Constraints on tree-level higher order gravitational couplings in superstring theory.

Area of Science:

• Theoretical Physics
• String Theory
• Quantum Gravity

Background:

• Superstring theory provides a framework for unifying quantum mechanics and general relativity.
• Graviton scattering amplitudes are crucial for understanding quantum gravity effects.

Purpose of the Study:

• To analyze tree-level scattering amplitudes of five and six gravitons in superstring theory.
• To investigate power series expansions in the Regge slope α' up to order α'(8).
• To identify constraints on higher-order gravitational couplings and transcendentality properties.

Main Methods:

• Analysis of power series expansions of scattering amplitudes.
• Examination of terms up to order α'(8) in the Regge slope.
• Application of conformal field theory descriptions for superstring backgrounds.

Main Results:

• Identified constraints on higher-order gravitational couplings, including the absence of R(5) terms.
• Observed transcendentality constraints on coefficients of nonvanishing couplings.
• Demonstrated the absence of even-weight zeta values and specific R(6) terms up to the analyzed order.

Conclusions:

• The findings impose significant restrictions on the structure of effective superstring actions.
• The results are general and applicable to any superstring background in any spacetime dimension.
• This work contributes to a deeper understanding of quantum gravity and string theory predictions.