457 research outputs found
String Creation, D-branes and Effective Field Theory
This paper addresses several unsettled issues associated with string creation
in systems of orthogonal Dp-D(8-p) branes. The interaction between the branes
can be understood either from the closed string or open string picture. In the
closed string picture it has been noted that the DBI action fails to capture an
extra RR exchange between the branes. We demonstrate how this problem persists
upon lifting to M-theory. These D-brane systems are analysed in the closed
string picture by using gauge-fixed boundary states in a non-standard lightcone
gauge, in which RR exchange can be analysed precisely. The missing piece in the
DBI action also manifests itself in the open string picture as a mismatch
between the Coleman-Weinberg potential obtained from the effective field theory
and the corresponding open string calculation. We show that this difference can
be reconciled by taking into account the superghosts in the (0+1)effective
theory of the chiral fermion, that arises from gauge fixing the spontaneously
broken world-line local supersymmetries.Comment: 33 page
String Pair Creations in D-brane Systems
We investigate the criterion, on the Born-Infeld background fields, for the
open string pair creation to occur in D-(anti-)D-brane systems. Although
the pair creation occurs generically in both D-D and D-anti-D
systems for the cases which meet the criterion, it is more drastic in
D-anti-D-brane systems by some exponential factor depending on the
background fields. Various configurations exhibiting pair creations are
obtained via duality transformations. These include the spacelike scissors and
two D-strings (slanted at different angles) passing through each other. We
raise the scissors paradox and suggest a resolution based on the triple
junction in IIB setup.Comment: V2. 1+28 pages, 5 figures in JHEP3, minor changes, added reference
Null Brane Intersections
We study pairs of planar D-branes intersecting on null hypersurfaces, and
other related configurations. These are supersymmetric and have finite energy
density. They provide open-string analogues of the parabolic orbifold and
null-fluxbrane backgrounds for closed superstrings. We derive the spectrum of
open strings, showing in particular that if the D-branes are shifted in a
spectator dimension so that they do not intersect, the open strings joining
them have no asymptotic states. As a result, a single non-BPS excitation can in
this case catalyze a condensation of massless modes, changing significantly the
underlying supersymmetric vacuum state. We argue that a similar phenomenon can
modify the null cosmological singularity of the time-dependent orbifolds. This
is a stringy mechanism, distinct from black-hole formation and other strong
gravitational instabilities, and one that should dominate at weak string
coupling. A by-product of our analysis is a new understanding of the appearance
of 1/4 BPS threshold bound states, at special points in the moduli space of
toroidally-compactified type-II string theory.Comment: Tex file, uses harvmac, 24 pages with 5 figures. Corrected typos and
added references. Final version to appear in JHE
One-Loop Effect of Null-Like Cosmology's Holographic Dual Super-Yang-Mills
We calculate the 1-loop effect in super-Yang-Mills which preserves
1/4-supersymmetries and is holographically dual to the null-like cosmology with
a big-bang singularity. Though the bosonic and fermionic spectra do not agree
precisely, we do obtain vanishing 1-loop vacuum energy for generic warped
plane-wave type backgrounds with a big-bang singularity. Moreover, we find that
the cosmological "constant" contributed either by bosons or fermions is
time-dependent. The issues about the particle production of some background and
about the UV structure are also commented. We argue that the effective higher
derivative interactions are suppressed as long as the Fourier transform of the
time-dependent coupling is UV-finite. Our result holds for scalar
configurations that are BPS but with arbitrary time-dependence. This suggests
the existence of non-renormalization theorem for such a new class of
time-dependent theories. Altogether, it implies that such a super-Yang-Mills is
scale-invariant, and that its dual bulk quantum gravity might behave regularly
near the big bang.Comment: 20 pages, v2 add comments and references, v3 clarify BPS condition &
add new discussion on particle production and UV structure, v4&v5 minor
changes, final to JHE
Holographic U(1)_A and String Creation
We analyze the resolution of the U(1)_A problem in the Sakai-Sugimoto
holographic dual of large N_c QCD at finite temperature. It has been shown that
in the confining phase the axial symmetry is broken at order 1/N_c, in
agreement with the ideas of Witten and Veneziano. We show that in the
deconfined phase the axial symmetry remains unbroken to all orders in 1/N_c. In
this case the breaking is due to instantons which are described by spacelike
D0-branes, in agreement with 'tHooft's resolution. The holographic dual of the
symmetry breaking fermion condensate is a state of spacelike strings between
