Physics Maths Engineering
Effective action of string theory at order α in the presence of boundary
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Mohammad R. Garousi
Mohammad R. Garousi
Department of Physics, Faculty of Science, Ferdowsi University of Mashhad,
Related Subjects
Abstract
Recently, using the assumption that the string theory effective action at the critical dimension is background independent, the classical on-shell effective action of the bosonic string theory at order α in a spacetime manifold without boundary has been reproduced, up to an overall parameter, by imposing the O(1, 1) symmetry when the background has a circle. In the presence of the boundary, we consider a background which has boundary and a circle such that the unit normal vector of the boundary is independent of the circle. Then the O(1, 1) symmetry can fix the bulk action without using the lowest order equation of motion. Moreover, the above constraints and the constraint from the principle of the least action in the presence of boundary can fix the boundary action, up to five boundary parameters. In the least action principle, we assume that not only the values of the massless fields but also the values of their first derivatives are arbitrary on the boundary. We have also observed that the cosmological reduction of the leading order action in the presence of the Hawking–Gibbons boundary term, produces zero cosmological boundary action. Imposing this as another constraint on the boundary couplings at order α, we find the boundary action up to two parameters. For a specific value for these two parameters, the gravity couplings in the boundary become the Chern–Simons gravity plus another term which has the Laplacian of the extrinsic curvature.
Key Questions
What is the main focus of this study?
The study explores the effective action of string theory at the α' order in scenarios involving boundaries, analyzing how boundary conditions impact string dynamics and effective actions.
What does "effective action" mean in string theory?
The effective action in string theory describes an approximation of string interactions and dynamics that emerge at low energy scales, simplifying the complex behavior of strings while retaining essential features.
Why is the presence of boundaries significant in string theory?
Boundaries introduce additional constraints and modifications to the equations governing string dynamics, significantly impacting the resulting physical predictions and effective actions.
What is the role of α' in string theory?
The parameter α' represents the string tension's inverse and controls higher-order corrections to the string effective action, playing a crucial role in understanding string interactions at small scales.
What are the key findings of this research?
The study identifies the specific contributions of boundary terms to the α'-order effective action and demonstrates how these terms influence the consistency of string dynamics and equations of motion.
How does this study contribute to string theory research?
By incorporating boundary effects at the α'-order, the research enhances our understanding of string dynamics in bounded spaces, paving the way for deeper insights into string theory's applications in physics.
