1,720,987 research outputs found
A deep classifier of chaos and order in Hamiltonian systems of two degrees of freedom
No full text<p>Chaos is an intriguing phenomenon that can be found in an immense variate of systems. Its detection and discrimination from its counterpart order poses an interesting challenge. To address it, we present a deep classifier capable of classifying chaos from order in the discretised dynamics of Hamiltonian systems of two degrees of freedom, through the machinery of Poincare maps. Our deep network is based predominantly on a convolutional architecture, and generalises with good accuracy on unseen datasets, thanks to the universal features of a perturbed pendulum learned by the deep network. We discuss in detail the significance and the preparation of our training set, and we showcase how our deep network can be applied to the dynamics of geodesic motion in an axi-symmetric and stationary spacetime of a compact object deviating from the Kerr black hole paradigm. Finally, we discuss current challenges and some promising future directions.</p>
Dark Matter-Induced Stellar Oscillations
No full textReproduction package for the paper "Dark Matter-Induced Stellar Oscillations"
EMRI_MC: A GPU-based code for Bayesian inference of EMRI waveforms
Get PDFInternational audienceWe describe a simple and efficient Python code to perform Bayesian forecasting for gravitational waves (GW) produced by Extreme-Mass-Ratio-Inspiral systems (EMRIs). The code runs on GPUs for an efficient parallelised computation of thousands of waveforms and sampling of the posterior through a Markov-Chain-Monte-Carlo (MCMC) algorithm. EMRI_MC generates EMRI waveforms based on the so--called kludge scheme, and propagates it to the observer accounting for cosmological effects in the observed waveform due to modified gravity/dark energy. Extending the code to more accurate schemes for the generation of the waveform is straightforward. Despite the known limitations of the kludge formalism, we believe that the code can provide a helpful resource for the community working on forecasts for interferometry missions in the milli-Hz scale, predominantly, the satellite-mission LISA
Deep learning inference of the neutron star equation of state
Get PDFWe present a pipeline to infer the equation of state of neutron stars from
observations based on deep neural networks. In particular, using the standard
(deterministic), as well as Bayesian (probabilistic) deep networks, we explore
how one can infer the interior speed of sound of the star given a set of mock
observations of total stellar mass, stellar radius and tidal deformability. We
discuss in detail the construction of our simulated dataset of stellar
observables starting from the solution of the gravitational equations, as well
as the relevant architectures for the deep networks, along with their
performance and accuracy. We further explain how our pipeline is capable to
detect a possible QCD phase transition in the stellar core. Our results show
that deep networks offer a promising tool towards solving the inverse problem
of neutron stars, and the accurate inference of their interior from future
stellar observations.Comment: 15 pages, 11 figures, code and supplementary material available at
https://zenodo.org/records/1121658
Vainshtein in the UV and a Wilsonian analysis of derivatively coupled scalars
Get PDFIn the first part of this paper we critically examine the ultra-violet implications of theories that exhibit Vainshtein screening, taking into account both the standard Wilsonian perspective as well as more exotic possibilities. Aspects of this discussion draw on results from the second part of the paper in which we perform a general study of derivatively coupled scalar theories using non–perturbative exact renormalisation group techniques, which are of interest independently of their application to modified gravity. In this context, we demonstrate the suppression of quantum corrections within the Vainshtein radius and discuss the potential relation with the classicalisation conjecture. We question whether the latter can be considered a realistic candidate for UV completion of large-scale modifications of gravity on account of a dangerously low classicalisation/strong coupling scale
Dark Matter-Induced Stellar Oscillations
Get PDFIt has been hypothesized that dark matter is comprised of ultra-light bosons
whose collective phenomena can be described as a scalar field undergoing
coherent oscillations. Examples include axion and fuzzy dark matter models. In
this ultra-light dark matter scenario, the harmonic variation in the field's
energy-momentum tensor sources an oscillating component of the gravitational
potential that we show can resonantly-excite stellar oscillations. A
mathematical framework for predicting the amplitude of these oscillations is
developed, which reveals that ultra-light dark matter predominantly excites
p-modes of degree . An investigation of resonantly-excited solar
oscillations is presented, from which we conclude that dark matter-induced
oscillations of the Sun are likely undetectable. We discuss prospects for
constraining ultra-light dark matter using other stellar objects.Comment: 5 pages, no figures. Comments welcome. A reproduction package for our
numerical analysis is available here: https://zenodo.org/record/789403
Obtaining Precision Constraints on Modified Gravity with Helioseismology
No full textInternational audienceWe propose helioseismology as a new, precision probe of fifth forces at astrophysical scales, and apply it on the most general scalar-tensor theories for dark energy, known as degenerate higher-order scalar-tensor theories. We explain how the effect of the fifth force on the solar interior leaves an observable imprint on the acoustic oscillations, and under certain assumptions we numerically compute the nonradial pulsation eigenfrequencies within modified gravity. We illustrate its constraining power by showing that helioseismic observations have the potential to improve constraints on the strength of the fifth force by more than 2 orders of magnitude, as -1.8×10-3≤Y≤1.2×10-3 (at 2σ). This in turn would suggest constraints of similar order for the theory’s free functions around a cosmological background (αH, β1)
Measuring the propagation speed of gravitational waves with LISA
Get PDFThe propagation speed of gravitational waves, cT, has been tightly constrained by the binary neutron star merger GW170817 and its electromagnetic counterpart, under the assumption of a frequency-independent cT. Drawing upon arguments from Effective Field Theory and quantum gravity, we discuss the possibility that modifications of General Relativity allow for transient deviations of cT from the speed of light at frequencies well below the band of current ground-based detectors. We motivate two representative Ansätze for cT(f), and study their impact upon the gravitational waveforms of massive black hole binary mergers detectable by the LISA mission. We forecast the constraints on cT(f) obtainable from individual systems and a population of sources, from both inspiral and a full inspiral-merger-ringdown waveform. We show that LISA will enable us to place stringent independent bounds on departures from General Relativity in unexplored low-frequency regimes, even in the absence of an electromagnetic counterpart
- …
