21 research outputs found
Identities among relations for higher-dimensional rewriting systems
We generalize the notion of identities among relations, well known for
presentations of groups, to presentations of n-categories by polygraphs. To
each polygraph, we associate a track n-category, generalizing the notion of
crossed module for groups, in order to define the natural system of identities
among relations. We relate the facts that this natural system is finitely
generated and that the polygraph has finite derivation type.Comment: 16 pages, corrected version after review, to appear in S\'eminaires
et Congr\`e
Application of the non-extensive statistical approach to high energy particle collisions
In high-energy collisions the number of the created particles is far less
than the thermodynamic limit, especially in small colliding systems (e.g.
proton-proton). Therefore final-state effects and fluctuations in the
one-particle energy distribution are appreciable. As a consequence the
characterization of identified hadron spectra with the Boltzmann\,--\,Gibbs
thermodynamical approach is insufficient. Instead particle spectra measured in
high-energy collisions can be described very well with Tsallis\,--\,Pareto
distributions, derived from non-extensive thermodynamics. Using the Tsallis
q-entropy formula, a generalization of the Boltzmann\,--\,Gibbs entropy, we
interpret the microscopical physics by analysing the Tsallis and
parameters. In this paper we give a quick overview on these parameters,
analyzing identified hadron spectra from recent years in a wide center of mass
energy range. We demonstrate that the fitted Tsallis-parameters show dependency
on this energy and on the particle species. Our findings are described well by
a QCD inspired evolution ansatz
Systematic analysis of the non-extensive statistical approach in high energy particle collisions-experiment vs. theory
The analysis of high-energy particle collisions is an excellent testbed for
the non-extensive statistical approach. In these reactions we are far from the
thermodynamical limit. In small colliding systems, such as electron-positron or
nuclear collisions, the number of particles is several orders of magnitude
smaller than the Avogadro number; therefore, finite-size and fluctuation
effects strongly influence the final-state one-particle energy distributions.
Due to the simple characterization, the description of the identified hadron
spectra with the Boltzmann-Gibbs thermodynamical approach is insufficient.
These spectra can be described very well with Tsallis-Pareto distributions
instead, derived from non-extensive thermodynamics. Using the -entropy
formula, we interpret the microscopic physics in terms of the Tsallis and
parameters. In this paper we give a view on these parameters, analyzing
identified hadron spectra from recent years in a wide center-of-mass energy
range. We demonstrate that the fitted Tsallis-parameters show dependency on the
center-of-mass energy and particle species (mass). Our findings are described
well by a QCD (Quantum Chromodynamics) inspired parton evolution ansatz. Based
on this comprehensive study, apart from the evolution, both mesonic and
baryonic components found to be non-extensive (), besides the mass ordered
hierarchy observed in the parameter . We also study and compare in details
the theory-obtained parameters for the case of PYTHIA8 Monte Carlo Generator,
perturbative QCD and quark coalescence models.Comment: 21 pages, 12 figures. This is an extended version of our paper at the
36th International Workshop on Bayesian Inference and Maximum Entropy Methods
in Science and Engineering (MaxEnt 2016), 10-15 July 2016, Ghent, Belgiu
The non-Abelian gauge theory of matrix big bangs
We study at the classical and quantum mechanical level the time-dependent
Yang-Mills theory that one obtains via the generalisation of discrete
light-cone quantisation to singular homogeneous plane waves. The non-Abelian
nature of this theory is known to be important for physics near the
singularity, at least as far as the number of degrees of freedom is concerned.
We will show that the quartic interaction is always subleading as one
approaches the singularity and that close enough to t=0 the evolution is driven
by the diverging tachyonic mass term. The evolution towards asymptotically flat
space-time also reveals some surprising features.Comment: 29 pages, 8 eps figures, v2: minor changes, references added: v3
small typographical changes
Sommerfeld effect in heavy quark chemical equilibration
B枚deker D, Laine M. Sommerfeld effect in heavy quark chemical equilibration. Journal of High Energy Physics. 2013;2013(1): 37.The chemical equilibration of heavy quarks in a quark-gluon plasma proceeds via annihilation or pair creation. For temperatures T much below the heavy quark mass M, when kinetically equilibrated heavy quarks move very slowly, the annihilation in the colour singlet channel is enhanced because the quark and antiquark attract each other which increases their probability to meet, whereas the octet contribution is suppressed. This is the so-called Sommerfeld effect. It has not been taken into account in previous calculations of the chemical equilibration rate, which are therefore incomplete for T < alphas^2 M. We compute the leading-order equilibration rate in this regime/ there is a large enhancement in the singlet channel, but the rate is dominated by the octet channel, and therefore the total effect is small. In the course of the computation we demonstrate how operators that represent the annihilation of heavy quarks in non-relativistic QCD can be incorporated into the imaginary-time formalism