This paper illustrates the derivation of the low-energy background field solutions of D2-branes and D4-branes intersecting at nontrivial angles by solving directly the bosonic equations of motion of II supergravity coupled to a dilaton and antisymmetric fields. We also argue for how a similar analysis can be performed for any similar Dp-branes oriented at angles. Finally, the calculation presented here serves as a basis in the search for a systematic derivation of the background fields of the more general configuration of a p-brane ''angled'' with a q-brane (p q).The bosonic part of the low-energy action for type-IIA string theory in ten dimensions is ͓10͔ *Electronic address: hambli@ihes.fr 1 Recently in ͓3͔, however, a similar counting of states was performed for a certain class of nonsupersymmetric but extremal black holes. In this case, supersymmetry alone does not protect the spectrum and yet the degeneracy at strong coupling was shown to be the same as that at weak coupling.

Polchinski has argued that the prediction of Hawking radiation must be independent of the details of unknown high-energy physics because the calculation may be performed using ''nice slices,'' for which the adiabatic theorem may be used. If this is so, then any calculation using a manifestly covariant-and so slice-independent-ultraviolet regularization must reproduce the standard Hawking result. We investigate the dependence of the Hawking radiation on such a short-distance regulator by calculating it using a Pauli-Villars regularization scheme. We find that the regulator scale ⌳ only contributes to the Hawking flux by an amount that is exponentially small in the large variable ⌳/T H ӷ1, where T H is the Hawking temperature, in agreement with Polchinski's arguments. Using the techniques of effective Lagrangians, we demonstrate the robustness of our results. We also solve a technical puzzle concerning the relation between the short-distance singularities of the propagator and the Hawking effect. ͓S0556-2821͑96͒03610-7͔

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String theory is spacetimes with boundaries is shown to be equivalent, in some instances, to string theory or orbifolds. This equivalence is used to calculate the Casimir energy of the string between two infinite parallel plates in spacetime. The calculation mimics some features of string theory in Rindler and Schwarzschild spacetimes and supports the conjecture that string theories avoid the singularity problem by giving particle production rates that diverge in the presence of large, but finite, fields.

A new set of polynomial states (to be called character states) are derived for Sp (4) reduced to its SU (2) × U (1) subgroup, and the relevant generator matrix elements are evaluated for generic representations (a, b) of Sp(4). (The degenerate representations (a, 0) and (0, b) were treated in our previous work and are also given in this paper). The group-subgroup in question is that of the seniority model of nuclear physics.