556 research outputs found
Charged Higgs Production in the 1 TeV Domain as a Probe of Supersymmetric Models
We consider the production, at future lepton colliders, of charged Higgs
pairs in supersymmetric models. Assuming a relatively light SUSY scenario, and
working in the MSSM, we show that, for c.m. energies in the one TeV range, a
one-loop logarithmic Sudakov expansion that includes an "effective" next-to
subleading order term is adequate to the expected level of experimental
accuracy. We consider then the coefficient of the linear (subleading) SUSY
Sudakov logarithm and the SUSY next to subleading term of the expansion and
show that their dependence on the supersymmetric parameters of the model is
drastically different. In particular the coefficient of the SUSY logarithm is
only dependent on while the next to subleading term depends on a
larger set of SUSY parameters. This would allow to extract from the data
separate informations and tests of the model.Comment: 18 pages and 13 figures e-mail: [email protected]
Sudakov expansions at one loop and beyond for charged scalar and fermion pair production in SUSY models at future Linear Colliders
We consider the high energy behaviour of the amplitudes for pair production
of charged leptons, quarks, Higgs bosons, sleptons, squarks and charginos at
lepton colliders. We give the general expressions of the leading quadratic and
subleading linear logarithms that appear at the one loop level, and derive the
corresponding resummed expansions to \underline{subleading} logarithmic order
accuracy. Under the assumption of a relatively light SUSY scenario and choosing
the MSSM as a specific model, we compare the predictions of the one-loop and of
the resummed expansions at variable energy. We show that the two predictions
are very close in the one TeV regime, but drastically differ in the few ()
TeV range.Comment: 43 pages, 13 Encapsulated PostScript figure
SUSY Scalar Production in the Electroweak Sudakov Regime of Lepton Colliders
We consider the production of SUSY scalar pairs at lepton colliders, for c.m.
energies much larger than the mass of the heaviest SUSY (real or virtual)
particle involved in the process. In that energy regime, we derive the leading
and subleading terms of the electroweak Sudakov logarithms in the MSSM, first
working at one loop with physical states and then resumming to all orders with
asymptotic expansions. We show that the first order of the resummed expression
reproduces the physical one loop approximation, and compute systematically the
possible effects on various observables both at one loop and to all orders. We
discuss the regimes and the processes where the one loop approximation can or
cannot be trusted, working in an energy range between 1 TeV and 4 TeV under a
"light" SUSY mass assumption. As a byproduct of our analysis, we propose a
determination of the MSSM parameter tan(beta) showing how a relative accuracy
of about 25 percent can be easily achieved in the region tan(beta)>14, under
reasonable experimental assumptions.Comment: 35 pages and 15 figures e-mail: [email protected]
A Study Of Phosphorus Adsorption And Desorption Kinetics On Silicon (111) Surfaces
Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) methods were used to characterize the (111) surface of Si wafers before and after the deposition of P2 molecules. Before deposition, the well-known Si(111)-7 LEED pattern was easily obtained by thermal cleaning at 1200 °C. Cleaning was done by electron bombardment in a vacuum chamber with a base pressure of ∼ 10-10 Torr. After cleaning, AES showed that about 10-2 atomic layer of carbon was the only surface contaminant. The sensitivity of our cylindrical AES apparatus for phosphorus was about 10-3 atomic layer. We found that ∼5x10-2 atomic layer of phosphorus deposited on a Si(111) surface caused the fractional order spots to disappear from the LEED pattern, so that a sharp Si(111)-1 pattern remained. The kinetics of phosphorus desorption from the Si(111) surface was investigated with AES and mass spectrometry. P2 was found to be the main desorption procuct. The desorption process obeyed second order kinetics. The activation energy for the desorption of P2 was 68.6 ± 0.8 kcal mole-1 for phosphorus coverages between 0.1 and 0.5 atomic layer. © 1972
Resummation of Yukawa enhanced and subleading Sudakov logarithms in longitudinal gauge boson and Higgs production
Future colliders will probe the electroweak theory at energies much larger
than the gauge boson masses. Large double (DL) and single (SL) logarithmic
virtual electroweak Sudakov corrections lead to significant effects for
observable cross sections. Recently, leading and subleading universal
corrections for external fermions and transverse gauge boson lines were
resummed by employing the infrared evolution equation method. The results were
confirmed at the DL level by explicit two loop calculations with the physical
Standard Model (SM) fields. Also for longitudinal degrees of freedom the
approach was utilized for DL-corrections via the Goldstone boson equivalence
