141 research outputs found
BPS branes in discrete torsion orbifolds
We investigate D-branes in a Z_3xZ_3 orbifold with discrete torsion. For this
class of orbifolds the only known objects which couple to twisted RR potentials
have been non-BPS branes. By using more general gluing conditions we construct
here a D-brane which is BPS and couples to RR potentials in the twisted and in
the untwisted sectors.Comment: 20 pages, LaTe
Twisted brane charges for non-simply connected groups
The charges of the twisted branes for strings on the group manifold SU(n)/Z_d
are determined. To this end we derive explicit (and remarkably simple) formulae
for the relevant NIM-rep coefficients. The charge groups of the twisted and
untwisted branes are compared and found to agree for the cases we consider.Comment: 30 page
On conformal Jordan cells of finite and infinite rank
This work concerns in part the construction of conformal Jordan cells of
infinite rank and their reductions to conformal Jordan cells of finite rank. It
is also discussed how a procedure similar to Lie algebra contractions may
reduce a conformal Jordan cell of finite rank to one of lower rank. A conformal
Jordan cell of rank one corresponds to a primary field. This offers a picture
in which any finite conformal Jordan cell of a given conformal weight may be
obtained from a universal covering cell of the same weight but infinite rank.Comment: 9 pages, LaTeX, v2: typo corrected, comments added, version to be
publishe
Quantization of Wilson loops in Wess-Zumino-Witten models
We describe a non-perturbative quantization of classical Wilson loops in the
WZW model. The quantized Wilson loop is an operator acting on the Hilbert space
of closed strings and commuting either with the full Kac-Moody chiral algebra
or with one of its subalgebras. We prove that under open/closed string duality,
it is dual to a boundary perturbation of the open string theory. As an
application, we show that such operators are useful tools for identifying fixed
points of the boundary renormalization group flow.Comment: 24 pages. Version published in JHE
Charges of twisted branes: the exceptional cases
The charges of the twisted D-branes for the two exceptional cases (SO(8) with
the triality automorphism and E_6 with charge conjugation) are determined. To
this end the corresponding NIM-reps are expressed in terms of the fusion rules
of the invariant subalgebras. As expected the charge groups are found to agree
with those characterising the untwisted branes.Comment: 15 page
Generalised permutation branes
We propose a new class of non-factorising D-branes in the product group GxG
where the fluxes and metrics on the two factors do not necessarily coincide.
They generalise the maximally symmetric permutation branes which are known to
exist when the fluxes agree, but break the symmetry down to the diagonal
current algebra in the generic case. Evidence for the existence of these branes
comes from a Lagrangian description for the open string world-sheet and from
effective Dirac-Born-Infeld theory. We state the geometry, gauge fields and, in
the case of SU(2)xSU(2), tensions and partial results on the open string
spectrum. In the latter case the generalised permutation branes provide a
natural and complete explanation for the charges predicted by K-theory
including their torsion.Comment: 33 pages, 6 figures, v2: Extended discussion of K-theory
interpretation of our branes for products of higher rank groups in the
conclusions; v3: Correction of formula (35) and adjustment of the discussion
below equation (45) (no change of result). Footnote 9 points out a previously
unnoticed subtlety and provides a reference to a more detailed discussio
Boundary States of c=1 and 3/2 Rational Conformal Field Theories
We study the boundary states for the rational points in the moduli spaces of
c=1 conformal and c=3/2 superconformal field theories, including the isolated
Ginsparg points. We use the orbifold and simple-current techniques to relate
the boundary states of different theories and to obtain symmetry-breaking,
non-Cardy boundary states. We show some interesting examples of fractional and
twisted branes on orbifold spaces.Comment: Latex, 46 pages, 1 figur
D-brane charges on non-simply connected groups
The maximally symmetric D-branes of string theory on the non-simply connected
Lie group SU(n)/Z_d are analysed using conformal field theory methods, and
their charges are determined. Unlike the well understood case for simply
connected groups, the charge equations do not determine the charges uniquely,
and the charge group associated to these D-branes is therefore in general not
cyclic. The precise structure of the charge group depends on some number
theoretic properties of n, d, and the level of the underlying affine algebra k.
The examples of SO(3)=SU(2)/Z_2 and SU(3)/Z_3 are worked out in detail, and the
charge groups for SU(n)/Z_d at most levels k are determined explicitly.Comment: 31 pages, 1 figure. 2 refs added. Added the observation: the charge
group for each su(2) theory equals the centre of corresponding A-D-E grou
Higher string functions, higher-level Appell functions, and the logarithmic ^sl(2)_k/u(1) CFT model
We generalize the string functions C_{n,r}(tau) associated with the coset
^sl(2)_k/u(1) to higher string functions A_{n,r}(tau) and B_{n,r}(tau)
associated with the coset W(k)/u(1) of the W-algebra of the logarithmically
extended ^sl(2)_k conformal field model with positive integer k. The higher
string functions occur in decomposing W(k) characters with respect to level-k
theta and Appell functions and their derivatives (the characters are neither
quasiperiodic nor holomorphic, and therefore cannot decompose with respect to
only theta-functions). The decomposition coefficients, to be considered
``logarithmic parafermionic characters,'' are given by A_{n,r}(tau),
B_{n,r}(tau), C_{n,r}(tau), and by the triplet \mathscr{W}(p)-algebra
characters of the (p=k+2,1) logarithmic model. We study the properties of
A_{n,r} and B_{n,r}, which nontrivially generalize those of the classic string
functions C_{n,r}, and evaluate the modular group representation generated from
A_{n,r}(tau) and B_{n,r}(tau); its structure inherits some features of modular
transformations of the higher-level Appell functions and the associated
transcendental function Phi.Comment: 34 pages, amsart++, times. V2: references added; minor changes; some
nonsense in B.3.3. correcte
D-brane charges on SO(3)
In this letter we discuss charges of D-branes on the group manifold SO(3).
Our discussion will be based on a conformal field theory analysis of boundary
states in a Z_2-orbifold of SU(2). This orbifold differs from the one recently
discussed by Gaberdiel and Gannon in its action on the fermions and leads to a
drastically different charge group. We shall consider maximally symmetric
branes as well as branes with less symmetry, and find perfect agreement with a
recent computation of the corresponding K-theory groups.Comment: 11 pages, 1 figure. Some comments adde
- …