2,112 research outputs found
Heavy quark effects on parton distribution functions in the unpolarized virtual photon up to the next-to-leading order in QCD
We investigate the heavy quark mass effects on the parton distribution
functions in the unpolarized virtual photon up to the next-to-leading order in
QCD. Our formalism is based on the QCD-improved parton model described by the
DGLAP evolution equation as well as on the operator product expansion
supplemented by the mass-independent renormalization group method. We evaluate
the various components of the parton distributions inside the virtual photon
with the massive quark effects, which are included through the initial
condition for the heavy quark distributions, or equivalently from the matrix
element of the heavy quark operators. We discuss some features of our results
for the heavy quark effects and their factorization-scheme dependence.Comment: 16 pages, 16 figures, version to appear in Phys. Rev.
Target Mass Corrections for the Virtual Photon Structure Functions to the Next-to-next-to-leading Order in QCD
We investigate target mass effects in the unpolarized virtual photon
structure functions and in
perturbative QCD for the kinematical region , where
is the mass squared of the probe (target) photon and is
the QCD scale parameter. We obtain the Nachtmann moments for the structure
functions and then, by inverting the moments, we get the expressions in closed
form for up to the next-to-next-to-leading order and
for up to the next-to-leading order, both of which
include the target mass corrections. Numerical analysis exhibits that target
mass effects appear at large and become sizable near , the maximal value of , as the ratio
increases.Comment: 24 pages, LaTeX, 7 eps figures, REVTeX
LOWER EXTREMITY JOINT TORQUE OF TAI CHI GAIT – A PILOT STUDY
INTRODUCTION: Tai Chi is becoming popular among people of all age groups. Although a number of studies have reported the effect of Tai Chi practice on physical fitness [1], the evidence from biomechanical aspect has not been researched sufficiently. To interpret its effect, such as balance and muscle strength, biomechanical information is important. Therefore, the purpose of this study was to obtain information on the biomechanical characteristics of Tai Chi gait (TCG). In this study, TCG was compared to normal walking (NW) to characterize it
Parton Distributions of the Virtual Photon
We propose a generic ansatz for the extension of parton distributions of the
real photon to those of the virtual photon. Alternatives and approximations are
studied that allow closed-form parametrizations.Comment: 1+10 pages, LaTeX2e, 2 eps figures included in file using
filecontents environment
Spin Structure Function of the Virtual Photon Beyond the Leading Order in QCD
Polarized photon structure can be studied in the future polarized
colliding-beam experiments. We investigate the spin-dependent
structure function of the virtual photon , in
perturbative QCD for , where () is the
mass squared of the probe (target) photon. The analysis is performed to
next-to-leading order in QCD. We particularly emphasize the renormalization
scheme independence of the result.The non-leading corrections significantly
modify the leading log result, in particular, at large as well as at small
. We also discuss the non-vanishing first moment sum rule of ,
where corrections are computed.Comment: 39 pages, LaTeX, 6 Postscript Figures, eqsection.sty file include
The corrections to the first moment of the polarized virtual photon structure function
We present the next-to-next-to-leading order () corrections
to the first moment of the polarized virtual photon structure function
in the kinematical region ,
where is the mass squared of the probe (target) photon and
is the QCD scale parameter. In order to evaluate the three-loop-level
photon matrix element of the flavor singlet axial current, we resort to the
Adler-Bardeen theorem for the axial anomaly and we calculate in effect the
two-loop diagrams for the photon matrix element of the gluon operator. The
corrections are found to be about 3% of the sum of the
leading order () andthe next-to-leading order ()
contributions, when and , and the
number of active quark flavors is three to five.Comment: 21 page
A dopaminergic switch for fear to safety transitions
Overcoming aversive emotional memories requires neural systems that detect when fear responses are no longer appropriate so that they can be extinguished. The midbrain ventral tegmental area (VTA) dopamine system has been implicated in reward and more broadly in signaling when a better-than-expected outcome has occurred. This suggests that it may be important in guiding fear to safety transitions. We report that when an expected aversive outcome does not occur, activity in midbrain dopamine neurons is necessary to extinguish behavioral fear responses and engage molecular signaling events in extinction learning circuits. Furthermore, a specific dopamine projection to the nucleus accumbens medial shell is partially responsible for this effect. In contrast, a separate dopamine projection to the medial prefrontal cortex opposes extinction learning. This demonstrates a novel function for the canonical VTA-dopamine reward system and reveals opposing behavioral roles for different dopamine neuron projections in fear extinction learning
Squark Contributions to Photon Structure Functions and Positivity Constraints
Photon structure functions in supersymmetric QCD are investigated in terms of
the parton model where squark contributions are evaluated. We calculate the
eight virtual photon structure functions by taking the discontinuity of the
squark massive one-loop diagrams of the photon-photon forward amplitude. The
model-independent positivity constraints derived from the Cauchy-Schwarz
inequalities are satisfied by the squark parton model calculation and actually
the two equality relations hold for the squark contribution. We also show that
our polarized photon structure function for the real photon leads
to the vanishing 1st moment sum rule, and the constraint is satisfied by the real photon. We also discuss a squark signature
in the structure function .Comment: 24 pages, 14 figures. typos and references corrected, comments added
in section
Target Mass Effects in Polarized Virtual Photon Structure Functions
We study target mass effects in the polarized virtual photon structure
functions , in the kinematic
region , where is the mass squared of
the probe (target) photon. We obtain the expressions for and in closed form by inverting the
Nachtmann moments for the twist-2 and twist-3 operators. Numerical analysis
shows that target mass effects appear at large and become sizable near
, the maximal value of , as the ratio
increases. Target mass effects for the sum rules of and
are also discussed.Comment: 24 pages, LaTeX, 9 eps figure
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