796 research outputs found
RG-Flow, Gravity and the Cosmological Constant
We study the low energy effective action of gravity, induced by
integrating out gauge and matter fields, in a general class of Randall-Sundrum
type string compactification scenarios with exponential warp factors. Our
method combines dimensional reduction with the holographic map between between
5-d supergravity and 4-d large field theory. Using the classical
supergravity approximation, we derive a flow equation of the effective action
that controls its behavior under scale transformations. We find that as a
result each extremum of automatically describes a complete RG trajectory of
classical solutions. This implies that, provided the cosmological constant is
canceled in the high energy theory, classical flat space backgrounds naturally
remain stable under the RG-flow. The mechanism responsible for this stability
is that the non-zero vacuum energy generated by possible phase transitions, is
absorbed by a dynamical adjustment of the contraction rate of the warp factor.Comment: 23 pages, 1 figur
Black Hole Evaporation and Quantum Gravity
In this note we consider some consequences of quantum gravity on the process
of black hole evaporation. In particular, we will explain the suggestion by 't
Hooft that quantum gravitational interactions effectively exclude simultaneous
measurements of the Hawking radiation and of the matter falling into the black
hole. The complementarity of these measurements is supported by the fact that
the commutators between the corresponding observables can be shown to grow
uncontrollably large. The only assumption that is needed to obtain this result
is that the creation and annihilation modes of the in-falling and out-going
matter act in the same Hilbert space. We further illustrate this phenomenon in
the context of two-dimensional dilaton gravity.Comment: 28 pages, LaTex, uses epsf.tex, CERN-TH.7142/94, PUPT-144
Elliptic Genera of Symmetric Products and Second Quantized Strings
In this note we prove an identity that equates the elliptic genus partition
function of a supersymmetric sigma model on the N-fold symmetric product
of a manifold M to the partition function of a second quantized
string theory on the space . The generating function of these
elliptic genera is shown to be (almost) an automorphic form for O(3,2,Z). In
the context of D-brane dynamics, this result gives a precise computation of the
free energy of a gas of D-strings inside a higher-dimensional brane.Comment: 17 pages, latex, 1 figure, to appear in Commun. Math. Phy
Black Extended Objects, Naked Singularities and P-Branes
We treat the horizons of charged, dilaton black extended objects as quantum
mechanical objects. We show that the S matrix for such an object can be written
in terms of a p-brane-like action. The requirements of unitarity of the S
matrix and positivity of the p-brane tension equivalent severely restrict the
number of space-time dimensions and the allowed values of the dilaton parameter
a. Generally, black objects transform at the extremal limit into p-branes.Comment: 9 pages, REVTE
Notes on Matrix and Micro Strings
We review some recent developments in the study of M-theory compactifications
via Matrix theory. In particular we highlight the appearance of IIA strings and
their interactions, and explain the unifying role of the M-theory five-brane
for describing the spectrum of the T^5 compactification and its duality
symmetries. The 5+1-dimensional micro-string theory that lives on the fivebrane
world-volume takes a central place in this presentation.Comment: 27 pages, latex with espcrc2, 3 figures. References added. Some
corrections at the end of section 10. Based on lectures given by H.V. at the
APCTP Winter School held in Sokcho, Korea (Feb 1997) and joint lectures at
Cargese Summer School (June 1997), as well as on talks given by H.V. at
SUSY'97 (May 1997), and by R.D. and E.V. at STRINGS'97 (June 1997
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
Quantum Black Hole Evaporation
We investigate a recently proposed model for a full quantum description of
two-dimensional black hole evaporation, in which a reflecting boundary
condition is imposed in the strong coupling region. It is shown that in this
model each initial state is mapped to a well-defined asymptotic out-state,
provided one performs a certain projection in the gravitational zero mode
sector. We find that for an incoming localized energy pulse, the corresponding
out-going state contains approximately thermal radiation, in accordance with
semi-classical predictions. In addition, our model allows for certain acausal
strong coupling effects near the singularity, that give rise to corrections to
the Hawking spectrum and restore the coherence of the out-state. To an
asymptotic observer these corrections appear to originate from behind the
receding apparent horizon and start to influence the out-going state long
before the black hole has emitted most of its mass. Finally, by putting the
system in a finite box, we are able to derive some algebraic properties of the
scattering matrix and prove that the final state contains all initial
information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file),
Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor
corrections, one reference added
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