S-wave absorption of scalars by noncommutative D3-branes - art. no. 044031

On the supergravity side, we study the propagation of the Ramond-Ramond (RR ) scalar and the dilaton in the D3-branes with a NS B held. To obtain the n oncommutative effect in a simple way, we consider the interesting case of B -->infinity(theta --> pi/2). We represent this as the smeared D1-brane back ground with (F) over bar(5)=(H) over bar=0 approximately. in this backgroun d, considering the RR scaler equation only, it induces an instability of th e near-horizon geometry. However, it turns out that, considering all couple d equations, the RR scalar is nonpropagating. On the other hand, the dilato n is a physically propagating mode. We calculate the s-wave absorption cros s section of the dilaton. One finds sigma(0)(phi)\B(-->infinity)similar to( <(omega)over tilde>(R) over tilde(pi/2))(8.9)/omega(5), while sigma(0)(phi) \(B=0)similar to(<(omega)over tilde>R-0)(8)/omega(5) in the leading order c alculation. This means that although the dilaton belongs to a minimally cou pled scalar in the absence of a B field, it becomes a sort of fixed scalar in the limit of B-->infinity.