Weak String Coupling Research Articles

On the Space–Time Uncertainty Relations of Liouville Strings and D-Branes

Within a Liouville approach to noncritical string theory, we argue for a nontrivial commutation relation between space and time observables, leading to a nonzero space–time uncertainty relation δx δt>0, which vanishes in the limit of weak string coupling.

D-branes and short distances in string theory

We study the behavior of D-branes at distances far shorter than the string length scale l s . We argue that short-distance phenomena are described by the IR behavior of the D-brane worldvolume quantum theory. This description is valid until the brane motion becomes relativistic. At weak string coupling g s this corresponds to momenta and energies far above string scale. We use 0-brane quantum mechanics to study 0-brane collisions and find structure at length scales corresponding to the eleven-dimensional Planck length ( l p 11 ∼ g s 1 3 l ss ) and to the radius of the eleventh dimension in M-theory ( R 11, ∼ g s l s ). We use 0-branes to probe non-trivial geometries and topologies at sub-stringy scales. We study the 0-brane 4-brane system, calculating the 0-brane moduli space metric, and find the bound state at threshold, which has characteristic size l p 11. We examine the blowup of an orbifold and are able to resolve the resulting S 2 down to size l p 11. A 0-brane with momentum approaching 1/ R 11 is able to explore a larger configuration space in which the blowup is embedded. Analogous phenomena occur for small instantons. We finally turn to 1-branes and calculate the size of a bound state to be ∼ g s 1 2 l s , the l-brane tension scale.

Counting states of black strings with traveling waves. II

We extend our recent analysis of the entropy of extremal black strings with traveling waves. We previously considered waves carrying linear momentum on black strings in six dimensions. Here we study waves carrying angular momentum on these strings, and also waves carrying linear momentum on black strings in five dimensions. In both cases, we show that the horizon remains homogeneous and compute its area. We also count the number of BPS states at weak string coupling with the same distribution of linear and angular momentum, and find complete agreement with the black string entropy.

Zero-Brane Quantum Mechanics.

Daniel Kabat and Philippe PouliotDepartment of Physics and AstronomyRutgers UniversityPiscataway, NJ 08855–0849kabat, pouliot@physics.rutgers.eduWe consider low energy, non-relativistic scattering of two Dirichlet zero-branes as an ex-ercise in quantum mechanics. For weak string coupling and sufficiently small velocity, thedynamics is governed by an effective U(2) gauge theory in 0+1 dimensions. At low ener-gies, D-brane scattering can reliably probe distances much shorter than the string scale.The only length scale in the quantum mechanics problem is the eleven dimensional Plancklength. This provides evidence for the role of scales shorter than the string length in theweakly coupled dynamics of type IIA strings.