43,721 research outputs found
Physics at high Q^2 and p^2_t: Summary of DIS 2000
We summarize the experimental and theoretical results presented in the
"Physics at the Highest Q^2 and p^2_t" working group at the DIS 2000 Workshop.
High Q^2 and p^2_t processes measured at current and future colliders allow to
improve our knowledge of Standard Model (SM) physics, by providing precise
measurements of the SM parameters and, consequently, consistency checks of the
SM. Moreover, they give information on key quantities for the calculation of
the SM expectations in a yet unexplored domain, such as the parton densities of
the proton or the photon. In addition to these experimental inputs,
higher-order calculations are also needed to obtain precise expectations for SM
processes, which are a key ingredient for the searches for new phenomena in
high Q^2 and p^2_t processes at current and future experiments. The
experimental and theoretical status of SM physics at high Q^2 and p^2_t is
reviewed in the first part of this summary, with the remaining being dedicated
to physics beyond the Standard Model.Comment: 17 pages, 10 figures. Typos correcte
Correlations in nuclear energy recurrence relations
The excitation energies of states belonging to the ground state bands of
heavy even-even nuclei are analysed using recurrence relations. Excellent
agreement with experimental data at the 10 keV level is obtained by taking into
account strong correlations which emerge in the analysis. This implies that the
excitation energies can be written as a polynomial of maximum degree four in
the angular momentum.Comment: 4 pages, 1 figure, 1 table, 9 reference
Classification of the phases of 1D spin chains with commuting Hamiltonians
We consider the class of spin Hamiltonians on a 1D chain with periodic
boundary conditions that are (i) translational invariant, (ii) commuting and
(iii) scale invariant, where by the latter we mean that the ground state
degeneracy is independent of the system size. We correspond a directed graph to
a Hamiltonian of this form and show that the structure of its ground space can
be read from the cycles of the graph. We show that the ground state degeneracy
is the only parameter that distinguishes the phases of these Hamiltonians. Our
main tool in this paper is the idea of Bravyi and Vyalyi (2005) in using the
representation theory of finite dimensional C^*-algebras to study commuting
Hamiltonians.Comment: 8 pages, improved readability, added exampl
Numerical simulations of strong incompressible magnetohydrodynamic turbulence
Magnetised plasma turbulence pervades the universe and is likely to play an
important role in a variety of astrophysical settings. Magnetohydrodynamics
(MHD) provides the simplest theoretical framework in which phenomenological
models for the turbulent dynamics can be built. Numerical simulations of MHD
turbulence are widely used to guide and test the theoretical predictions;
however, simulating MHD turbulence and accurately measuring its scaling
properties is far from straightforward. Computational power limits the
calculations to moderate Reynolds numbers and often simplifying assumptions are
made in order that a wider range of scales can be accessed. After describing
the theoretical predictions and the numerical approaches that are often
employed in studying strong incompressible MHD turbulence, we present the
findings of a series of high-resolution direct numerical simulations. We
discuss the effects that insufficiencies in the computational approach can have
on the solution and its physical interpretation
Role of cross helicity in magnetohydrodynamic turbulence
Strong incompressible three-dimensional magnetohydrodynamic turbulence is
investigated by means of high resolution direct numerical simulations. The
simulations show that the configuration space is characterized by regions of
positive and negative cross-helicity, corresponding to highly aligned or
anti-aligned velocity and magnetic field fluctuations, even when the average
cross-helicity is zero. To elucidate the role of cross-helicity, the spectra
and structure of turbulence are obtained in imbalanced regions where
cross-helicity is non-zero. When averaged over regions of positive and negative
cross-helicity, the result is consistent with the simulations of balanced
turbulence. An analytical explanation for the obtained results is proposed.Comment: 4 pages, 4 figure
Pinworms of the red howler monkey (Alouatta seniculus) in Colombia. Gathering the pieces of the pinworm-primate puzzle
Pinworms of primates are believed to be highly host specific parasites, forming co-evolutionary associations with their hosts. In order to assess the strength and reach of such evolutionary links, we need to have a broad understanding of the pinworm diversity associated with primates. Here, we employed an integrative taxonomic approach to assess pinworm diversity in red howler monkeys in Colombia. Molecular and morphological evidence validate the presence of at least four different species of Trypanoxyuris occurring in red howler monkeys: T. minutus, a widely distributed species, and three new species, T. seunimiii n. sp., T. kemuimae n. sp. and T. kotudoi n. sp. The mitochondrial COI gene and the 28S ribosomal gene were used for phylogenetic assessments through Bayesian inference. The three new species were morphologically distinct and formed reciprocally monophyletic lineages. Further molecular lineage subdivision in T. minutus and T. kotudoi n. sp. without morphological correspondence, suggests the potential scenario for the existence of cryptic species. Phylogenetic relationships imply that the different species of Trypanoxyuris occurring in each howler monkey species were acquired through independent colonization events. On-going efforts to uncover pinworm diversity will allow us to test the degree of host specificity and the co-phylogenetic hypothesis, as well as to further unravel the primate-pinworm evolutionary history puzzle
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