theorem. In all cases, the electroweak Sudakov logarithms exponentiate. In this
paper we extend the same approach to both Yukawa enhanced as well as subleading
Sudakov corrections to longitudinal gauge boson and Higgs production. We use
virtual contributions to splitting functions of the appropriate Goldstone
bosons in the high energy regime and find that all universal subleading terms
exponentiate. The approach is verified by employing a non-Abelian version of
Gribov's factorization theorem and by explicit comparison with existing one
loop calculations. As a side result, we obtain also all top-Yukawa enhanced
subleading logarithms for chiral fermion production at high energies to all
orders. In all cases, the size of the subleading contributions at the two loop
level is non-negligible in the context of precision measurements at future
linear colliders.Comment: 32 pages, 7 figures, uses LaTeX2
The processes in SM and MSSM
We present the results of a complete analysis of the one loop electroweak
corrections to in the Standard (SM) and
the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on
the high energy behaviour of the various helicity amplitudes and the way the
logarithmic structure is generated. The large magnitude of these effects, which
induce striking differences between the SM and MSSM cases at high energies,
offers the possibility of making global tests which could check the consistency
of these models, and even decide whether any additional new physics is
required.Comment: Short version (16 pages and 9 figures) of the paper hep-ph/0207273,
to appear in Phy.Rev.D. e-mail: [email protected]
High energy behaviour of gamma gamma to f f(bar) processes in SM and MSSM
We compute the leading logarithms electroweak contributions to gamma gamma to
f f(bar) processes in SM and MSSM. Several interesting properties are pointed
out, such as the importance of the angular dependent terms, of the Yukawa
terms, and especially of the dependence in the SUSY
contributions. These properties are complementary to those found in e+e- to f
f(bar). These radiative correction effects should be largely observable at
future high energy gamma gamma colliders. Polarized beams would bring
interesting checks of the structure of the one loop corrections. We finally
discuss the need for two-loop calculations and resummation.Comment: 22 pages and 12 figures. e-mail: [email protected]
Master integrals for massive two-loop Bhabha scattering in QED
We present a set of scalar master integrals (MIs) needed for a complete
treatment of massive two-loop corrections to Bhabha scattering in QED,
including integrals with arbitrary fermionic loops. The status of analytical
solutions for the MIs is reviewed and examples of some methods to solve MIs
analytically are worked out in more detail. Analytical results for the pole
terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge
The role of universal and non universal Sudakov logarithms in four fermion processes at TeV energies: the one-loop approximation revisited
We consider the separate effects on four fermion processes, in the TeV energy
range, produced at one loop by Sudakov logarithms of universal and not
universal kind, working in the 't Hooft xi=1 gauge. Summing the various vertex
and box contributions allows to isolate two quite different terms.The first one
is a combination of vertex and box quadratic and linear logarithms that are
partially universal and partially not universal and independent of the
scattering angle theta. The second one is theta-dependent, not universal,
linearly logarithmic and only produced by weak boxes. We show that for several
observables, measurable at future linear e+e- colliders (LC, CLIC), the role of
the latter term is dominant and we discuss the implications of this fact for
what concerns the reliability of a one-loop approximation.Comment: 22 pages and 13 figures; version to appear in Phys.Rev.D. e-mail:
[email protected]
Estudos sobre a nutrição mineral do cafeeiro: XXXVIII. Efeitos da aplicação foliar de doses de sulfato de zinco na produção e na composição mineral das folhas do cafeeiro (Coffea arabica L.) (Nota prévia)
An experiment was carried out with 8 year old coffee plants, Mundo Novo variety, in order to study the effect of various concentrations of zinc sulfate (plus urea), split into different number of foliar applications, on yield and leaf composition. The highest yield, 1647 kg of clean coffee per ha (646 kg above the no zinc treatment) was reached when 9.4 kg of zinc, split into three sprays, was applied. This yield was associated to 21-25 ppm of Zn and with a ratio P/Zn equal to 70-90 in the leaves.Foi conduzido um ensaio de aplicação foliar de sulfato de zinco em cafeeiros de 8 anos de idade, cv. Mundo Novo, localizado em S. Sebastião do Paraíso, MG. A produção máxima foi obtida quando se aplicaram 9,4 kg de sulfato de zinco/ha divididos em três aplicações: 1647kg de café limpo por ha, 646 kg mais que a testemunha sem aplicação de zinco nas folhas. A maior colheita esteve associada com 21-25 ppm de Zn nas folhas e com um quociente P/Zn = 70-90
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