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Do solar system experiments constrain scalar-tensor gravity?

ABSTRACT: It is now established that, contrary to common belief, (electro-)vacuum Brans-Dicke gravity does not reduce to general relativity (GR) for large values of the Brans-Dicke coupling ? . Since the essence of experimental tests of scalar-tensor gravity consists of providing lower bounds on ? , in light of the misguided assumption of the equivalence between the limit ??? and the GR limit of Brans-Dicke gravity, the parametrized post-Newtonian (PPN) formalism on which these tests are based could be in jeopardy. We show that, in the linearized approximation used by the PPN formalism, the anomaly in the limit to general relativity disappears. However, it survives to second (and higher) order and in strong gravity. In other words, while the weak gravity regime cannot tell apart GR and ??? Brans-Dicke gravity, when higher order terms in the PPN analysis of Brans-Dicke gravity are included, the latter never reduces to the one of GR in this limit. This fact is relevant for experiments aiming to test second order light deflection and Shapiro time delay.

SUBMITTER: Faraoni V

PROVIDER: S-EPMC7045786 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Do solar system experiments constrain scalar-tensor gravity?

Faraoni Valerio V Côté Jeremy J Giusti Andrea A

The European physical journal. C, Particles and fields 20200215 2

It is now established that, contrary to common belief, (electro-)vacuum Brans-Dicke gravity does not reduce to general relativity (GR) for large values of the Brans-Dicke coupling ω . Since the essence of experimental tests of scalar-tensor gravity consists of providing lower bounds on ω , in light of the misguided assumption of the equivalence between the limit ω → ∞ and the GR limit of Brans-Dicke gravity, the parametrized post-Newtonian (PPN) formalism on which these tests are based could be ...[more]

PMID: 32165858

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Project description:BACKGROUND: Although two-dimensional (2-D) monolayer cell cultures provide important information on basic tumor biology and radiobiology, they are not representative of the complexity of three-dimensional (3-D) solid tumors. In particular, new models reproducing clinical conditions as closely as possible are needed for radiobiological studies to provide information that can be translated from bench to bedside. METHODS: We developed a novel system for the irradiation, under sterile conditions, of 3-D tumor spheroids, the in vitro model considered as a bridge between the complex architectural organization of in vivo tumors and the very simple one of in vitro monolayer cell cultures. The system exploits the same equipment as that used for patient treatments, without the need for dedicated and highly expensive instruments. To mimic the passage of radiation beams through human tissues before they reach the target tumor mass, 96-multiwell plates containing the multicellular tumor spheroids (MCTS) are inserted into a custom-built phantom made of plexiglass, the material most similar to water, the main component of human tissue. RESULTS: The system was used to irradiate CAEP- and A549-derived MCTS, pre-treated or not with 20 ?M cisplatin, with a dose of 20 Gy delivered in one session. We also tested the same treatment schemes on monolayer CAEP and A549 cells. Our preliminary results indicated a significant increment in radiotoxicity 20 days after the end of irradiation in the CAEP spheroids pre-treated with cisplatin compared to those treated with cisplatin or irradiation alone. Conversely, the effect of the radio- chemotherapy combination in A549-derived MCTS was similar to that induced by cisplatin or irradiation alone. Finally, the 20 Gy dose did not affect cell survival in monolayer CAEP and A549 cells, whereas cisplatin or cisplatin plus radiation caused 100% cell death, regardless of the type of cell line used. CONCLUSIONS: We set up a system for the irradiation, under sterile conditions, of tumor cells grown in 3-D which allows for the use of the same dose intensities and schedules utilized in clinical practice. This irradiation system, coupled with 3-D cell cultures, has the potential to generate information that could be used to individually tailor radiotherapy.

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Do solar system experiments constrain scalar-tensor gravity?

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Do solar system experiments constrain scalar-tensor gravity?

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