548 research outputs found
Scaling laws in hadronic processes and string theory
We propose a possible scheme for getting the known QCD scaling laws within
string theory. In particular, we consider amplitudes for exclusive scattering
of hadrons at large momentum transfer, hadronic form factors and distribution
functions.Comment: 13 pages, 2 figures, a comment and a reference added, a final version
to appear in Physical Review
Regge spectrum from holographic models inspired by OPE
The problem of obtaining the Regge-like behaviour for meson mass spectrum in
the hard-wall AdS/QCD models is addressed. We show that the problem can be
solved by a simple incorporation of the effects of local vacuum condensates
into such models. The slope of trajectories turns out to be determined by the
local condensate of dimension~2 that is absent in the standard Operator Product
Expansion. This pitfall, however, can be escaped by means of physically
plausible modification of boundary conditions for the holographic fields
corresponding to the usual gluon condensate, the latter then determines the
slope.Comment: 10 pages, Introduction and Concuding remarks are enlarged, accepted
by Phys. Lett.
Description of a domain by a squeezed state in a scalar field theory
The author attempted to describe a domain by using a squeezed state in
quantum field theory. An extended squeeze operator was used to construct the
state. In a scalar field theory, the author described a domain that the
distributions of the condensate and of the fluctuation are Gaussian. The
momentum distribution, chaoticity and correlation length were calculated. It
was found that the typical value of the momentum is about the inverse of the
domain size, and that the chaoticity reflects the ratio of the size of the
squeeze region to that of the coherent region. The results indicate that the
quantum state of a domain is surmised by these quantities under the assumption
that the distributions are Gaussian. As an example, this method was applied to
a pion field, and the momentum distribution and the chaoticity were shown.Comment: 10 pages, 5 figures, a typographical error in the reference is
correcte
Thermodynamics of AdS/QCD
We study finite temperature properties of four dimensional QCD-like gauge
theories in the gauge theory/gravity duality picture. The gravity dual contains
two deformed 5d AdS metrics, with and without a black hole, and a dilaton. We
study the thermodynamics of the 4d boundary theory and constrain the two
metrics so that they correspond to a high and a low temperature phase separated
by a first order phase transition. The equation of state has the standard form
for the pressure of a strongly coupled fluid modified by a vacuum energy, a bag
constant. We determine the parameters of the deformation by using QCD results
for and the hadron spectrum. With these parameters, we show that the
phase transition in the 4d boundary theory and the 5d bulk Hawking-Page
transition agree. We probe the dynamics of the two phases by computing the
quark-antiquark free energy in them and confirm that the transition corresponds
to confinement-deconfinement transition.Comment: 1+19 pages, 6 figures, references added, section 3 improve
The Magnetic Phase Diagram and the Pressure and Field Dependence of the Fermi Surface in UGe
The ac susceptibility and de Haas-van Alphen (dHvA) effect in UGe are
measured at pressures {\it P} up to 17.7 kbar for the magnetic field {\it B}
parallel to the {\it a} axis, which is the easy axis of magnetization. Two
anomalies are observed at {\it B}({\it P}) and {\it B}({\it P}) ({\it
B} {\it B} at any {\it P}), and the {\it P}-{\it B} phase diagram
is presented. The Fermi surface and quasiparticle mass are found to vary
smoothly with pressure up to 17.7 kbar unless the phase boundary {\it
B}({\it P}) is crossed. The observed dHvA frequencies may be grouped into
three according to their pressure dependences, which are largely positive,
nearly constant or negative. It is suggested that the quasiparticle mass
moderately increases as the boundary {\it B}({\it P}) is approached. DHvA
effect measurements are also performed across the boundary at 16.8 kbar.Comment: to be published in Phys. Rev.
QED Effects in Heavy Few-Electron Ions
Accurate calculations of the binding energies, the hyperfine splitting, the
bound-electron g-factor, and the parity nonconservation effects in heavy
few-electron ions are considered. The calculations include the relativistic,
quantum electrodynamic (QED), electron-correlation, and nuclear effects. The
theoretical results are compared with available experimental data. A special
attention is focused on tests of QED in a strong Coulomb field.Comment: 28 pages, 6 tables, 5 figure
Improved Holographic QCD
We provide a review to holographic models based on Einstein-dilaton gravity
with a potential in 5 dimensions. Such theories, for a judicious choice of
potential are very close to the physics of large-N YM theory both at zero and
finite temperature. The zero temperature glueball spectra as well as their
finite temperature thermodynamic functions compare well with lattice data. The
model can be used to calculate transport coefficients, like bulk viscosity, the
drag force and jet quenching parameters, relevant for the physics of the
Quark-Gluon Plasma.Comment: LatEX, 65 pages, 28 figures, 9 Tables. Based on lectures given at
several Schools. To appear in the proceedinds of the 5th Aegean School
(Milos, Greece
Confront Holographic QCD with Regge Trajectories of vectors and axial-vectors
We derive the general 5-dimension metric structure of the system in
type II superstring theory, and demonstrate the physical meaning of the
parameters characterizing the 5-dimension metric structure of the
\textit{holographic} QCD model by relating them to the parameters describing
Regge trajectories. By matching the spectra of vector mesons with
deformed soft-wall model, we find that the spectra of vector mesons
can be described very well in the soft-wall model, i.e,
soft-wall model. We then investigate how well the soft-wall
model can describe the Regge trajectory of axial-vector mesons . We find
that the constant component of the 5-dimension mass square of axial-vector
mesons plays an efficient role to realize the chiral symmetry breaking in the
vacuum, and a small negative correction in the 5-dimension mass square is
helpful to realize the chiral symmetry restoration in high excitation states.Comment: 9 pages, 3 figure and 3 tables, one section adde
Linear square-mass trajectories of radially and orbitally excited hadrons in holographic QCD
We consider a new approach towards constructing approximate holographic duals
of QCD from experimental hadron properties. This framework allows us to derive
a gravity dual which reproduces the empirically found linear square-mass
trajectories of universal slope for radially and orbitally excited hadrons.
Conformal symmetry breaking in the bulk is exclusively due to infrared
deformations of the anti-de Sitter metric and governed by one free mass scale
proportional to Lambda_QCD. The resulting background geometry exhibits dual
signatures of confinement and provides the first examples of holographically
generated linear trajectories in the baryon sector. The predictions for the
light hadron spectrum include new relations between trajectory slopes and
ground state masses and are in good overall agreement with experiment.Comment: 33 pages, 5 figures, updated to the extended version published in
JHEP, vector meson bulk potential and metric corrected, comments and
references added, phenomenology and conclusions unchange
Mesons and baryons in a soft-wall holographic approach
We discuss a holographic soft-wall model developed for the description of
mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is
based on an action which describes hadrons with broken conformal invariance and
which incorporates confinement through the presence of a background dilaton
field.Comment: 6 pages, Presented by Valery E. Lyubovitskij at LIGHTCONE 2011, 23 -
27 May, 2011, Dalla
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