528 research outputs found
Gravitational collapse and thermalization in the hard wall model
We study a simple example of holographic thermalization in a confining field
theory: the homogeneous injection of energy in the hard wall model. Working in
an amplitude expansion, we find black brane formation for sufficiently fast
energy injection and a scattering wave solution for sufficiently slow
injection. We comment on our expectations for more sophisticated holographic
QCD models.Comment: 33 pages, 5 figure
Topology change in commuting saddles of thermal N=4 SYM theory
We study the large N saddle points of weakly coupled N=4 super Yang-Mills
theory on S^1 x S^3 that are described by a commuting matrix model for the
seven scalar fields {A_0, \Phi_J}. We show that at temperatures below the
Hagedorn/`deconfinement' transition the joint eigenvalue distribution is S^1 x
S^5. At high temperatures T >> 1/R_{S^3}, the eigenvalues form an ellipsoid
with topology S^6. We show how the deconfinement transition realises the
topology change S^1 x S^5 --> S^6. Furthermore, we find compelling evidence
that when the temperature is increased to T = 1/(\sqrt\lambda R_{S^3}) the
saddle with S^6 topology changes continuously to one with S^5 topology in a new
second order quantum phase transition occurring in these saddles.Comment: 1+40 pages, 6 figures. v2: Title changed. Status of commuting saddles
clarified: New high T phase transition claimed in the commuting sector only,
not in the full theor
Scalar Spectrum from a Dynamical Gravity/Gauge model
We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge
trajectories for the light-flavor sector of mesons with high spin and also for
the scalar and pseudoscalar ones. In addition the model has confinement by the
Wilson loop criteria and a mass gap. We also calculate the decay amplitude of
scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and
Relativistic Astrophysic
Deconfinement and Thermodynamics in 5D Holographic Models of QCD
We review 5D holographic approaches to finite temperature QCD. Thermodynamic
properties of the "hard-wall" and the "soft-wall" models are derived. Various
non-realistic features in these models are cured by the set-up of improved
holographic QCD, that we review here.Comment: Invited review paper for Mod. Phys. Let
On the Temperature Dependence of the Shear Viscosity and Holography
We examine the structure of the shear viscosity to entropy density ratio
eta/s in holographic theories of gravity coupled to a scalar field, in the
presence of higher derivative corrections. Thanks to a non-trivial scalar field
profile, eta/s in this setup generically runs as a function of temperature. In
particular, its temperature behavior is dictated by the shape of the scalar
potential and of the scalar couplings to the higher derivative terms. We
consider a number of dilatonic setups, but focus mostly on phenomenological
models that are QCD-like. We determine the geometric conditions needed to
identify local and global minima for eta/s as a function of temperature, which
translate to restrictions on the signs and ranges of the higher derivative
couplings. Finally, such restrictions lead to an holographic argument for the
existence of a global minimum for eta/s in these models, at or above the
deconfinement transition.Comment: references adde
The yield and quality properties of chickpea seeds (cicer arietinum l.) affected by harvest times
Harvesting of chickpea (Cicer arietinum L.) seeds at right time of maturity is one of the important issues because pod dropping and shattering is a major problem during harvest. Also, the physical properties of chickpea seeds can be affected by harvest time. For this
purpose, a field experiment was carried out to examine the effects of harvest times after physiological maturity on the seed yield per plant and the seed quality properties in chickpea production. The treatments used in the experiment consisted of five harvest times, which chickpea pods were harvested at physiological maturity (H1) and 5, 10, 15,
and 20 days after physiological maturity (H2, H3, H4 and H5, respectively). The
physiological maturity time (R7) was considered as the stage that leaves start to yellow and 50% of pods are yellow. Moisture content, dimension properties, hundred seed weight, true density, bulk density and porosity and seed yield per plant was determined in the study. The results showed that all measured variables were affected by harvest time. The true density and porosity increased with delayed harvest time. But, the other
measured variables decreased when harvest was delayed
Holography and Thermodynamics of 5D Dilaton-gravity
The asymptotically-logarithmically-AdS black-hole solutions of 5D dilaton
gravity with a monotonic dilaton potential are analyzed in detail. Such
theories are holographically very close to pure Yang-Mills theory in four
dimensions. The existence and uniqueness of black-hole solutions is shown. It
is also shown that a Hawking-Page transition exists at finite temperature if
and only if the potential corresponds to a confining theory. The physics of the
transition matches in detail with that of deconfinement of the Yang-Mills
theory. The high-temperature phase asymptotes to a free gluon gas at high
temperature matching the expected behavior from asymptotic freedom. The thermal
gluon condensate is calculated and shown to be crucial for the existence of a
non-trivial deconfining transition. The condensate of the topological charge is
shown to vanish in the deconfined phase.Comment: LaTeX, 61 pages (main body) + 58 pages (appendix), 25 eps figures.
Revised version, published in JHEP. Two equations added in Section 7.4; typos
corrected; references adde
Holographic Conformal Window - A Bottom Up Approach
We propose a five-dimensional framework for modeling the background geometry
associated to ordinary Yang-Mills (YM) as well as to nonsupersymmetric gauge
theories possessing an infrared fixed point with fermions in various
representations of the underlying gauge group. The model is based on the
improved holographic approach, on the string theory side, and on the
conjectured all-orders beta function for the gauge theory one. We first analyze
the YM gauge theory. We then investigate the effects of adding flavors and show
that, in the holographic description of the conformal window, the geometry
becomes AdS when approaching the ultraviolet and the infrared regimes. As the
number of flavors increases within the conformal window we observe that the
geometry becomes more and more of AdS type over the entire energy range.Comment: 20 Pages, 3 Figures. v2: references adde
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