arXiv subjects

Gideon Koekoek

Publications and source records attributed to Gideon Koekoek.

7 recordsLinked to original sources

arXiv2024

Polar magnetic fields in black-hole space-times

To model magnetic fields of compact objects we solve the Maxwell equations in the background of the exterior static Schwarzschild and slowly rotating Kerr space-times. We impose the boundary condition that the electromagnetic fields are to vanish at infinity. A full set of solutions is obtained, describing axially symmetric magnetic fields, supplemented by axial electric fields in the case of non-vanishing rotation of the gravitational background. We study the motion of charged test particles in these combined gravitational and electromagnetic fields, in particular considering the conditions for circular equatorial orbits. Such orbits always exist in odd-multipole magnetic fields, and they can exist for particular radii in a combination of two or more even-multipole magnetic fields. Combinations of several odd-multipole fields can give rise to radial variation in the field orientation and the direction of motion of charged particles. Deviations from circularity are described using a perturbative approach. This also allows to study the stability of the parent circular orbits.

gr-qc↗

arXiv2023

Searching for ring-like structures in the Cosmic Microwave Background

In this research, we present an alternative methodology to search for ring-like structures in the sky with unusually large temperature gradients, namely Hawking points (HP), in the Cosmic Microwave Background (CMB), which are possible observational effects associated with Conformal Cyclic Cosmology (CCC). To assess the performance of our method, we constructed an artificial data set of HP, according to CCC, and we were able to retrieve $95 \%$ of ring-like anomalies from it. Furthermore, we scanned the \textit{Planck} CMB sky map and compared it to simulations according to $ΛCDM$, where we applied robust statistical tests to assess the existence of HP. Even though no significant ring-like structures were observed, we report the largest excess of HP candidates found at $α= $1\% significance level for the analyzed sky maps (CMB at 70GHz, SEVEM, SMICA, and Commander-Ruler), and we stress the need to continue the theoretical and experimental research in this direction.

astro-ph.CO↗

arXiv2022

Hybrid Quantum Singular Spectrum Decomposition for Time Series Analysis

Classical data analysis requires computational efforts that become intractable in the age of Big Data. An essential task in time series analysis is the extraction of physically meaningful information from a noisy time series. One algorithm devised for this very purpose is singular spectrum decomposition (SSD), an adaptive method that allows for the extraction of narrow-banded components from non-stationary and non-linear time series. The main computational bottleneck of this algorithm is the singular value decomposition (SVD). Quantum computing could facilitate a speedup in this domain through superior scaling laws. We propose quantum SSD by assigning the SVD subroutine to a quantum computer. The viability for implementation and performance of this hybrid algorithm on a near term hybrid quantum computer is investigated. In this work we show that by employing randomised SVD, we can impose a qubit limit on one of the circuits to improve scalibility. Using this, we efficiently perform quantum SSD on simulations of local field potentials recorded in brain tissue, as well as GW150914, the first detected gravitational wave event.

quant-ph↗

arXiv2022

Determining the equation of state of neutron stars with Einstein Telescope using tidal effects and r-mode excitations from a population of binary inspirals

Third-generation gravitational wave (GW) observatories such as Einstein Telescope (ET) and Cosmic Explorer (CE) will be ideal instruments to probe the structure of neutron stars through the GWs they emit when undergoing binary coalescence. In this work we make predictions about how well ET in particular will enable us to reconstruct the neutron star equation of state through observations of tens of binary neutron star coalescences with signal-to-noise ratios in the hundreds. We restrict ourselves to information that can be extracted from the inspiral, which includes tidal effects and possibly r-mode resonances. In treating the latter we go beyond the Newtonian approximation, introducing and utilizing new universal relations. We find that the ability to observe resonant r-modes would have a noticeable impact on neutron star equation of state measurements with ET.

gr-qc↗

arXiv2022

The path to Special Relativity

Following an early observation of Ignatowsky, we present a derivation of the transformation rules between inertial systems making no other assumptions than the existence of the latter, and show that generically these rules are characterized by a constant of nature with the dimensions of an inverse velocity squared having the same value in all inertial frames. No independent postulate of the existence of an absolute velocity for light waves or other carriers of physical information is necessary. Aside from the usual Lorentz- and galilean transformations, our analysis also allows for the existence of four-dimensional Euclidian transformation rules between inertial systems.

physics.gen-ph↗

arXiv2021

Bounding dark charges on binary black holes using gravitational waves

In models of minicharged dark matter associated with a hidden $U(1)$ symmetry, astrophysical black holes may acquire a "dark" charge, in such a way that the inspiral dynamics of binary black holes can be formally described by an Einstein-Maxwell theory. Charges enter the gravitational wave signal predominantly through a dipole term, but their effect is known to effectively first post-Newtonian order in the phase, which enables measuring the size of the charge-to-mass ratios, $|q_i/m_i|$, $i = 1,2$, of the individual black holes in a binary. We set up a Bayesian analysis to discover, or constrain, dark charges on binary black holes. After testing our framework in simulations, we apply it to selected binary black hole signals from the second Gravitational Wave Transient Catalog (GWTC-2), namely those with low masses so that most of the signal-to-noise ratio is in the inspiral regime. We find no evidence for charges on the black holes, and place typical 1-$σ$ bounds on the charge-to-mass ratios of $|q_i/m_i| \lesssim 0.2 - 0.3$.

gr-qc↗

arXiv2021

Modeling and detecting resonant tides of exotic compact objects

The event horizon of a black hole in general relativity absorbs all infalling radiation. Any observation of the contrary would immediately challenge the expectation that astrophysical black holes are described by the vacuum Kerr geometry. If a putative black hole does reflect part of the ingoing radiation, its quasinormal mode structure is drastically altered. Low frequency modes can be introduced that are resonantly excited during the inspiral of a binary system. We study the resulting phase shift of the gravitational wave signal. Building on neutron star results, we obtain a model-independent expression for the phase shift that depends only on quasinormal modes and Love numbers of the compact object. We find that the phase shift might be detectable with Einstein Telescope for asymmetric binaries in high signal-to-noise events ($\sim 10^3$), but by far cannot explore the Planck scale.

gr-qc↗