New class of exact solutions in string theory.
We prove that a large class of leading-order string solutions which generalize both the plane-wave and fundamental string backgrounds are, in fact, exact solutions to all orders in [alpha][prime]. These include, in particular, the traveling waves along the fundamental string. The key features of these solutions are a null symmetry and a chiral coupling of the string to the background. Using dimensional reduction, one finds that the extremal electric dilatonic black holes and their recently discovered generalizations with NUT charge and rotation are also exact solutions. We show that our bosonic solutions are also exact solutions of the heterotic string theory with no extra gauge field background.

title: Microstates of a neutral black hole in M theory.
abstract: We consider vacuum solutions in M theory of the form of a five-dimensional Kaluza-Klein black hole cross T6. In a certain limit, these include the five-dimensional neutral rotating black hole (cross T6). From a type-IIA standpoint, these solutions carry D0 and D6 charges. We show that there is a simple D-brane description which precisely reproduces the Hawking-Bekenstein entropy in the extremal limit, even though supersymmetry is completely broken.

title: Photoemission “experiments” on holographic superconductors
abstract: We study the effects of a superconducting condensate on holographic Fermi surfaces. With a suitable coupling between the fermion and the condensate, there are stable quasiparticles with a gap. We find some similarities with the phenomenology of the cuprates: in systems whose normal state is a non-Fermi liquid with no stable quasiparticles, a stable quasiparticle peak appears in the condensed phase.

title: Origin of gauge invariance in string theory.
abstract: We present a first quantization of the space-time embedding X/sup ..mu../ and the world-sheet metric rho of the open bosonic string. The world-sheet metric rho decouples from S-matrix elements in 26 dimensions. This formulation of the theory naturally includes 26-dimensional gauge transformations. The gauge invariance of S-matrix elements is a direct consequence of the decoupling of rho. Second quantization leads to a string field Phichemically bondX/sup ..mu../,rhochemically bond with a gauge-covariant equation of motion.

title: Where is the information stored in black holes
abstract: It is shown that many modes of the gravitational field exist only inside the horizon of an extreme black hole in string theory. At least in certain cases, the number of such modes is sufficient to account for the Bekenstein-Hawking entropy. These modes are associated with sources which carry Ramond-Ramond charge, and so may be viewed as the strong coupling limit of D-branes. Although these sources naturally live at the singularity, they are well defined and generate modes which extend out to the horizon. This suggests that the information in an extreme black hole is not localized near the singularity or the horizon, but extends between them.

title: Pair creation of extremal black holes and Kaluza-Klein monopoles.
abstract: Classical solutions describing charged dilaton black holes accelerating in a background magnetic field have recently been found. They include the Ernst metric of the Einstein-Maxwell theory as a special case. We study the extremal limit of these solutions in detail, both at the classical and quantum levels. It is shown that near the event horizon the extremal solutions reduce precisely to the static extremal black hole solutions. For a particular value of the dilaton coupling, these extremal black holes are five-dimensional Kaluza-Klein monopoles. The Euclidean sections of these solutions can be interpreted as instantons describing the pair creation of extremal black holes and/or Kaluza-Klein monopoles in a magnetic field. The action of these instantons is calculated and found to agree with the Schwinger result in the weak-field limit. For the Euclidean Ernst solution, the action for the extremal solution differs from that of the previously discussed wormhole instanton by the Bekenstein-Hawking entropy. However, in many cases quantum corrections become large in the vicinity of the black hole, and the precise description of the creation process is unknown.

title: Density dependence of nuclear neutrino-pair production.
abstract: Nuclear decay via neutrino-pair production is found to have a large density dependence because of intermediate electromagnetic couplings to electrons. These are calculated in a relativistic random phase approximation. The decay rate for vector (Fermi) transitions producing electron type neutrino pairs can be enhanced by 10{sup 5} or more at densities relevant for stellar collapse. Axial-vector (Gamow-Teller) transitions are not enhanced.

title: Isospin-violating meson-nucleon vertices as an alternate mechanism of charge-symmetry breaking.
abstract: We compute isospin-violating meson-nucleon coupling constants and their consequent charge-symmetry-breaking (CSB) nucleon-nucleon potentials. The couplings result from evaluating matrix elements of quark currents between nucleon states in a nonrelativistic constituent quark model; the isospin violations arise from the difference in the up and down constituent quark masses. We find, in particular, that isospin violation in the omega-meson{endash}nucleon vertex dominates the class IV CSB potential obtained from these considerations. We evaluate the resulting spin-singlet{endash}triplet mixing angles, the quantities germane to the difference of neutron and proton analyzing powers measured in elastic {ital n}{searrow}-{ital p}{searrow} scattering, and find them commensurate to those computed originally using the on-shell value of the {rho}-{omega} mixing amplitude. The use of the on-shell {rho}-{omega} mixing amplitude at {ital q}{sup 2}=0 has been called into question; rather, the amplitude is zero in a wide class of models. Our model possesses no contribution from {rho}-{omega} mixing at {ital q}{sup 2}=0, and we find that omega-meson exchange suffices to explain the measured {ital n}-{ital p} analyzing power difference at 183 MeV. {copyright} {ital 1996 The American Physical Society.

title: Charge-symmetry-breaking potentials from isospin-violating meson-baryon coupling constants.
abstract: We consider charge-symmetry violations in the nucleon-nucleon force that result from isospin-violating meson-baryon coupling constants. The isospin violations arise from the difference in the up and down constituent quark masses. We show that a class IV charge-symmetry-breaking potential exists in the resulting {omega} exchange contribution to the {ital NN} force. The magnitude of this contribution is consistent with that phenomenologically required by the measured difference of {ital n} and {ital p} analyzing powers in elastic {ital {rvec n}}{minus}{ital {rvec p}} scattering at 183 MeV.

title: Quasielastic proton-nucleus scattering in a relativistic plane-wave impulse approximation.
abstract: Proton-nucleus quasielastic scattering cross sections and spin observables are calculated in a relativistic plane-wave impulse approximation for nuclei from $^{12}\mathrm{C}$ to $^{208}\mathrm{Pb}$ at energies of 300 to 800 MeV. Relativistic effects are incorporated by using Dirac spinors with enhanced lower components characterized by an effective mass from 0.8 to 0.9M. The analyzing power is found to decrease significantly from free NN values when relativistic spinors are used. This reduction is in good agreement with data. Little change in polarization transfer coefficients ${D}_{i\mathcal{'}j}$ is found at 500 MeV. However, predictions of enhanced ${D}_{s\mathcal{'}s}$ and ${D}_{l\mathcal{'}l}$ are made at lower energies. Calculations are also presented for (p,n) quasifree charge exchange reactions. Here the analyzing power is almost unchanged but large changes in cross section and polarization transfer coefficients are possible. These changes depend on how pion contributions to the NN amplitudes are treated. Suggestions for future theoretical and experimental work are made.

title: Resolution of the magnetic moment problem in relativistic theories.
abstract: A Landau-Migdal approach to relativistic mean field theory of nuclear matter is used to define the single particle isoscalar current. By virtue of the near cancellation of scalar and vector potentials, this current is very close to the standard nonrelativistic isoscalar current; and hence the single particle isoscalar magnetic moment operator gives results in agreement with the nonrelativistic shell model. Calculations of magnetic moments for closed shell plus (or minus) one nucleon using this effective current operator recover the Schmidt values, thus resolving a longstanding problem with relativistic models of nuclear structure.