45 research outputs found
Conservative (failed)-tail effects at the fifth post-Newtonian order
This work deals with the tail and ``failed'' tail sectors of the conservative
dynamics for compact binary systems at the 5PN order. We employ the Fokker
Lagrangian method with dimensional regularization, and our results for the tail
sector are perfectly consistent with the previous EFT computations. As for the
``failed'' tail sector, we have good hopes that this new computation will help
solving the current discrepancy in the literature.Comment: 8 pages. v2: local report number added, harmless typo corrected in
Eq. (3.8
Where does curvaton reside? Differences between bulk and brane frames
Some classes of inflationary models naturally introduce two distinct
metrics/frames, and their equivalence in terms of observables has often been
put in question. D-brane inflation proposes candidates for an inflaton embedded
in the string theory and possesses descriptions on the brane and bulk
metrics/frames, which are connected by a conformal/disformal transformation
that depends on the inflaton and its derivatives. It has been shown that
curvature perturbations generated by the inflaton are identical in both frames,
meaning that observables such as the spectrum of cosmic microwave background
(CMB) anisotropies are independent of whether matter fields---including those
in the standard model of particle physics---minimally couple to the brane or
the bulk metric/frame. This is true despite the fact that the observables are
eventually measured by the matter fields and that the total action including
the matter fields is different in the two cases. In contrast, in curvaton
scenarios, the observables depend on the frame to which the curvaton minimally
couples. Among all inflationary scenarios, we focus on two models motivated by
the KKLMMT fine-tuning problem: a slow-roll inflation with an inflection-point
potential and a model of a rapidly rolling inflaton that conformally couples to
gravity. In the first model, the difference between the frames in which the
curvaton resides is encoded in the spectral index of the curvature
perturbations, depicting the nature of the frame transformation. In the second
model, the curvaton on the brane induces a spectral index significantly
different from that in the bulk and is even falsified by the observations. This
work thus demonstrates that two frames connected by a conformal/disformal
transformation lead to different physical observables such as CMB anisotropies
in curvaton models.Comment: 16 pages, v2: published versio
The Quadrupole Moment of Compact Binaries to the Fourth post-Newtonian Order: Relating the Harmonic and Radiative Metrics
Motivated by the completion of the fourth post-Newtonian (4PN)
gravitational-wave generation from compact binary systems, we analyze and
contrast different constructions of the metric outside an isolated system,
using post-Minkowskian expansions. The metric in "harmonic" coordinates has
been investigated previously, in particular to compute tails and memory
effects. However, it is plagued by powers of the logarithm of the radial
distance when (with const). As a result, the tedious
computation of the "tail-of-memory" effect, which enters the gravitational-wave
flux at 4PN order, is more efficiently performed in the so-called "radiative"
coordinates, which admit a (Bondi-type) expansion at infinity in simple powers
of , without any logarithms. Here we consider a particular
construction, performed order by order in the post-Minkowskian expansion, which
directly yields a metric in radiative coordinates. We relate both
constructions, and prove that they are physically equivalent as soon as a
relation between the "canonical" moments which parametrize the radiative
metric, and those parametrizing the harmonic metric, is verified. We provide
the appropriate relation for the mass quadrupole moment at 4PN order, which
will be crucial when deriving the "tail-of-memory" contribution to the
gravitational flux.Comment: Updated a reference: Blanchet, Faye & Larrouturou 2022 in CQ
Upwind stabilization of Navier-Stokes solvers
We present a study of the effect of upwinding on stabilisation of both advective and pressure terms in a family of primitive-variable Navier-Stokes solvers. We consider two MUSCL schemes, the first one applies to compressible flow, the second one to incompressible flow. We illustrate the fact that both numerical models suffer oscillations if a minimal (but not large) amount of upwinding is not associated with acoustics, while advection can be stabilized by the physical diffusion terms when the mesh Reynolds number is small enough
Electromagnetic fields in compact binaries: post-Newtonian wave generation and application to double white dwarfs systems
The aim of this work is twofold: (i) to properly define a wave-generation
formalism for compact-supported sources embedded in Einstein-Maxwell theory,
relying on matched post-Newtonian and multipolar-post-Minkowskian expansions;
(ii) to apply this formalism (which is valid for any type of post-Newtonian
sources) to the case of two stars with constant and aligned magnetic dipoles,
by computing the fluxes of energy and angular momentum to the next-to-leading
order, as well as the gravitational amplitude modes. Assuming eccentric orbits,
we derive the evolution of orbital parameters, as well as the observables of
the system, notably the gravitational phase for quasi-circular orbits. Finally,
we give some numerical estimates for the contribution of the magnetic dipoles
for some realistic systems.Comment: 44 page
Electromagnetic fields in compact binaries: a post-Newtonian approach
Galactic binaries, and notably double white dwarfs systems, will be a
prominent source for the future LISA and Einstein Telescope detectors.
