863 research outputs found
World-Sheet Supersymmetry Without Contact Terms
Green and Seiberg showed that, in simple treatments of fermionic string
theory, it is necessary to introduce contact interactions when vertex operators
collide. Otherwise, certain superconformal Ward identities would be violated.
In this note, we show how these contact terms arise naturally when proper
account is taken of the superconformal geometry involved when punctures
collide. More precisely, we show that there is no contact term at all! Rather,
corrections arise to the ``na\"\i ve" formula when the boundary of moduli space
is described correctly.Comment: 14pp., 2 figures (included
Entropy bounds and Cardy-Verlinde formula in Yang-Mills theory
Using gauge formulation of gravity the three-dimensional SU(2) YM theory
equations of motion are presented in equivalent form as FRW cosmological
equations. With the radiation, the particular (periodic, big bang-big crunch)
three-dimensional universe is constructed. Cosmological entropy bounds
(so-called Cardy-Verlinde formula) have the standard form in such universe.
Mapping such universe back to YM formulation we got the thermal solution of YM
theory. The corresponding holographic entropy bounds (Cardy-Verlinde formula)
in YM theory are constructed. This indicates to universal character of
holographic relations.Comment: LaTeX file, 11 pages, a reference is adde
On RG-flow and the Cosmological Constant
The AdS/CFT correspondence implies that the effective action of certain
strongly coupled large gauge theories satisfy the Hamilton-Jacobi equation
of 5d gravity. Using an analogy with the relativistic point particle, I
construct a low energy effective action that includes the Einstein action and
obeys a Callan-Symanzik-type RG-flow equation. It follows from the flow
equation that under quite general conditions the Einstein equations admit a
flat space-time solution, but other solutions with non-zero cosmological
constant are also allowed. I discuss the geometric interpretation of this
result in the context of warped compactifications.Comment: 11 pages, 1 figure, contribution to the proceedings of Strings '99,
misprint correcte
Black Hole Horizons and Complementarity
We investigate the effect of gravitational back-reaction on the black hole
evaporation process. The standard derivation of Hawking radiation is
re-examined and extended by including gravitational interactions between the
infalling matter and the outgoing radiation. We find that these interactions
lead to substantial effects. In particular, as seen by an outside observer,
they lead to a fast growing uncertainty in the position of the infalling matter
as it approaches the horizon. We argue that this result supports the idea of
black hole complementarity, which states that, in the description of the black
hole system appropriate to outside observers, the region behind the horizon
does not establish itself as a classical region of space-time. We also give a
new formulation of this complementarity principle, which does not make any
specific reference to the location of the black hole horizon.Comment: Some minor modifications in text and the title chang
Poisson-sigma model for 2D gravity with non-metricity
We present a Poisson-sigma model describing general 2D dilaton gravity with
non-metricity, torsion and curvature. It involves three arbitrary functions of
the dilaton field, two of which are well-known from metric compatible theories,
while the third one characterizes the local strength of non-metricity. As an
example we show that alpha' corrections in 2D string theory can generate
(target space) non-metricity.Comment: 9 page
Geometric Gravitational Forces on Particles Moving in a Line
In two-dimensional space-time, point particles can experience a geometric,
dimension-specific gravity force, which modifies the usual geodesic equation of
motion and provides a link between the cosmological constant and the vacuum
-angle. The description of such forces fits naturally into a gauge
theory of gravity based on the extended Poincar\'e group, {\it i.e.\/}
``string-inspired'' dilaton gravity.Comment: 10 pages, CTP#214
Conformal Moduli and b-c Pictures for NSR Strings
We explore the geometry of the superconformal moduli of the NSR superstring
theory in order to construct the consistent sigma-model for the NSR strings,
free of picture-changing ambiguities. The sigma-model generating functional is
constructed by the integration over the bosonic and anticommuting moduli,
corresponding to insertions of the vertex operators in scattering amplitudes.
In particular, the integration over the bosonic moduli results in the
appearance of picture-changing operators for the b-c system. Important example
of the b-c pictures involves the unintegrated and integrated forms of the
vertex operators. We derive the BRST-invariant expressions for the b-c
picture-changing operators for open and closed strings and study some of their
properties. We also show that the superconformal moduli spaces of the NSR
superstring theory contain the global singularities, leading to the appearance
of non-perturbative solitonic D-brane creation operators.Comment: 22 pages, references adde
Loop and surface operators in N=2 gauge theory and Liouville modular geometry
Recently, a duality between Liouville theory and four dimensional N=2 gauge
theory has been uncovered by some of the authors. We consider the role of
extended objects in gauge theory, surface operators and line operators, under
this correspondence. We map such objects to specific operators in Liouville
theory. We employ this connection to compute the expectation value of general
supersymmetric 't Hooft-Wilson line operators in a variety of N=2 gauge
theories.Comment: 60 pages, 11 figures; v3: further minor corrections, published
versio
A Black Hole Levitron
We study the problem of spatially stabilising four dimensional extremal black
holes in background electric/magnetic fields. Whilst looking for stationary
stable solutions describing black holes kept in external fields we find that
taking a continuum limit of Denef et al's multi-center solutions provides a
supergravity description of such backgrounds within which a black hole can be
trapped in a given volume. This is realised by levitating a black hole over a
magnetic dipole base. We comment on how such a construction resembles a
mechanical Levitron.Comment: 5 pages, 1 figur
Newtonian gravity as an entropic force: Towards a derivation of G
It has been suggested that the Newtonian gravitational force may emerge as an
entropic force from a holographic microscopic theory. In this framework, the
possibility is reconsidered that Newton's gravitational coupling constant G can
be derived from the fundamental constants of the underlying microscopic theory.Comment: 10 pages. v6: published versio
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