1,101 research outputs found
Quark structure of hadrons and high energy collisions
There exists a large field for phenomenological models in which the knowledge
of the structure of hadrons in terms of QCD constituents obtained from deep
inelastic scatterings is related to their behaviour in soft processes. One of
the simplest and oldest models is the additive quark model, with the rules of
quark statistics following from it. Originally, the relations of quark
combinatorics for hadron yields were based on the qualitative description of a
multiparticle production process as a process of the production of
non-correlated quarks and antiquarks followed by their subsequent fusion into
hadrons [20],[21]. As a large amount of new precision measurements appear, and,
on the other hand, our understanding of QCD becomes deeper, a new level of
understanding of quark-gluon physics in the region of soft interactions forces
us to review the relations of quark combinatorics. To do so, an especially good
possibility is provided by the experimental data for hadronic Z^0 decays which
allow us to check the relations of quark combinatorics for a new type of
processes: quark jets in the decays Z^0 -> q\bar{q} -> hadrons [32].Comment: 55 pages, 23 figure
Necessary Conditions for K/2 Degrees of Freedom
Stotz et al., 2016, reported a sufficient (injectivity) condition for each
user in a K-user single-antenna constant interference channel to achieve 1/2
degree of freedom. The present paper proves that this condition is necessary as
well and hence provides an equivalence characterization of interference channel
matrices allowing full degrees of freedom
New form of matter at CERN SPS: Quark Matter but not Quark Gluon Plasma
I argue that a new form of matter is indeed seen in Pb+Pb collisions at CERN
SPS. However, this Quark Matter (QM) is different from the theoretically
predicted Quark Gluon Plasma (QGP) because its effective degrees of freedom
seem to be the massive (dressed) constituent quarks instead of almost massless
quarks and gluons. The equation of state of QM is hard,the time of its
rehadronization is short, while the equation of state of a QGP is soft and the
time of its rehadronization is long. Other similarities and differences are
also summarized.Comment: Invited review talk at the IX International Workshop on Multiparticle
Production Torino 2000, full version, 18 pages, 9 figures, uses espcrc2.st
Recommended from our members
Entropy bounds on abelian groups and the ruzsa divergence
Over the past few years, a family of interesting new inequalities for the
entropies of sums and differences of random variables has been developed by
Ruzsa, Tao and others, motivated by analogous results in additive
combinatorics. The present work extends these earlier results to the case of
random variables taking values in or, more generally, in
arbitrary locally compact and Polish abelian groups. We isolate and study a key
quantity, the Ruzsa divergence between two probability distributions, and we
show that its properties can be used to extend the earlier inequalities to the
present general setting. The new results established include several variations
on the theme that the entropies of the sum and the difference of two
independent random variables severely constrain each other. Although the
setting is quite general, the result are already of interest (and new) for
random vectors in . In that special case, quantitative bounds are
provided for the stability of the equality conditions in the entropy power
inequality; a reverse entropy power inequality for log-concave random vectors
is proved; an information-theoretic analog of the Rogers-Shephard inequality
for convex bodies is established; and it is observed that some of these results
lead to new inequalities for the determinants of positive-definite matrices.
Moreover, by considering the multiplicative subgroups of the complex plane, one
obtains new inequalities for the differential entropies of products and ratios
of nonzero, complex-valued random variables
A discrete history of the Lorentzian path integral
In these lecture notes, I describe the motivation behind a recent formulation
of a non-perturbative gravitational path integral for Lorentzian (instead of
the usual Euclidean) space-times, and give a pedagogical introduction to its
main features. At the regularized, discrete level this approach solves the
problems of (i) having a well-defined Wick rotation, (ii) possessing a
coordinate-invariant cutoff, and (iii) leading to_convergent_ sums over
geometries. Although little is known as yet about the existence and nature of
an underlying continuum theory of quantum gravity in four dimensions, there are
already a number of beautiful results in d=2 and d=3 where continuum limits
have been found. They include an explicit example of the inequivalence of the
Euclidean and Lorentzian path integrals, a non-perturbative mechanism for the
cancellation of the conformal factor, and the discovery that causality can act
as an effective regulator of quantum geometry.Comment: 38 pages, 16 figures, typos corrected, some comments and references
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Learning effective amino acid interactions through iterative stochastic techniques
The prediction of the three-dimensional structures of the native state of
proteins from the sequences of their amino acids is one of the most important
challenges in molecular biology. An essential ingredient to solve this problem
within coarse-grained models is the task of deducing effective interaction
potentials between the amino acids. Over the years several techniques have been
developed to extract potentials that are able to discriminate satisfactorily
between the native and non-native folds of a pre-assigned protein sequence. In
general, when these potentials are used in actual dynamical folding
simulations, they lead to a drift of the native structure outside the
quasi-native basin. In this study, we present and validate an approach to
overcome this difficulty. By exploiting several numerical and analytical tools
we set up a rigorous iterative scheme to extract potentials satisfying a
pre-requisite of any viable potential: the stabilization of proteins within
their native basin (less than 3-4 \AA cRMS). The scheme is flexible and is
demonstrated to be applicable to a variety of parametrizations of the energy
function and provides, in each case, the optimal potentials.Comment: Revtex 17 pages, 10 eps figures. Proteins: Structure, Function and
Genetics (in press
A Hexagon Model for 3D Lorentzian Quantum Cosmology
We formulate a dynamically triangulated model of three-dimensional Lorentzian
quantum gravity whose spatial sections are flat two-tori. It is shown that the
combinatorics involved in evaluating the one-step propagator (the transfer
matrix) is that of a set of vicious walkers on a two-dimensional lattice with
periodic boundary conditions and that the entropy of the model scales
exponentially with the volume. We also give explicit expressions for the
Teichm\"uller parameters of the spatial slices in terms of the discrete
parameters of the 3d triangulations, and reexpress the discretized action in
terms of them. The relative simplicity and explicitness of this model make it
ideally suited for an analytic study of the conformal-factor cancellation
observed previously in Lorentzian dynamical triangulations and of its relation
to alternative, reduced phase space quantizations of 3d gravity.Comment: 34 pages, 20 figures, some clarifying remarks added, final version to
appear in Phys Rev
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