7,009 research outputs found
Holography and the conformal window in the Veneziano limit
We discuss holographic QCD in the Veneziano limit (the V-QCD models),
concentrating on phenomena near the "conformal" phase transition taking place
at a critical value of the ratio x = N_f/N_c. In particular, we review the
results for the S-parameter, the technidilaton, and the masses of the mesons.Comment: 15 pages, 7 figures. Contribution to Sakata Memorial KMI Workshop on
"Origin of Mass and Strong Coupling Gauge Theories (SCGT15)", 3-6 March 2015,
Nagoya Universit
Recent progress in backreacted bottom-up holographic QCD
Recent progress in constructing holographic models for QCD is discussed,
concentrating on the bottom-up models which implement holographically the
renormalization group flow of QCD. The dynamics of gluons can be modeled by
using a string-inspired model termed improved holographic QCD, and flavor can
be added by introducing space filling branes in this model. The flavor fully
backreacts to the glue in the Veneziano limit, giving rise to a class of models
which are called V-QCD. The phase diagrams and spectra of V-QCD are in good
agreement with results for QCD obtained by other methods.Comment: 6 pages, 3 figures. To appear in the proceedings of the conference
'XIth Quark Confinement and the Hadron Spectrum', St. Petersburg, September
8-12, 2014. v2: references updated. arXiv admin note: text overlap with
arXiv:1508.0068
Towards an implementable dependency grammar
The aim of this paper is to define a dependency grammar framework which is
both linguistically motivated and computationally parsable. See the demo at
http://www.conexor.fi/analysers.html#testingComment: 10 page
Late time behavior of non-conformal plasmas
We determine analytically the dependence of the approach to thermal
equilibrium of strongly coupled plasmas on the breaking of scale invariance.
The theories we consider are the holographic duals to Einstein gravity coupled
to a scalar with an exponential potential. The coefficient in the exponent,
, is the parameter that controls the deviation from the conformally
invariant case. For these models we obtain analytic solutions for the plasma
expansion in the late-time limit, under the assumption of boost-invariance, and
we determine the scaling behaviour of the energy density, pressure, and
temperature as a function of time. We find that the temperature decays as a
function of proper time as with determined in terms of
the non-conformality parameter as . This agrees with the
result of Janik and Peschanski, , for the conformal plasmas and
generalizes it to non-conformal plasmas with . We also consider more
realistic potentials where the exponential is supplemented by power-law terms.
Even though in this case we cannot have exact solutions, we are able under
certain assumptions to determine the scaling of the energy, that receives
logarithmic corrections.Comment: 31 page
Factorization at fixed Q^2(1-x)
We consider QCD factorization between hard and soft subprocesses in inclusive
reactions where the momentum fraction x of one parton approaches unity as the
hard scale Q^2 -> \infty, such that Q^2(1-x) is fixed. In this "BB limit" the
entire (multi-parton) Fock state containing the high x parton is coherent with
the hard subprocess. The soft contribution is given by a forward multiparton
matrix element. The BB limit corresponds to a fixed (large or small) missing
mass and is thus closely connected to exclusive production. We analyze the
Drell-Yan process h + N -> \gamma^* + X in detail, explaining why the virtual
photon is longitudinally polarized for h = \pi and transversely polarized for h
= p. The BB limit may be relevant also for other phenomena observed at high x,
such as the large single spin asymmetries of p p -> \Lambda^\uparrow X and in p
p^\uparrow -> \pi X.Comment: 18 pages, 6 figures. v2: Version published in JHEP. Text modified as
suggested by the refere
Holographic QCD in the Veneziano limit at finite Magnetic Field and Chemical Potential
We investigate the phase diagram of QCD-like gauge theories at strong
coupling at finite magnetic field , temperature and baryon chemical
potential using the improved holographic QCD model including the full
backreaction of the quarks in the plasma. In addition to the phase diagram we
study the behavior of the quark condensate as a function of , and
and discuss the fate of (inverse) magnetic catalysis at finite . In
particular we observe that inverse magnetic catalysis exists only for small
values of the baryon chemical potential. The speed of sound in this holographic
quark-gluon plasma exhibits interesting dependence on the thermodynamic
parameters.Comment: 7 pages, 6 figure
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