Testing gravity against the early time integrated Sachs-Wolfe effect

Zhang, Pengjie

doi:10.1103/physrevd.73.123504

Cited by 181 publications

(58 citation statements)

References 25 publications

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“…Though measurements from binary pulsar timing to the cosmic microwave background (CMB) and big bang nucleosynthesis are all consistent with GR, there is still room for order unity deviations in the cosmos today, on scales of kpc and larger. Thus, testing gravity on cosmological scales is an interesting frontier and the focus of much current research [1][2][3][4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Dynamical masses in modified gravity

2010

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Differences in masses inferred from dynamics, such as velocity dispersions or x rays, and those inferred from lensing are a generic prediction of modified gravity theories. Viable models, however, must include some nonlinear mechanism to restore general relativity (GR) in dense environments, which is necessary to pass Solar System constraints on precisely these deviations. In this paper, we study the dynamics within virialized structures in the context of two modified gravity models, fðRÞ gravity and Dvali-GabadadzePorrati (DGP). The nonlinear mechanisms to restore GR, which fðRÞ and DGP implement in very different ways, have a strong impact on the dynamics in bound objects; they leave distinctive signatures in the dynamical mass-lensing mass relation as a function of mass and radius. We present measurements from N-body simulations of fðRÞ and DGP, as well as semianalytical models that match the simulation results to surprising accuracy in both cases. The semianalytical models are useful for making the connection to observations. Our results confirm that the environment and scale dependence of the modified gravity effects have to be taken into account when confronting gravity theories with observations of dynamics in galaxies and clusters.

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Section: Introductionmentioning

confidence: 99%

Dynamical masses in modified gravity

2010

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“…Furthermore, we do not expect to be able to reproduce the entire cosmological phenomenology by means of a simple power-law model, which is not sufficiently versatile [78]. For example, it can be easily demonstrated that this model fails when it is analyzed with respect to its ability of providing the correct evolutionary conditions for the perturbation spectra of matter overdensities [117]. This point is typically regarded as one of the most important arguments suggesting the need for darm matter.…”

Section: Dark Energy As Curvaturementioning

confidence: 99%

“…[117] for fourth order gravity. This equation can be deduced in the Newtonian conformal gauge for the perturbed metric [117].…”

Section: Dark Energy As Curvaturementioning

confidence: 99%

“…To obtain the matter power spectrum suggested by this model, we resort to the equation for the matter contrast obtained in Ref. [117] for fourth order gravity. This equation can be deduced in the Newtonian conformal gauge for the perturbed metric [117].…”

Section: Dark Energy As Curvaturementioning

confidence: 99%

“…Such a scheme seems too simple to account for the entire cosmological phenomenology. In [117] a gravity Lagrangian considering an exponential correction to the Ricci scalar…”

Section: Dark Energy As Curvaturementioning

confidence: 99%

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A Bird's Eye View of f (R)-Gravity

Capozziello¹,

Laurentis²,

Faraoni³

2010

TOAAJ

112

135

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Abstract:The currently observed accelerated expansion of the Universe suggests that cosmic flow dynamics is dominated by some unknown form of dark energy characterized by a large negative pressure. This picture comes out when such a new ingredient, beside baryonic and dark matter, is considered as a source in the r.h.s. of the field equations. Essentially, it should be some form of un-clustered, non-zero vacuum energy which, together with (clustered) dark matter, should drive the global cosmic dynamics. Among the proposals to explain the experimental situation, the "concordance model", addressed as ! CDM, gives a reliable snapshot of the today observed Universe according to the CMBR, LSS and SNeIa data, but presents dramatic shortcomings as the "coincidence and cosmological constant problems" which point out its inadequacy to fully trace back the cosmological dynamics. On the other hand, alternative theories of gravity, extending in some way General Relativity, allow to pursue a different approach giving rise to suitable cosmological models where a late-time accelerated expansion can be achieved in several ways. This viewpoint does not require to find out candidates for dark energy and dark matter at fundamental level (they have not been detected up to now), it takes into account only the "observed" ingredients (i.e. gravity, radiation and baryonic matter), but the l.h.s. of the Einstein equations has to be modified. Despite of this modification, it could be in agreement with the spirit of General Relativity since the only request is that the Hilbert-Einstein action should be generalized asking for a gravitational interaction acting, in principle, in different ways at different scales. We survey the landscape of ) (R f theories of gravity in their various formulations, which have been used to model the cosmic acceleration as alternatives to dark energy and dark matter. Besides, we take into account the problem of gravitational waves in such theories. We discuss some successes of ) (R f -gravity (whereis a generic function of Ricci scalar R ), theoretical and experimental challenges that they face in order to satisfy minimal criteria for viability.

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Modeling Wormholes Generated by Dark Matter Galactic Halos in f(R)$f(R)$ Modified Gravity

et al. 2023

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Wormholes (WHs) are hypothetical topologically non‐trivial spacetime structures that can be freely traversed by observers and connect two asymptotic regions or infinities. From the current theoretical development, the prospect of their existence is challenging but cannot be excluded. In this paper, generalized Ellis–Bronikov (GEB) traversable WH geometries for static and spherically symmetric spacetime in the background of gravity is explored. First, the Tsujikawa‐like model and the shape function for the GEB model is considered, which depend on a sequence of simple Lorentzian WHs with two parameters: a free even integer exponent, n, besides the throat radius, r0. One also consider that these WHs are generated by dark matter galactic halos (DMGHs), based on the three most common phenomenological models, viz., Navarro–Frenk–White (NFW), Thomas–Fermi (TF), and pseudo‐isothermal (PI). In this concern, the satisfaction of the energy conditions (ECs) which are dependent on the dark matter (DM) models, viz., dominant energy condition (DEC) and strong energy condition (SEC) and those which are not dependent viz., null energy condition (NEC) and WEC at the WH throat and its neighborhood is investigated. Finally, the presence of exotic matter is confirmed by the violation of the NEC in all cases, revealing the supremacy and physical acceptability to support the existence of the WHs and making them compatible and traversable in Tsujikawa's‐like model.

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Testing gravity against the early time integrated Sachs-Wolfe effect

Cited by 181 publications

References 25 publications

Dynamical masses in modified gravity

Dynamical masses in modified gravity

A Bird's Eye View of f (R)-Gravity

Modeling Wormholes Generated by Dark Matter Galactic Halos in f(R)$f(R)$ Modified Gravity

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