Origin of gauge invariance in string theory.
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: Zero-energy theorem for scale-invariant gravity
abstract: The general scale-invariant Lagrangian, -(1/4) ..integral.. d/sup 4/x(-g)/sup 1/2/(..cap alpha..C/sup munulambdasigma/C/sub munulambda/ /sub sigma/+..beta..R/sup 2/), with ..cap alpha beta..> or =0, is considered. Although this theory admits linearized solutions with negative energy, it is shown that all exact solutions representing isolated systems have precisely zero energy. This result also holds in the presence of arbitrary matter. It can be understood as resulting from a confinement of energy. The implications of this result for quantum gravity are discussed.

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: 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: Spacetime in string theory
abstract: We give a brief overview of the nature of spacetime emerging from string theory. This is radically different from the familiar spacetime of Einstein's relativity. At a perturbative level, the spacetime metric appears as 'coupling constants' in a two-dimensional quantum field theory. Nonperturbatively (with certain boundary conditions), spacetime is not fundamental but must be reconstructed from a holographic, dual theory.

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: 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.

title: Parity-violating quasielastic electron scattering.
abstract: The parity-violating asymmetry [ital A] is calculated for quasielastic electron scattering. We use a relativistic mean field model of the nuclear matter response. A Lorentz scalar mean field (which reduces the nucleon's mass) decreases [vert bar][ital A][vert bar] by a relatively large amount. This effect must be understood before information on strange quark contributions or weak axial currents can be extracted. Alternatively, very interesting information on isoscalar convection currents could be obtained.

title: Relativistic effects on spin observables in quasielastic proton scattering.
abstract: The spin observables in quasielastic proton scattering are calculated in a simple relativistic model where the NN interaction is assumed to depend on the enhancement of the lower components of nucleon wave functions (because of strong nuclear potentials). This enhancement is characterized by an average effective mass M( of (0.8--0.9)M which is calculated in an eikonal model. The M( dependence of the NN interaction is taken from relativistic impulse approximation calculations. The polarization is found to decrease by 40 percent compared to the free NN value at 500 MeV. Next, simple formulas are provided to estimate the effects of spin-orbit potential distortions on spin observables. At 500 MeV and 18.5/sup 0/ in /sup 208/Pb, the polarization is decreased by 5 percent while D/sub l/'l and D/sub s/'s are decreased by 15 percent and D/sub n/n is almost unchanged.

title: Polarizing stored beams by interaction with polarized electrons.
abstract: A polarized, internal electron target gradually polarizes a proton beam in a storage ring. Here we derive the spin-transfer cross section for [ital [rvec e]]([ital p],[ital [rvec p]])[ital e] scattering. A recent measurement of the polarizing effect of a polarized atomic hydrogen target is explained when the effect of the atomic electrons is included. We also consider the interaction of a stored beam with a pure electron target which can be realized either by a comoving electron beam or by trapping of electrons in a potential well. In the future, this could provide a practical way to polarize antiprotons.

title: Relativistic Love-Franey model: Covariant representation of the NN interaction for N-nucleus scattering.
abstract: A Lorentz invariant form of the NN amplitude is fit with a simple model which includes direct and exchange first Born terms from a number of ''mesons.'' The (complex) couplings and nucleon-meson form factors are adjusted to fit the NN amplitudes directly without iteration. The resulting parameters agree well with one-boson-exchange potentials and have a systematic and small energy dependence. Detailed analytic representations of the relativistic NN amplitudes are provided at lab energies of 135, 200, and 400 MeV. The model separation of the NN amplitudes into direct and exchange contributions does not involve sensitive cancellations and is contrasted with the very different nonrelativistic results. The model amplitudes are used to construct optical potentials in a relativistic impulse approximation using both pseudovector and pseudoscalar ..pi..-N coupling. The pseudoscalar result reproduces earlier relativistic impulse approximation calculations which diverge at low energies, while the pseudovector results are nearly constant with energy and in good agreement with phenomenological potentials.