1,720,975 research outputs found
CompHEP - PYTHIA interface: integrated package for the collision events generation based on exact matrix elements
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Single top quark at future hadron colliders: Complete signal and background study
No full textWe perform a detailed theoretical study including decays and jet fragmentation of all the important modes of single top quark production and all the basic background processes at the upgraded Fermilab Tevatron and CERN LHC colliders. Special attention is paid to the complete tree level calculation of the QCD fake background which was not considered in previous studies. An analysis of the various kinematical distributions for the signal and backgrounds allow us to work out a set of cuts for an efficient background suppression and extraction of the signal. It is shown that the signal to background ratio after optimized cuts could reach about 0.4 at the Tevatron and 1 at the LHC. The remaining after cuts signal rate at the LHC for the lepton+jets signature is expected to be about 6.1 pb and will be enough to study single top quark physics even during LHC operation at a low luminosity. ©1999 The American Physical Society.Inst. de Fis. Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 São PauloSkobeltsyn Inst. of Nuclear Physics Moscow State University, 119899 MoscowInst. de Fis. Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 São Paul
Precise test of Higgs boson properties via triple Higgs boson production in vector boson fusion at future colliders
No full textFor certain classes of beyond the standard model theories, including composite Higgs models, the coupling of the Higgs to gauge bosons can be different from the standard model one. In this case, the multiboson production via vector boson fusion (VBF) can be hugely enhanced in comparison to the SM production one due to the lack of cancellation in longitudinal vector boson scattering. Among these processes, triple Higgs boson production in VBF plays a special role - its enhancement is especially spectacular due to the absence of background from transversely polarized vector bosons in the final state. While the rates from pp→jjhhh production in vector boson fusion are too low at the LHC and even at future 33 TeV pp colliders, we have found that the 100 TeV pp future circular collider (FCC) has the unique opportunity to probe the hVV coupling far beyond the LHC sensitivity. We have evaluated the pp→jjhhh rates as a function of deviation from the hVV coupling and have found that the background is much smaller than the signal for observable signal rates. We also found that the 100 TeV pp FCC can probe the hVV coupling up to the permille level, which is far beyond the LHC reach. These results highlight a special role of the hhh VBF production and stress once more the importance of the 100 TeV pp FCC.</p
The action for the (propagating) torsion and the limits on the torsion parameters from present experimental data
No full textStarting from the well established form of the Dirac action coupled to the electromagnetic and torsion field we find that there is some additional softly broken local symmetry associated with torsion. This symmetry fixes the form of divergences of the effective action after the spinor fields are integrated out. Then the requirement of renormalizability fixes the torsion field to be equivalent to some massive pseudovector and its action is fixed with accuracy to the values of coupling constant of torsion-spinor interaction, mass of the torsion and higher derivative terms. Implementing this action into the abelian sector of the Standard Model we establish the upper bounds on the torsion mass and coupling. In our study we used results of present experimental limits on four-fermion contact interaction (LEP, HERA, SLAC, SLD, CCFR) and TEVATRON limits on the cross section of new gauge boson, which could be produced as a resonance at high energy pp̄ collisions. © 1998 Elsevier Science B.V. All rights reserved.Inst. de Fis. Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 São Paolo, S.P.Skobeltsyn Inst. of Nuclear Physics Moscow State University, 119 899 MoscowTomsk State Pedagogical University, 634041 TomskInst. de Fis. Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 São Paolo, S.P
Torsion action and its possible observables
No full textThe methods of effective field theory are used to explore the theoretical and phenomenological aspects of the torsion field. The spinor action coupled to the electromagnetic field and torsion possesses an additional softly broken gauge symmetry. This symmetry enables one to derive the unique form of the torsion action compatible with unitarity and renormalizability. It turns out that the antisymmetric torsion field is equivalent to a massive axial vector field. The introduction of scalars leads to serious problems which are revealed after the calculation of the leading two-loop divergences. Thus the phenomenological aspects of torsion may be studied only for the fermion-torsion systems. In this part of the paper we obtain upper bounds for the torsion parameters using present experimental data on forward-backward Z-pole asymmetries, data on the experimental limits on four-fermion contact interaction (LEP, HERA, SLAC, SLD, CCFR) and also TEVATRON limits on the cross section of a new gauge boson, which could be produced as a resonance at high energy pp collisions. The present experimental data enable one to put limits on the torsion parameters for the various ranges of the torsion mass. We emphasize that for a torsion mass of the order of the Planck mass no independent theory for torsion is possible, and one must directly use string theory. © 1999 Elsevier Science B.V.Instituto de Fisica Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 Sao Paolo, S.P.Skobeltsyn Inst. of Nuclear Physics Moscow State University, 119 899, MoscowTomsk State Pedagogical University, 634041, TomskInstituto de Fisica Teórica Universidade Estadual Paulista, Rua Pamplona 145, 01405-900 Sao Paolo, S.P
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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