Periodic Reporting for period 1 - upgradeFDM (Upgrading the Fuzzy Dark Matter Model)
Okres sprawozdawczy: 2021-01-11 do 2023-01-10
The project is aiming to investigate exotic characters and properties of the populated dark matter candidate with ultralight mass, called fuzzy dark matter (FDM) or Bose-Einstein-condensate (BEC) dark matter, by incorporating new ingredients, a self interaction and thermal/incoherent component, and investigate the role of quantized vortices on the dark matter (DM) halo structures with the FDM wavy nature via numerical simulations. It would upgrade our understanding of DM and the results will help further dark matter search.
Our extensive investigations guide us to our first publication, “Coherent and incoherent structures in fuzzy dark matter halos” [DOI: 10.1093/mnras/stad591] bringing several new insights into FDM halos. To understand the primary properties of the FDM field, we first investigate the coherent properties of FDM
via 'galaxy collision' numerical experiments and integrate the concept of the classical-field method from atomic BECs, the fellow's original discipline. We find out that the core of a halo is fully coherent but is surrounded by a highly incoherent field and such a coherent-incoherent crossover can surprisingly be captured by a bimodal core-halo profile, matching the solitonic core profile in FDM and the cold DM profile in the outer region. This bimodal profile can be further used to describe the dynamical halos and the extracted core length scale is anti-correlated to the peak location of the power spectrum of the whole FDM density field. This indicates that the oscillation of the core can be probed by the observational power spectrum.
We also identify the source of fluctuations leading to the decoherence at the outer region of FDM halos by looking at the energy distributions. The core area is dominated by the quantum pressure, against the gravitational collapse. In the outer region, we found that quantum pressure energy is comparable with the classical kinetic energy (while there is a quantum component in the FDM) consisting of the sound-like and rotational components, and the latter plays a crucial role. This suggests that vortices are the source of fluctuations, and our unique visualization shows that there are large amounts of quantized vortices in the outer hallos (see the attached figure) and the FDM halos are actually in a turbulent state. In addition, we notice that the characteristic size of granules (local density lumps in the outer halo) is associated with the intervortex distance from the granule and vortex energy spectra.
We have applied the methods/concepts in atomic BEC studies and brought new insights into the FDM halo profiles, showing the highly excited halos are not just density fluctuations from the waviness effects. It builds up the benchmark with great high-quality scientific results and paves the way for our exploration of the role of self interaction and additional incoherent component from the dark matter particles.
Apart from the current published work, we are preparing further publications on the role of self-interaction and the core oscillation from the semi-analytical and quasi-particle approaches, rather than the perspective of a single-particle excited state considered in the existing literature. This project has been very successful in both the extraordinary scientific finding and the fellow’s career development.
Our extensive investigations guide us to our first publication, “Coherent and incoherent structures in fuzzy dark matter halos” [DOI: 10.1093/mnras/stad591] bringing several new insights into FDM halos. To understand the primary properties of the FDM field, we first investigate the coherent properties of FDM
via 'galaxy collision' numerical experiments and integrate the concept of the classical-field method from atomic BECs, the fellow's original discipline. We find out that the core of a halo is fully coherent but is surrounded by a highly incoherent field and such a coherent-incoherent crossover can surprisingly be captured by a bimodal core-halo profile, matching the solitonic core profile in FDM and the cold DM profile in the outer region. This bimodal profile can be further used to describe the dynamical halos and the extracted core length scale is anti-correlated to the peak location of the power spectrum of the whole FDM density field. This indicates that the oscillation of the core can be probed by the observational power spectrum.
We also identify the source of fluctuations leading to the decoherence at the outer region of FDM halos by looking at the energy distributions. The core area is dominated by the quantum pressure, against the gravitational collapse. In the outer region, we found that quantum pressure energy is comparable with the classical kinetic energy (while there is a quantum component in the FDM) consisting of the sound-like and rotational components, and the latter plays a crucial role. This suggests that vortices are the source of fluctuations, and our unique visualization shows that there are large amounts of quantized vortices in the outer hallos (see the attached figure) and the FDM halos are actually in a turbulent state. In addition, we notice that the characteristic size of granules (local density lumps in the outer halo) is associated with the intervortex distance from the granule and vortex energy spectra.
We have applied the methods/concepts in atomic BEC studies and brought new insights into the FDM halo profiles, showing the highly excited halos are not just density fluctuations from the waviness effects. It builds up the benchmark with great high-quality scientific results and paves the way for our exploration of the role of self interaction and additional incoherent component from the dark matter particles.
Apart from the current published work, we are preparing further publications on the role of self-interaction and the core oscillation from the semi-analytical and quasi-particle approaches, rather than the perspective of a single-particle excited state considered in the existing literature. This project has been very successful in both the extraordinary scientific finding and the fellow’s career development.
During the project period, the work has been achieved by the fellow is summarized below
* Deliverables and Milestones
Most of the deliverables and milestones are achieved. Only WP2 is slightly detoured.
* Numerical Script
The work within the project period, the state-of-the-art method for modelling the FDM system is developed and seriously tested to compare with the fundamental properties from existing literature and the numerical scripts in both MATLAB and JULIA languages are uploaded on GitHub, https://github.com/ligeston/FuzzyDarkMatter(odnośnik otworzy się w nowym oknie) which will be openly accessed once the documentation is completed. For now, it is only privately shared with a few collaborators, including PhD students and postdoctoral researchers at Newcastle University, as a trial for finalizing documentation and improving the generality for users, but people requesting access to code will be added as collaborators on GitHub on their demands.
