188,238 research outputs found
Localized Backreacted Flavor Branes in Holographic QCD
We investigate the perturbative (in ) backreaction of localized
D8 branes in D4-D8 systems including in particular the Sakai Sugimoto model. We
write down the explicit expressions of the backreacted metric, dilaton and RR
form. We find that the backreaction remains small up to a radial value of , and that the background functions are smooth except
at the D8 sources. In this perturbative window, the original embedding remains
a solution to the equations of motion. Furthermore, the fluctuations around the
original embedding, describing scalar mesons, do not become tachyonic due to
the backreaction in the perturbative regime. This is is due to a cancelation
between the DBI and CS parts of the D8 brane action in the perturbed
background.Comment: 1+48 pages (7 figures) + 15 pages, citations added & minor
correction
Coisotropic D8-branes and Model-building
Up to now chiral type IIA vacua have been mostly based on intersecting
D6-branes wrapping special Lagrangian 3-cycles on a CY three-fold. We argue
that there are additional BPS D-branes which have so far been neglected, and
which seem to have interesting model-building features. They are coisotropic
D8-branes, in the sense of Kapustin and Orlov. The D8-branes wrap 5-dimensional
submanifolds of the CY which are trivial in homology, but contain a worldvolume
flux that induces D6-brane charge on them. This induced D6-brane charge not
only renders the D8-brane BPS, but also creates D=4 chirality when two
D8-branes intersect. We discuss in detail the case of a type IIA Z2 x Z2
orientifold, where we provide explicit examples of coisotropic D8-branes. We
study the chiral spectrum, SUSY conditions, and effective field theory of
different systems of D8-branes in this orientifold, and show how the magnetic
fluxes generate a superpotential for untwisted Kahler moduli. Finally, using
both D6-branes and coisotropic D8-branes we construct new examples of MSSM-like
type IIA vacua.Comment: 63 pages, 11 figures. Typos corrected and comments adde
d8···d10 RhI···AuI Interactions in Rh 2,6-Xylylisocyanide Complexes with [Au(CN)2]: Bond Analysis and Crystal Effects
ProducciĂłn CientĂficaThe well known [RhL4]n(anion)n structures, with RhI···RhI d8···d8
interactions, are replaced by others with RhI···AuI d8···d10
interactions such as [{RhL4}{Au(CN)2}] (L = 2,6-Xylylisocyanide) or
[{RhL4}{Au(CN)2} {RhL4}{Au2(CN)3}·4(CHCl3)]â when the anion is
[Au(CN)2]â. Orbital (Rh···Au), coulombic, and inter-unit Ï-Ï aryl
stacking interactions stabilize these crystal structures.Ministerio de EconomĂa, Industria y Competitividad (grant CTQ2017-89217-P)Junta de Castilla y LeĂłn (project VA038G18
D-branes from N non-BPS D9-branes in Type IIA theory
We construct unstable system D8-brane+D8-antibrane as a kink solution on
world-volume of non-BPS D9-brane in Type IIA theory. Further we will make other
checks confirming validity of our appro.Comment: 30 pages, corrected some typo
Electromagnetic and Axial Current Form Factors and Spectroscopy of Three-Flavor Holographic Baryons
We present an analysis of the three-flavor holographic model of QCD
associated to a brane configuration, with symmetry breaking induced by
a worldsheet instanton associated to a closed loop connecting
. We calculate the electromagnetic and axial couplings
of all octet and decuplet baryons, as well as several negative parity
excitations, with and without symmetry breaking effects, and demonstrate
qualitative and quantitative agreement with many available experimental
measurements, with marked improvement over the analogous two-flavor models.Comment: 23 page
Stable D8-branes and Tachyon Condensation in Type 0 Open String Theory
We consider non-BPS D8 (and D7) branes in type 0 open string theory and
describe under which circumstances these branes are stable. We find stable
non-BPS D7 and D8 in type 0 with and without D9-branes in the background. By
extending the descent relations between D-branes to type 0 theories, the
non-BPS D8-brane is considered as the result of a tachyon condensation of a D9
anti-D9 pair in type 0. We study the condensation of the open string tachyons
in type 0 with generic gauge groups giving rise to different configurations
involving non-BPS D8-branes and discuss the stability in each case. The results
agree with the topological analysis of the vacuum manifold of the tachyon
potential for each case.Comment: 16 pages, LaTeX, 1 figure, minor changes, references adde
Holographic QCD with Topologically Charged Domain-Wall/Membranes
We study the thermodynamical phase structures of holographic QCD with
nontrivial topologically charged domain-wall/membranes which are originally
related to the multiple -vacua in the large limit. We realize the
topologically charged membranes as the holographic D6-brane fluxes in the
Sakai-Sugimoto model. The D6-brane fluxes couple to the probe D8-anti-D8 via
Chern-Simon term, and act as the source for the baryonic current density of
QCD. We find rich phase structures of the dual meson system by varying
asymptotic separation of D8 and anti-D8. Especially, there can be a
thermodynamically favored and stable phase of finite baryonic current density.
This provides the supporting evidence for the discovery of the topologically
charged membranes found in the lattice QCD calculations. We also find a
crossover phase with the limiting baryonic current density and temperature
which suggest a Hagedorn-like phase transition of meson dissociation.Comment: 23 pages, 19 figures;v2 typos corrected;v3 text improve
Microscopic string analysis of the D0-D8 brane system and dual R-R states
Using the boundary state formalism, we perform a microscopic string analysis
of the interaction between two D-branes and provide a local interpretation for
the R-R force in the D0-D8 brane system. To do so, we construct BRST invariant
vertex operators for the massless R-R states in the asymmetric picture that are
proportional to potentials rather than field strengths. The Hilbert space of
such R-R states contains combinations of two vectors that decouple from all
physical amplitudes, even in the presence of boundaries. Identifying these
vectors, we remove the null states and recover duality relations among R-R
potentials. If we specify to the D0-D8 brane system, this mechanism implies
that the R-R 1-form state has a non-zero overlap with both the D0-brane and the
D8-brane, thus explaining from a local point of view the non-vanishing R-R
contribution in the interaction for the D0-D8 brane system and those related to
it by duality.Comment: 31 pages, final version to be published in Nucl. Phys.
Baryons in Holographic QCD
We study the baryon in holographic QCD with multi- brane
system. In holographic QCD, the baryon appears as a topologically non-trivial
chiral soliton in a four-dimensional effective theory of mesons. We call this
topological soliton as Brane-induced Skyrmion. Some review of
holographic QCD is presented from the viewpoints of recent hadron physics and
phenomenologies. Four-dimensional effective theory with pions and mesons
is uniquely derived from the non-abelian Dirac-Born-Infeld (DBI) action of
brane with supergravity background, without small amplitude expansion of
meson fields to discuss chiral solitons. For the hedgehog configuration of pion
and -meson fields, we derive the energy functional and the Euler-Lagrange
equation of Brane-induced Skyrmion from the meson effective action induced by
holographic QCD. Performing the numerical calculation, we obtain the pion
profile and the -meson profile of the Brane-induced
Skyrmion, and estimate its total energy, energy density distribution, and
root-mean-square radius. These results are compared with the experimental
quantities of baryons and also with the profiles of standard Skyrmion without
mesons. We analyze interaction terms of pions and mesons in
Brane-induced Skyrmion, and consider the role of -meson component
appearing in baryons.Comment: 28 pages, 11 figure
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