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In Search of de Sitter Space in Light of Swampland Program

Mehin Rasulian, Ida | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 55772 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Torabian, Mahdi
  7. Abstract:
  8. Exponential expansion of the universe is an important issue in early-time and late-time cosmology . In the widely accepted standard model of cosmology, there are two assumed exponentially expanding phases , early-time inflationary phase and late-time dark energy phase . On the other hand, there are ideas from string theory that limit the possibility of constructing the de Sitter space, which are categorized in the Swampland program . In this work, we first examine no-scale models of de Sitter space in supergravity from the point of view of de Sitter conjectures . In this regard, we observe that satisfying these conjectures limits the parameter and field space and the trans-Planckian censorship conjecture puts weaker bounds on the models . Considering the obstacles in constructing the de Sitter space, we later propose an effective model for de Sitter space based on a 5-dimensional black hole and a 3-brane close to its horizon . Studying the Einstein equations at the perturbative level and in homogeneous and isotropic coordinates we find the 4D gravitational constant and observe that the bulk energy density below the brane that behaves like matter on the brane contributes to the effective energy density on the brane . Studying the stability of the setup, we also observe that the brane becomes stabilized with a de Sitter length that is proportional to the Schwarzschild radius of the observable universe . In this model, the lifetime of de Sitter spacetime depends on the classical effect of matter collapsing towards the black hole and respects the Trans-Planckian Censorship Conjecture . The change in observer's position relative to the center of the static patch can lead to small deviations from homogeneity and isotropy in the resulting metric
  9. Keywords:
  10. Dark Energy ; Swampland Conjectures ; Inflation ; De Sitter Space ; Supergravity ; No-Scale Supergravity ; Brane-World

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