668 research outputs found
Stoponium Search at Photon Linear Collider
In some supersymmetric extensions of the Standard Model fairly light
superpartner of t-quark is predicted, which may form bound states ({\it
stoponiums}) under certain conditions. We study prospects of search for
stoponium at the future Photon Linear Collider. It is found that this machine
could be the best machine for discovery and study of these resonances at some
scenarios of supersymmetric extension of the Standard Model. In particular, if
the decay channel is dominant stoponium could be observed at the beginning
of PLC run with collision energy tuned at the stoponium mass. If this channel
is kinematically closed stoponium could be discovered in ,
and decay channels but higher statistics are needed. Effects of the
stoponium-Higgs mixing and degeneracy are briefly discussed.Comment: 11 pages, 2 figures added, corrections taken into account result in
increasing of signal significanc
A Quality and Cost Approach for Comparison of Small-World Networks
We propose an approach based on analysis of cost-quality tradeoffs for
comparison of efficiency of various algorithms for small-world network
construction. A number of both known in the literature and original algorithms
for complex small-world networks construction are shortly reviewed and
compared. The networks constructed on the basis of these algorithms have basic
structure of 1D regular lattice with additional shortcuts providing the
small-world properties. It is shown that networks proposed in this work have
the best cost-quality ratio in the considered class.Comment: 27 pages, 16 figures, 1 tabl
Strange and charm quark-pair production in strong non-Abelian field
We have investigated strange and charm quark-pair production in the early
stage of heavy ion collisions. Our kinetic model is based on a Wigner function
method for fermion-pair production in strong non-Abelian fields. To describe
the overlap of two colliding heavy ions we have applied the time-dependent
color field with a pulse-like shape. The calculations have been performed in an
SU(2)-color model with finite current quark masses. For strange quark-pair
production the obtained results are close to the Schwinger limit, as we
expected. For charm quark the large inverse temporal width of the field pulse,
instead of the large charm quark mass, determines the efficiency of the
quark-pair production. Thus we do not observe the expected suppression of charm
quark-pair production connecting to the usual Schwinger-formalism, but our
calculation results in a relatively large charm quark yield. This effect
appears in Abelian models as well, demonstrating that particle-pair production
for fast varying non-Abelian gluon field strongly deviates from the Schwinger
limit for charm quark. We display our results on number densities for light,
strange, charm quark-pairs, and different suppression factors as the function
of characteristic time of acting chromo-electric field.Comment: 6 pages, 2 figures; to appear in the proceedings of the International
Conference on Strangeness in Quark matter (SQM2008), Beijing, China, Oct
6-10, 2008; version accepted to J. Phys.
Optimization of symbolic evaluation of helicity amplitudes
We present a method for symbolic evaluation of Feynman amplitudes. We
construct special polarization basis for spinor particles which produces
compact expressions for tensor products of basis spinors.Comment: Standard LaTeX, 6 pages. To appear in the proceedings of the Seventh
International Workshop on Advanced Computing and Analysis Technics in Physics
Research (ACAT2000, Fermilab, October 16-20, 2000
Accretion and outflow activity on the late phases of pre-main-sequence evolution. The case of RZ Piscium
RZ Psc is an isolated high-latitude post-T Tauri star that demonstrates a UX
Ori-type photometric activity. The star shows very weak spectroscopic
signatures of accretion, but at the same time possesses the unusual footprints
of the wind in Na I D lines. In the present work we investigate new
spectroscopic observations of RZ Psc obtained in 2014 during two observation
runs. We found variable blueshifted absorption components (BACs) in lines of
the other alcali metals, K I 7699 \AA\ and Ca II IR triplet. We also confirmed
the presence of a weak emission component in the H line, which allowed
us to estimate the mass accretion rate on the star as Msun yr. We could not reveal any clear periodicity in the
appearance of BACs in sodium lines. Nevertheless, the exact coincidence of the
structure and velocities of the Na I D absorptions observed with the interval
of about one year suggests that such a periodicity should exist
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