arXiv subjects

Olivier Minazzoli

Publications and source records attributed to Olivier Minazzoli.

At least 37 records · Page 2Linked to original sources

arXiv2021

Charged black hole and radiating solutions in entangled relativity

In this manuscript, we show that the external Schwarzschild metric can be a good approximation of exact black hole solutions of entangled relativity. Since entangled relativity cannot be defined from vacuum, the demonstrations need to rely on the definition of matter fields. The electromagnetic field being the easiest (and perhaps the only) existing matter field with infinite range to consider, we study the case of a charged black hole -- for which the solution of entangled relativity and a dilaton theory agree -- as well as the case of a pure radiation -- for which the solution of entangled relativity and general relativity seem to agree, despite an apparent ambiguity in the field equations. Based on these results, we argue that the external Schwarzschild metric is an appropriate mathematical idealization of a spherical black hole in entangled relativity. The extension to rotating cases is briefly discussed.

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arXiv2021

De Sitter space-times in Entangled Relativity

It is argued that de Sitter space-times might be solutions of entangled relativity once the quantum trace anomaly from matter fields in curved space-times is taken into account. This hypothesis would be an elegant solution to the acceleration of the expansion of the universe within the rigid framework of entangled relativity.

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arXiv2020

Compact Objects in Entangled Relativity

We describe the first numerical Tolman-Oppenheimer-Volkoff solutions of compact objects in entangled relativity, which is an alternative to the framework of general relativity that does not have any additional free parameter. Assuming a simple polytropic equation of state and the conservation of the rest-mass density, we notably show that, for any given density, compact objects are always heavier (up to $\sim 8\%$) in entangled relativity than in general relativity -- for any given central density within the usual range of neutron stars' central densities, or for a given radius of the resulting compact object.

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arXiv2020

Strong lensing in multimessenger astronomy as a test of the equivalence principle

Standard Shapiro delay-based test of the equivalence principle, which are grounded on the measurement of two arrival times from a unique source but from messengers with different properties, cannot produce a reliable quantitative test of the Einstein equivalence principle. Essentially because they are based on the estimation for different messengers of the one-way propagation time between the emission and the observation that is not an observable per se. As a consequence, such tests are extremely model dependent, at best. In what follows, I argue that the differential arrival times for strongly lensed multimessengers can be used to define a new test of the Einstein equivalence principle that is both well-defined from a relativistic point of view and model independent---because it is entirely based on actual observables.

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arXiv2019

Shortcomings of Shapiro delay-based tests of the equivalence principle on cosmological scales

The "Shapiro delay" experienced by an astronomical messenger traveling through a gravitational field has been used to place constraints on possible deviations from the equivalence principle. The standard Shapiro delay used to obtain these constraints is not itself an observable in general relativity, but is rather obtained by comparing with a fiducial Euclidean distance. There is not a mapping between the constraints obtained in this manner and alternative theories that exhibit equivalence principle violations. However, even assuming that the comparison with the fiducial Euclidean distance is carried out in a way that is useful for some class of alternative theories, we show that the standard calculation of these constraints cannot be applied on cosmological scales, as is often done. Specifically, we find that the Shapiro delay computed in the standard way (taking the Newtonian potential to vanish at infinity) diverges as one includes many remote sources. We use an infinite homogeneous lattice model to illustrate this divergence, and also show how the divergence can be cured by using Fermi coordinates associated with an observer. With this correction, one finds that the Shapiro delay is no longer monotonic with the number of sources. Thus, one cannot compute a conservative lower bound on the Shapiro delay using a subset of the sources of the gravitational field without further assumptions and/or observational input. As an illustration, we compute the Shapiro delay by applying the Fermi coordinate expression to two catalogs of galaxy clusters, illustrating the dependence of the result on the completeness of the catalogue and the mass estimates.

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arXiv2018

Rethinking the link between matter and geometry

In the present manuscript, I examine an intriguing relation at the classical level between general relativity and a theory where matter couples uniquely multiplicatively to geometry in the Lagrangian density. Interestingly, the gravitational constant $G$ is replaced by a novel fundamental constant, whose value is not tied to any classical phenomenon; while the value of $G$ itself becomes related to the dynamics of the universe. I concentrate on different aspects of the Equivalence Principle, as the theory is expected to violate all of its different formulations.