the D0-brane and the flavor D8-branes, which result from a spacelike version of
the string creation effect. In the intermediate phase of deconfinement with
broken chiral symmetry the instanton gas approximation is possibly regulated in
the IR, which would imply an eta' mass-squared of order exp(-N_c).Comment: 18 pages, 19 figures, minor change
Superstars and Giant Gravitons in M-theory
Following hep-th/0109127, we show that a certain class of BPS naked
singularities (superstars) found in compactifications of M-theory can be
interpreted as being composed of giant gravitons. More specifically, we study
superstars which are asymptotically AdS_7 x S^4 and AdS_4 x S^7 and show that
these field configurations can be interpreted as being sourced by continuous
distributions of spherical M2- and M5-branes, respectively, which carry
internal momenta and have expanded on the spherical component of the
space-time.Comment: 13 page
QED and String Theory
We analyze the D9-D9bar system in type IIB string theory using Dp-brane
probes. It is shown that the world-volume theory of the probe Dp-brane contains
two-dimensional and four-dimensional QED in the cases with p=1 and p=3,
respectively, and some applications of the realization of these well-studied
quantum field theories are discussed. In particular, the two-dimensional QED
(the Schwinger model) is known to be a solvable theory and we can apply the
powerful field theoretical techniques, such as bosonization, to study the
D-brane dynamics. The tachyon field created by the D9-D9bar strings appears as
the fermion mass term in the Schwinger model and the tachyon condensation is
analyzed by using the bosonized description. In the T-dualized picture, we
obtain the potential between a D0-brane and a D8-D8bar pair using the Schwinger
model and we observe that it consists of the energy carried by fundamental
strings created by the Hanany-Witten effect and the vacuum energy due to a
cylinder diagram. The D0-brane is treated quantum mechanically as a particle
trapped in the potential, which turns out to be a system of a harmonic
oscillator.
As another application, we obtain a matrix theory description of QED using
Taylor's T-duality prescription, which is actually applicable to a wide variety
of field theories including the realistic QCD. We show that the lattice gauge
theory is naturally obtained by regularizing the matrix size to be finite.Comment: 33 pages, Latex, 4 figures, a reference adde
Quantization of the Chern-Simons Coupling Constant
We investigate the quantum consistency of p-form Maxwell-Chern-Simons
electrodynamics in 3p+2 spacetime dimensions (for p odd). These are the
dimensions where the Chern--Simons term is cubic, i.e., of the form FFA. For
the theory to be consistent at the quantum level in the presence of magnetic
and electric sources, we find that the Chern--Simons coupling constant must be
quantized. We compare our results with the bosonic sector of eleven dimensional
supergravity and find that the Chern--Simons coupling constant in that case
takes its corresponding minimal allowed value.Comment: 15 pages, 1 figure, JHEP3.cls. Equation (8.6) corrected and perfect
agreement with previous results is obtaine
Black hole microstate geometries from string amplitudes
In this talk we review recent calculations of the asymptotic supergravity
fields sourced by bound states of D1 and D5-branes carrying travelling waves.
We compute disk one-point functions for the massless closed string fields. At
large distances from the branes, the effective open string coupling is small,
even in the regime of parameters where the classical D1-D5-P black hole may be
considered. The fields sourced by the branes differ from the black hole
solution by various multipole moments, and have led to the construction of a
new 1/8-BPS ansatz in type IIB supergravity.Comment: 14 pages, 3 figures, Contribution to the proceedings of the Black
Objects in Supergravity School, Frascati, 201
Permeable conformal walls and holography
We study conformal field theories in two dimensions separated by domain
walls, which preserve at least one Virasoro algebra. We develop tools to study
such domain walls, extending and clarifying the concept of `folding' discussed
in the condensed-matter literature. We analyze the conditions for unbroken
supersymmetry, and discuss the holographic duals in AdS3 when they exist. One
of the interesting observables is the Casimir energy between a wall and an
anti-wall. When these separate free scalar field theories with different
target-space radii, the Casimir energy is given by the dilogarithm function of
the reflection probability. The walls with holographic duals in AdS3 separate
two sigma models, whose target spaces are moduli spaces of Yang-Mills
instantons on T4 or K3. In the supergravity limit, the Casimir energy is
computable as classical energy of a brane that connects the walls through AdS3.
We compare this result with expectations from the sigma-model point of view.Comment: Latex file, 34 pages, 8 figures, uses JHEP3.cls. Typos corrected and
references adde
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