49,488 research outputs found
Conservation and persistence of spin currents and their relation to the Lieb-Schulz-Mattis twist operators
Systems with spin-orbit coupling do not conserve "bare" spin current
. A recent proposal for a conserved spin current [J. Shi {\it
et.al} Phys. Rev. Lett. {\bf 96}, 076604 (2006)] does not flow persistently in
equilibrium. We suggest another conserved spin current that may
flow persistently in equilibrium. We give two arguments for the instability of
persistent current of the form : one based on the equations of motions
and another based on a variational construction using Lieb-Schulz-Mattis twist
operators. In the absence of spin-orbit coupling, the three forms of spin
current coincide.Comment: 5 pages; added references, simplified notation, clearer introductio
The impact of the LHCb production cross-section on parton distribution functions and determining the mass of heavy quarks
In this work, the impact of recent measurements of heavy-flavour production
in collisions on parton distribution functions (PDFs) and their
uncertainties is studied. In this regard, the absolute and normalised cross
sections of beauty hadron production measured by LHCb at center-of-mass energy
of 7 TeV and 13 TeV are separately included in the next-to-leading order (NLO)
global QCD analysis together with the measurements of the inclusive and
heavy-flavour production cross sections at HERA. It is illustrated that the
heavy-flavour data of the LHCb experiment impose additional constraints on the
PDFs, especially on the gluon distribution at low partonic fractions of the
proton momentum. One of the most important results of the present analysis is
the significant reduction of the gluon uncertainties in the region less than
that can play a crucial rule in many areas of high energy physics
investigations.Comment: 36 pages, 8 figures, has been accepted for publication in Nuclear
Physics
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