Periodic Reporting for period 1 - GRU (Gravitational Universe: Challenges and Opportunities)
Periodo di rendicontazione: 2021-10-01 al 2023-09-30
The landmark detection of gravitational waves (GWs) emitted by merging black-hole (BH) and neutron-star binaries has opened a new era in physics, giving us access to the strong-field regime of the gravitational interaction. In this new observational window, we could learn that general relativity is not adequate to describe the strong-field regime of gravity; new fundamental fields beyond the standard model, or new kinds of compact objects, could challenge current understanding of dark matter and dark energy.
In order to reach these results, an effort is needed by the theoretical and the data-analysis communities. On one hand, we need to develop new data-analysis algorithms, to extract meaningful results from the impressive amount of data which will be delivered. On the other hand, we need to develop theoretical models of GW sources which do not assume the standard theories and paradigms which we want to test, in order to perform non-biased tests and to use observational results to address fundamental problems. To this aim, scientists with different expertise and addressing different challenges should exchange their views and learn from each other’s problems. The proposed studies can be loosely classified into four groups with considerable overlap: i) Perturbation techniques in general relativity and beyond ii) Non-linear simulations of binary compact objects beyond general relativity iii) GWs from the dark universe iv) Data analysis for GW experiments.
In order to reach these results, an effort is needed by the theoretical and the data-analysis communities. On one hand, we need to develop new data-analysis algorithms, to extract meaningful results from the impressive amount of data which will be delivered. On the other hand, we need to develop theoretical models of GW sources which do not assume the standard theories and paradigms which we want to test, in order to perform non-biased tests and to use observational results to address fundamental problems. To this aim, scientists with different expertise and addressing different challenges should exchange their views and learn from each other’s problems. The proposed studies can be loosely classified into four groups with considerable overlap: i) Perturbation techniques in general relativity and beyond ii) Non-linear simulations of binary compact objects beyond general relativity iii) GWs from the dark universe iv) Data analysis for GW experiments.
WP1:
• We have computed the gravitational and scalar flux and the gravitational waveform in scalar-tensor theories, up to 1.5PN order beyond leading GR contribution, including tail and non-linear memory terms, and comparing the results with NR simulations.
• We have clarified the role of tidal effects in the equations of motion of a binary BH, up to next-to-next-to leading order in scalar-tensor and scalar Gauss-Bonnet theories, i.e. up to 5PN order.
• We have developed an alternative approach to study, with a modified PN approximation scheme, the conservative dynamics of a compact binary system in a class of scalar-tensor theories of gravity.
• We have determined the corrections to the dynamics of a compact binary system due to generic, non-axisymmetric mass quadrupole moment, to leading order in the PN expansion.
• We have studied the dynamics of an EMRI system near orbital resonance, deriving an effective resonant Hamiltonian for the case that the EMRI moves across the resonance regime.
• We have studied the dynamics of EMRIs in presence of scalar fields, finding that the LISA will be able to find out whether the smaller body in the EMRI is coupled with the scalar field, and that the gravitational waveform emitted in this process would have a general form.
• We have computed the QNMs of rotating BHs in scalar Gauss-Bonnet gravity, up to second order in the BH angular momentum.
WP2:
• We have developed an original approach to address the well-posednesss problems that plague scalar Gauss-Bonnet gravity. In this approach the field equations are modified to get a well-defined time evolution.
• We have performed NR simulations of the collapse to a BH in scalar Gauss-Bonnet gravity, showing that these BH solutions may naturally evolve into naked singularities.
• We have started studying the well-posedness of a class of Lorentz-violating gravity theories (Horava-Lifschitz gravity). Our preliminary results seem to indicate a possible instability in these theories near the universal horizon of black holes.
• We have started developing an alternative approach to perform numerical simulations of binary BH coalescences beyond GR and the BH paradigm, the so-called close-limit approximation, in which the two BHs near the merger are perturbations of the final BHs.
