skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Modified gravity inside astrophysical bodies

Abstract

Many theories of modified gravity, including the well studied Horndeski models, are characterized by a screening mechanism that ensures that standard gravity is recovered near astrophysical bodies. In a recently introduced class of gravitational theories that goes beyond Horndeski, it has been found that new derivative interactions lead to a partial breaking of the Vainshtein screening mechanism inside any gravitational source, although not outside. We study the impact of this new type of deviation from standard gravity on the density profile of a spherically symmetric matter distribution, in the nonrelativistic limit. For simplicity, we consider a polytropic equation of state and derive the modifications to the standard Lane-Emden equations. We also show the existence of a universal upper bound on the amplitude of this type of modified gravity, independently of the details of the equation of state.

Authors:
;  [1];  [2];  [3];  [4]
  1. AstroParticule et Cosmologie, CNRS-Universite Paris 7, 10 rue Alice Domon et Léonie Duquet, Paris (France)
  2. Research Center for the Early Universe, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo (Japan)
  3. Waseda Institute for Advanced Study, Waseda University, 1-6-1 Nishi-Waseda Shinjuku-ku, Tokyo (Japan)
  4. Institut de Physique Théorique, CEA, Gif-sur-Yvette (France)
Publication Date:
OSTI Identifier:
22525787
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2015; Journal Issue: 06; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; ASTROPHYSICS; COSMOLOGICAL MODELS; EQUATIONS OF STATE; GRAVITATION; MODIFICATIONS; SPHERICAL CONFIGURATION; SYMMETRY

