S-wave absorption of scalars by noncommutative D3-branes

TL;DR

This paper investigates how the propagation and absorption of the dilaton scalar are affected by noncommutative geometry in D3-branes with a strong B-field, revealing a transition from minimal to fixed scalar behavior.

Contribution

It provides the first analysis of s-wave dilaton absorption in the noncommutative D3-brane background at infinite B-field, highlighting the change in scalar nature.

Findings

Dilaton becomes a fixed scalar at infinite B-field.

Absorption cross section scales differently with frequency in noncommutative case.

RR scalar induces instability but does not propagate.

Abstract

On the supergravity side, we study the propagation of the RR scalar and the dilaton in the D3-branes with NS $B$-field. To obtain the noncommutative effect, we consider the case of $B\to \infty(\theta \to\pi/2)$. We approximate this as the smeared D1-brane background with $F_5=H=0$. In this background, the RR scalar induces an instability of the near-horizon geometry. However, it turns out that the RR scalar is nonpropagating, while the dilaton is a physically propagating mode. We calculate the s-wave absorption cross section of the dilaton. One finds $\sigma_0^\phi |_{B\to\infty} \sim (\tilde \omega \tilde R_{\pi \over 2})^{8.9} / \omega^5$ in the leading-order while $\sigma_0^\phi|_{B=0} \sim (\tilde \omega R_0)^{8}/\omega^5$ in the D3-branes without $B$-field. This means that although the dilaton belongs to a minimally coupled scalar in the absence of $B$-field, it becomes a sort of fixed scalar in the limit of $B \to \infty$.