S-Wave Scattering of Charged Fermions by a Magnetic Black Hole

We argue that, classically, $s$-wave electrons incident on a magnetically charged black hole are swallowed with probability one: the reflection coefficient vanishes. However, quantum effects can lead to both electromagnetic and gravitational backscattering. We show that, for the case of extremal, magnetically charged, dilatonic black holes and a single flavor of low-energy charged particles, this backscattering is described by a perturbatively computable and unitary $S$-matrix, and that the Hawking radiation in these modes is suppressed near extremality. The interesting and much more difficult case of several flavors is also discussed.Comment: 9p

The anomaly-free quantization of two-dimensional relativistic string. I

An anomaly-free quantum theory of a relativistic string is constructed in two-dimensional space-time. The states of the string are found to be similar to the states of a massless chiral quantum particle. This result is obtained by generalizing the concept of an ``operator'' in quantum field theory.Comment: LaTeX, 19 pages, no figure

Unitary Theory of Evaporating 2D Black Holes

We study a manifestly unitary formulation of 2d dilaton quantum gravity based on the reduced phase space quantization. The spacetime metric can be expanded in a formal power series of the matter energy-momentum tensor operator. This expansion can be used for calculating the quantum corrections to the classical black hole metric by evaluating the expectation value of the metric operator in an appropriate class of the physical states. When the normal ordering in the metric operator is chosen to be with respect to Kruskal vacuum, the lowest order semiclassical metric is exactly the one-loop effective action metric discovered by Bose, Parker and Peleg. The corresponding semiclassical geometry describes an evaporating black hole which ends up as a remnant. The calculation of higher order corrections and implications for the black hole fate are discussed.Comment: LaTex fil

Black hole formation in bidimensional dilaton gravity coupled to scalar matter systems

This work deals with the formation of black hole in bidimensional dilaton gravity coupled to scalar matter fields. We investigate two scalar matter systems, one described by a sixth power potential and the other defined with two scalar fields containing up to the fourth power in the fields. The topological solutions that appear in these cases allow the formation of black holes in the corresponding dilaton gravity models.Comment: Latex, 9 pages. Published in Mod. Phys. Lett. A14 (1999) 268

Kaluza-Klein Black Holes in String Theory

Exact solutions of heterotic string theory corresponding to four-dimensional magnetic black holes in $N=4$ supergravity are described. The solutions describe the black holes in the throat limit, and consist of a tensor product of an $SU(2)$ WZW orbifold with the linear dilaton vacuum, supersymmetrized to $(1,0)$ world sheet SUSY. One dimension of the $SU(2)$ model is interpreted as a compactified fifth dimension, leading to a four dimensional solution with a Kaluza-Klein gauge field having a magnetic monopole background; this corresponds to a solution in $N=4$ supergravity, since that theory is obtained by dimensional reduction of string theory.Comment: 13p. uses Harvma

Quarterly Economic Commentary, January 1984

The international economic recovery became quite firmly established in 1983, with substantial growth recorded in North America, Japan, and to a lesser extent the UK. Against this background, the decline in the Irish economy was halted, and substantial gains were made in several aspects. The overall growth rate was miniscule at about Y2 per cent, but there was a massive improvement in the balance of payments, a significant increase in industrial output, a marked reduction in the rate of inflation, some slowing down in the growth of unemployment, and a small reduction in tpe budget deficit as a proportion of Gross National Product. It seems likely that 1984 will see a continuation of most of these trends. Gross National Product should increase by about 2 per cent in volume, the current account balance of payments deficit should fall to around £50 million, and the increase in consumer prices should be held to about 8Y2 per cent. However, the indications are that progress will continue to be very slow in relation to the two major problems of unemployment and the public finances. Employment could well stabilise at about its present level and even increase slightly later in the year, but this would still leave unemployment increasing at a rate of some 18,000 per year because of the growth in the labour force. On the assumption of a passive budget, in which both income tax bands and specific rates of excise duty are indexed in line with inflation, it seems probable that there would be very little change in the size of the nominal current budget deficit, although it would be reduced as a proportion of Gross National Product. While neither of these outcomes can be regarded as at all satisfactory, there is little room for manouevre in budgetary strategy. Too determined an attempt to reduce the deficit could impair the expected recovery and increase the rise in unemployment, while trying to reduce unemployment by allowing the deficit to rise would be a short-term expedient which would intensify both problems in the longer term. Probably the most hopeful strategy would be to aim for a slightly lower deficit, while hoping that this and other current forecasts of the rate of economic recovery prove unduly cautious

