16,495 research outputs found
Conformal Field Theories: From Old to New
In a short review of recent work, we discuss the general problem of
constructing the actions of new conformal field theories from old conformal
field theories. Such a construction follows when the old conformal field theory
admits new conformal stress tensors in its chiral algebra, and it turns out
that the new conformal field theory is generically a new spin-two gauge theory.
As an example we discuss the new spin-two gauged sigma models which arise in
this fashion from the general conformal non-linear sigma model.Comment: 7 pages, LaTeX, to appear in a memorial issue of Theoretical and
Mathematical Physics in memory of F.A. Lune
Unification of the General Non-Linear Sigma Model and the Virasoro Master Equation
The Virasoro master equation describes a large set of conformal field
theories known as the affine-Virasoro constructions, in the operator algebra
(affine Lie algebra) of the WZW model, while the Einstein equations of the
general non-linear sigma model describe another large set of conformal field
theories. This talk summarizes recent work which unifies these two sets of
conformal field theories, together with a presumable large class of new
conformal field theories. The basic idea is to consider spin-two operators of
the form in the background of a general
sigma model. The requirement that these operators satisfy the Virasoro algebra
leads to a set of equations called the unified Einstein-Virasoro master
equation, in which the spin-two spacetime field couples to the usual
spacetime fields of the sigma model. The one-loop form of this unified system
is presented, and some of its algebraic and geometric properties are discussed.Comment: 18 pages, Latex. Talk presented by MBH at the NATO Workshop `New
Developments in Quantum Field Theory', June 14-20, 1997, Zakopane, Polan
The orbifold-string theories of permutation-type: II. Cycle dynamics and target space-time dimensions
We continue our discussion of the general bosonic prototype of the new
orbifold-string theories of permutation type. Supplementing the extended
physical-state conditions of the previous paper, we construct here the extended
Virasoro generators with cycle central charge
, where is the length of cycle
in twisted sector . We also find an equivalent, reduced formulation
of each physical-state problem at reduced cycle central charge
. These tools are used to begin the study of the target
space-time dimension of cycle in sector , which
is naturally defined as the number of zero modes (momenta) of each cycle. The
general model-dependent formulae derived here will be used extensively in
succeeding papers, but are evaluated in this paper only for the simplest case
of the "pure" permutation orbifolds.Comment: 32 page
Unified Einstein-Virasoro Master Equation in the General Non-Linear Sigma Model
The Virasoro master equation (VME) describes the general affine-Virasoro
construction T=L^{ab}J_aJ_b+iD^a \dif J_a in the operator algebra of the WZW
model, where is the inverse inertia tensor and is the
improvement vector. In this paper, we generalize this construction to find the
general (one-loop) Virasoro construction in the operator algebra of the general
non-linear sigma model. The result is a unified Einstein-Virasoro master
equation which couples the spacetime spin-two field to the background
fields of the sigma model. For a particular solution , the unified
system reduces to the canonical stress tensors and conventional Einstein
equations of the sigma model, and the system reduces to the general
affine-Virasoro construction and the VME when the sigma model is taken to be
the WZW action. More generally, the unified system describes a space of
conformal field theories which is presumably much larger than the sum of the
general affine-Virasoro construction and the sigma model with its canonical
stress tensors. We also discuss a number of algebraic and geometrical
properties of the system, including its relation to an unsolved problem in the
theory of -structures on manifolds with torsion.Comment: LaTeX, 55 pages, one postscript figure, uses epsfig.sty. contains a
few minor corrections; version to be published in Int. J. Mod. Phys.
The Orbifold-String Theories of Permutation-Type: III. Lorentzian and Euclidean Space-Times in a Large Example
To illustrate the general results of the previous paper, we discuss here a
large concrete example of the orbifold-string theories of permutation-type. For
each of the many subexamples, we focus on evaluation of the \emph{target
space-time dimension} , the \emph{target space-time
signature} and the \emph{target space-time symmetry} of each cycle in each
twisted sector . We find in particular a gratifying \emph{space-time
symmetry enhancement} which naturally matches the space-time symmetry of each
cycle to its space-time dimension. Although the orbifolds of
-permutation-type are naturally Lorentzian, we find that the target
space-times associated to larger permutation groups can be Lorentzian,
Euclidean and even null (\hat{D}_{j}(\sigma)=0), with varying space-time
dimensions, signature and symmetry in a single orbifold.Comment: 36 page
Twisted Open Strings from Closed Strings: The WZW Orientation Orbifolds
Including {\it world-sheet orientation-reversing automorphisms}
in the orbifold program, we construct the operator
algebras and twisted KZ systems of the general WZW {\it orientation orbifold}
. We find that the orientation-orbifold sectors corresponding
to each are {\it twisted open} WZW strings, whose
properties are quite distinct from conventional open-string orientifold
sectors. As simple illustrations, we also discuss the classical (high-level)
limit of our construction and free-boson examples on abelian .Comment: 65 pages, typos correcte
New Duality Transformations in Orbifold Theory
We find new duality transformations which allow us to construct the stress
tensors of all the twisted sectors of any orbifold A(H)/H, where A(H) is the
set of all current-algebraic conformal field theories with a finite symmetry
group H \subset Aut(g). The permutation orbifolds with H = Z_\lambda and H =
S_3 are worked out in full as illustrations but the general formalism includes
both simple and semisimple g. The motivation for this development is the
recently-discovered orbifold Virasoro master equation, whose solutions are
identified by the duality transformations as sectors of the permutation
orbifolds A(D_\lambda)/Z_\lambda.Comment: 48 pages,typos correcte
Physical mechanisms may be as important as brain mechanisms in evolution of speech [Commentary on Ackerman, Hage, & Ziegler. Brain Mechanisms of acoustic communication in humans and nonhuman primates: an evolutionary perspective]
We present two arguments why physical adaptations for vocalization may be as important as neural adaptations. First, fine control over vocalization is not easy for physical reasons, and modern humans may be exceptional. Second, we present an example of a gorilla that shows rudimentary voluntary control over vocalization, indicating that some neural control is already shared with great apes
The Orbifolds of Permutation-Type as Physical String Systems at Multiples of c=26 IV. Orientation Orbifolds Include Orientifolds
In this fourth paper of the series, I clarify the somewhat mysterious
relation between the large class of {\it orientation orbifolds} (with twisted
open-string CFT's at ) and {\it orientifolds} (with untwisted open
strings at ), both of which have been associated to division by
world-sheet orientation-reversing automorphisms. In particular -- following a
spectral clue in the previous paper -- I show that, even as an {\it interacting
string system}, a certain half-integer-moded orientation orbifold-string system
is in fact equivalent to the archetypal orientifold. The subtitle of this
paper, that orientation orbifolds include and generalize standard orientifolds,
then follows because there are many other orientation orbifold-string systems
-- with higher fractional modeing -- which are not equivalent to untwisted
string systems.Comment: 22 pages, typos correcte
The General Coset Orbifold Action
Recently an action formulation, called the general WZW orbifold action, was
given for each sector of every WZW orbifold. In this paper we gauge this action
by general twisted gauge groups to find the action formulation of each sector
of every coset orbifold. Connection with the known current-algebraic
formulation of coset orbifolds is discussed as needed, and some large examples
are worked out in further detail.Comment: 31 pages, some typos correcte
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