The effect of spatial variations of the Newton constant on the cosmic microwave background is stu... more The effect of spatial variations of the Newton constant on the cosmic microwave background is studied. Constraints on the strong equivalence principle violation at the recombination time are then obtained with the help of WMAP data and of the standard theory of big-bang nucleosynthesis.
The latest results in cosmography as well as the lat-est observations of the cosmic microwave bac... more The latest results in cosmography as well as the lat-est observations of the cosmic microwave background (CMB) and of supernovae have reinforced the emer-gence of a canonical paradigm for cosmology. Most of the cosmological parameters constituting this con-cordance ...
Publications of the Astronomical Society of the Pacific, 2018
We report on the search for optical counterparts of Planck Sunyaev-Zel'dovich (SZ) cluster candid... more We report on the search for optical counterparts of Planck Sunyaev-Zel'dovich (SZ) cluster candidates using a 0.6 m non-professional telescope. Among the observed sources, an unconfirmed candidate, PSZ2 G156.24+22.32, is found to be associated with a region of more than 100 galaxies within a 3 arcminute radius around the Sunyaev-Zel'dovich maximum signal coordinates. Using 14 hours of cumulated exposure over the Sloan color filters g', r', i', and z', we estimate the photometric redshift of these galaxies at z phot = 0.29 ± 0.08. Using the red-sequence galaxy method gives a photometric redshift of . Combined with the Planck SZ proxy mass function, this would favor a cluster of 4.4 × 1014 solar masses. This result suggests that a dedicated pool of observatories equipped with such instruments could collectively contribute to optical follow-up programs of massive cluster candidates at moderate redshifts.
According to the general theory of relativity, the current paradigm for gravitation and concordan... more According to the general theory of relativity, the current paradigm for gravitation and concordant observational data, about 95% of the Universe’s content is only perceivable through gravitational effects. Consolidating the predictions of this theory is then of primordial importance. Those predictions are structured around two dimensional constants : Newton’s and Einstein’s constants. The former, namely the universal constant, yields the universality of free fall of light and compact objects. The latter, also named cosmological constant, explains the late expansion acceleration of the Universe on cosmological scales. The main goal of this thesis is to explore the foundations of general relativity by promoting these constants as dynamical fields.
First of all, we propose a generic test seeking for possible Newton’s constant variations in the primeval plasma. The modified weight of baryons translates the equilibrium point of the acoustic oscillations. A constraint on the amplitude of such variations is extracted from the anisotropies of the cosmic microwave background. Secondly, we scrutinize a simple modification of general relativity providing a minimal violation of the strong equivalence principle. Although the additional scalar field acts as a dark radiation at the cosmological expansion level, the imprint left on the matter field perturbations is clearly distinguishable from other radiations because of the particular scalar field anisotropic stress. Several constraints for this alternative gravitational theory are derived from the analysis of the cosmic microwave background, Type Ia supernovae and the measure of the Lemaître-Hubble constant.
Finally, we replace the cosmological constant by a quintessence field. For selected realistic models agreeing with current cosmological data, it is shown that the non-linear processes driving the growth of matter’s large scale structures encode the nature and the dynamics of dark energy.
Although the confrontation between the investigated alternative models and available cosmological data currently does not raise deviation to the concordant ΛCDM model, the present study shows that predictions and signatures of these models are unique compared to the standard scenario.
The effect of spatial variations of the Newton constant on the cosmic microwave background is stu... more The effect of spatial variations of the Newton constant on the cosmic microwave background is studied. Constraints on the strong equivalence principle violation at the recombination time are then obtained with the help of WMAP data and of the standard theory of big-bang nucleosynthesis.
The latest results in cosmography as well as the lat-est observations of the cosmic microwave bac... more The latest results in cosmography as well as the lat-est observations of the cosmic microwave background (CMB) and of supernovae have reinforced the emer-gence of a canonical paradigm for cosmology. Most of the cosmological parameters constituting this con-cordance ...
Publications of the Astronomical Society of the Pacific, 2018
We report on the search for optical counterparts of Planck Sunyaev-Zel'dovich (SZ) cluster candid... more We report on the search for optical counterparts of Planck Sunyaev-Zel'dovich (SZ) cluster candidates using a 0.6 m non-professional telescope. Among the observed sources, an unconfirmed candidate, PSZ2 G156.24+22.32, is found to be associated with a region of more than 100 galaxies within a 3 arcminute radius around the Sunyaev-Zel'dovich maximum signal coordinates. Using 14 hours of cumulated exposure over the Sloan color filters g', r', i', and z', we estimate the photometric redshift of these galaxies at z phot = 0.29 ± 0.08. Using the red-sequence galaxy method gives a photometric redshift of . Combined with the Planck SZ proxy mass function, this would favor a cluster of 4.4 × 1014 solar masses. This result suggests that a dedicated pool of observatories equipped with such instruments could collectively contribute to optical follow-up programs of massive cluster candidates at moderate redshifts.