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arXiv2017

Polarization-based Tests of Gravity with the Stochastic Gravitational-Wave Background

The direct observation of gravitational waves with Advanced LIGO and Advanced Virgo offers novel opportunities to test general relativity in strong-field, highly dynamical regimes. One such opportunity is the measurement of gravitational-wave polarizations. While general relativity predicts only two tensor gravitational-wave polarizations, general metric theories of gravity allow for up to four additional vector and scalar modes. The detection of these alternative polarizations would represent a clear violation of general relativity. The LIGO-Virgo detection of the binary black hole merger GW170814 has recently offered the first direct constraints on the polarization of gravitational waves. The current generation of ground-based detectors, however, is limited in its ability to sensitively determine the polarization content of transient gravitational-wave signals. Observation of the stochastic gravitational-wave background, in contrast, offers a means of directly measuring generic gravitational-wave polarizations. The stochastic background, arising from the superposition of many individually unresolvable gravitational-wave signals, may be detectable by Advanced LIGO at design-sensitivity. In this paper, we present a Bayesian method with which to detect and characterize the polarization of the stochastic background. We explore prospects for estimating parameters of the background, and quantify the limits that Advanced LIGO can place on vector and scalar polarizations in the absence of a detection. Finally, we investigate how the introduction of new terrestrial detectors like Advanced Virgo aid in our ability to detect or constrain alternative polarizations in the stochastic background. We find that, although the addition of Advanced Virgo does not notably improve detection prospects, it may dramatically improve our ability to estimate the parameters of backgrounds of mixed polarization.

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arXiv2017

Universality of free fall versus ephemeris

When a light scalar field with gravitational strength interacts with matter, the weak equivalence principle is in general violated, leading for instance to a violation of the universality of free fall. This has been known and tested for a while. However, recent developments [Minazzoli & Hees, PRD 2016] showed that a novel manifestation of the universality of free fall can appear in some models. Here we discuss this new scenario and expose how we intend to constrain it with INPOP ephemeris.

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arXiv2016

On dilatons with intrinsic decouplings

In this paper, we show that there exists a class of dilaton models with non-trivial scalar-Ricci and scalar-matter couplings that strongly reduces observational deviations from general relativity in the dust limit. Essentially, depending on the coupling between the dilaton and the fundamental matter fields, various strengths of decoupling can appear. They range from no decoupling at all to a total decoupling state. In this latter case, the theory becomes indistinguishable from general relativity (in the dust limit), as all dilatonic effects can be re-absorbed through a simple change of unit. Furthermore, for particular decouplings, we show that the phenomenology used to constrain theories from universality of free fall observations is significantly different from what is commonly used. Finally, from a fundamental perspective, the class of non-dynamical decouplings proposed in this paper might play a role in the current non-observation of any deviation from general relativity (in both tests of the equivalence principle and of the parametrized post-Newtonian formalism).

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arXiv2015

Merging matter and geometry in the same Lagrangian

We show that a Lagrangian density proportional to $\sqrt{-g} Ł_m^2/R$ reduces to a pressuron theory of gravity that is indistinguishable from General Relativity in the dust limit. The combination of matter and geometry in the same Lagrangian density intrinsically satisfies Mach's Principle --- since matter cannot exist without curvature and vice versa --- while it may have the correct phenomenology in order to describe actual gravity.

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arXiv2015

Basics of the pressuron

The pressuron is a specific case of a dilaton-like field that leads to a decoupling of the scalar-field in the field equation for pressureless fluids. Hence, the pressuron recovers general relativity in the limit of weak pressure. Here we review its basics.

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arXiv2014

Late-time cosmology of scalar-tensor theories with universal multiplicative coupling between the scalar field and the matter Lagrangian

We investigate the late-time cosmological behaviour of scalar-tensor theories with a universal multiplicative coupling between the scalar field and the matter Lagrangian in the matter era. This class of theory encompasses the case of the massless string dilaton (see Damour and Polyakov, General Relativity and Gravitation, 26, 1171) as well as a theory with an intrinsic decoupling mechanism in the solar system (see Minazzoli and Hees, Phys. Rev. D 88, 041504). The cosmological evolution is studied in the General Relativity limit justified by solar system constraints on the gravitation theory. The behaviour of these cosmological evolutions are then compared to two types of observations: the constraints on temporal variations of the constants of Nature and the distance-luminosity measurements. In particular, the non-minimal coupling implies that the distance-luminosity relation is modified compared to General Relativity. Theories producing a cosmological behaviour in agreement with these observations are identified.

