Engineering topics
Brax, Philippe
Publications and source records attributed to Brax, Philippe.
Quantum chameleons
We initiate a quantum treatment of chameleonlike particles, deriving classical and quantum forces directly from the path integral. It is found that the quantum force can potentially dominate the classical one by many orders of magnitude.We calculate the quantum chameleon pressure between infinite plates, which is found to interpolate between the Casimir and the integrated Casimir-Polder pressures, respectively in the limits of full screening and no screening. To this end we calculate the chameleon propagator in the presence of an arbitrary number of one-dimensional layers of material. For the Eöt-Wash experiment, the five-layer propagator is used to take into account the intermediate shielding sheet, and it is found that the presence of the sheet enhances the quantum pressure by two orders of magnitude. As an example of implication, we show that in both the standard chameleon and symmetron models, large and previously unconstrained regions of the parameter space are excluded once the quantum pressure is taken into account.
K-mouflage imprints on cosmological observables and data constraints
We investigate cosmological constraints on K-mouflage models of modified gravity. We consider two scenarios: one where the background evolution is free to deviate from ΛCDM (K-mouflage) and another one which reproduces a ΛCDM expansion (K-mimic), implementing both of them into the EFTCAMB code. We discuss the main observational signatures of these models and we compare their cosmological predictions to different datasets, including CMB, CMB lensing, SNIa and different galaxy catalogues. We argue about the possibility of relieving the H 0 and weak lensing tensions within these models, finding that K-mouflage scenarios effectively ease the tension on the Hubble Constant. Our final 95% C.L. bounds on the ϵ 2,0 parameter that measures the overall departure from ΛCDM (corresponding to ϵ 2,0 = 0) are -0.04≤ ϵ 2,0 ≤ 0 for K-mouflage and 0 ≤ ϵ 2,0 ≤≤ 0.002 for K-mimic. These translate into an upper bound for the coupling strength: β <0.22 for K-mouflage and β < 0.026 for K-mimic. In the former case the main constraining power comes from changes in the background expansion history, while in the latter case the model is strongly constrained by measurements of the amplitude of matter perturbations. The sensitivity of these cosmological constraints closely matches that of solar system probes. We show that these constraints could be significantly tightened with future ideal probes like CORE.