2,152 research outputs found
Towards understanding Regge trajectories in holographic QCD
We reassess a work done by Migdal on the spectrum of low-energy vector mesons
in QCD in the light of the AdS-QCD correspondence. Recently, a tantalizing
parallelism was suggested between Migdal's work and a family of holographic
duals of QCD. Despite the intriguing similarities, both approaches face a major
drawback: the spectrum is in conflict with well-tested Regge scaling. However,
it has recently been shown that holographic duals can be modified to accomodate
Regge behavior. Therefore, it is interesting to understand whether Regge
behavior can also be achieved in Migdal's approach. In this paper we
investigate this issue. We find that Migdal's approach, which is based on a
modified Pade approximant, is closely related to the issue of quark-hadron
duality breakdown in QCD.Comment: 17 pages, 1 figure. Typos fixed, references added, improved
discussion. Minor changes to match the journal versio
Massive Pions, Anomalies and Baryons in Holographic QCD
We consider a holographic model of QCD, obtained by a very simple
modification of the original construction, which describes at the same time the
pion mass, the QCD anomalies and the baryons as topological solitons. We study
in detail its phenomenological implications in both the mesonic and baryonic
sectors and compare with the observations.Comment: 31 pages, 2 figures; v2: Version published in Nucl. Phys.
Structure of Vector Mesons in Holographic Model with Linear Confinement
Wave functions and form factors of vector mesons are investigated in the
holographic dual model of QCD with a smooth oscillator-like wall. We introduce
wave functions conjugate to solutions of the 5D equation of motion and develop
a formalism based on these wave functions, which are very similar to those of a
quantum-mechanical oscillator. For the lowest bound state (rho-meson), we show
that, in this model, the basic elastic form factor exhibits the perfect vector
meson dominance, i.e., it is given by the rho-pole contribution alone. The
electric radius of the rho-meson is calculated, _C = 0.655 fm^2, which
is larger than in case of the hard-wall cutoff. The squared radii of higher
excited states are found to increase logarithmically rather than linearly with
the radial excitation number. We calculate the coupling constant f_rho and find
that the experimental value is closer to that calculated in the hard-wall
model.Comment: 8 pages, RevTex4, references, comments and a figure added. Some
terminoloy change
Anomaly mediated neutrino-photon interactions at finite baryon density
We propose new physical processes based on the axial vector anomaly and
described by the Wess-Zumino-Witten term that couples the photon, Z-boson, and
the omega-meson. The interaction takes the form of a pseudo-Chern-Simons term,
. This term
induces neutrino-photon interactions at finite baryon density via the coupling
of the Z-boson to neutrinos. These interactions may be detectable in various
laboratory and astrophysical arenas. The new interactions may account for the
MiniBooNE excess. They also produce a competitive contribution to neutron star
cooling at temperatures >10^9 K. These processes and related axion--photon
interactions at finite baryon density appear to be relevant in many
astrophysical regimes.Comment: 4 pages, 2 figures; references adde
Holography and Unquenched Quark-Gluon Plasmas
We employ the string/gauge theory correspondence to study properties of
strongly coupled quark-gluon plasmas in thermal gauge theories with a large
number of colors and flavors. In particular, we analyze non-critical string
duals of conformal (S)QCD, as well as ten dimensional wrapped fivebrane duals
of SQCD-like theories. We study general properties of the dual plasmas,
including the drag force exerted on a probe quark and the jet quenching
parameter. We find that these plasma observables depend on the number of colors
and flavors in the ``QCD dual''; in particular, we find that the jet quenching
parameter increases linearly with N_f/N_c at leading order in the probe limit.
In the ten dimensional case we find a non trivial drag coefficient but a
vanishing jet quenching parameter. We comment on the relation of this result
with total screening and argue that the same features are shared by all known
plasmas dual to fivebranes in ten dimensions. We also construct new D5 black
hole solutions with spherical horizon and show that they exhibit the same
features.Comment: 30 pages. v2: Comments in section 2 and references updated, a typo
fixe
Melting Spectral Functions of the Scalar and Vector Mesons in a Holographic QCD Model
We investigate the finite-temperature spectral functions of heavy quarkonia
by using the soft-wall AdS/QCD model. We discuss the scalar, the pseudo-scalar,
the vector, and the axial-vector mesons and compare their qualitative features
of the melting temperature and growing width. We find that the axial-vector
meson melts earlier than the vector meson, while there appears only a slight
difference between the scalar and pseudo-scalar mesons which also melt earlier
than the vector meson.Comment: 27 pages, 10 figure
The fifth dimension as an analogue computer for strong interactions at the LHC
We present a mechanism to get S ~ 0 or even negative, without bringing into
play the SM fermion sector. This mechanism can be applied to a wide range of 5D
models, including composite Higgs and Higgsless models. As a realization of the
mechanism we introduce a simple model, although the effect on S does not rely
on the underlying dynamics generating the background. Models that include this
mechanism enjoy the following features: weakly-coupled light resonances (as
light as 600 GeV) and degenerate or inverted resonance spectrum.Comment: JHEP version. References adde
Holographic Bosonic Technicolor
We consider a technicolor model in which the expectation value of an
additional, possibly composite, scalar field is responsible for the generation
of fermion masses. We define the dynamics of the strongly coupled sector by
constructing its holographic dual. Using the AdS/CFT correspondence, we study
the S parameter and the phenomenology of the light technihadrons. We find that
the S parameter is small over a significant region of the model's parameter
space. The particle spectrum is distinctive and includes a nonstandard Higgs
boson as well as heavier hadronic resonances. Technihadron masses and decay
rates are calculated holographically, as a function of the model's parameters.Comment: 20 Pages, 4 eps figures, REVTex. Minor corrections and comments adde
Linear Confinement and AdS/QCD
In a theory with linear confinement, such as QCD, the masses squared m^2 of
mesons with high spin S or high radial excitation number n are expected, from
semiclassical arguments, to grow linearly with S and n. We show that this
behavior can be reproduced within a putative 5-dimensional theory
holographically dual to QCD (AdS/QCD). With the assumption that such a dual
theory exists and describes highly excited mesons as well, we show that
asymptotically linear m^2 spectrum translates into a strong constraint on the
INFRARED behavior of that theory. In the simplest model which obeys such a
constraint we find m^2 ~ (n+S).Comment: 14 pages, 1 figur
Euclidean Correlation Functions in a Holographic Model of QCD
We compute euclidean coordinate space correlation functions in a holographic
model of QCD. We concentrate, in particular, on channels that are related to
the U(1)_A problem, the flavor-singlet axialvector, pseudoscalar meson, and
pseudoscalar glueball (topological charge) correlator. We find that even a very
simple holographic model defined on a slice of AdS_5 provides a qualitatively
correct description of QCD correlation functions. We study the role of anomaly
terms, and show that both euclidean positivity and low energy theorems based on
the axial anomaly relation are correctly implemented. We compare the results
with expectations from an instanton model of the QCD vacuum.Comment: 16 pages, 5 figures, minor changes (references added), to appear in
Phys Rev
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