Conclusion

Khoury, Philip S.

doi:10.1017/cbo9780511563522.008

Cited by 18 publications

(32 citation statements)

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“…Archetypal modified-gravity models such as f (R) [88][89][90] are equivalent to instances of these theories [91]. Chameleons [92] and symmetrons [93] also belong to this class of theories (see [94] for a review). Certain freedom exists in writing the theory due to the possibility of rescaling the metric g µν →ḡ µν = C(φ)g µν and redefining the scalar field, i.e.…”

Section: Horndeski Theories [74]mentioning

confidence: 99%

Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy

Ezquiaga

Zumalacárregui

2018

Front. Astron. Space Sci.

207

202

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Gravitational waves (GWs) provide a new tool to probe the nature of dark energy (DE) and the fundamental properties of gravity. We review the different ways in which GWs can be used to test gravity and models for late-time cosmic acceleration. Lagrangian-based gravitational theories beyond general relativity (GR) are classified into those breaking fundamental assumptions, containing additional fields and massive graviton(s). In addition to Lagrangian based theories we present the effective theory of DE and the µ-Σ parametrization as general descriptions of cosmological gravity. Multi-messenger GW detections can be used to measure the cosmological expansion (standard sirens), providing an independent test of the DE equation of state and measuring the Hubble parameter. Several key tests of gravity involve the cosmological propagation of GWs, including anomalous GW speed, massive graviton excitations, Lorentz violating dispersion relation, modified GW luminosity distance and additional polarizations, which may also induce GW oscillations. We summarize present constraints and their impact on DE models, including those arising from the binary neutron star merger GW170817. Upgrades of LIGO-Virgo detectors to design sensitivity and the next generation facilities such as LISA or Einstein Telescope will significantly improve these constraints in the next two decades.

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Section: Horndeski Theories [74]mentioning

confidence: 99%

Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy

Ezquiaga

Zumalacárregui

2018

Front. Astron. Space Sci.

207

202

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“…Several screening mechanisms were proposed and widely discussed in the literature, e.g. a popular chameleon field model suggested by Khoury & Weltman (2004), when coupling strength depends on the environmental matter density, or a concept of emergent gravity recently developed by Verlinde (2017), where additional coupling is modulated by surface mass density of baryons. However, non of these screening models has yet been verified experimentally.…”

Section: Introductionmentioning

confidence: 99%

Testing the weak equivalence principle by differential measurements of fundamental constants in the Magellanic Clouds

Levshakov

Henkel

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Non-standard fields are assumed to be responsible for phenomena attributed to dark energy and dark matter. Being coupled to ordinary matter, these fields modify the masses and/or charges of the elementary particles, thereby violating the Weak Equivalence Principle. Thus, values of fundamental constants such as the proton-to-electron mass ratio, µ, and/or the fine structure constant, α, measured in different environment conditions can be used as probes for this coupling. Here we perform differential measurements of F = µα 2 to test a non-standard coupling in the Magellanic Clouds -dwarf galaxies where the overall mass budget is dominated by dark matter. The analysis is based on [C i] and CO lines observed with the Herschel Space Observatory. Since these lines have different sensitivities to changes in µ and α, the combined α and µ variations can be evaluated through the radial velocity offsets, ∆V , between the CO and [C i] lines. Averaging over nine positions in the Magellanic Clouds, we obtain ∆V = −0.02 ± 0.07 km s −1 , leading to |∆F/F | < 2 × 10 −7 (1σ), where ∆F/F = (F obs − F lab )/F lab . However, for one position observed with five times higher spectral resolution we find ∆V = −0.05 ± 0.02 km s −1 , resulting in ∆F/F = (−1.7 ± 0.7) × 10 −7 . Whether this offset is due to changes in the fundamental constants, due to chemical segregation in the emitting gas or merely due to Doppler noise requires further investigations.

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“…There are many reasons why the CDD could in principle be violated in nature, at least one of which was invoked to test non-standard cosmologies by Bassett & Kunz (2004a). The violation could arise if the spacetime is not described by a metric theory of gravity, which many believe is unlikely (see, e.g., Adler 1971;Bassett & Kunz 2004b), or perhaps because photons arriving from presumed standard candles, such as Type Ia SNe, are altered by absorption or scattering along the line of sight (see, e.g., Sikivie 1983;Bassett & Kunz 2004a;Raffelt 1999;Chen 1995;Deffayet & Uzan 2000;Khoury & Weltman 2004;Burrage 2008;Liao et al 2015). Following early papers on this topic by Bassett & Kunz (2004a, 2004b, many have attempted to validate the CDD using ⋆ John Woodruff Simpson Fellow.…”

Section: Introductionmentioning

confidence: 99%

A comparison of the Rh = ct and ΛCDM cosmologies using the cosmic distance duality relation

Melia

2018

Monthly Notices of the Royal Astronomical Society

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The cosmic distance duality (CDD) relation (based on the Etherington reciprocity theorem) plays a crucial role in a wide assortment of cosmological measurements. Attempts at confirming it observationally have met with mixed results, though the general consensus appears to be that the data do support its existence in nature. A common limitation with past approaches has been their reliance on a specific cosmological model, or on measurements of the luminosity distance to Type Ia SNe, which introduces a dependence on the presumed cosmology in spite of beliefs to the contrary. Confirming that the CDD is actually realized in nature is crucial because its violation would require exotic new physics. In this paper, we study the CDD using the observed angular size of compact quasar cores and a Gaussian Process reconstruction of the HII galaxy Hubble diagram-without pre-assuming any particular background cosmology. In so doing, we confirm at a very high level of confidence that the angular-diameter and luminosity distances do indeed satisfy the CDD. We then demonstrate the potential power of this result by utilizing it in a comparative test of two competing cosmological models-the R h = ct universe and ΛCDM-and show that R h = ct is favoured by the CDD data with a likelihood ∼ 82.3% compared with ∼ 17.7% for the standard model.

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Conclusion

Cited by 18 publications

References 0 publications

Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy

Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy

Testing the weak equivalence principle by differential measurements of fundamental constants in the Magellanic Clouds

A comparison of the Rh = ct and ΛCDM cosmologies using the cosmic distance duality relation

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