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On structure and primordial origin of black holes
On structure and primordial origin of black holes
Understanding the microscopic structure of black holes remains one of the most important tasks of theoretical physics. It is especially valuable when this structure can be formulated in terms of transparent physical phenomena with observational consequences. In the first part of this dissertation, I discuss such an idea. Concretely, I argue for the presence of vortex sub-structure within black holes. This is supported by two different paradigms addressing the quantum properties of black holes. The first one consists of a correspondence between black holes and generic objects of maximal entropy compatible with unitarity, so-called saturons. In this work, a specific realization of the latter is worked out explicitly. Remarkably, from the simple requirement of unitarity saturation, several properties analogous to the ones of black holes emerge in a simple non-gravitational model. In particular, a correspondence between such saturons with vorticity and close-to-extremal rotating black holes is made apparent. The second one is the so-called N-portrait, where black holes are understood as condensates of marginally bounded gravitons. Motivated by both the former and the latter, it is natural to conjecture that vorticity is a necessary property of highly-spinning black holes. One one hand, this can have profound astrophysical consequences, and, on the other, it can be of interest from a many-body perspective. The former is relevant for powerful jets observed in active galactic nulei such as M87. These emissions can be explained without the need of a coherently magnetized disk, contrary to the standard picture, providing a clear smoking gun for the scenario. This result is generally relevant for supermassive black holes in the galactic centres, since these are expected, and observed, to be highly spinning due to their late-time dynamics. The second part of this thesis focuses on lighter, sub-solar mass black holes. Standard stellar dynamics cannot account for them and, if detected, an explanation for their origin would be required: for example, they could be primordial. These objects are phenomenologically motivated dark matter candidates. However, there is currently no consensus on their formation mechanism. The rest of this dissertation is therefore dedicated to presenting one of those mechanisms, as well as its consequences. In this scenario black holes are formed due to confinement of quarks produced in the Early Universe. The mechanism requires minimal hypothesis to work both within “our" QCD sector or in a dark sector, while avoiding several issues encountered in the standard formation scenarios based on the collapse of inflationary overdensities. One of its peculiar features lies in the natural production of highly spinning black holes at formation – relevant in view of the previously discussed vortex sub-structure. Yet another property is the specific gravitational-wave energy density produced by the collapsing dynamics, which is almost frequency-independent. The resulting spectrum can potentially explain the stochastic gravitational background observed via pulsar timing arrays and will be probed in the near future by other observational missions operating at higher frequencies. Motivated by the phenomenological relevance, a numerical study of the collapsing dynamics of two confined monopoles is performed. This is expected to capture the main features of the previously mentioned quark collapse. In fact, a quark/anti=-quark pair connected by a gluon string is similar to a monopole/anti-monopole pair connected by a magnetic flux tube. A long-standing question is how much the latter system can inform us about the former. Therefore, while this analysis extends previous studies on the dynamics of confined monopoles performed in the point-like limit, it provides new insights on its correspondence with QCD physics. Intriguingly, unitarity saturation plays a key-role in shedding light on such correspondence.
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Zantedeschi, Michael
2022
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Zantedeschi, Michael (2022): On structure and primordial origin of black holes. Dissertation, LMU München: Faculty of Physics
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Abstract

Understanding the microscopic structure of black holes remains one of the most important tasks of theoretical physics. It is especially valuable when this structure can be formulated in terms of transparent physical phenomena with observational consequences. In the first part of this dissertation, I discuss such an idea. Concretely, I argue for the presence of vortex sub-structure within black holes. This is supported by two different paradigms addressing the quantum properties of black holes. The first one consists of a correspondence between black holes and generic objects of maximal entropy compatible with unitarity, so-called saturons. In this work, a specific realization of the latter is worked out explicitly. Remarkably, from the simple requirement of unitarity saturation, several properties analogous to the ones of black holes emerge in a simple non-gravitational model. In particular, a correspondence between such saturons with vorticity and close-to-extremal rotating black holes is made apparent. The second one is the so-called N-portrait, where black holes are understood as condensates of marginally bounded gravitons. Motivated by both the former and the latter, it is natural to conjecture that vorticity is a necessary property of highly-spinning black holes. One one hand, this can have profound astrophysical consequences, and, on the other, it can be of interest from a many-body perspective. The former is relevant for powerful jets observed in active galactic nulei such as M87. These emissions can be explained without the need of a coherently magnetized disk, contrary to the standard picture, providing a clear smoking gun for the scenario. This result is generally relevant for supermassive black holes in the galactic centres, since these are expected, and observed, to be highly spinning due to their late-time dynamics. The second part of this thesis focuses on lighter, sub-solar mass black holes. Standard stellar dynamics cannot account for them and, if detected, an explanation for their origin would be required: for example, they could be primordial. These objects are phenomenologically motivated dark matter candidates. However, there is currently no consensus on their formation mechanism. The rest of this dissertation is therefore dedicated to presenting one of those mechanisms, as well as its consequences. In this scenario black holes are formed due to confinement of quarks produced in the Early Universe. The mechanism requires minimal hypothesis to work both within “our" QCD sector or in a dark sector, while avoiding several issues encountered in the standard formation scenarios based on the collapse of inflationary overdensities. One of its peculiar features lies in the natural production of highly spinning black holes at formation – relevant in view of the previously discussed vortex sub-structure. Yet another property is the specific gravitational-wave energy density produced by the collapsing dynamics, which is almost frequency-independent. The resulting spectrum can potentially explain the stochastic gravitational background observed via pulsar timing arrays and will be probed in the near future by other observational missions operating at higher frequencies. Motivated by the phenomenological relevance, a numerical study of the collapsing dynamics of two confined monopoles is performed. This is expected to capture the main features of the previously mentioned quark collapse. In fact, a quark/anti=-quark pair connected by a gluon string is similar to a monopole/anti-monopole pair connected by a magnetic flux tube. A long-standing question is how much the latter system can inform us about the former. Therefore, while this analysis extends previous studies on the dynamics of confined monopoles performed in the point-like limit, it provides new insights on its correspondence with QCD physics. Intriguingly, unitarity saturation plays a key-role in shedding light on such correspondence.