780 research outputs found
Looking for anomalous gamma-gamma-H and Z-gamma-H couplings at future linear collider
We consider the possibility of studying anomalous contributions to the
gamma-gamma-H and Z-gamma-H vertices through the process e-gamma--> e-H at
future e-gamma linear colliders, with Sqrt(S)=500-1500 GeV. We make a model
independent analysis based on SU(2)xU(1) invariant effective operators of dim=6
added to the standard model lagrangian. We consider a light Higgs boson (mostly
decaying in bar(b)-b pairs), and include all the relevant backgrounds. Initial
e-beam polarization effects are also analyzed. We find that the process
e-gamma--> e-H provides an excellent opportunity to strongly constrain both the
CP-even and the CP-odd anomalous contributions to the gamma-gamma-H and
Z-gamma-H vertices.Comment: LaTeX, 33 pages, 16 eps figures, extended section
Simplification of Flavour Combinatorics in the Evaluation of Hadronic Processes
A serious computational problem in the evaluation of hadronic collision
processes is connected with the large number of partonic subprocesses included
in the calculation. These are from the quark and gluon content of the initial
hadrons, and from CKM quark mixing. For example, there are 180 subprocesses
which contribute to the +2jets process, and 292 subprocesses in +3jets
production at the LHC, even when quarks from only the first two generations are
taken into account.
We propose a simple modification of the rules for evaluation of cross
sections and distributions, which avoids multiplication of channels from the
mixture of quark states. The method is based on a unitary rotation of down
quarks, thus, transporting the mixing matrix elements from vertices of Feynman
diagrams to the parton distribution functions (PDF). As a result, one can
calculate cross sections with significantly fewer subprocesses. For the example
mentioned above, with the new rules, one need evaluate only 21 and 33
subprocesses respectively. The matrix elements of the subprocesses are
calculated without quark mixing but with a modified PDF convolution which
depends on the quark mixing angle, and on the topologies of gauge invariant
classes of diagrams. The proposed method has been incorporated into the CompHEP
program and checked with various examples.Comment: 10 pages (standard LaTeX code), 3 figures, 2 table
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
Branching Fraction Measurements of the SM Higgs with a Mass of 160 GeV at Future Linear \ee Colliders
Assuming an integrated luminosity of 500 fb and a center-of-mass
energy of 350 GeV, we examine the prospects for measuring branching fractions
of a Standard Model-like Higgs boson with a mass of 160 GeV at the future
linear \ee collider TESLA when the Higgs is produced via the Higgsstrahlung
mechanism, \ee \pfr HZ. We study in detail the precisions achievable for the
branching fractions of the Higgs into WW, ZZ and \bb. However, the
measurement of BF(H \pfr \gaga) remains a great challence. Combined with the
expected error for the inclusive Higgsstrahlung production rate the uncertainty
for the total width of the Higgs is estimated.Comment: 17 pages Latex, including 7 figure
Non-Universality of the Specific Heat in Glass Forming Systems
We present new simulation results for the specific heat in a classical model
of a binary mixture glass-former in two dimensions. We show that in addition to
the formerly observed specific heat peak there is a second peak at lower
temperatures which was not observable in earlier simulations. This is a
surprise, as most texts on the glass transition expect a single specific heat
peak. We explain the physics of the two specific heat peaks by the
micro-melting of two types of clusters. While this physics is easily
accessible, the consequences are that one should not expect any universality in
the temperature dependence of the specific heat in glass formers
Seasonal and interannual variability of the water exchange in the Turkish Straits System estimated by modelling
A chain of simple linked models is used to simulate the seasonal and interannual variability of the Turkish Straits System. This chain includes two-layer hydraulic models of the Bosphorus and Dardanelles straits simulating the exchange in terms of level and density difference along each strait, and a one-dimensional area averaged layered model of the Marmara Sea. The chain of models is complemented also by the similar layered model of the Black Sea proper and by a one-layer Azov Sea model with the Kerch Strait. This linked chain of models is used to study the seasonal and interannual variability of the system in the period 1970-2009. The salinity of the Black Sea water flowing into the Aegean Sea increases by approximately 1.7 times through entrainment from the lower layer. The flow entering into the lower layer of the Dardanelles Strait from the Aegean Sea is reduced by nearly 80% when it reaches the Black Sea. In the seasonal scale, a maximal transport in the upper layer and minimal transport in the bottom layer are during winter/spring for the Bosphorus and in spring for the Dardanelles Strait, whereas minimal transport in upper layer and maximal undercurrent are during the summer for the Bosphorus Strait and autumn for the Dardanelles Strait. The increase of freshwater flux into the Black Sea in interannual time scales (41 m3s-1 per year) is accompanied by a more than twofold growth of the Dardanelles outflow to the North Aegean (102 m3s-1 per year)
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