4,311 research outputs found
String and M-theory: answering the critics
Using as a springboard a three-way debate between theoretical physicist Lee
Smolin, philosopher of science Nancy Cartwright and myself, I address in
layman's terms the issues of why we need a unified theory of the fundamental
interactions and why, in my opinion, string and M-theory currently offer the
best hope. The focus will be on responding more generally to the various
criticisms. I also describe the diverse application of string/M-theory
techniques to other branches of physics and mathematics which render the whole
enterprise worthwhile whether or not "a theory of everything" is forthcoming.Comment: Update on EPSRC. (Contribution to the Special Issue of Foundations of
Physics: "Forty Years Of String Theory: Reflecting On the Foundations",
edited by Gerard 't Hooft, Erik Verlinde, Dennis Dieks and Sebastian de Haro.
22 pages latex
Spectrum of D=6, N=4b Supergravity on AdS_3 x S^3
The complete spectrum of D=6, N=4b supergravity with n tensor multiplets
compactified on AdS_3 x S^3 is determined. The D=6 theory obtained from the K_3
compactification of Type IIB string requires that n=21, but we let n be
arbitrary. The superalgebra that underlies the symmetry of the resulting
supergravity theory in AdS_3 coupled to matter is SU(1,1|2)_L x SU(1,1|2)_R.
The theory also has an unbroken global SO(4)_R x SO(n) symmetry inherited from
D=6. The spectrum of states arranges itself into a tower of spin-2
supermultiplets, a tower of spin-1, SO(n) singlet supermultiplets, a tower of
spin-1 supermultiplets in the vector representation of SO(n) and a special
spin-1/2 supermultiplet also in the vector representation of SO(n). The SU(2)_L
x SU(2)_R Yang-Mills states reside in the second level of the spin-2 tower and
the lowest level of the spin-1, SO(n) singlet tower and the associated field
theory exhibits interesting properties.Comment: 37 pages, latex, 5 tables and 3 figures, typos corrected, a reference
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Reducing - duality to - duality
The infrared limit of Yang-Mills theory with compact gauge group
compactified on a two-torus is governed by an effective superconformal
field theory. We conjecture that this is a certain orbifold involving the
maximal torus of . Yang-Mills -duality makes predictions for all
correlators of this effective conformal field theory. These predictions are
shown to be implied by the standard -duality of the conformal field theory.
Consequently, Montonen-Olive duality between electric and magnetic states
reduces to the standard two-dimensional duality between momentum and winding
states.Comment: 13 pages, harvmac, no figures. (Some Comments added. Some references
added.
Vacuum interpolation in supergravity via super p-branes
We show that many of the recently proposed supersymmetric p-brane solutions
of d=10 and d=11 supergravity have the property that they interpolate between
Minkowski spacetime and a compactified spacetime, both being supersymmetric
supergravity vacua. Our results imply that the effective worldvolume action for
small fluctuations of the super p-brane is a supersingleton field theory for
, as has been often conjectured in the past.Comment: 8p
Nonsupersymmetric multibrane solutions
Gravity coupled to an arbitrary number of antisymmetric tensors and scalar
fields in arbitrary space-time dimensions is studied in a context of general,
static, spherically symmetric solutions with many orthogonally intersecting
branes. Neither supersymmetry nor harmonic gauge is assumed. It is shown that
the system reduces to a Toda-like system after an adequate redefinition of
transverse radial coordinate . Duality in the set of solutions
is observed
Complementarity of the Maldacena and Karch-Randall Pictures
We perform a one-loop test of the holographic interpretation of the
Karch-Randall model, whereby a massive graviton appears on an AdS_4 brane in an
AdS_5 bulk. Within the AdS/CFT framework, we examine the quantum corrections to
the graviton propagator on the brane, and demonstrate that they induce a
graviton mass in exact agreement with the Karch-Randall result. Interestingly
enough, at one loop order, the spin 0, spin 1/2 and spin 1 loops contribute to
the dynamically generated (mass)^2 in the same 1: 3: 12 ratio as enters the
Weyl anomaly and the 1/r^3 corrections to the Newtonian gravitational
potential.Comment: 20 pages, Revtex 3, Discussion on the absence of a scalar ghost
clarified; Additional details on the computation give
Dirac equation for membranes
Dirac's idea of taking the square root of constraints is applied to the case
of extended objects concentrating on membranes in D=4 space-time dimensions.
The resulting equation is Lorentz invariant and predicts an infinite hierarchy
of positive and negative masses (tension). There are no tachyonic solutions.Comment: 5 pages, 1 figure, v2: improved version, accepted for publication as
a Brief Report in Physical Review
String/-brane Duality and Duality as Symmetries of Actions
We realize the string/-brane duality on the action level between the
-compactified heterotic string effective action and the -
brane effective action in dimensions by managing a Lagrange multiplier
field. A dual dictionary is composed to be available for the translation
between the elementary or solitonic solutions of the dual pair of actions. In
the same way the duality is also reconstructed on the action level as a
double dualization for the -compactified heterotic string effective
action.Comment: 9 pages, latex, no figure
Vanishing Cosmological Constant by Gravitino-Dressed Compactification of 11D Supergravity
We consider compactifications induced by the gravitino field of eleven
dimensional supergravity. Such compactifications are not trivial in the sense
that the gravitino profiles are not related to pure bosonic ones by means of a
supersymmetry transformation. The basic property of such backgrounds is that
they admit -torsion although they have vanishing Riemann tensor. Thus,
these backgrounds may be considered also as solutions of the teleparallel
formulation of supergravity. We construct two classes of solutions, one with
both antisymmetric three-form field, gravity and gravitino and one with only
gravity and gravitino. In these classes of solutions, the internal space is a
parallelized compact manifold, so that it does not inherit any cosmological
constant to the external spacetime. The latter turns out to be flat Minkowski
in the maximally symmetric case. The elimination of the cosmological constant
in the spontaneously compactified supergravity seems to be a generic property
based on the trading of the cosmological constant for parallelizing torsion.Comment: 17 pages, no figure
Null Branes in String Theory Backgrounds
We consider null bosonic p-branes moving in curved space-times and develop a
method for solving their equations of motion and constraints, which is suitable
for string theory backgrounds. As an application, we give an exact solution for
such background in ten dimensions.Comment: 11 pages, LaTeX. Final version, to appear in Phys. Rev.
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