* Dissemination
After a year of the project, Dr Liu visited several groups and attended conferences to interact with international experts and present our findings. He visited Prof Shive’s group at National Taiwan University and Prof. Ying-Nong Chen and Prof. Chorng-Yuan Hwang at National Central University from January to February, Prof Thomas Gasenzer and Prof Luca Amendola at Heidelberg University and Prof Franco Dalfovo at Trento University with group discussions and giving seminars about our results. He presented our work at conference venues in person, including Identification of Dark Matter 2022 in Vienna in July, International Conference on QUANTUM GASES FUNDAMENTAL INTERACTIONS AND COSMOLOGY in August in Pisa, Italy, and XV Tonale Winter School on Cosmology in December in Italy, and had given online seminar invited at University of Oslo and Max-Planck-Institut für Astrophysik. It has been giving him sufficient exposure and enriching him with lots of experience in interacting with cosmology groups around the world.
* Data analysis
Our findings are based on comprehensive investigations led by the beneficiary on the possible physical quantities, including, classical kinetic, quantum pressure, self-interaction and gravitational potential energies and their energy density distribution, power and energy spectra, etc. In addition, the unique data visualization skills bring insightful images for the features we have found.
* Proceeding works for publication
Apart from the current published work, we are preparing further publications on the role of self-interaction, see attached figures, and on the core oscillation from the perspective of elementary excitations via a quasi-particle approach, rather than a single-particle excited states perspective. The former will potentially guide us to constrain the fundamental properties of FDM, such as mass and self-coupling strength, and further unveils more features on quantum vortices in the system with additional length scale. The latter can provide us with more precise results and different pictures of how the core is oscillating and interacting with the outer halo from the elementary excitation point of view. In addition, we are examining our current finding via cooperating with one of the world's leading groups, Prof Shi-Yu Schive at National Taiwan University, Taiwan, to ensure our finding is generic. These works are expected to be published with open-access licenses in suitable journals.
* Deliverables and Milestones
Most of the deliverables and milestones are achieved. Only WP2 is slightly detoured.
* Numerical Script
The work within the project period, the state-of-the-art method for modelling the FDM system is developed and seriously tested to compare with the fundamental properties from existing literature and the numerical scripts in both MATLAB and JULIA languages are uploaded on GitHub, https://github.com/ligeston/FuzzyDarkMatter(odnośnik otworzy się w nowym oknie) which will be openly accessed once the documentation is completed. For now, it is only privately shared with a few collaborators, including PhD students and postdoctoral researchers at Newcastle University, as a trial for finalizing documentation and improving the generality for users, but people requesting access to code will be added as collaborators on GitHub on their demands.
* Dissemination
After a year of the project, Dr Liu visited several groups and attended conferences to interact with international experts and present our findings. He visited Prof Shive’s group at National Taiwan University and Prof. Ying-Nong Chen and Prof. Chorng-Yuan Hwang at National Central University from January to February, Prof Thomas Gasenzer and Prof Luca Amendola at Heidelberg University and Prof Franco Dalfovo at Trento University with group discussions and giving seminars about our results. He presented our work at conference venues in person, including Identification of Dark Matter 2022 in Vienna in July, International Conference on QUANTUM GASES FUNDAMENTAL INTERACTIONS AND COSMOLOGY in August in Pisa, Italy, and XV Tonale Winter School on Cosmology in December in Italy, and had given online seminar invited at University of Oslo and Max-Planck-Institut für Astrophysik. It has been giving him sufficient exposure and enriching him with lots of experience in interacting with cosmology groups around the world.
* Data analysis
Our findings are based on comprehensive investigations led by the beneficiary on the possible physical quantities, including, classical kinetic, quantum pressure, self-interaction and gravitational potential energies and their energy density distribution, power and energy spectra, etc. In addition, the unique data visualization skills bring insightful images for the features we have found.
* Proceeding works for publication
Apart from the current published work, we are preparing further publications on the role of self-interaction, see attached figures, and on the core oscillation from the perspective of elementary excitations via a quasi-particle approach, rather than a single-particle excited states perspective. The former will potentially guide us to constrain the fundamental properties of FDM, such as mass and self-coupling strength, and further unveils more features on quantum vortices in the system with additional length scale. The latter can provide us with more precise results and different pictures of how the core is oscillating and interacting with the outer halo from the elementary excitation point of view. In addition, we are examining our current finding via cooperating with one of the world's leading groups, Prof Shi-Yu Schive at National Taiwan University, Taiwan, to ensure our finding is generic. These works are expected to be published with open-access licenses in suitable journals.
This project has brought out unforeseen insights for the FDM halos and the fellow also brings collaboration for Newcastle University, UK and National Taiwan University, Taiwan. The proceeding works will be published in the following months to discover more exotic features and physics for the system, to potentially shed solutions for the existing problems and to provide new directions for observation. In addition, he has been assisting PhD students with their research projects and has obtained the HEA associate fellowship as a certificate for the evidence of his teaching. We believe the beneficiary's skills and experience have been largely extended and make him one of handful researchers mastering two very different fields.