Chameleon mechanism with a new potential

Saaidi, Kh.; Sheikhahmadi, Haidar; Afzali, J.

doi:10.1007/s10509-011-0675-0

Cited by 13 publications

(11 citation statements)

References 24 publications

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“…A further analysis by Mota and Shaw [19] strengthened the conclusion that the non linearities inherent to the chameleon models are, in fact, responsible for suppressing the effective violation of WEP in the actual experiments even when the coupling constants are very large, and not just when they are of order unity as it was initially thought [1] 3 . Moreover, these authors argued that the predicted effective violations of the WEP in low density environments (like in space-based laboratories) would be further suppressed for some adjusted values of the parameters of the scalar-field potential.Based on such analyses, a good part of the community working on the area [1,19,21,22,24,[27][28][29][30] has come to believe the chameleon fields should not lead to any relevant forces in experiments on Earth designed to search for a dependence on the composition of the acceleration of a falling test body, or in general, to any observable interaction between ordinary bodies mediated by chameleon-type fields.However, it should be noted that there is no universal consensus in the community regarding even qualitative aspects of the theoretical predictions, with some arguments indicating the chameleon force on the test body is composition dependent [1,19,21,22,[27][28][29] and others indicating that it is not [30]. Defining a "screened" test body one in which the thin shell condition is satisfied and an "unscreened" test body one in which it is not satisfied, most authors make 1 In this context by matter we mean any field other that the scalar-field at hand, which in the situation of interest would be the ordinary matter making up the objects present in the experiment including the atmosphere.…”

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confidence: 99%

“…Based on such analyses, a good part of the community working on the area [1,19,21,22,24,[27][28][29][30] has come to believe the chameleon fields should not lead to any relevant forces in experiments on Earth designed to search for a dependence on the composition of the acceleration of a falling test body, or in general, to any observable interaction between ordinary bodies mediated by chameleon-type fields.…”

mentioning

confidence: 99%

“…However, it should be noted that there is no universal consensus in the community regarding even qualitative aspects of the theoretical predictions, with some arguments indicating the chameleon force on the test body is composition dependent [1,19,21,22,[27][28][29] and others indicating that it is not [30]. Defining a "screened" test body one in which the thin shell condition is satisfied and an "unscreened" test body one in which it is not satisfied, most authors make 1 In this context by matter we mean any field other that the scalar-field at hand, which in the situation of interest would be the ordinary matter making up the objects present in the experiment including the atmosphere.…”

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confidence: 99%

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Equivalence principle in chameleon models

et al. 2018

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results of the detailed analyses indicate that those world-lines do not, in general, correspond to geodesics. Quantum aspects further complicate the analysis of the motion of even the simplest things, which one might want to take as paradigmatic point like objects, such as photons [4]. Even though such UFF violating effects are normally very small, they are always there in principle, and therefore these considerations should serve as warnings when we go on to analyze more complex situations.Of particular interest for us here will be any theory in which the local coupling constants are taken to be effectively space-time dependent, while respecting the principles of locality and general covariance, as those entail some kind of fundamental field controlling the spatial dependence, with the field, generically, coupling in different manners to the various types of matter. Such field, usually taken to be a scalar field, generically mediates new forces between macroscopic objects, which would look, at the empirical level, as modifications of gravitation which might, in principle, lead to effective violations of the UFF for test bodies in external gravitational fields. For this reason, most theories that predict variations of fundamental constants also predict effective violations of the WEP [5][6][7][8][9]. For instance, the rest energy of a macroscopic body is made of many contributions related to the energies associated with various kinds of interactions (strong, weak, electromagnetic) and such components would be affected differently by a light scalar field. From the experimental point of view, one needs to confront the very strong limits on possible violations of the WEP that come from Eötvös-Roll-Krotkov-Dicke and Braginsky-Panov experiments and their modern reincarnations [10-15] which explore the differential acceleration of test bodies in gravitational contexts. In fact current bounds reach sensitivities of order ∆a a ≃ 10 −13 (or more), and thus can, in principle, constrain the viability of many models. Recently, there has been a great level of interest in models that claim to be able to avoid the stringent bounds resulting from experimental tests looking for violations of the WEP based on schemes where the effects of the fields are hidden by suitable non-linearities, as in the chameleon models and the Dilaton-Matter-gravity model with strong coupling [16]. Chameleon models were introduced by Khoury and Weltman in 2004 [1] and have been further developed by several authors [18][19][20][21][22][23][24][25]27]. Generically a chameleon consists of a scalar field that is coupled non-minimally to matter and minimally to the curvature (or the other way around via a conformal transformation), and where the field's effective mass depends on the density and pressure of the matter that constitutes the environment. This, in turn, is the result of the nontrivial coupling of the scalar field with the trace of the energy-momentum tensor of the matter sector of the theory 1 . The coupling of the scalar field with matter might...

