Negative Corrections to Black Hole Entropy from String Theory

TL;DR

This paper shows that in certain string theory models, the leading corrections to rotating black string entropy can be negative, challenging previous assumptions about entropy positivity and the weak gravity conjecture.

Contribution

It demonstrates for the first time that higher-order corrections to black hole entropy in heterotic and IIA string compactifications can be negative, revealing new complexities in effective field theories.

Findings

Leading $oldsymbol{ ext{α'}}$ corrections to entropy can be negative.

Correction to extremal rotating string mass is positive.

Results challenge the positivity assumption of entropy shifts.

Abstract

We report for the first time that in heterotic string compactified on 4-torus or equivalently IIA string compactified on K3, the leading $\alpha'$ corrections to the rotating black string entropy at fixed conserved charges can be negative. This further implies that the correction to the mass of extremal rotating string is positive, opposite to the standard expectation from the weak gravity conjecture. Our result suggests that the validity of positivity of entropy shift due to higher order operators depends on other factors omitted previously in the effective field theory analysis.