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arXiv2014

On the cosmic convergence mechanism of the massless dilaton

The converging mechanism discussed in [Damour & Nordtvedt, Physical Review Letters,70,15] for scalar-tensor theories has been applied to dilaton-like theories in several subsequent papers. In the present communication, we show that an unfortunate assumption in those studies led to a scalar-field equation unsuitable for the study of the dilaton field. The corrected scalar-field equation turns to change the numerical outcome of those studies in general, but even sometimes their qualitative aftermath. Therefore, the present result call for new investigations of the subject. On the other hand, our result shows that the string-inspired theory presented in [Minazzoli & Hees, Physical Review D,88,4] is naturally solution to the problem of the effective constancy of the fundamental coupling constants at late cosmic times, while it requires less fine-tuning than other massless dilaton or usual stalar-tensor theories.

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arXiv2013

The γ parameter in Brans-Dicke-like (light-)Scalar-Tensor theory with a universal scalar/matter coupling

The post-Newtonian parameter γ resulting from a universal scalar/matter coupling is investigated in Brans-Dicke-like Scalar-Tensor theories where the scalar potential is assumed to be negligible. Conversely to previous studies, we use a perfect fluid formalism in order to get the explicit scalar-field equation. It is shown that the metric can be put in its standard post-Newtonian form. However, it is pointed out that 1-γ could be either positive, null or negative for finite value of ω_0, depending on the coupling function; while Scalar-Tensor theories without coupling always predict γ<1 for finite value of ω_0.

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arXiv2013

Intrinsic Solar System decoupling of a scalar-tensor theory with a universal coupling between the scalar field and the matter Lagrangian

In this communication, we present a class of Brans-Dicke-like theories with a universal coupling between the scalar field and the matter Lagrangian. We show this class of theories naturally exhibits a decoupling mechanism between the scalar field and matter. As a consequence, this coupling leads to almost the same phenomenology as general relativity in the Solar System: the trajectories of massive bodies and the light propagation differ from general relativity only at the second post-Newtonian order. Deviations from general relativity are beyond present detection capabilities. However, this class of theories predicts a deviation of the gravitational redshift at a level detectable by the future ACES and STE/QUEST missions.

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arXiv2013

Conservation laws in theories with universal gravity/matter coupling

In this paper, we investigate the conservation laws of different type of particles in theories with a universal gravity/matter coupling. The result brings new insights about previous studies on universal gravity/matter theories. Especially, the paper demonstrates that for perfect fluids, there is an equivalence between the assumption $Ł_m=-ε$, where $ε$ is the total energy density; and the assumption that the matter fluid current is conserved ($\nabla_σ(ρu^σ)=0$, where $ρ$ is the rest mass density). However, the main result is given in the general case where one does not make any assumption on the conservation of the matter fluid current.

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arXiv2013

Time Transfer functions as a way to validate light propagation solutions for space astrometry

Given the extreme accuracy of modern space astrometry, a precise relativistic modeling of observations is required. Concerning light propagation, the standard procedure is the solution of the null-geodesic equations. However, another approach based on the Time Transfer Functions (TTF) has demonstrated its capability to give access to key quantities such as the time of flight of a light signal between two point-events and the tangent vector to its null-geodesic in a weak gravitational field using an integral-based method. The availability of several models, formulated in different and independent ways, must not be considered like an oversized relativistic toolbox. Quite the contrary, they are needed as validation to put future experimental results on solid ground. The objective of this work is then twofold. First, we build the time of flight and tangent vectors in a closed form within the TTF formalism giving the case of a time dependent metric. Second, we show how to use this new approach to obtain a comparison of the TTF with two existing modelings, namely GREM and RAMOD. In this way, we evidentiate the mutual consistency of the three models, opening the basis for further links between all the approaches, which is mandatory for the interpretation of future space missions data. This will be illustrated through two recognized cases: a static gravitational field and a system of monopoles in uniform motion.

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arXiv2013

The $γ$ parameter in Brans-Dicke-like (light-)Scalar-Tensor theory with a universal scalar/matter coupling and a new decoupling scenario

The post-Newtonian parameter $γ$ resulting from a universal scalar/matter coupling is investigated in Brans-Dicke-like Scalar-Tensor theories where the scalar potential is assumed to be negligible. Conversely to previous studies, we use a perfect fluid formalism in order to get the explicit scalar-field equation. It is shown that the metric can be put in its standard post-Newtonian form. However, it is pointed out that $1-γ$ could be either positive, null or negative for finite value of $ω_0$, depending on the coupling function; while Scalar-Tensor theories without coupling always predict $γ<1$ for finite value of $ω_0$. Moreover, regardless the value of $ω_0$, the subclass of theories satisfying $γ=1$ and $β=1$ surprisingly leads to almost the same phenomenology as general relativity in the solar system.

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