1,381 research outputs found
Post-Newtonian phenomenology of a massless dilaton
In this paper, we present extensively the observational consequences of
massless dilaton theories at the post-Newtonian level. We extend previous work
by considering a general model including a dilaton-Ricci coupling as well as a
general dilaton kinetic term while using the microphysical dilaton-matter
coupling model proposed in [Damour and Donoghue, PRD 2010].
We derive all the expressions needed to analyze local gravitational
observations in a dilaton framework, which is useful to derive constraints on
the dilaton theories. In particular, we present the equations of motion of
celestial bodies (in barycentric and planetocentric reference frames), the
equation of propagation of light and the evolution of proper time as measured
by specific clocks. Particular care is taken in order to derive properly the
observables. The resulting equations can be used to analyse a large numbers of
observations: universality of free fall tests, planetary ephemerides analysis,
analysis of satellites motion, Very Long Baseline Interferometry, tracking of
spacecraft, gravitational redshift tests, ...Comment: 27 pages, comments welcom
Observables in theories with a varying fine structure constant
We show how two seemingly different theories with a scalar multiplicative
coupling to electrodynamics are actually two equivalent parametrisations of the
same theory: despite some differences in the interpretation of some
phenemenological aspects of the parametrisations, they lead to the same
physical observables. This is illustrated on the interpretation of observations
of the Cosmic Microwave Background.Comment: 14 pages, matched published versio
Breaking of the equivalence principle in the electromagnetic sector and its cosmological signatures
This paper proposes a systematic study of cosmological signatures of
modifications of gravity via the presence of a scalar field with a
multiplicative coupling to the electromagnetic Lagrangian. We show that, in
this framework, variations of the fine structure constant, violations of the
distance duality relation, evolution of the cosmic microwave background (CMB)
temperature and CMB distortions are intimately and unequivocally linked. This
enables one to put very stringent constraints on possible violations of the
distance duality relation, on the evolution of the CMB temperature and on
admissible CMB distortions using current constraints on the fine structure
constant. Alternatively, this offers interesting possibilities to test a wide
range of theories of gravity by analysing several datasets concurrently. We
discuss results obtained using current data as well as some forecasts for
future data sets such as those coming from EUCLID or the SKA.Comment: 14 pages, 4 figures, matched published version. Note: title changed
upon suggestion of PRD editor
Relativistic formulation of coordinate light time, Doppler and astrometric observables up to the second post-Minkowskian order
Given the extreme accuracy of modern space science, a precise relativistic
modeling of observations is required. In particular, it is important to
describe properly light propagation through the Solar System. For two decades,
several modeling efforts based on the solution of the null geodesic equations
have been proposed but they are mainly valid only for the first order
Post-Newtonian approximation. However, with the increasing precision of ongoing
space missions as Gaia, GAME, BepiColombo, JUNO or JUICE, we know that some
corrections up to the second order have to be taken into account for future
experiments. We present a procedure to compute the relativistic coordinate time
delay, Doppler and astrometric observables avoiding the integration of the null
geodesic equation. This is possible using the Time Transfer Function formalism,
a powerful tool providing key quantities such as the time of flight of a light
signal between two point-events and the tangent vector to its null-geodesic.
Indeed we show how to compute the Time Transfer Functions and their derivatives
(and thus range, Doppler and astrometric observables) up to the second
post-Minkowskian order. We express these quantities as quadratures of some
functions that depend only on the metric and its derivatives evaluated along a
Minkowskian straight line. This method is particularly well adapted for
numerical estimations. As an illustration, we provide explicit expressions in
static and spherically symmetric space-time up to second post-Minkowskian
order. Then we give the order of magnitude of these corrections for the
range/Doppler on the BepiColombo mission and for astrometry in a GAME-like
observation.Comment: 22 pages, 5 figures, accepted in Phys. Rev.
Frequency shift up to the 2-PM approximation
A lot of fundamental tests of gravitational theories rely on highly precise
measurements of the travel time and/or the frequency shift of electromagnetic
signals propagating through the gravitational field of the Solar System. In
practically all of the previous studies, the explicit expressions of such
travel times and frequency shifts as predicted by various metric theories of
gravity are derived from an integration of the null geodesic differential
equations. However, the solution of the geodesic equations requires heavy
calculations when one has to take into account the presence of mass multipoles
in the gravitational field or the tidal effects due to the planetary motions,
and the calculations become quite complicated in the post-post-Minkowskian
approximation. This difficult task can be avoided using the time transfer
function's formalism. We present here our last advances in the formulation of
the one-way frequency shift using this formalism up to the
post-post-Minkowskian approximation.Comment: 4 pages, submitted to proceedings of SF2
Light propagation in the field of a moving axisymmetric body: theory and application to JUNO
Given the extreme accuracy of modern space science, a precise relativistic
modeling of observations is required. We use the Time Transfer Functions
formalism to study light propagation in the field of uniformly moving
axisymmetric bodies, which extends the field of application of previous works.
We first present a space-time metric adapted to describe the geometry of an
ensemble of uniformly moving bodies. Then, we show that the expression of the
Time Transfer Functions in the field of a uniformly moving body can be easily
derived from its well-known expression in a stationary field by using a change
of variables. We also give a general expression of the Time Transfer Function
in the case of an ensemble of arbitrarily moving point masses. This result is
given in the form of an integral easily computable numerically. We also provide
the derivatives of the Time Transfer Function in this case, which are mandatory
to compute Doppler and astrometric observables. We particularize our results in
the case of moving axisymmetric bodies. Finally, we apply our results to study
the different relativistic contributions to the range and Doppler tracking for
the JUNO mission in the Jovian system.Comment: 17 pages, 4 figures, submitted to Phys. Rev. D, some corrections
after revie
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