683 research outputs found
Comments on Black Holes in Matrix Theory
The recent suggestion that the entropy of Schwarzschild black holes can be
computed in matrix theory using near-extremal D-brane thermodynamics is
examined. It is found that the regime in which this approach is valid actually
describes black strings stretched across the longitudinal direction, near the
transition where black strings become unstable to the formation of black holes.
It is argued that the appropriate dynamics on the other (black hole) side of
the transition is that of the zero modes of the corresponding super Yang-Mills
theory. A suggestive mean field theory argument is given for the entropy of
black holes in all dimensions. Consequences of the analysis for matrix theory
and the holographic principle are discussed.Comment: 15 pages, harvmac, minor errors correcte
Hermitian D-brane solutions
A low-energy background field solution describing D-membrane configurations
is constructed which is distinguished by the appearance of a Hermitian metric
on the internal space. This metric is composed of a number of independent
harmonic functions on the transverse space. Thus this construction generalizes
the usual harmonic superposition rule. The BPS bound of these solutions is
shown to be saturated indicating that they are supersymmetric. By means of
T-duality, we construct more solutions of the IIA and IIB theories.Comment: 14 pages, Latex, no figure
Gauge Dependence in Chern-Simons Theory
We compute the contribution to the modulus of the one-loop effective action
in pure non-Abelian Chern-Simons theory in an arbitrary covariant gauge. We
find that the results are dependent on both the gauge parameter () and
the metric required in the gauge fixing. A contribution arises that has not
been previously encountered; it is of the form . This is possible as in three dimensions
is dimensionful. A variant of proper time regularization is used to render
these integrals well behaved (although no divergences occur when the
regularization is turned off at the end of the calculation). Since the original
Lagrangian is unaltered in this approach, no symmetries of the classical theory
are explicitly broken and is handled unambiguously
since the system is three dimensional at all stages of the calculation. The
results are shown to be consistent with the so-called Nielsen identities which
predict the explicit gauge parameter dependence using an extension of BRS
symmetry. We demonstrate that this dependence may potentially
contribute to the vacuum expectation values of products of Wilson loops.Comment: 17 pp (including 3 figures). Uses REVTeX 3.0 and epsfig.sty
(available from LANL). Latex thric
Localized Branes and Black Holes
We address the delocalization of low dimensional D-branes and NS-branes when
they are a part of a higher dimensional BPS black brane, and the homogeneity of
the resulting horizon. We show that the effective delocalization of such branes
is a classical effect that occurs when localized branes are brought together.
Thus, the fact that the few known solutions with inhomogeneous horizons are
highly singular need not indicate a singularity of generic D- and NS-brane
states. Rather, these singular solutions are likely to be unphysical as they
cannot be constructed from localized branes which are brought together from a
finite separation.Comment: 13 pages, RevTex, no figures, few references and comments adde
Statistical Effects and the Black Hole/D-brane Correspondence
The horizon area and curvature of three-charge BPS black strings are studied
in the D-brane ensemble for the stationary black string. The charge
distributions along the string are used to translate the classical expressions
for the horizon area and curvature of BPS black strings with waves into
operators on the D-brane Hilbert space. Despite the fact that any `wavy' black
string has smaller horizon area and divergent curvature, the typical values of
the horizon area and effects of the horizon curvature in the D-brane ensemble
deviate negligibly from those of the original stationary black string in the
limit of large integer charges. Whether this holds in general will depend on
certain properties of the quantum bound states.Comment: 13 pages, RevTex, small errors corrected, some interpretation changed
in light of new result
The Nielsen Identities for the Two-Point Functions of QED and QCD
We consider the Nielsen identities for the two-point functions of full QCD
and QED in the class of Lorentz gauges. For pedagogical reasons the identities
are first derived in QED to demonstrate the gauge independence of the photon
self-energy, and of the electron mass shell. In QCD we derive the general
identity and hence the identities for the quark, gluon and ghost propagators.
The explicit contributions to the gluon and ghost identities are calculated to
one-loop order, and then we show that the quark identity requires that in
on-shell schemes the quark mass renormalisation must be gauge independent.
Furthermore, we obtain formal solutions for the gluon self-energy and ghost
propagator in terms of the gauge dependence of other, independent Green
functions.Comment: 25 pages, plain TeX, 4 figures available upon request, MZ-TH/94-0
Can the effective string see higher partial waves?
The semi-classical cross-sections for arbitrary partial waves of ordinary
scalars to fall into certain five-dimensional black holes have a form that
seems capable of explanation in terms of the effective string model. The
kinematics of these processes is analyzed in detail on the effective string and
is shown to reproduce the correct functional form of the semi-classical
cross-sections. But it is necessary to choose a peculiar value of the effective
string tension to obtain the correct scaling properties. Furthermore, the
assumptions of locality and statistics combine to forbid the effective string
from absorbing more than a finite number of partial waves. The relation of this
limitation to cosmic censorship is discussed.Comment: 19 pages, uses harvmac, version to appear in Phys. Rev.
The Perturbative Pole Mass in QCD
It is widely believed that the pole mass of a quark is infrared-finite and
gauge-independent to all orders in perturbation theory. This seems not to have
been proved in the literature. A proof is provided here.Comment: 12 pages REVTeX with 2 figures; archiving published version with note
and references added. If you thought this was proven long ago see
http://www-theory.fnal.gov/people/ask/TeX/mPole
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