Sharif Digital Repository

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... 

The purpose of this thesis is to study the behaviour of open strings between two parallel D-Branes in the presence of a background Kalb-Ramond field linearly varying perpendicular to D-Branes. In an attempt to solve the nonlinear equations of motion we found two sets of nontrivial solutions: String wrapped around a cylinder with constant velocity along its axis and a rotating string with oscillatory radius perpendicular to D-Branes, such that knots are shaped. Considering the boundary conditions, the constraints on these solutions, conserved currents and Mass are found. In particular calculated linear momentum for the first set of solutions suggests the possibility of using this setup as an... 

Online searching for product information or buying some certain goods online has become increasingly popular during the last few years. Despite this fact there is still little empirical evidence about the relationship between in-store shopping and e-shopping. The substitution effect between these two types of shopping can have significant outcomes in urban transportation. Hence Analyzing different aspects of this new phenomenon and using its potential substitution effect on in-store shopping to decrease the amount of mobility in transportation system can be an attractive subject for urban transportation planners. The main purpose of this study is to reveal the relationship between the...