Contrarily to the black holes observed by the current LIGO-Virgo-KAGRA network,
such objects bear intense magnetic fields, that are naturally expected to leave
some imprints on the gravitational wave emission. The purpose of this work is
thus to study those imprints within the post-Newtonian (PN) framework,
particularly adapted to double white dwarfs systems. To this end, we construct
an effective action that takes into account the whole electromagnetic structure
of a star, and then specify it to dipolar order. With this action at hand, we
compute the acceleration and Noetherian quantities for generic electric and
magnetic dipoles, at a relative 2PN order. Finally, focusing on physically
relevant systems, we show that the magnetic effects on the orbital frequency,
energy and angular momentum is significant, confirming previous works
conclusions.Comment: 23 pages, no figure, supplementary material attached v2: references
and acknowledgments update
Black holes and stars in the minimal theory of massive gravity
In this letter, we show that any solution of general relativity (GR) that can
be rendered spatially flat by a coordinate change is also a solution of the
self-accelerating branch of the minimal theory of massive gravity (MTMG), with
or without matter. We then for the first time obtain black hole and star
solutions in a theory of massive gravity that agree with the corresponding
solutions in GR and that are free from strong coupling issues. This in
particular implies that the parametrized post-Newtonian parameters and are unity, as in GR. We further show how these
solutions can be embedded in a cosmological setting. While cosmological scales
have already been considered in previous works, this is the first study of the
phenomenology at shorter scales of the self-accelerating branch of MTMG.Comment: 5 page
Gravitational-Wave Phasing of Quasi-Circular Compact Binary Systems to the Fourth-and-a-Half post-Newtonian Order
The inspiral phase of gravitational waves emitted by spinless compact binary
systems is derived through the fourth-and-a-half post-Newtonian (4.5PN) order
beyond quadrupole radiation, and the leading amplitude mode (, m) = (2,
2) is obtained at 4PN order. We also provide the radiated flux, as well as the
phase in the stationary phase approximation. Rough numerical estimates for the
contribution of each PN order are provided for typical systems observed by
current and future gravitational wave detectors.Comment: 9 pages, 1 table. v2: reference of the companion paper updated. v3:
post-referee version, typo corrected in Eq. (9
Gravitational Wave Flux and Quadrupole Modes from Quasi-Circular Non-Spinning Compact Binaries to the Fourth Post-Newtonian Order
This article provides the details on the technical derivation of the
gravitational waveform and total gravitational-wave energy flux of non-spinning
compact binary systems to the 4PN (fourth post-Newtonian) order beyond the
Einstein quadrupole formula. In particular: (i) we overview the link between
the radiative multipole moments measured at infinity and the source moments in
the framework of dimensional regularization; (ii) we compute special
corrections to the source moments due to "infrared" commutators arising at the
4PN order; (iii) we derive a "post-adiabatic" correction needed to evaluate the
tail integral with 2.5PN relative precision; (iv) we discuss the relation
between the binary's orbital frequency in quasi-circular orbit and the
gravitational-wave frequency measured at infinity; (v) we compute the
hereditary effects at the 4PN order, including those coming from the recently
derived tails-of-memory; and (vi) we describe the various tests we have
performed to ensure the correctness of the results. Those results are collected
in an ancillary file.Comment: 32 pages, no figure. v2: reference of the companion letter updated.
v3: post-referee versio
Domain walls without a potential
International audienceWe show that domain walls, or kinks, can be constructed in simple scalar theories where the scalar has no potential. These theories belong to a class of k-essence where the Lagrangian vanishes identically when one lets the derivatives of the scalar vanish. The domain walls we construct have positive energy and stable quadratic perturbations. As particular cases, we find families of theories with domain walls and their quadratic perturbations identical to the ones of the canonical Mexican hat or sine-Gordon scalar theories. We show that canonical and noncanonical cases are nevertheless distinguishable via higher order perturbations or a careful examination of the energies. In particular, in contrast to the usual case, our walls are local minima of the energy among the field configuration having some fixed topological charge, but not global minima