Absorption of fixed scalar in scattering off 4D N=4 black holes

TL;DR

This paper analyzes how a fixed scalar field is absorbed during scattering off 4D N=4 supergravity black holes, revealing the scalar's unique role among propagating modes and calculating its low-frequency absorption cross-section.

Contribution

It provides a detailed perturbation analysis showing the fixed scalar's unique propagation and computes its absorption cross-section in extremal black hole backgrounds.

Findings

Dilaton is the only propagating mode among scalar and gauge fields.

The absorption cross-section for the fixed scalar is explicitly calculated.

The scalar's absorption behavior is characterized at low frequencies.

Abstract

We perform the perturbation analysis of the black holes in the 4D, N=4 supergravity. Analysis around the black holes reveals a complicated mixing between the dilaton and other fields (metric and two U(1) Maxwell fields). It turns out that considering both s-wave (l=0) and higher momentum modes (l \neq 0), the dilaton as a fixed scalar is the only propagating mode with $P=Q, h_1=h_2=0$ and $F = -G = 2\phi$. We calculate the absorption cross-section for scattering of low frequency waves of fixed scalar and U(1) Maxwell fields off the extremal black hole.