Nonlinear structure formation in the cubic Galileon gravity model

In this work we will test an alternative model of gravity belonging to the large family of galileon models. It is characterized by an intrinsic breaking of the Vainshtein mechanism inside large astrophysical objects, thus having possibly detectable observational signatures. We will compare theoretical predictions from this model with the observed total mass profile for a sample of clusters of galaxies. The profiles are derived using two complementary tools: X-ray hot intra-cluster gas dynamics, and strong and weak gravitational lensing. We find that a dependence with the dynamical internal status of each cluster is possible; for those clusters which are very close to be relaxed, and thus less perturbed by possible astrophysical local processes, the galileon model gives a quite good fit to both X-ray and lensing observations. Both masses and concentrations for the dark matter halos are consistent with earlier results found in numerical simulations and in the literature, and no compelling statistical evidence for a deviation from general relativity is detectable from the present observational state. Actually, the characteristic galileon parameter Υ is always consistent with zero, and only an upper limit ( 0.086 at 1σ, 0.16 at 2σ, and 0.23 at 3σ) can be established. Some interesting distinctive deviations might be operative, but the statistical validity of the results is far from strong, and better data would be needed in order to either confirm or reject a potential tension with general relativity.PACS numbers: 04.50. Kd, 98.80.Es, 95.35. + d

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“…(8), (9) and (11), we have two main unknown quantities: the theoretical parameter Υ, and the matter density ρ, which we need to define.…”

Section: Theorymentioning

confidence: 99%

Breaking the Vainshtein screening in clusters of galaxies

et al. 2017

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“…Here, we focus on the portion of the parameter space that avoids these problems, which is known as the cubic Galileon model. This model was, however, thought to be unable to fit the currently available observational data, due to its strong integrated Sachs-Wolfe (ISW) effect, enhanced matter clustering on large scales [11,12] and difficulties in matching the position of the baryonic acoustic oscillation (BAO) peak.…”

Section: Introductionmentioning

confidence: 99%

“…For later stages of structure formation, the picture becomes more complex due to the nonlinearities of the screening mechanism [9,11,21].…”

Section: Introductionmentioning

confidence: 99%

Modified gravity with massive neutrinos as a testable alternative cosmological model

Baugh

Pascoli

2014

Phys. Rev. D

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Reprinted with permission from the American Physical Society: Alexandre Barreira, Baojiu Li, Carlton M. Baugh, and Silvia Pascoli. Modi ed gravity with massive neutrinos as a testable alternative cosmological model. Physical Review D, 90, 2, 023528 c 2014 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modi ed, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society. Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We show that, in the presence of massive neutrinos, the Galileon gravity model provides a very good fit to the current cosmic microwave background (CMB) temperature, CMB lensing and baryonic acoustic oscillation data. This model, which we dub νGalileon, when assuming its stable attractor background solution, contains the same set of free parameters as lambda cold dark matter (ΛCDM), although it leads to different expansion dynamics and nontrivial gravitational interactions. The data provide compelling evidence (≳6σ) for nonzero neutrino masses, with Σm ν ≳ 0.4 eV at the 2σ level. Upcoming precision terrestrial measurements of the absolute neutrino mass scale therefore have the potential to test this model. We show that CMB lensing measurements at multipoles l ≲ 40 will be able to discriminate between the νGalileon and ΛCDM models. Unlike ΛCDM, the νGalileon model is consistent with local determinations of the Hubble parameter. The presence of massive neutrinos lowers the value of σ 8 substantially, despite of the enhanced gravitational strength on large scales. Unlike ΛCDM, the νGalileon model predicts a negative ISW effect, which is difficult to reconcile with current observational limits.

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“…For the purely cubic Galileons, the condition that the equation of state should be close to -1 implies that c 2 < 0 [35], a case that we discard as we require a well-defined Minkowski limit. We will see that one can preserve a positive c 2 and still impose that c 4 is small together with an equation of state close to -1 when the Galileon scalar field does not lead to all the dark energy of the Universe.…”

Section: Cubic Galileonsmentioning

confidence: 99%

“…Constraints on the allowed cosmology of Galileon theories can be obtained from a wide variety of observations, unveiling a very rich phenomenology [12,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Here we consider for the first time the constraints that current and near future observations of gravitational waves can place on these theories.…”

Section: Introductionmentioning

confidence: 97%

The speed of Galileon gravity

Brax

Burrage

Davis

2016

J. Cosmol. Astropart. Phys.

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Abstract:We analyse the speed of gravitational waves in coupled Galileon models with an equation of state ω φ = −1 now and a ghost-free Minkowski limit. We find that the gravitational waves propagate much faster than the speed of light unless these models are small perturbations of cubic Galileons and the Galileon energy density is sub-dominant to a dominant cosmological constant. In this case, the binary pulsar bounds on the speed of gravitational waves can be satisfied and the equation of state can be close to -1 when the coupling to matter and the coefficient of the cubic term of the Galileon Lagrangian are related. This severely restricts the allowed cosmological behaviour of Galileon models and we are forced to conclude that Galileons with a stable Minkowski limit cannot account for the observed acceleration of the expansion of the universe on their own. Moreover any sub-dominant Galileon component of our universe must be dominated by the cubic term. For such models with gravitons propagating faster than the speed of light, the gravitons become potentially unstable and could decay into photon pairs. They could also emit photons by Cerenkov radiation. We show that the decay rate of such speedy gravitons into photons and the Cerenkov radiation are in fact negligible. Moreover the time delay between the gravitational signal and light emitted by explosive astrophysical events could serve as a confirmation that a modification of gravity acts on the largest scales of the Universe.

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Nonlinear structure formation in the cubic Galileon gravity model

Cited by 149 publications

References 184 publications

Breaking the Vainshtein screening in clusters of galaxies

Breaking the Vainshtein screening in clusters of galaxies

Modified gravity with massive neutrinos as a testable alternative cosmological model

The speed of Galileon gravity

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