• We have studied boson stars, a class of exotic compact objects, and performed NR simulations of the merger of a binary system of these objects.
• We have found evidence that the standard description of the ringdown stage of a binary BH coalescence as a BH oscillating in its QNMs, based on the linear approximation of GR, is not accurate.
WP3:
• We have studied, using numerical simulations, the evolution of a BH placed at the center of a self-gravitating DM soliton.
• We have performed numerical simulations of axionic clouds evolution in the presence of plasmas, evolving the axion, electromagnetic field and plasma density.
• We have found that non-topological scalar field solitons, calles Q-balls, can enhance the energy of waves scattering on them, through a new mechanism, which is different from superradiance
• We have studied the effect of a ultralight scalar field cloud on the GW signal from binary BH mergers, finding that the cloud would lead to a non-vanishing tidal deformability of the BHs, potentially detectable by 3G GW detectors.
• We have developed a fully relativistic approach to study extreme mass-ratio inspirals (EMRIs) of compact objects into BHs surrounded by generic matter disrtibutions.
• We have studied how the drag exerted by gas on BHs would affect the GW signal from binary BH systems.
• We ave studied primordial BHs orbiting around Sgr A*, finding under which conditions the GW signal from these objects would be detectable by LISA.
WP4:
• We have shown, by analysing GW150915 postmerger data, that previous claims of the presence of on overtones the signal were unsubstantiated, since the overtone detection was noise dominated.
• We have found similar evidence (that claims about overtones in GW150915 were unsubstantiated) by analysing the GW150915 signal using a novel data analysis approach based on machine learning techniques .
• We have studied the prospects of both LISA and the Einstein Telescope to perform precision BH spectroscopy, by extracting the QNM frequency from the ringdown signal.
• We have shown that the non-linear memory effect will be observable in massive BH binaries with LISA
• We have developed a data-analysis strategy to employ future GW observations from multiple detectors (on the ground and in space) to set more stringent constraints on the propagation speed of GWs.
• We have assessed the impact of different choices for the design of third generation GW detectors (L-shaped vs. triangular shapte) on parameter estimation for stellar-origin BH binaries.
• We have computed the gravitational and scalar flux and the gravitational waveform in scalar-tensor theories, up to 1.5PN order beyond leading GR contribution, including tail and non-linear memory terms, and comparing the results with NR simulations.
• We have clarified the role of tidal effects in the equations of motion of a binary BH, up to next-to-next-to leading order in scalar-tensor and scalar Gauss-Bonnet theories, i.e. up to 5PN order.
• We have developed an alternative approach to study, with a modified PN approximation scheme, the conservative dynamics of a compact binary system in a class of scalar-tensor theories of gravity.
• We have determined the corrections to the dynamics of a compact binary system due to generic, non-axisymmetric mass quadrupole moment, to leading order in the PN expansion.
• We have studied the dynamics of an EMRI system near orbital resonance, deriving an effective resonant Hamiltonian for the case that the EMRI moves across the resonance regime.
• We have studied the dynamics of EMRIs in presence of scalar fields, finding that the LISA will be able to find out whether the smaller body in the EMRI is coupled with the scalar field, and that the gravitational waveform emitted in this process would have a general form.
• We have computed the QNMs of rotating BHs in scalar Gauss-Bonnet gravity, up to second order in the BH angular momentum.
WP2:
• We have developed an original approach to address the well-posednesss problems that plague scalar Gauss-Bonnet gravity. In this approach the field equations are modified to get a well-defined time evolution.
• We have performed NR simulations of the collapse to a BH in scalar Gauss-Bonnet gravity, showing that these BH solutions may naturally evolve into naked singularities.
• We have started studying the well-posedness of a class of Lorentz-violating gravity theories (Horava-Lifschitz gravity). Our preliminary results seem to indicate a possible instability in these theories near the universal horizon of black holes.
