高次元理論における真空崩壊の促進に関する研究
Year: 2025
Type: dissertation
Abstract: String theory is widely regarded as a promising candidate for quantum gravity that naturally incorporates gravitational interactions.However, its vacuum structure is known to be extremely complicated.This complexity arises from the absence of a definitive guiding principle for compactifying extra dimensions in higher-dimensional theories.As a result, it has been suggested that an enormous number of vacua might emerge.In this scenario, transitions between vacua are expected to occur universally.Many scenarios of vacuum decay are premised on the nucleation of bubbles in a homogeneous false vacuum.However, in nature, many examples are known where the presence of impurities catalyzes phase transitions.Similar phenomena have been observed in highenergy physics, where topological solitons or black holes can enhance phase transitions in the early universe.Since such impurities are expected to exist universally in realistic models involving symmetry breaking, examining the inhomogeneous nucleation of bubbles influenced by these impurities can be regarded as a more natural direction.Thus, when considering stringy vacuum decay in higher dimensions, there remains room to account for impurities and phenomena that can enhance decay.Such enhancement of decay is also intriguing from the perspective of formulating the mathematical conditions for effective theories coupled with gravity.In the bottom-up approach known as a Swampland program, various conjectures and constraints have been proposed based on empirical insights from grand unified theories and cosmology.Recent developments in the Swampland program suggest that dS vacua consistent with quantum gravity must, at least, be metastable and decay sufficiently quickly.Under this conjecture, most metastable vacua in low-energy effective theories are thought to be incompatible with quantum gravity.However, if contributions from impurities or singularities could enhance the instability of the system, it might be possible to construct UV-consistent de Sitter vacua within an effective theory.In light of these considerations, we discuss two objects, Dp-branes, and singular instantons, as potential objects for enhancing vacuum decay in higher-dimensional theories.First, we discuss the enhancement of instability due to Dp-branes as a catalytic effect specific to string theory.Dp-branes are higher-dimensional objects in string theory, frequently utilized to construct metastable vacua.In this study, we construct a geometrically metastable vacuum by wrapping D5-branes and anti D5-branes on a higher-dimensional manifold with singularities.We also consider wrapping D3-branes in the internal space.These D3-branes dissolve into the domain wall D5-branes, forming bound states.We generalize the calculation method for the fluctuation operator and derive an exact 1-loop expression for the decay rate using the WKB approximation.Numerical calculations based on this expression confirm that, within a reliable parameter region for the approximation, increasing the number of D3-branes reduces the life-time of the metastable vacuum.Furi First, I would like to express my deepest gratitude to my academic supervisor, Prof. Yutaka Ookouchi.Through the Ph.D. course, he provided invaluable guidance and support, enabling me to devote myself wholeheartedly to my research.Without the daily discussions with him, it would have been challenging to bring my research to fruition.I would also like to thank my collaborator, Mr. Ryota Sato, for the daily discussions.Our regular discussions on the study of singular instantons significantly deepened my understanding of this topic.Additionally, I would like to express my special thanks to Dr. Yuri Okubo, who was a member of our research group.Although we did not collaborate directly, our daily discussions on physics served as a driving force in advancing my research.
Author: 塚原, 壮平
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7054190238