821 research outputs found
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
Polyakov Loops in Strongly-Coupled Plasmas with Gravity Duals
We study the properties of the Polyakov loop in strongly-coupled gauge
plasmas that are conjectured to be dual to five dimensional theories of gravity
coupled to a nontrivial single scalar field. We find a gravity dual that can
describe the thermodynamic properties and also the expectation value of the
Polyakov loop in the deconfined phase of quenched SU(3) QCD up to .Comment: 7 pages, 2 figures, talk presented at the International Conference on
Strangeness in Quark Matter, Buzios, Rio de Janeiro, Brazil, Sept. 27 - oct.
2, 200
Impact of trust on local residents' mega-event perceptions and their support
This study examines the influence of residents’ trust in government and organizing committee on their impact perceptions and support for a mega-event, namely, 2014 FIFA World Cup. Findings suggest significant relationships between impact perceptions and support. While trust in government is found to be a significant determinant of impact perceptions, findings indicate no significant relationship between trust in government and support, which suggest that the relationship is mediated by impact perceptions. While a positive relationship between trust in the organizing committee and positive impact perceptions is found, findings suggest no significant relationship between trust in the organizing committee and negative impact perceptions. Trust in the organizing committee is also found to have significant positive impact on support
Torsional Newton Cartan gravity from non-relativistic strings
We study propagation of closed bosonic strings in torsional Newton-Cartan
geometry based on a recently proposed Polyakov type action derived by
dimensional reduction of the ordinary bosonic string along a null direction. We
generalize the Polyakov action proposal to include matter, i.e. the 2-form and
the 1-form that originates from the Kalb-Ramond field and the dilaton. We
determine the conditions for Weyl invariance which we express as the
beta-function equations on the worldsheet, in analogy with the usual case of
strings propagating on a pseudo-Riemannian manifold. The critical dimension of
the TNC space-time turns out to be 25. We find that Newton's law of gravitation
follows from the requirement of quantum Weyl invariance in the absence of
torsion. Presence of the 1-form requires torsion to be non vanishing. Torsion
has interesting consequences, in particular it yields a mass term and an
advection term in the generalized Newton's law. U(1) mass invariance of the
theory is an important ingredient in deriving the beta functions.Comment: Summary of results added. Reorganization and generalization of
results. Typos fixe
Optimal Detector Randomization in Cognitive Radio Systems in the Presence of Imperfect Sensing Decisions
Cataloged from PDF version of article.In this study, optimal detector randomization is developed for secondary users in a cognitive radio system in the presence of imperfect spectrum sensing decisions. It is shown that the minimum average probability of error can be achieved by employing no more than four maximum a-posteriori probability (MAP) detectors at the secondary receiver. Optimal MAP detectors and generic expressions for their average probability of error are derived in the presence of possible sensing errors. Also, sufficient conditions are presented related to improvements due to optimal detector randomization. © 2014 IEEE
Dressed spectral densities for heavy quark diffusion in holographic plasmas
We analyze the large frequency behavior of the spectral densities that govern
the generalized Langevin diffusion process for a heavy quark in the context of
the gauge/gravity duality. The bare Langevin correlators obtained from the
trailing string solution have a singular short-distance behavior. We argue that
the proper dressed spectral functions are obtained by subtracting the
zero-temperature correlators. The dressed spectral functions have a
sufficiently fast fall-off at large frequency so that the Langevin process is
well defined and the dispersion relations are satisfied. We identify the cases
in which the subtraction does not modify the associated low-frequency transport
coefficients. These include conformal theories and the non-conformal,
non-confining models. We provide several analytic and numerical examples in
conformal and non-conformal holographic backgrounds.Comment: 51 pages, 2 figure
On the YM and QCD spectra from five dimensional strings
We consider a non-critical five dimensional string setup which could provide
a dual description of QCD in the limit of large number of colors and flavors.
The model corresponds to N_c color D3-branes and N_f D4/anti D4-brane pairs
supporting flavor degrees of freedom. The matching of the string model spectrum
with the dual field theory one is considered. We discuss the consequences of
the possible matching of the gravity modes with the light glueballs and the
interpretation of the brane spectrum in Yang-Mills and QCD.Comment: 21 pages; V2: added corrections and references to match the published
versio
A Holographic Model of Strange Metals
We give a review on our recent work arXiv:1006.0779 [hep-th] and
arXiv:1006.1719 [hep-th], in which properties of holographic strange metals
were investigated. The background is chosen to be anisotropic scaling solution
in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of
bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC
conductivity, the DC Hall conductivity and the AC conductivity are extensively
analyzed. We classify behaviors of the conductivities according to the
parameter ranges in the bulk theory and characterize conditions when the
holographic results can reproduce experimental data.Comment: 34 pages, 15 figures, minor correction
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
Soft-Wall Stabilization
We propose a general class of five-dimensional soft-wall models with AdS
metric near the ultraviolet brane and four-dimensional Poincar\'e invariance,
where the infrared scale is determined dynamically. A large UV/IR hierarchy can
be generated without any fine-tuning, thus solving the electroweak/Planck scale
hierarchy problem. Generically, the spectrum of fluctuations is discrete with a
level spacing (mass gap) provided by the inverse length of the wall, similar to
RS1 models with Standard Model fields propagating in the bulk. Moreover two
particularly interesting cases arise. They can describe: (a) a theory with a
continuous spectrum above the mass gap which can model unparticles
corresponding to operators of a CFT where the conformal symmetry is broken by a
mass gap, and; (b) a theory with a discrete spectrum provided by linear Regge
trajectories as in AdS/QCD models.Comment: 27 pages, 6 figures, 1 table. v2: references added, version to appear
in NJP Focus Issue on Extra Dimension
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