• We have started developing an alternative approach to perform numerical simulations of binary BH coalescences beyond GR and the BH paradigm, the so-called close-limit approximation, in which the two BHs near the merger are perturbations of the final BHs.
• We have studied boson stars, a class of exotic compact objects, and performed NR simulations of the merger of a binary system of these objects.
• We have found evidence that the standard description of the ringdown stage of a binary BH coalescence as a BH oscillating in its QNMs, based on the linear approximation of GR, is not accurate.
WP3:
• We have studied, using numerical simulations, the evolution of a BH placed at the center of a self-gravitating DM soliton.
• We have performed numerical simulations of axionic clouds evolution in the presence of plasmas, evolving the axion, electromagnetic field and plasma density.
• We have found that non-topological scalar field solitons, calles Q-balls, can enhance the energy of waves scattering on them, through a new mechanism, which is different from superradiance
• We have studied the effect of a ultralight scalar field cloud on the GW signal from binary BH mergers, finding that the cloud would lead to a non-vanishing tidal deformability of the BHs, potentially detectable by 3G GW detectors.
• We have developed a fully relativistic approach to study extreme mass-ratio inspirals (EMRIs) of compact objects into BHs surrounded by generic matter disrtibutions.
• We have studied how the drag exerted by gas on BHs would affect the GW signal from binary BH systems.
• We ave studied primordial BHs orbiting around Sgr A*, finding under which conditions the GW signal from these objects would be detectable by LISA.
WP4:
• We have shown, by analysing GW150915 postmerger data, that previous claims of the presence of on overtones the signal were unsubstantiated, since the overtone detection was noise dominated.
• We have found similar evidence (that claims about overtones in GW150915 were unsubstantiated) by analysing the GW150915 signal using a novel data analysis approach based on machine learning techniques .
• We have studied the prospects of both LISA and the Einstein Telescope to perform precision BH spectroscopy, by extracting the QNM frequency from the ringdown signal.
• We have shown that the non-linear memory effect will be observable in massive BH binaries with LISA
• We have developed a data-analysis strategy to employ future GW observations from multiple detectors (on the ground and in space) to set more stringent constraints on the propagation speed of GWs.
• We have assessed the impact of different choices for the design of third generation GW detectors (L-shaped vs. triangular shapte) on parameter estimation for stellar-origin BH binaries.
Our results go substantially beyond the state of the art. For instance:
• We have computed the gravitational and scalar flux and the gravitational waveform in scalar-tensor theories to the highest PN order to date.
• We have been the first to show that EMRI signals detectable by LISA are sensitive to the presence of scalar fields coupled to the secondary body, and that this effect has an universal form.
• We have performed the first computation of QNMs of BHs in a modified gravity theory (different from those of GR) to 2nd in the rotation rate.
• No dynamical evolution of axionic clouds had been done before in the presence of plasma, and our observational strategies – of direct importance for observatories like the EHT and others – are novel.
• We have performed the first non-linear numerical simulations of compact binary collisions and mergers involving exotic compact objects.
• We have assessed the impact of different choices for the design of third-generation GW detectors in parameter estimation for stellar-origin BH binaries.
• We have computed the gravitational and scalar flux and the gravitational waveform in scalar-tensor theories to the highest PN order to date.
• We have been the first to show that EMRI signals detectable by LISA are sensitive to the presence of scalar fields coupled to the secondary body, and that this effect has an universal form.
• We have performed the first computation of QNMs of BHs in a modified gravity theory (different from those of GR) to 2nd in the rotation rate.
• No dynamical evolution of axionic clouds had been done before in the presence of plasma, and our observational strategies – of direct importance for observatories like the EHT and others – are novel.
• We have performed the first non-linear numerical simulations of compact binary collisions and mergers involving exotic compact objects.
• We have assessed the impact of different choices for the design of third-generation GW detectors in parameter estimation for stellar-origin BH binaries.