1,279 research outputs found
World-Volume Interactions on D-Branes
We examine in detail various string scattering amplitudes in order to extract
the world-volume interactions of massless fields on a Dirichlet brane. We find
that the leading low-energy interactions are consistent with the Born-Infeld
and Chern-Simons actions. In particular, our results confirm that the
background closed string fields appearing in these actions must be treated as
functionals of the non-abelian scalar fields describing transverse fluctuations
of the D-brane.Comment: 14 page
Gamma-Ray Burst Afterglows as Analogues of High Frequency-Peaked BL Lac Objects
The spectral properties from radio to optical bands are compared between the
18 optically bright Gamma-ray burst afterglows and well established
power-spectrum sequence in Blazars. The comparison shows that the afterglows
are well agreement with the well known Blazar sequence (i.e., the - correlation, where
is the broad-band spectral slope from radio to optical
bands). The afterglows are, however, clustered at the low luminosity end of the
sequence, which is typically occupied by high frequency-peaked BL Lac objects.
The correlation suggests that Gamma-ray burst afterglows share the similar
emission process with high frequency-peaked BL Lac objects. We further identify
a deviation at a significance level larger than 2 from the sequence for
three typical optically "dark" bursts. The deviation favors a heavy extinction
in optical bands for the "dark" bursts. The extinction is estimated to be
larger than 0.5-0.6 magnitude from the - sequence.Comment: 13 pages, 2 figures and 2 tables, to be published in ApJ
The Nematic Energy Scale and the Missing Electron Pocket in FeSe
Superconductivity emerges in proximity to a nematic phase in most iron-based
superconductors. It is therefore important to understand the impact of
nematicity on the electronic structure. Orbital assignment and tracking across
the nematic phase transition prove to be challenging due to the multiband
nature of iron-based superconductors and twinning effects. Here, we report a
detailed study of the electronic structure of fully detwinned FeSe across the
nematic phase transition using angle-resolved photoemission spectroscopy. We
clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and
dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a
maximum of 50 meV at the Brillouin zone corner. We are also able to track the
dxz electron pocket across the nematic transition and explain its absence in
the nematic state. Our comprehensive data of the electronic structure provide
an accurate basis for theoretical models of the superconducting pairing in
FeSe
Observability of Quantum State of Black Hole
We analyze terms subleading to Rutherford in the -matrix between black
hole and probes of successively high energies. We show that by an appropriate
choice of the probe one can read off the quantum state of the black hole from
the S-matrix, staying asymptotically far from the BH all the time. We interpret
the scattering experiment as scattering off classical stringy backgrounds which
explicitly depend on the internal quantum numbers of the black hole.Comment: 19 pages, latex, no figure
Three Point Tree Level Amplitude in Superstring Theory
In order to check the definite amplitude and the exact zero result of the
amplitude of three massless points in both string theory and field
theory side for case and to find all gauge field couplings to R-R closed
string, we investigate the disk level S-matrix element of one Ramond-Ramond
field and two gauge field vertex operators in the world volume of BPS branes.Comment: 5 pages,prepared for Cargese Summer School on String Theory: Formal
Developments and Applications, Cargese, France, June 21-July 3 2010,to appear
in the proceeding
Monopoles in non-Abelian Einstein-Born-Infeld Theory
We study static spherically symmetric monopole solutions in non-Abelian
Einstein-Born-Infeld-Higgs model with normal trace structure. These monopoles
are similar to the corresponding solution with symmetrised trace structure and
are existing only up to some critical value of the strength of the
gravitational interaction. In addition, similar to their flat space
counterpart, they also admit a critical value of the Born-Infeld parameter
\b.Comment: 10 pages, 3 figure
Path-Integral Formulation of Dirichlet String in General Backgrounds
We investigate the dynamics of an arbitrary Dirichlet (D-) string in presence
of general curved backgrounds following a path-integral formalism. In
particular, we consider the interaction of D-string with the massless
excitations of closed string in open bosonic string theory. The background
fields induce invariant curvatures on the D-string manifold and the extrinsic
curvature can be seen to contain a divergence at the disk boundary. The
re-normalization of D-string coordinates, next to the leading order in its
derivative expansion, is performed to handle the divergence. Then we obtain the
generalized Dirac-Born-Infeld action representing the effective dynamics of
D-string in presence of the non-trivial backgrounds. On the other hand,
D-string acts as a source for the Ramond-Ramond two-form which induces an
additional (lower) form due to its coupling to the U(1) gauge invariant fields
on the D-string. These forms are reviewed in this formalism for an arbitrary
D-string and is encoded in the Wess-Zumino action. Quantization of the D-string
collective coordinates, in the U(1) gauge sector, is performed by taking into
account the coupling to the lower form and the relevant features of D-string
are analyzed in presence of the background fields.Comment: 23 pages, LaTex, corrected typos, added reference, version to appear
in Nuclear Physics
On gravitational couplings in D-brane action
We compute the two closed string graviton - two open string scalar scattering
amplitude on the disc to show that there is no second-derivative curvature -
scalar coupling term R X^2 in the low-energy effective action of a D-brane in
curved space in type II superstring theory.Comment: 15 pages, 1 figure, LaTex JHEP style; v2: reference added, typos
corrected; v3: section 2 rewritten due to an error in gauge fixing, appendix
added, conclusions unchange
Gravitational lensing by p-branes
The scattering of R-R gauge bosons off of Dirichlet p-branes is computed to
leading order in the string coupling. The results are qualitatively similar to
those found in the scattering of massless NS-NS bosons: all p-branes with p >=
0 exhibit stringy properties, in particular the Regge behavior. Both the R-R
and NS-NS scattering amplitudes agree in the limit of small momentum transfer
with scattering off the extremal R-R charged p-brane solutions found in the
low-energy supergravities. We interpret this as evidence that Dirichlet-branes
are an exact world-sheet description of the extremal p-branes. The -1-brane
(D-instanton) is a special object which, unlike all other Dirichlet-branes,
exhibits point-like behavior. We find the R-R charged instanton solution to
type IIB supergravity and confirm that the field theoretic scattering off of
this solution miraculously reproduces the full stringy calculation. As an
aside, we include a discussion of the entropy of non-extremal black holes in
ten dimensions, produced by exciting the 0-brane. We show that, for large black
holes, the entropy grows linearly with the black hole mass.Comment: LaTeX, 18 pages, 1 figure, uses psfig.sty, available from
http://xxx.lanl.gov/ftp/hep-th/papers/macros/psfig.sty Final version to
appear in Nuclear Physics
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