1,034 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
Entropic-gravity derivation of MOND
A heuristic entropic-gravity derivation has previously been given of the
gravitational two-body force of modified Newtonian dynamics (MOND). Here, it is
shown that also another characteristic of MOND can be recovered, namely, the
external field effect (implying a violation of the Strong Equivalence
Principle). In fact, the derivation gives precisely the modified Poisson
equation which Bekenstein and Milgrom proposed as a consistent nonrelativistic
theory of MOND.Comment: 6 pages; v5: published versio
On the partition sum of the NS five-brane
We study the Type IIA NS five-brane wrapped on a Calabi-Yau manifold X in a
double-scaled decoupling limit. We calculate the euclidean partition function
in the presence of a flat RR 3-form field. The classical contribution is given
by a sum over fluxes of the self-dual tensor field which reduces to a
theta-function. The quantum contributions are computed using a T-dual IIB
background where the five-branes are replaced by an ALE singularity. Using the
supergravity effective action we find that the loop corrections to the free
energy are given by B-model topological string amplitudes. This seems to
provide a direct link between the double-scaled little strings on the
five-brane worldvolume and topological strings. Both the classical and quantum
contributions to the partition function satisfy (conjugate) holomorphic anomaly
equations, which explains an observation of Witten relating topological string
theory to the quantization of three-form fields.Comment: 35 page
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
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