Quasi-normal mode of a Planck star

In this work we present a calculation of the quasi-normal modes of a Planck star, a supposed state in the life of a large mass star in which quantum effects should reverse the collapse causing the star to explode. In order to solve the Regge-Wheeler equations and to calculate the quasi-normal modes, we apply the shooting method

Including topology change in loop quantum gravity with topspin network formalism with application to homogeneous and isotropic cosmology

none1noWe apply topspin network formalism to Loop Quantum Gravity in order to include in the theory the possibility of changes in the topology of spacetime. We apply this formalism to three toy models: with the first, we find that the topology can actually change due to the action of the Hamiltonian constraint and with the second we find that the final state might be a superposition of states with different topologies. In the third and last application, we consider an homogeneous and isotropic Universe, calculating the difference equation that describes the evolution of the system and which are the final topological states after the action of the Hamiltonian constraint. For this last case, we also calculate the transition amplitudes and probabilities from the initial to the final states.openVillani, MattiaVillani, Matti

Semi-analytical and numerical solutions to Teukolsky equations for large fermion mass over black hole mass ratio

In a recent paper, we have studied the Teukolsky equations for fermions with mass $m_e\neq 0$ and rotating black hole of mass $M$. There, we have studied two cases: $\tilde{m}_e=m_e\,M^{-1}\ll 1$ and $a\omega\ll 1$; $\tilde{m}_e\ll 1$ and $a\omega \gtrsim 1$. Here we study the two remaining case case in which $\tilde{m}_e\gtrsim 1$ and $a\omega\ll 1$ using a semi-analytical approach and $\tilde{m}_e\gtrsim 1$ and $a\omega\gtrsim 1$ using a numerical approach. This case could be of some interest for the study of the interactions of fermions with small black holes, such as those formed in the last stages of the the Hawking evaporation process.Comment: 7 pages, two tables. arXiv admin note: text overlap with arXiv:2310.1364

Effects of neutron stars magnetic dipole on the generation of gravitational waves

In this paper we shall consider the potential effect of the magnetic dipole moment of a neutron star (NS) in a binary NS-NS system. We shall derive the Lagrangian of the binary system and show how to find a Multipolar Post Minkowskian (MPM) solution to the linearized Einstein- Maxwell system and the energy flux of the electromagnetic waves; we shall calculate at the higher order the equations of motion and precession. At the end, we will provide calculations proving that the effect of the magnetic moment on the binary system is barely observable

Low-energy electromagnetic processes affecting free-falling test-mass charging for LISA and future space interferometers

Galactic cosmic rays and solar energetic particles charge gold-platinum, free-falling test masses (TMs) on board interferometers for the detection of gravitational waves in space. The charging process induces spurious forces on the test masses that affect the sensitivity of these instruments mainly below $10^{-3}$ Hz. Geant4 and FLUKA Monte Carlo simulations were carried out to study the TM charging process on board the LISA Pathfinder mission that remained into orbit around the Sun-Earth Lagrange point L1 between 2016 and 2017. While a good agreement was observed between simulations and measurements of the TMs net charging, the shot noise associated with charging fluctuations of both positive and negative particles resulted 3-4 times higher that predicted. The origin of this mismatch was attributed to the propagation of electrons and photons only above 100 eV in the simulations. In this paper, low-energy electromagnetic processes to be included in the future Monte Carlo simulations for LISA and LISA-like space interferometers TM charging are considered. {It is found that electrons and photons below 100 eV give a contribution to the effective charging comparable to that of the whole sample of particles above this energy. In particular, for incident protons ionization contributes twice with respect to low energy kinetic emission and electron backscattering. The other processes are found to play a negligible role. For heavy nuclei only sputtering must be considered.Comment: Accepted for publication in Classical and Quantum Gravit

Bridging the gap between Monte Carlo simulations and measurements of the LISA Pathfinder test-mass charging for LISA

Cubic gold-platinum free-falling test masses (TMs) constitute the mirrors of future LISA and LISA-like interferometers for low-frequency gravitational wave detection in space. High-energy particles of Galactic and solar origin charge the TMs and thus induce spurious electrostatic and magnetic forces that limit the sensitivity of these interferometers. Prelaunch Monte Carlo simulations of the TM charging were carried out for the LISA Pathfinder (LPF) mission, that was planned to test the LISA instrumentation. Measurements and simulations were compared during the mission operations. The measured net TM charging agreed with simulation estimates, while the charging noise was three to four times higher. We aim to bridge the gap between LPF TM charging noise simulations and observations. New Monte Carlo simulations of the LPF TM charging due to both Galactic and solar particles were carried out with the FLUKA/LEI toolkit. This allowed propagating low-energy electrons down to a few electronvolt. These improved FLUKA/LEI simulations agree with observations gathered during the mission operations within statistical and Monte Carlo errors. The charging noise induced by Galactic cosmic rays is about one thousand charges per second. This value increases to tens of thousands charges per second during solar energetic particle events. Similar results are expected for the LISA TM charging.Comment: 11 pages, 9 figure

Study of Galactic Cosmic-Ray Flux Modulation by Interplanetary Plasma Structures for the Evaluation of Space Instrument Performance and Space Weather Science Investigations

The role of high-energy particles in limiting the performance of on-board instruments was studied for the European Space Agency (ESA) Laser Interferometer Space Antenna (LISA) Pathfinder (LPF) and ESA/National Astronautics and Space Administration Solar Orbiter missions. Particle detectors (PD) placed on board the LPF spacecraft allowed for testing the reliability of pre-launch predictions of galactic cosmic-ray (GCR) energy spectra and for studying the modulation of proton and helium overall flux above 70 MeV n − 1 on a day-by-day basis. GCR flux variations up to approximately 15% in less than a month were observed with LPF orbiting around the Lagrange point L1 between 2016 and 2017. These variations appeared barely detected or undetected in neutron monitors. In this work the LPF data and contemporaneous observations carried out with the magnetic spectrometer AMS-02 experiment are considered to show the effects of GCR flux short-term variations with respect to monthly averaged measurements. Moreover, it is shown that subsequent large-scale interplanetary structures cause a continuous modulation of GCR fluxes. As a result, small Forbush decreases cannot be considered good proxies for the transit of interplanetary coronal mass ejections and for geomagnetic storm forecasting