378 research outputs found
Threshold Resummation for Top-Pair Hadroproduction to Next-to-Next-to-Leading Log
We derive the threshold-resummed total cross section for heavy quark
production in hadronic collisions accurate to next-to-next-to-leading
logarithm, employing recent advances on soft anomalous dimension matrices for
massive pair production in the relevant kinematic limit. We also derive the
relation between heavy quark threshold resummations for fixed pair kinematics
and the inclusive cross section. As a check of our results, we have verified
that they reproduce all poles of the color-averaged q\bar{q} -> t\bar{t}
amplitudes at two loops, noting that the latter are insensitive to the
color-antisymmetric terms of the soft anomalous dimension.Comment: 18 pages; Expanded discussion, added references. Results unchanged
Limiting Distributions for Lifetimes in Alternating Renewal Processes
2000 Mathematics Subject Classification: 60K05The spent life time and the residual life time are well investigated characteristics of an ordinary renewal process. In the present paper a generalization of these lifetime processes associated with an alternating renewal process is considered. Limiting distributions are presented in the case of in finite mean renewal periods.The paper is supported by NFSI-Bulgaria, Grant No. MM-1101/2001
Branching Stochastic Processes: Regulation, Regeneration, Estimation, Applications
2000 Mathematics Subject Classification: 60J80.This is a survey of the works of Bulgarian mathematicians in the area of Branching Stochastic Processes
Characterization of nanodimensional Ni-Zn ferrite prepared by mechanochemical and thermal methods.
Nickel zinc ferrite nanoparticles, Ni1−xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8, 1.0), with dimensions below 10 nm have been prepared by combining chemical precipitation with high-energy ball milling. For comparison, their analogues obtained by thermal synthesis have also been studied. Mössbauer spectroscopy, X-ray diffraction, and magnetic measurements are used for the characterization of the obtained materials. X-ray diffraction shows that after 3h of mechanical treatment ferrites containing zinc are formed, while 6h of treatment is needed to obtain NiFe2O4. The magnetic properties of the samples exhibit a strong dependence on the phase composition, particle size and preparation method
On the Bound States in a Non-linear Quantum Field Theory of a Spinor Field with Higher Derivatives
We consider a model of quantum field theory with higher derivatives for a
spinor field with quartic selfinteraction. With the help of the Bethe-Salpeter
equation we study the problem of the two particle bound states in the "chain"
approximation. The existence of a scalar bound state is established.Comment: 14 pages, no figures, LaTe
Total Progeny in a Subcritical Branching Process with two Types of Immigration
2000 Mathematics Subject Classification: 60J80, 60F05We consider subcritical Bellman-Harris branching processes with two types of immigration - one appears whenever the process hits zero state and an other one is in accordance of an independent renewal process. The law of large numbers (LLN) for the total progeny of these processes and Anscombe's type central limit theorem (CLT) for the total number of particles in the cycles completely finished by the moment t are obtained.The paper is supported by NFSI-Bulgaria, Grant No. MM-1101/2001
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Single-jet inclusive rates with exact color at O (αs4)
Next-to-next-to-leading order QCD predictions for single-, double- and even
triple-differential distributions of jet events in proton-proton collisions
have recently been obtained using the NNLOjet framework based on antenna
subtraction. These results are an important input for Parton Distribution
Function fits to hadron-collider data. While these calculations include all of
the partonic channels occurring at this order of the perturbative expansion,
they are based on the leading-color approximation in the case of channels
involving quarks and are only exact in color in the pure-gluon channel. In the
present publication, we verify that the sub-leading color effects in the
single-jet inclusive double-differential cross sections are indeed negligible
as far as phenomenological applications are concerned. This is the first
independent and complete calculation for this observable. We also take the
opportunity to discuss the necessary modifications of the sector-improved
residue subtraction scheme that made this work possible
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