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Equivalence principle in chameleon models

et al. 2018

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“…It should be noted that L is the Lagrangian density of matter which consists of both dark matter and dark energy sectors as perfect fluid [47][48][49]52,53]. It should be noticed that the background is a spatially flat Friedmann-Lemaître-RobertsonWalker (FLRW) Universe, with signature (+2).…”

Section: Conservation and Field's Equations In An Effective Dark Enermentioning

confidence: 99%

Interacting scalar tensor cosmology in light of SNeIa, CMB, BAO and OHD observational data sets

et al. 2016

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In this work, an interacting chameleon-like scalar field scenario, by considering SNeIa, CMB, BAO, and OHD data sets, is investigated. In fact, the investigation is realized by introducing an ansatz for the effective dark energy equation of state, which mimics the behavior of chameleonlike models. Based on this assumption, some cosmological parameters, including the Hubble, deceleration, and coincidence parameters, in such a mechanism are analyzed. It is realized that, to estimate the free parameters of a theoretical model, by regarding the systematic errors it is better that the whole of the above observational data sets would be considered. In fact, if one considers SNeIa, CMB, and BAO, but disregards OHD, it maybe leads to different results. Also, to get a better overlap between the contours with the constraint χ 2 m ≤ 1, the χ 2 T function could be re-weighted. The relative probability functions are plotted for marginalized likelihood L ( m0 , ω 1 , β) according to the two dimensional confidence levels 68.3, 90, and 95.4 %. Meanwhile, the value of the free parameters which maximize the marginalized likelihoods using the above confidence levels are obtained. In addition, based on these calculations the minimum value of χ 2 based on the free parameters of the ansatz for the effective dark energy equation of state is achieved.

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“…As we mentioned above one of the important inflationary parameters is the tensor-to-scalar ratio which by considering Eqs. (38) and (39), it can be attained as…”

Section: Chaotic Inflationmentioning

confidence: 99%

Non-local scalar fields inflationary mechanism in light of Planck 2013

Sheikhahmadi

Ghorbani

Saaidi

2015

Astrophys Space Sci

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A generalization of the canonical and non-canonical theory of inflation is introduced in which the kinetic energy term in action is written as non-local term. The inflationary universe within the framework of considering this non-locality will be studied. To investigate the effects of non-locality on the inflationary parameters we consider two well known models of inflationary scenario includes of chaotic and exponential inflation proposals. For such scenarios some important parameters include slow roll parameters, scalar and tensor power spectra, spectral indices, the tensor-to-scalar ratio and so on for both mentioned models, chaotic and exponential inflationary scenarios, will be calculated. Also the Hamilton-Jacobi formalism, as an easiest way to study the effect of perturbation based on e-folding number N , to investigate inflationary attractors will be used. The free theoretical parameters of this model will be compared with observations by means of Planck 2013, W M AP 9 + eCM B + BAO + H 0 data sets in addition to BICEP 2 data surveying. It will be shown that our theoretical results are in acceptable range in comparison to observations. For instance the tensor-to-scalar ratio for exponential potential, by considering BICEP 2 is in best agreement in comparison with chaotic inflation.

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Chameleon mechanism with a new potential

Cited by 13 publications

References 24 publications

Equivalence principle in chameleon models

Equivalence principle in chameleon models

Interacting scalar tensor cosmology in light of SNeIa, CMB, BAO and OHD observational data sets

Non-local scalar fields inflationary mechanism in light of Planck 2013

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