According to the general theory of relativity, the current paradigm for gravitation and concordan... more According to the general theory of relativity, the current paradigm for gravitation and concordant observational data, about 95% of the Universe’s content is only perceivable through gravitational effects. Consolidating the predictions of this theory is then of primordial importance. Those predictions are structured around two dimensional constants : Newton’s and Einstein’s constants. The former, namely the universal constant, yields the universality of free fall of light and compact objects. The latter, also named cosmological constant, explains the late expansion acceleration of the Universe on cosmological scales. The main goal of this thesis is to explore the foundations of general relativity by promoting these constants as dynamical fields.
First of all, we propose a generic test seeking for possible Newton’s constant variations in the primeval plasma. The modified weight of baryons translates the equilibrium point of the acoustic oscillations. A constraint on the amplitude of such variations is extracted from the anisotropies of the cosmic microwave background. Secondly, we scrutinize a simple modification of general relativity providing a minimal violation of the strong equivalence principle. Although the additional scalar field acts as a dark radiation at the cosmological expansion level, the imprint left on the matter field perturbations is clearly distinguishable from other radiations because of the particular scalar field anisotropic stress. Several constraints for this alternative gravitational theory are derived from the analysis of the cosmic microwave background, Type Ia supernovae and the measure of the Lemaître-Hubble constant.
Finally, we replace the cosmological constant by a quintessence field. For selected realistic models agreeing with current cosmological data, it is shown that the non-linear processes driving the growth of matter’s large scale structures encode the nature and the dynamics of dark energy.
Although the confrontation between the investigated alternative models and available cosmological data currently does not raise deviation to the concordant ΛCDM model, the present study shows that predictions and signatures of these models are unique compared to the standard scenario.
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Papers by Vincent Boucher
First of all, we propose a generic test seeking for possible Newton’s constant variations in the primeval plasma. The modified weight of baryons translates the equilibrium point of the acoustic oscillations. A constraint on the amplitude of such variations is extracted from the anisotropies of the cosmic microwave background.
Secondly, we scrutinize a simple modification of general relativity providing a minimal violation of the strong equivalence principle. Although the additional scalar field acts as a dark radiation at the cosmological expansion level, the imprint left on the matter field perturbations is clearly distinguishable from other radiations because of the particular scalar field anisotropic stress. Several constraints for this alternative gravitational theory are derived from the analysis of the cosmic microwave background, Type Ia supernovae and the measure of the Lemaître-Hubble constant.
Finally, we replace the cosmological constant by a quintessence field. For selected realistic models agreeing with current cosmological data, it is shown that the non-linear processes driving the growth of matter’s large scale structures encode the nature and the dynamics of dark energy.
Although the confrontation between the investigated alternative models and available cosmological data currently does not raise deviation to the concordant ΛCDM model, the present study shows that predictions and signatures of these models are unique compared to the standard scenario.
First of all, we propose a generic test seeking for possible Newton’s constant variations in the primeval plasma. The modified weight of baryons translates the equilibrium point of the acoustic oscillations. A constraint on the amplitude of such variations is extracted from the anisotropies of the cosmic microwave background.
Secondly, we scrutinize a simple modification of general relativity providing a minimal violation of the strong equivalence principle. Although the additional scalar field acts as a dark radiation at the cosmological expansion level, the imprint left on the matter field perturbations is clearly distinguishable from other radiations because of the particular scalar field anisotropic stress. Several constraints for this alternative gravitational theory are derived from the analysis of the cosmic microwave background, Type Ia supernovae and the measure of the Lemaître-Hubble constant.
Finally, we replace the cosmological constant by a quintessence field. For selected realistic models agreeing with current cosmological data, it is shown that the non-linear processes driving the growth of matter’s large scale structures encode the nature and the dynamics of dark energy.
Although the confrontation between the investigated alternative models and available cosmological data currently does not raise deviation to the concordant ΛCDM model, the present study shows that predictions and signatures of these models are unique compared to the standard scenario.