA but could provide crucial information to help disentangle the sources which contribute to the gravitationalwave background. Here, we develop a targeted search pipeline which uses this prior knowledge to enable unbiased and minimum-variance inference of the dipole magnitude. Our search generalizes existing methods to allow for a time-dependent signal model, which captures the annual modulation of the dipole due to the Earth's orbit. We validate our pipeline on mock data, demonstrating that neglecting this time dependence can bias the inferred dipole by as much as Oð10%Þ. We then run our analysis on the full LIGO/Virgo O1 þ O2 þ O3 dataset, obtaining upper limits on the dipole amplitude that are consistent with existing anisotropic search results.

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“…In that case, the dipole of the luminosity distance directly yields the Hubble parameter. Although it is usually assumed that our peculiar velocity can be deduced from the dipole of the CMB, it should be noted that there are some indications in observational data that this expectation is violated [38][39][40]. Nonetheless, it will here be assumed that jv 0 j can be extracted from other data than that used for obtaining the luminosity distance.…”

Section: Introductionmentioning

confidence: 99%

Quantifying effects of inhomogeneities and curvature on gravitational wave standard siren measurements of H(z)

Koksbang

2022

Phys. Rev. D

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A Challenge to the Standard Cosmological Model

Cited by 3 publications

References 0 publications

Is the observable Universe consistent with the cosmological principle?

Is the observable Universe consistent with the cosmological principle?

Targeted search for the kinematic dipole of the gravitational-wave background

Quantifying effects of inhomogeneities and curvature on gravitational wave standard siren measurements of H(z)

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