896 research outputs found
Knowledge management challenges in corporate venturing and technological capability building through radical innovations
radical innovation, technological capability, corporate venturing, knowledge management
Sideband cooling while preserving coherences in the nuclear spin state in group-II-like atoms
We propose a method for laser cooling group-II-like atoms without changing
the quantum state of their nuclear spins, thus preserving coherences that are
usually destroyed by optical pumping. As group-II-like atoms have a
closed-shell ground state, nuclear spin and electronic degrees of freedom are
decoupled, allowing for independent manipulation. The hyperfine interaction
that couples these degrees of freedom in excited states can be suppressed
through the application of external magnetic fields. Our protocol employs
resolved-sideband cooling on the forbidden clock transition, , with quenching via coupling to the rapidly decaying state,
deep in the Paschen-Back regime. This makes it possible to laser cool neutral
atomic qubits without destroying the quantum information stored in their
nuclear spins, as shown in two examples, Yb and Sr.Comment: 4 pages, 3 figures v4: minor changes in text, changes in the
references, published versio
Weyl-van-der-Waerden formalism for helicity amplitudes of massive particles
The Weyl-van-der-Waerden spinor technique for calculating helicity amplitudes
of massive and massless particles is presented in a form that is particularly
well suited to a direct implementation in computer algebra. Moreover, we
explain how to exploit discrete symmetries and how to avoid unphysical poles in
amplitudes in practice. The efficiency of the formalism is demonstrated by
giving explicit compact results for the helicity amplitudes of the processes
gamma gamma -> f fbar, f fbar -> gamma gamma gamma, mu^- mu^+ -> f fbar gamma.Comment: 24 pages, late
Heavy Top Quark Searches in the Di-Lepton Mode at the Tevatron
We present the results of a detailed study of the effects of -tagging on
the heavy top-quark signal and backgrounds for the modes of the di-lepton plus
two high transverse energy jets at the Fermilab Tevatron. The general
characteristics of the heavy top-quark signal events are also discussed so that
a comparison can be made between -tagging and imposing stringent kinematical
cuts to eliminate backgrounds.Comment: uses PHYZZX and TABLES macros, 10 pages, four figures not included
(available by request), FERMILAB-Pub-93/105-
Multiphoton Production at High Energies in the Standard Model I
We examine multiphoton production in the electroweak sector of the Standard
Model in the high energy limit using the equivalence theorem in combination
with spinor helicity techniques. We obtain recursion relations for currents
consisting of a charged scalar, spinor, or vector line that radiates
photons. Closed form solutions to these recursion relations for arbitrary
are presented for the cases of like-helicity and one unlike-helicity photon
production. We apply the currents singly and in pairs to obtain amplitudes for
processes involving the production of photons with up to two unlike
helicities from a pair of charged particles. The replacement of one or more
photons by transversely polarized Z$-bosons is also discussed.Comment: 75 pages, CLNS 91/111
Amplitudes With Different Helicity Configurations Of Noncommutative QED
The amplitudes of purely photonic and photon{2-fermion processes of non-
commutative QED (NCQED) are derived for different helicity configurations of
photons. The basic ingredient is the NCQED counterpart of Yang-Mills recursion
relations by means of Berends and Giele. The explicit solutions of recursion
relations for NCQED photonic processes with special helicity configurations are
presented.Comment: 23 pages, 2 figure
Charge asymmetry in hadroproduction of heavy quarks
A sizeable difference in the differential production cross section of top and
antitop quarks, respectively, is predicted for hadronically produced heavy
quarks. It is of order and arises from the interference between
charge odd and even amplitudes respectively. For the TEVATRON it amounts to
approximately 5-10% in the region where the cross section is large and could
therefore be measured in the next round of experiments. At the LHC the
asymmetry can be studied by selecting appropriately chosen kinematical regions.Comment: LaTeX, 5pp, 5 figures, uses revtex. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ Final version as
published in Phys.Rev.Let
Local Interactions of Higher-Spin Potentials That are Gauge Invariant in Linear Approximation
We study connected Wightman functions of conserved currents, each of
which is formed from a scalar field and has even spin . The UV
divergence of this vertex function is regularized by the analytic continuation
in the space dimension . We evaluate the residue
of only, which is a local interaction Lagrangian density and
gauge invariant in linearComment: Talk given at Group XXVII Yerevan, Armenia, August 13-29, 2008, v.2
published in Yadernaya Fizika 73 (2010) 518-52
On the Cause of the MidâPleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to âŒ100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
On the Cause of the Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to âŒ100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
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