1,363 research outputs found
Heavy quarkonium production: Nontrivial transition from pA to AA collisions
Two novel QCD effects, double color filtering and mutual boosting of the
saturation scales in colliding nuclei, affect the transparency of the nuclei
for quark dipoles in comparison with proton-nucleus collisions. The former
effect increases the survival probability of the dipoles, since color filtering
in one nucleus makes the other one more transparent. The second effect acts in
the opposite direction and is stronger, it makes the colliding nuclei more
opaque than in the case of pA collisions. As a result of parton saturation in
nuclei the effective scale is shifted upwards, what leads to an increase of the
gluon density at small x. This in turn leads to a stronger transverse momentum
broadening in AA compared with pA collisions, i.e. to an additional growth of
the saturation momentum. Such a mutual boosting leads to a system of
reciprocity equations, which result in a saturation scale, a few times higher
in AA than in pA collisions at the energies of LHC. Since the dipole cross
section is proportional to the saturation momentum squared, the nuclei become
much more opaque for dipoles in AA than in pA collisions. For the same reason
gluon shadowing turns out to be boosted to a larger magnitude compared with the
product of the gluon shadowing factors in each of the colliding nuclei. All
these effects make it more difficult to establish a baseline for anomalous
J/Psi suppression in heavy ion collisions at high energies.Comment: 10 pages 8 figures. The accuracy of calculations is improve
Democracia Deliberativa, una oportunidad para la emancipación política
Con este artículo queremos mostrar que si bien los modelos democráticos liberal y republicano pretenden defender la libertad, y la igualdad de los hombres, sus prácticas generan gran marginalidad. Aunque desde el siglo XX se ha intentado corregir la marginalidad que generan, tal como se observa en los esfuerzos por mostrar que tanto liberalismo como republicanismo no son modelos tajantemente opuesto, reflexión desde la cual se ha propuesto un tercer modelo; Democracia Deliberativa, ese esfuerzo aún no logra su cometido. De hecho en las críticas a este tercer modelo se observa que mientras se siga exigiendo condiciones de universalidad, especialmente de la razón como parámetro universal de argumentación, seguirá existiendo marginalidad, y en consecuencia necesidad de emancipación.In this article we aim show how democratic models; liberalism and republicanism are source of marginality even if they want to promote freedom and equality. In fact, this happened because their practices produce. In the last two centuries philosophers has tried to correct this source of marginality but until today, as Habermas shows with his article Religión in the public sphere, democracy still produces marginality, for instance when it think in reason as universal point of comprehension
Algunas de las exigencias de la crítica a la Filosofía Política
En esta comunicación se trata de develar la reducción de la función crítica a la función normativa en la que incurren Gerring y Yeznowitz en el artículo “A Normative Turn in Political Science?” (Gerring y Yeznowitz, 2006). A partir del debate entre las pretensiones positivistas de la ciencia política, y la defensa de una propuesta de corte normativo de la filosofía política en el artículo “A Normative Turn in Political Science?” se pueden infieren elementos que hacen parte de una tercera función, la función crítica de la filosofía política, y que los autores confunden con la función normativa. Esta reducción nos permitirá reflexionar acerca de una tarea de la filosofía política que parece olvidada, la crítica
Quenching of high-pT hadrons: Energy Loss vs Color Transparency
High-pT hadrons produced in hard collisions and detected inclusively bear
peculiar features: (i) they originate from jets whose initial virtuality and
energy are of the same order; (ii) such jets are rare and have a very biased
energy sharing among the particles, namely, the detected hadron carries the
main fraction of the jet energy. The former feature leads to an extremely
intensive gluon radiation and energy dissipation at the early stage of
hadronization, either in vacuum or in a medium. As a result, a leading hadron
must be produced on a short length scale. Evaluation within a model of
perturbative fragmentation confirms the shortness of the production length.
This result is at variance with the unjustified assumption of long production
length, made within the popular energy loss scenario. Thus we conclude that the
main reason of suppression of high-pT hadrons in heavy ion collisions is the
controlled by color transparency attenuation of a high-pT dipole propagating
through the hot medium. Adjusting a single parameter, the transport
coefficient, we describe quite well the data from LHC and RHIC for the
suppression factor R_{AA} as function of pT, collision energy and centrality.
