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The Large-Misalignment Mechanism for the Formation of Compact Axion Structures.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	The Large-Misalignment Mechanism for the Formation of Compact Axion Structures./
Author:	Thompson, Jedidiah Oliver.
Description:	1 online resource (125 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-06, Section: B.
Contained By:	Dissertations Abstracts International85-06B.
Subject:	Stars & galaxies. -
Online resource:	click for full text (PQDT)
ISBN:	9798381019032

The Large-Misalignment Mechanism for the Formation of Compact Axion Structures.
Thompson, Jedidiah Oliver.

The Large-Misalignment Mechanism for the Formation of Compact Axion Structures. - 1 online resource (125 pages)

Source: Dissertations Abstracts International, Volume: 85-06, Section: B.

Thesis (Ph.D.)--Stanford University, 2023.

Includes bibliographical references

The overwhelming majority of the energy density in the Universe appears to interact only gravitationally, in all available observational and experimental data so far. A quarter of this energy density is in the form of dark matter (DM), a matter component that does not emit or interact strongly with light. Two of the main pieces of evidence for DM are the fluctuations in the cosmic microwave background (CMB) and the formation of gravitational structures over a large range of length scales, from the size of the largest superclusters of galaxies down to the smallest observable dwarf galaxies. These two bodies of evidence are in mutual quantitative agreement with one another.Among the best motivated particle physics candidates for DM are axions, CP-odd scalar fields. The most famous one is the QCD axion [4, 5, 6], responsible for addressing the strong CP problem as it explains the smallness of the neutron's electric dipole moment. Axions are also ubiquitous in extensions of the Standard Model such as string theory, where they arise as the byproducts of complex topology.Axions have a natural production mechanism of near-pressureless energy density, through what is known as the misalignment production mechanism [8, 9, 10]. The dynamics of the axion field are described by four-dimensional partial di↵erential field equations which depend on the potential of the axion. Inflation irons out all spatial wrinkles, converting the axion into a spatially homogeneous but time-dependent field. Near the minimum of its potential (here at = 0), the potential of the axion is well approximated by a quadratic function of , which then behaves cosmologically as a damped harmonic oscillator Ф+ 3HФ + m2Ф = 0 where H is Hubble parameter and m the axion mass. Initially, the axion field value is frozen due to Hubble friction; the axion only starts oscillating once 3H ≤ m. The energy density associated with this oscillation redshifts exactly like cold DM: p Ф / a-3. However, there is no reason to expect that the axion will start close to the minimum. If the axion misalignment is large, the quadratic approximation to its potential is no longer adequate and higher order terms must be included. The axion potential generically contains quartic terms which convert its equation to that of a nonlinear damped anharmonic oscillator: Ф+ 3HФ + m2Ф- Ф3 + ... = 0.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798381019032Subjects--Topical Terms:

1474789
Stars & galaxies.
Index Terms--Genre/Form:

554714
Electronic books.

The Large-Misalignment Mechanism for the Formation of Compact Axion Structures.
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502 $a Thesis (Ph.D.)--Stanford University, 2023.
504 $a Includes bibliographical references
520 $a The overwhelming majority of the energy density in the Universe appears to interact only gravitationally, in all available observational and experimental data so far. A quarter of this energy density is in the form of dark matter (DM), a matter component that does not emit or interact strongly with light. Two of the main pieces of evidence for DM are the fluctuations in the cosmic microwave background (CMB) and the formation of gravitational structures over a large range of length scales, from the size of the largest superclusters of galaxies down to the smallest observable dwarf galaxies. These two bodies of evidence are in mutual quantitative agreement with one another.Among the best motivated particle physics candidates for DM are axions, CP-odd scalar fields. The most famous one is the QCD axion [4, 5, 6], responsible for addressing the strong CP problem as it explains the smallness of the neutron's electric dipole moment. Axions are also ubiquitous in extensions of the Standard Model such as string theory, where they arise as the byproducts of complex topology.Axions have a natural production mechanism of near-pressureless energy density, through what is known as the misalignment production mechanism [8, 9, 10]. The dynamics of the axion field are described by four-dimensional partial di↵erential field equations which depend on the potential of the axion. Inflation irons out all spatial wrinkles, converting the axion into a spatially homogeneous but time-dependent field. Near the minimum of its potential (here at = 0), the potential of the axion is well approximated by a quadratic function of , which then behaves cosmologically as a damped harmonic oscillator Ф+ 3HФ + m2Ф = 0 where H is Hubble parameter and m the axion mass. Initially, the axion field value is frozen due to Hubble friction; the axion only starts oscillating once 3H ≤ m. The energy density associated with this oscillation redshifts exactly like cold DM: p Ф / a-3. However, there is no reason to expect that the axion will start close to the minimum. If the axion misalignment is large, the quadratic approximation to its potential is no longer adequate and higher order terms must be included. The axion potential generically contains quartic terms which convert its equation to that of a nonlinear damped anharmonic oscillator: Ф+ 3HФ + m2Ф- Ф3 + ... = 0.
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