Equivalence principle in scalar-tensor gravity

Puetzfeld, Dirk; Obukhov, Yuri N.

doi:10.1103/physrevd.92.081502

Cited by 8 publications

(15 citation statements)

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“…In this paper, our treatment includes cases in which the test body has and 21 For instance, Khoury & Weltmann [1] use the test particle limit to estimate the force, Brax et al . [22] use the superposition principle to calculate the force, Puetzfeld & Obukov [30] consider the test particle limit, Mota & Shaw [19] consider two infinite parallel planes, Tamaki & Tsujikawa [28] consider the test bodies as test particles with the acceleration of the test particle proportional to an effective coupling of the field to the test body; and therefore miss the contribution of the test body on the chameleon field. 22 For the situations we have studied in this work, the large body is always screened for M = 2.4 meV and the considered values of n and β.…”

Section: Applicationsmentioning

confidence: 99%

“…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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Equivalence principle in chameleon models

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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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Section: Applicationsmentioning

confidence: 99%

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“…Also within their framework, the Weyl-Cartan space, and a straightforward extension of it, play an important role, see also Haghani et al [33]. Definite progress has also been achieved in the study of equations of motion within the scalar tensor theories of gravity, see Obukhov and Puetzfeld [76,81,82]. The breaking of scale invariance in the more general approach of metric-affine gravity was studied in [34], for example; for somewhat analogous breaking mechanisms, see [60,61,62].…”

Section: The Weyl-cartan Spacetime As a Natural Habitat Of The Dilatomentioning

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Axion and Dilaton + Metric Emerge Jointly from an Electromagnetic Model Universe with Local and Linear Response Behavior

Hehl

2016

Fundamental Theories of Physics

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We take a quick look at the different possible universally coupled scalar fields in nature. Then, we discuss how the gauging of the group of scale transformations (dilations), together with the Poincaré group, leads to a Weyl-Cartan spacetime structure. There the dilaton field finds a natural surrounding. Moreover, we describe shortly the phenomenology of the hypothetical axion field. -In the second part of our essay, we consider a spacetime, the structure of which is exclusively specified by the premetric Maxwell equations and a fourth rank electromagnetic response tensor density χ i jkl = −χ jikl = −χ i jlk with 36 independent components. This tensor density incorporates the permittivities, permeabilities, and the magneto-electric moduli of spacetime. No metric, no connection, no further property is prescribed. If we forbid birefringence (double-refraction) in this model of spacetime, we eventually end up with the fields of an axion, a dilaton, and the 10 components of a metric tensor with Lorentz signature. If the dilaton becomes a constant (the vacuum admittance) and the axion field vanishes, we recover the Riemannian spacetime of general relativity theory. Thus, the metric is encapsulated in χ i jkl , it can be derived from it.file CarlBrans80 08.This gauging of the P(1, 3) extends the geometrical framework of gravity. The 4 translational potentials e i α and the 6 Lorentz potentials Γ i αβ = −Γ i β α span a Riemann-Cartan spacetime, enriching the Riemannian spacetime of GR by the presence of Cartan's torsion; here α, β = 0, 1, 2, 3 are (anholonomic) frame indices. Whereas the translational potentials couple to the canonical energy-momentum ten-2 We skip here the plethora of scalar mesons, π ± , π 0 , η, f 0 (500), η ′ (958), f 0 (980), a 0 (980), ...,they are all composed of two quarks. Thus, the scalar mesons do not belong to the fundamental particles.

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Scale-invariant gauge theories of gravity: Theoretical foundations

Lasenby

Hobson²

2016

Journal of Mathematical Physics

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We consider the construction of gauge theories of gravity, focussing in particular on the extension of local Poincaré invariance to include invariance under local changes of scale. We work exclusively in terms of finite transformations, which allow for a more transparent interpretation of such theories in terms of gauge fields in Minkowski spacetime. Our approach therefore differs from the usual geometrical description of locally scale-invariant Poincaré gauge theory (PGT) and Weyl gauge theory (WGT) in terms of Riemann-Cartan and Weyl-Cartan spacetimes, respectively. In particular, we reconsider the interpretation of the Einstein gauge and also the equations of motion of matter fields and test particles in these theories. Inspired by the observation that the PGT and WGT matter actions for the Dirac field and electromagnetic field have more general invariance properties than those imposed by construction, we go on to present a novel alternative to WGT by considering an 'extended' form for the transformation law of the rotational gauge field under local dilations, which includes its 'normal' transformation law in WGT as a special case. The resulting 'extended' Weyl gauge theory (eWGT) has a number of interesting features that we describe in detail. In particular, we present a new scale-invariant gauge theory of gravity that accommodates ordinary matter and is defined by the most general parity-invariant eWGT Lagrangian that is at most quadratic in the eWGT field strengths, and we derive its field equations. We also consider the construction of PGTs that are invariant under local dilations assuming either the 'normal' or 'extended' transformation law for the rotational gauge field, but show that they are special cases of WGT and eWGT, respectively.

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Equivalence principle in scalar-tensor gravity

Cited by 8 publications

References 38 publications

Equivalence principle in chameleon models

Equivalence principle in chameleon models

Axion and Dilaton + Metric Emerge Jointly from an Electromagnetic Model Universe with Local and Linear Response Behavior

Scale-invariant gauge theories of gravity: Theoretical foundations

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