We observe that the complementary effect of initial state interaction causes a
flattening and even fall of R_{AA} at large pT. The azimuthal anisotropy of
hadron production, calculated with no further adjustment, also agrees well with
data at different energies and centralities.Comment: 17 pages, 19 figure
Coulomb's law corrections from a gauge-kinetic mixing
We study the static quantum potential for a gauge theory which includes the
mixing between the familiar photon and a second massive gauge
field living in the so-called hidden-sector . Our discussion is carried
out using the gauge-invariant but path-dependent variables formalism, which is
alternative to the Wilson loop approach. Our results show that the static
potential is a Yukawa correction to the usual static Coulomb potential.
Interestingly, when this calculation is done inside a superconducting box, the
Coulombic piece disappears leading to a screening phase.Comment: 4 page
Black hole radiance, short distances, and TeV gravity
Using a derivation of black hole radiance in terms of two-point functions one
can provide a quantitative estimate of the contribution of short distances to
the spectrum. Thermality is preserved for black holes with .
However, deviations from the Planckian spectrum can be found for mini black
holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: LaTeX, 4 pages, 1 figure. Misprints correcte
Ultra-low-noise supercontinuum generation with a flat near-zero normal dispersion fiber
A pure silica photonic crystal fiber with a group velocity dispersion
() of 4 ps/km at 1.55 m and less than 7 ps/km from 1.32
m to the zero dispersion wavelength (ZDW) 1.80 m was designed and
fabricated. The dispersion of the fiber was measured experimentally and found
to agree with the fiber design, which also provides low loss below 1.83 m
due to eight outer rings with increased hole diameter. The fiber was pumped
with a 1.55 m, 125 fs laser and, at the maximum in-coupled peak power
(P) of 9 kW, a 1.341.82 m low-noise spectrum with a relative
intensity noise below 2.2\% was measured. The numerical modeling agreed very
well with the experiments and showed that P could be increased to 26 kW
before noise from solitons above the ZDW started to influence the spectrum by
pushing high-noise dispersive waves through the spectrum
Form invariance symmetry generates a large set of FRW cosmologies
We show that Einstein's field equations for spatially flat
Friedmann-Robertson-Walker (FRW) space times have a form invariance symmetry
(FIS) realized by the form invariance transformations (FIT) which are indeed
generated by an invertible function of the source energy density. These
transformations act on the Hubble expansion rate, the energy density, and
pressure of the cosmic fluid; likewise such transformations are endowed with a
Lie group structure. Each representation of this group is associated with a
particular fluid and consequently a determined cosmology, so that, the FIS
defines a set of equivalent cosmological models. We focus our seek in the FIT
generated by a linear function because it provides a natural framework to
express the duality and also produces a large sets of cosmologies, starting
from a seed one, in several contexts as for instance in the cases of a perfect
fluid source and a scalar field driven by a potential depending linearly on the
scalar field kinetic energy density.Comment: 11 pages, 3 figures. Accepted for publication in Modern Physics
Letters A (2012
Planar Orthogonal Polynomials As Type I Multiple Orthogonal Polynomials
A recent result of S.-Y. Lee and M. Yang states that the planar orthogonal
polynomials orthogonal with respect to a modified Gaussian measure are also
multiple orthogonal polynomials of type II on a contour in the complex plane.
We show that the same polynomials are also type I orthogonal polynomials on a
contour, provided the exponents in the weight are integer. From this
orthogonality, we derive several equivalent Riemann-Hilbert problems. The proof
is based on the fundamental identity of Lee and Yang, which we establish using
a new technique.Comment: 20 pages, 1 figur
Most Complex Non-Returning Regular Languages
A regular language is non-returning if in the minimal deterministic
finite automaton accepting it there are no transitions into the initial state.
Eom, Han and Jir\'askov\'a derived upper bounds on the state complexity of
boolean operations and Kleene star, and proved that these bounds are tight
using two different binary witnesses. They derived upper bounds for
concatenation and reversal using three different ternary witnesses. These five
witnesses use a total of six different transformations. We show that for each
there exists a ternary witness of state complexity that meets the
bound for reversal and that at least three letters are needed to meet this
bound. Moreover, the restrictions of this witness to binary alphabets meet the
bounds for product, star, and boolean operations. We also derive tight upper
bounds on the state complexity of binary operations that take arguments with
different alphabets. We prove that the maximal syntactic semigroup of a
non-returning language has elements and requires at least
generators. We find the maximal state complexities of atoms of
non-returning languages. Finally, we show that there exists a most complex
non-returning language that meets the bounds for all these complexity measures.Comment: 22 pages, 6 figure
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