Search Results for « Higher derivative corrections »

Abstract We compute the first-order α ′ corrections to a general family of supersymmetric heterotic backgrounds which describes a rotating superposition of a fundamental string and a momentum wave. We focus on a particular solution within this family that gives rise, upon dimensional reduction to five dimensions, to a black ring with two charges and one dipole that has a singular horizon with vanishing area in the supergravity approximation, better known as small black ring. We show that the singularity at the horizon persists even after the first-order α ′ corrections have been taken into account. This would imply that, contrarily to what has been argued in the literature, higher-derivative corrections do not resolve the singular horizon of the five-dimensional small black ring, at least at first order in α ′ expansion.

We study duality-invariant higher-derivative corrections to the charged black hole geometry in two-dimensional heterotic string theory. We illustrate how the conventional perturbative approach to determine the corrected geometry breaks down. Using a nonperturbative (in α ′ ) parametrization of the solution, we find the corrected charge-to-mass ratio for extremal black holes. We remark on the results in relation to the weak gravity conjecture. We also consider the entropy of the extremal black hole within the attractor mechanism and find that the two-derivative entropy is not renormalized to any order. We make comments on interpretations of the results and their extension to near-extremal black holes.

Abstract We investigate the inflationary expansion of the universe induced by higher-curvature corrections in M-theory. The inflationary evolution of the geometry is discussed in K. Hiraga and Y. Hyakutake, Prog. Theor. Exp. Phys. 2018, 113B03 (2018), which we follow to analyze metric perturbations around the background. We especially focus on scalar perturbations and analyze linearized equations of motion for the scalar perturbations. By solving these equations explicitly, we evaluate the power spectrum of the curvature perturbation. The scalar spectrum index is estimated under some assumptions, and we show that it becomes close to 1.