77 research outputs found
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).Comment: 7 pages, comments welcom
Fab Four: When John and George play gravitation and cosmology
Scalar-tensor theories of gravitation have recently regained a great interest
after the discovery of the Chameleon mechanism and of the Galileon models. The
former allows, in principle, to reconcile the presence of cosmological scalar
fields with the constraints from experiments at the Solar System scale. The
latter open up the possibility of building inflationary models that, among
other things, do not need ad hoc potentials. Further generalizations have
finally led to the most general tensor-scalar theory, recently dubbed the "Fab
Four", with only first and second order derivatives of the fields in the
equations of motion and that self-tune to a vanishing cosmological constant.
This model has a very rich phenomenology that needs to be explored and
confronted with experimental data in order to constrain a very large parameter
space. In this paper, we present some results regarding a subset of the theory
named "John", which corresponds to a non-minimal derivative coupling between
the scalar field and the Einstein tensor in the action. We show that this
coupling gives rise to an inflationary model with very unnatural initial
conditions. Thus, we include a non-minimal, but non-derivative, coupling
between scalar field and Ricci scalar, a term named "George" in the Fab Four
terminology. In this way, we find a more sensible inflationary model, and, by
performing a post-newtonian expansion of spherically symmetric solutions, we
derive the set of equations that constrain the parameter space with data from
experiments in the solar system.Comment: Minor changes, references added. Version accepted for publication in
Advances in Astronom
Testing Lorentz symmetry with planetary orbital dynamics
Planetary ephemerides are a very powerful tool to constrain deviations from
the theory of General Relativity using orbital dynamics. The effective field
theory framework called the Standard-Model Extension (SME) has been developed
in order to systematically parametrize hypothetical violations of Lorentz
symmetry (in the Standard Model and in the gravitational sector). In this
communication, we use the latest determinations of the supplementary advances
of the perihelia and of the nodes obtained by planetary ephemerides analysis to
constrain SME coefficients from the pure gravity sector and also from
gravity-matter couplings. Our results do not show any deviation from GR and
they improve current constraints. Moreover, combinations with existing
constraints from Lunar Laser Ranging and from atom interferometry gravimetry
allow us to disentangle contributions from the pure gravity sector from the
gravity-matter couplings.Comment: 12 pages, 2 figures, version accepted for publication in Phys. Rev.
Constraining a companion of the galactic center black hole, Sgr A*
We use 23 years of astrometric and radial velocity data on the orbit of the
star S0-2 to constrain a hypothetical intermediate-mass black hole orbiting the
massive black hole Sgr A* at the Galactic center. The data place upper limits
on variations of the orientation of the stellar orbit (inclination, nodal
angle, and pericenter) at levels between 0.02 and 0.07 degrees per year. We use
a combination of analytic estimates and full numerical integrations of the
orbit of S0-2 in the presence of a black-hole binary. For a companion IMBH
whose semi-major axis is larger than that of S0-2 (1020 a.u.), we find
that in the region between 1000 and 4000 a.u., a companion black hole with mass
between and is excluded, with a boundary behaving
as . For a companion with a.u., we find that a
black hole with mass between and is again excluded,
with a boundary behaving as . These bounds arise from
quadrupolar perturbations of the orbit of S0-2. However, significantly stronger
bounds on the mass of an inner companion arise from the fact that the location
of S0-2 is measured relative to the bright emission of Sgr A*. As a
consequence, that separation is perturbed by the ``wobble'' of Sgr A* about the
center of mass between it and the companion, leading to ``apparent''
perturbations of S0-2's orbit that also include a dipole component. The result
is a set of bounds as small as at 200 a.u.; the numerical
simulations suggest a bound from these effects varying as .
We compare and contrast our results with those from a recent analysis by the
GRAVITY collaboration.Comment: 9 pages, 4 figure
Ranging Sensor Fusion in LISA Data Processing: Treatment of Ambiguities, Noise, and On-Board Delays in LISA Ranging Observables
Interspacecraft ranging is crucial for the suppression of laser frequency
noise via time-delay interferometry (TDI). So far, the effect of on-board
delays and ambiguities in the LISA ranging observables was neglected in LISA
modelling and data processing investigations. In reality, on-board delays cause
offsets and timestamping delays in the LISA measurements, and PRN ranging is
ambiguous, as it only determines the range up to an integer multiple of the
pseudo-random noise (PRN) code length. In this article, we identify the four
LISA ranging observables: PRN ranging, the sideband beatnotes at the
interspacecraft interferometer, TDI ranging, and ground-based observations. We
derive their observation equations in the presence of on-board delays, noise,
and ambiguities. We then propose a three-stage ranging sensor fusion to combine
these observables in order to gain optimal ranging estimates. We propose to
calibrate the on-board delays on ground and to compensate the associated
offsets and timestamping delays in an initial data treatment (stage 1). We
identify the ranging-related routines, which need to run continuously during
operation (stage 2), and implement them numerically. Essentially, this involves
the reduction of ranging noise, for which we develop a Kalman filter combining
the PRN ranging and the sideband beatnotes. We further implement crosschecks
for the PRN ranging ambiguities and offsets (stage 3). We show that both
ground-based observations and TDI ranging can be used to resolve the PRN
ranging ambiguities. Moreover, we apply TDI ranging to estimate the PRN ranging
offsets
Cold atoms in space: community workshop summary and proposed road-map
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.publishedVersio
Cold atoms in space: community workshop summary and proposed road-map
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies
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Cold atoms in space: community workshop summary and proposed road-map
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies
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