Citation Formats

Saito, Ryo, Langlois, David, Yamauchi, Daisuke, Mizuno, Shuntaro, and Gleyzes, Jérôme, E-mail: rsaito@apc.univ-paris7.fr, E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: shuntaro.mizuno@aoni.waseda.jp, E-mail: jerome.gleyzes@cea.fr, E-mail: langlois@apc.univ-paris7.fr. Modified gravity inside astrophysical bodies. United States: N. p., 2015. Web. doi:10.1088/1475-7516/2015/06/008.
Saito, Ryo, Langlois, David, Yamauchi, Daisuke, Mizuno, Shuntaro, & Gleyzes, Jérôme, E-mail: rsaito@apc.univ-paris7.fr, E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: shuntaro.mizuno@aoni.waseda.jp, E-mail: jerome.gleyzes@cea.fr, E-mail: langlois@apc.univ-paris7.fr. Modified gravity inside astrophysical bodies. United States. doi:10.1088/1475-7516/2015/06/008.
Saito, Ryo, Langlois, David, Yamauchi, Daisuke, Mizuno, Shuntaro, and Gleyzes, Jérôme, E-mail: rsaito@apc.univ-paris7.fr, E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: shuntaro.mizuno@aoni.waseda.jp, E-mail: jerome.gleyzes@cea.fr, E-mail: langlois@apc.univ-paris7.fr. Mon . "Modified gravity inside astrophysical bodies". United States. doi:10.1088/1475-7516/2015/06/008.
@article{osti_22525787,
title = {Modified gravity inside astrophysical bodies},
author = {Saito, Ryo and Langlois, David and Yamauchi, Daisuke and Mizuno, Shuntaro and Gleyzes, Jérôme, E-mail: rsaito@apc.univ-paris7.fr, E-mail: yamauchi@resceu.s.u-tokyo.ac.jp, E-mail: shuntaro.mizuno@aoni.waseda.jp, E-mail: jerome.gleyzes@cea.fr, E-mail: langlois@apc.univ-paris7.fr},
abstractNote = {Many theories of modified gravity, including the well studied Horndeski models, are characterized by a screening mechanism that ensures that standard gravity is recovered near astrophysical bodies. In a recently introduced class of gravitational theories that goes beyond Horndeski, it has been found that new derivative interactions lead to a partial breaking of the Vainshtein screening mechanism inside any gravitational source, although not outside. We study the impact of this new type of deviation from standard gravity on the density profile of a spherically symmetric matter distribution, in the nonrelativistic limit. For simplicity, we consider a polytropic equation of state and derive the modifications to the standard Lane-Emden equations. We also show the existence of a universal upper bound on the amplitude of this type of modified gravity, independently of the details of the equation of state.},
doi = {10.1088/1475-7516/2015/06/008},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 06,
volume = 2015,
place = {United States},
year = {Mon Jun 01 00:00:00 EDT 2015},
month = {Mon Jun 01 00:00:00 EDT 2015}
}
  • This paper is the third in a series on tests of gravity using observations of stars and nearby dwarf galaxies. We carry out four distinct tests using published data on the kinematics and morphology of dwarf galaxies, motivated by the theoretical work of Hui et al. (2009) and Jain and Vanderplas (2011). In a wide class of gravity theories a scalar field couples to matter and provides an attractive fifth force. Due to their different self-gravity, stars and gas may respond differently to the scalar force leading to several observable deviations from standard gravity. HI gas, red giant stars andmore » main sequence stars can be displaced relative to each other, and the stellar disk can display warps or asymmetric rotation curves aligned with external potential gradients. To distinguish the effects of modified gravity from standard astrophysical phenomena, we use a control sample of galaxies that are expected to be screened from the fifth force. In all cases we find no significant deviation from the null hypothesis of general relativity. The limits obtained from dwarf galaxies are not yet competitive with the limits from cepheids obtained in our first paper, but can be improved to probe regions of parameter space that are inaccessible using other tests. We discuss how our methodology can be applied to new radio and optical observations of nearby galaxies.« less
  • We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators—cepheids, tip of the red giant branch (TRGB) stars, and water masers—operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered (in opposite directions) over a range of chameleon gravity theory parameters well below the sensitivity of cosmological probes. Using published data, we havemore » compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. We use a comparable set of screened galaxies as a control sample. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value), we obtain constraints on both the chameleon and symmetron screening scenarios. In particular we show that f(R) models with background field values f {sub R0} above 5 × 10{sup –7} are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional improved tests with future observations.« less
  • Chameleon, environmentally dependent dilaton, and symmetron gravity are three models of modified gravity in which the effects of the additional scalar degree of freedom are screened in dense environments. They have been extensively studied in laboratory, cosmological, and astrophysical contexts. In this paper, we present a preliminary investigation into whether additional constraints can be provided by studying these scalar fields around black holes. By looking at the properties of a static, spherically symmetric black hole, we find that the presence of a non-uniform matter distribution induces a non-constant scalar profile in chameleon and dilaton, but not necessarily symmetron gravity. Anmore » order of magnitude estimate shows that the effects of these profiles on in-falling test particles will be sub-leading compared to gravitational waves and hence observationally challenging to detect.« less
  • A large fraction of cosmological information on dark energy and gravity is encoded in the nonlinear regime. Precision cosmology thus requires precision modeling of nonlinearities in general dark energy and modified gravity models. We modify the Gadget-2 code and run a series of N-body simulations on modified gravity cosmology to study the nonlinearities. The modified gravity model that we investigate in the present paper is characterized by a single parameter {zeta}, which determines the enhancement of particle acceleration with respect to general relativity (GR), given the identical mass distribution ({zeta}=1 in GR). The first nonlinear statistics we investigate is themore » nonlinear matter power spectrum at k < or approx. 3h/Mpc, which is the relevant range for robust weak lensing power spectrum modeling at l < or approx. 2000. In this study, we focus on the relative difference in the nonlinear power spectra at corresponding redshifts where different gravity models have the same linear power spectra. This particular statistics highlights the imprint of modified gravity in the nonlinear regime and the importance of including the nonlinear regime in testing GR. By design, it is less susceptible to the sample variance and numerical artifacts. We adopt a mass assignment method based on wavelet to improve the power spectrum measurement. We run a series of tests to determine the suitable simulation specifications (particle number, box size, and initial redshift). We find that, the nonlinear power spectra can differ by {approx}30% for 10% deviation from GR (|{zeta}-1|=0.1) where the rms density fluctuations reach 10. This large difference, on one hand, shows the richness of information on gravity in the corresponding scales, and on the other hand, invalidates simple extrapolations of some existing fitting formulae to modified gravity cosmology.« less