The speed of Galileon gravity

Brax, Philippe; Burrage, Clare; Davis, Anne-Christine

doi:10.1088/1475-7516/2016/03/004

Cited by 51 publications

(53 citation statements)

References 69 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, no distant GW-EM event will possibly be observed if c g is modified significantly, since the delay between both signals will be much larger than the monitoring time around the GW detection. This is the case of cosmic acceleration models without a cosmological constant such as covariant Galileons [52,62], for which |c g /c − 1| ∼ 10 − 100% (see [57] and Fig. 1 of Ref.…”

mentioning

confidence: 99%

Speed of gravitational waves and the fate of scalar-tensor gravity

et al. 2017

View full text Add to dashboard Cite

The direct detection of gravitational waves (GWs) is an invaluable new tool to probe gravity and the nature of cosmic acceleration. A large class of scalar-tensor theories predict that GWs propagate with velocity different than the speed of light, a difference that can be O(1) for many models of dark energy. We determine the conditions behind the anomalous GW speed, namely that the scalar field spontaneously breaks Lorentz invariance and couples to the metric perturbations via the Weyl tensor. If these conditions are realized in nature, the delay between GW and electromagnetic (EM) signals from distant events will run beyond human timescales, making it impossible to measure the speed of GWs using neutron star mergers or other violent events. We present a robust strategy to exclude or confirm an anomalous speed of GWs using eclipsing binary systems, whose EM phase can be exquisitely determined. he white dwarf binary J0651+2844 is a known example of such system that can be used to probe deviations in the GW speed as small as cg/c − 1 2 · 10 −12 when LISA comes online. This test will either eliminate many contender models for cosmic acceleration or wreck a fundamental pillar of general relativity.PACS numbers: 04.30.Nk 04.50. Kd, 95.36.+x, Introduction and summary. The direct detection of gravitational radiation [1,2] has initiated a new era for astronomy, astrophysics and fundamental physics. The observed gravitational wave (GW) events and the ones to come will usher in novel ways to test the nature of gravity [3]. Here, we will argue that probing the speed of GWs will be a decisive test for gravity and dark energy models.

show abstract

mentioning

confidence: 99%

Speed of gravitational waves and the fate of scalar-tensor gravity

et al. 2017

View full text Add to dashboard Cite

show abstract

“…it can be noted that the effect ofȳ in the Friedmann equation is to renormalise the Newton constant G N by a factor (1 − 2c 0ȳ ) (Brax et al, 2015). In order to avoid adding a new parameter y 0 to constrain, it is physically motivated to restrain our study to the case where the Newton constant at cosmological scales has its standard value today, i.e.ȳ 0 = 0.…”

Section: Cosmological Equationsmentioning

confidence: 99%

“…The disformal coupling plays a role in the field cosmological evolution, which makes this kind of Galileon model interesting to compare with cosmological data. Such a coupling between a scalar field and matter has also been widely studied in Koivisto (2012); Zumalacarregui (2013); Brax et al (2012Brax et al ( , 2013; Brax & Burrage (2014);and Brax et al (2015).…”

Section: Introductionmentioning

confidence: 99%

Constraining the ΛCDM and Galileon models with recent cosmological data

Neveu

Ruhlmann-Kleider

Astier

et al. 2017

A&A

View full text Add to dashboard Cite

Aims. The Galileon theory belongs to the class of modified gravity models that can explain the late-time accelerated expansion of the Universe. In previous works, cosmological constraints on the Galileon model were derived, both in the uncoupled case and with a disformal coupling of the Galileon field to matter. There, we showed that these models agree with the most recent cosmological data. In this work, we used updated cosmological data sets to derive new constraints on Galileon models, including the case of a constant conformal Galileon coupling to matter. We also explored the tracker solution of the uncoupled Galileon model. Methods. After updating our data sets, especially with the latest Planck data and baryonic acoustic oscillation (BAO) measurements, we fitted the cosmological parameters of the ΛCDM and Galileon models. The same analysis framework as in our previous papers was used to derive cosmological constraints, using precise measurements of cosmological distances and of the cosmic structure growth rate. Results. We show that all tested Galileon models are as compatible with cosmological data as the ΛCDM model. This means that present cosmological data are not accurate enough to distinguish clearly between the two theories. Among the different Galileon models, we find that a conformal coupling is not favoured, contrary to the disformal coupling which is preferred at the 2.3σ level over the uncoupled case. The tracker solution of the uncoupled Galileon model is also highly disfavoured owing to large tensions with supernovae and Planck +BAO data. However, outside of the tracker solution, the general uncoupled Galileon model, as well as the general disformally coupled Galileon model, remain the most promising Galileon scenarios to confront with future cosmological data. Finally, we also discuss constraints coming from the Lunar Laser Ranging experiment and gravitational wave speed of propagation.

show abstract

“…Cosmic acceleration could instead be driven by a dark energy field that permeates the Universe or be due to a breakdown of general relativity on large scales [6][7][8], perhaps with an unrelated mechanism suppressing the vacuum contributions. Dark energy must closely mimic a cosmological constant however (e.g., [9]), and the combination of large-scale structure and gravitational wave observations poses a challenge to the concept of cosmic self acceleration from a genuine modification of gravity [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Is there another coincidence problem at the reionization epoch?

Lombriser

Smer-Barreto

2017

Phys. Rev. D

View full text Add to dashboard Cite

The cosmological coincidences between the matter and radiation energy densities at recombination as well as between the densities of matter and the cosmological constant at present time are well known. We point out that moreover the third intersection between the energy densities of radiation and the cosmological constant coincides with the reionization epoch. To quantify the statistical relevance of this concurrence, we compute the Bayes factor between the concordance cosmology with free Thomson scattering optical depth and a model for which this parameter is inferred from imposing a match between the time of density equality and the epoch of reionization. This is to characterize the potential explanatory gain if one were to find a parameter-free physical connection. We find a very strong preference for such a concurrence on the Jeffreys scale from current cosmological observations. We furthermore discuss the effect of choice of priors, changes in reionization history, and free sum of neutrino masses. We also estimate the impact of adding intermediate polarization data from the Planck High Frequency Instrument and prospects for future 21 cm surveys. In the first case, preference for the correlation remains substantial, whereas future data may give results more decisive in pro or substantial in contra. Finally, we provide a discussion on different interpretations of these findings. In particular, we show how a connection between the star-formation history and the cosmological background dynamics can give rise to this concurrence.

show abstract

The speed of Galileon gravity

Cited by 51 publications

References 69 publications

Speed of gravitational waves and the fate of scalar-tensor gravity

Speed of gravitational waves and the fate of scalar-tensor gravity

Constraining the ΛCDM and Galileon models with recent cosmological data

Is there another coincidence problem at the reionization epoch?

Contact Info

Product

Resources

About