Toward One-Loop Tunneling Rates of Near-Extremal Magnetic Black Hole Pair-Production

Pair-production of magnetic Reissner-Nordstr\"{o}m black holes (of charges $\pm q$) was recently studied in the leading WKB approximation. Here, we consider generic quantum fluctuations in the corresponding instanton geometry given by the Euclidean Ernst metric, in order to simulate the behaviour of the one-loop tunneling rate. A detailed study of the Ernst metric suggests that for sufficiently weak field $B$, the problem can be reduced to that of quantum fluctuations around a single near-extremal Euclidean black hole in thermal equilibrium with a heat bath of finite size. After appropriate renormalization procedures, typical one-loop contributions to the WKB exponent are shown to be inversely proportional to $B$, as $B\rightarrow 0$, indicating that the leading Schwinger term is corrected by a small fraction $\sim \hbar /q^2$. We demonstrate that this correction to the Schwinger term is actually due to a semiclassical shift of the black hole mass-to-charge ratio that persists even in the extremal limit. Finally we discuss a few loose ends.Comment: LaTeX, 27pp, one uuencoded figure (A few sentences are rephrased to prevent a possible confusion; an extra paragraph Commenting on the strictly extremal case is added.

Black Hole Evaporation along Macroscopic Strings

We develop the quantization of a macroscopic string which extends radially from a Schwarzschild black hole. The Hawking process excites a thermal bath of string modes that causes the black hole to lose mass. The resulting typical string configuration is a random walk in the angular coordinates. We show that the energy flux in string excitations is approximately that of spacetime field modes.Comment: 26pp, EFI 93-73. (Original claim that string Hawking flux exceeds spacetime flux is WRONG. It is the same; revised version provides correct argument and additional comments.

Anomaly Cancellation in 2+1 dimensions in the presence of a domainwall mass

A Fermion in 2+1 dimensions, with a mass function which depends on one spatial coordinate and passes through a zero ( a domain wall mass), is considered. In this model, originally proposed by Callan and Harvey, the gauge variation of the effective gauge action mainly consists of two terms. One comes from the induced Chern-Simons term and the other from the chiral fermions, bound to the 1+1 dimensional wall, and they are expected to cancel each other. Though there exist arguments in favour of this, based on the possible forms of the effective action valid far from the wall and some facts about theories of chiral fermions in 1+1 dimensions, a complete calculation is lacking. In this paper we present an explicit calculation of this cancellation at one loop valid even close to the wall. We show that, integrating out the ``massive'' modes of the theory does produce the Chern-Simons term, as appreciated previously. In addition we show that it generates a term that softens the high energy behaviour of the 1+1 dimensional effective chiral theory thereby resolving an ambiguity present in a general 1+1 dimensional theory.Comment: 17 pages, LaTex file, CU-TP-61

Dynamics of Extremal Black Holes

Particle scattering and radiation by a magnetically charged, dilatonic black hole is investigated near the extremal limit at which the mass is a constant times the charge. Near this limit a neighborhood of the horizon of the black hole is closely approximated by a trivial product of a two-dimensional black hole with a sphere. This is shown to imply that the scattering of long-wavelength particles can be described by a (previously analyzed) two-dimensional effective field theory, and is related to the formation/evaporation of two-dimensional black holes. The scattering proceeds via particle capture followed by Hawking re-emission, and naively appears to violate unitarity. However this conclusion can be altered when the effects of backreaction are included. Particle-hole scattering is discussed in the light of a recent analysis of the two-dimensional backreaction problem. It is argued that the quantum mechanical possibility of scattering off of extremal black holes implies the potential existence of additional quantum numbers - referred to as ``quantum whiskers'' - characterizing the black hole.Comment: 31 page