382 research outputs found
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
A note on fermions in holographic QCD
We study the fermionic sector of a probe D8-brane in the supergravity
background made of D4-branes compactified on a circle with supersymmetry broken
explicitly by the boundary conditions. At low energies the dual field theory is
effectively four-dimensional and has proved surprisingly successful in
recovering qualitative and quantitative properties of QCD. We investigate
fluctuations of the fermionic fields on the probe D8-brane and interpret these
as mesinos (fermionic superpartners of mesons). We demonstrate that the masses
of these modes are comparable to meson masses and show that their interactions
with ordinary mesons are not suppressed.Comment: 21+1 pp, 1 figure; v2: typos corrected, refs. adde
Brane-induced Skyrmion on S^3: baryonic matter in holographic QCD
We study baryonic matter in holographic QCD with D4/D8/\bar{D8} multi-D brane
system in type IIA superstring theory. The baryon is described as the
"brane-induced Skyrmion", which is a topologically non-trivial chiral soliton
in the four-dimensional meson effective action induced by holographic QCD. We
employ the "truncated-resonance model" approach for the baryon analysis,
including pion and \rho meson fields below the ultraviolet cutoff scale M_KK
\sim 1GeV, to keep the holographic duality with QCD. We describe the baryonic
matter in large N_c as single brane-induced Skyrmion on the three-dimensional
closed manifold S^3 with finite radius R. The interactions between baryons are
simulated by the curvature of the closed manifold S^3, and the decrease of the
size of S^3 represents the increase of the total baryon-number density in the
medium in this modeling. We investigate the energy density, the field
configuration, the mass and the root-mean-square radius of single baryon on S^3
as the function of its radius R. We find a new picture of "pion dominance" near
the critical density in the baryonic matter, where all the (axial) vector meson
fields disappear and only the pion field survive. We also find the "swelling"
phenomena of the baryons as the precursor of the deconfinement, and propose the
mechanism of the swelling in general context of QCD. The properties of the
deconfinement and the chiral symmetry restoration in the baryonic matter are
examined by taking the proper order parameters. We also compare our
truncated-resonance model with another "instanton" description of the baryon in
holographic QCD, considering the role of cutoff scale M_KK.Comment: 25 pages, 12 figure
Sakai-Sugimoto model, Tachyon Condensation and Chiral symmetry Breaking
We modify the Sakai-Sugimoto model of chiral symmetry breaking to take into
account the open string tachyon which stretches between the flavour D8-branes
and anti D8-branes. There are several reasons of consistency for doing this:
(i) Even if it might be reasonable to ignore the tachyon in the ultraviolet
where the flavour branes and antibranes are well separated and the tachyon is
small, it is likely to condense and acquire large values in the infrared where
the branes meet. This takes the system far away from the perturbatively stable
minimum of the Sakai-Sugimoto model; (ii) The bifundamental coupling of the
tachyon to fermions of opposite chirality makes it a suitable candidate for the
quark mass and chiral condensate parameters. We show that the modified
Sakai-Sugimoto model with the tachyon present has a classical solution
satisfying all the desired consistency properties. In this solution chiral
symmetry breaking coincides with tachyon condensation. We identify the
parameters corresponding to the quark mass and the chiral condensate and also
briefly discuss the mesonic spectra.Comment: 18 pages, latex; v3; conclusion in subsection 3.1 modified and
appropriate changes made in the abstract and introduction to reflect this;
typos corrected; version to appear in JHE
Skyrmions with holography and hidden local symmetry
We study baryons as Skyrmions in holographic QCD with D4/D8/D8-bar multi-D
brane system in type IIA superstring theory, and also in the non-linear sigma
model with hidden local symmetry (HLS). Comparing these two models, we find
that the extra-dimension and its nontrivial curvature can largely change the
role of (axial) vector mesons for baryons in four-dimensional space-time. In
the HLS approach, the rho-meson field as a massive Yang-Mills field has a
singular configuration in Skyrmion, which gives a strong repulsion for the
baryon as a stabilizer. When a_1 meson is added in this approach, the stability
of Skyrmion is lost by the cancellation of rho and a_1 contributions. On the
contrary, in holographic QCD, the rho-meson field does not appear as a massive
Yang-Mills field due to the extra-dimension and its nontrivial curvature. We
show that the rho-meson field has a regular configuration in Skyrmion, which
gives a weak attraction for the baryon in holographic QCD. We argue that
Skyrmion with pi, rho and a_1 mesons become stable due to the curved
extra-dimension and also the presence of the Skyrme term in holographic QCD.
From this result, we also discuss the features of our truncated-resonance
analysis on baryon properties with pi and rho mesons below the cutoff scale
M_KK about 1GeV in holographic QCD, which is compared with other 5D instanton
analysis.Comment: 7 pages, 7 figure
A Qualitative Study of Women's Lived Experiences of Conflict and Domestic Violence in Afghanistan.
This article empirically explores women's lived experiences of domestic violence and conflict in Afghanistan. A thematic analysis of 20 semistructured interviews with women living in safe houses produced three main themes about the relationship between conflict and domestic violence: (a) violence from loss of patriarchal support, (b) violence from the drug trade as an economic driver, and (c) violence from conflict-related poverty. We discuss the bidirectional nature of this relationship: Not only does conflict contribute to domestic violence, but domestic violence contributes to conflict through justifying armed intervention, separating women from economic and public life, and perpetuating patriarchy
Dynamics of Baryons from String Theory and Vector Dominance
We consider a holographic model of QCD from string theory, a la Sakai and
Sugimoto, and study baryons. In this model, mesons are collectively realized as
a five-dimensional \ Yang-Mills field and baryons
are classically identified as solitons with a unit Pontryagin number
and electric charges. The soliton is shown to be very small in the large
't Hooft coupling limit, allowing us to introduce an effective field . Its coupling to the mesons are dictated by the soliton structure, and
consists of a direct magnetic coupling to the field strength as well
as a minimal coupling to the gauge field. Upon the dimensional
reduction, this effective action reproduces all interaction terms between
nucleons and an infinite tower of mesons in a manner consistent with the large
expansion. We further find that all electromagnetic interactions, as
inferred from the same effective action via a holographic prescription, are
mediated by an infinite tower of vector mesons, rendering the baryon
electromagnetic form factors completely vector-dominated as well. We estimate
nucleon-meson couplings and also the anomalous magnetic moments, which compare
well with nature.Comment: 65pages, 3 figures, vector mesons and axial-vector mesons are now
canonically normalized (comparisons with data and conclusions unaffected
The Orbital Stability of the Ground States and the Singularity Formation for the Gravitational Vlasov Poisson System
International audienceWe study the gravitational Vlasov Poisson system where , , \rho(x)=\int_{\RR^N} f(x,v)dxdv, in dimension . In dimension where the problem is subcritical, we prove using concentration compactness techniques that every minimizing sequence to a large class of minimization problems attained on steady states solutions are up to a translation shift relatively compact in the energy space. This implies in particular the orbital stability {\it in the energy space} of the spherically symmetric polytropes what improves the nonlinear stability results obtained for this class in \cite{Guo,GuoRein,Dol}. In dimension where the problem is critical, we obtain the polytropic steady states as best constant minimizers of a suitable Sobolev type inequality relating the kinetic and the potential energy. We then derive using an explicit pseudo-conformal symmetry the existence of critical mass finite time blow up solutions, and prove more generally a mass concentration phenomenon for finite time blow up solutions. This is the first result of description of a singularity formation in a Vlasov setting. The global structure of the problem is reminiscent to the one for the focusing non linear Schrödinger equation in the energy space
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