204 research outputs found
The NNLO non-singlet QCD analysis of parton distributions based on Bernstein polynomials
A non-singlet QCD analysis of the structure function up to NNLO is
performed based on the Bernstein polynomials approach. We use recently
calculated NNLO anomalous dimension coefficients for the moments of the
structure function in scattering. In the fitting procedure, Bernstein
polynomial method is used to construct experimental moments from the
data of the CCFR collaboration in the region of which is inaccessible
experimentally. We also consider Bernstein averages to obtain some unknown
parameters which exist in the valence quark densities in a wide range of
and . The results of valence quark distributions up to NNLO are in good
agreement with the available theoretical models. In the analysis we determined
the QCD-scale MeV (LO), 259 MeV (NLO)
and 230 MeV (NNLO), corresponding to LO,
NLO and NNLO. We compare our
results for the QCD scale and the with those obtained from
deep inelastic scattering processes.Comment: 20 pages, 7 figures, published in JHE
Asymptotic high energy behavior of the deeply virtual Compton scattering amplitude
We compute the deeply virtual Compton scattering (DVCS) amplitude for forward
and backward scattering in the asymptotic limit. Since this calculation does
not assume ordering of the transverse momenta, it includes important
logarithmic contributions that are beyond those summed by the DGLAP evolution.
These contributions lead to a power-like behavior for the forward DVCS
amplitude.Comment: Latex, 22 pages, 5 Figures; references enhanced; typos correcte
On the Resummation of the epe^+e^-$ Annihilation
The resummation of the non-singlet contributions is
performed for initial state QED corrections. As examples, the effect of the
resummation on neutral-current deep-inelastic scattering and the scattering cross section near the -peak is
investigated.Comment: 11 pages Latex, including 3 eps-figure
Parton distribution functions from the precise NNLO QCD fit
We report the parton distribution functions (PDFs) determined from the NNLO
QCD analysis of the world inclusive DIS data with account of the precise NNLO
QCD corrections to the evolution equations kernel. The value of strong coupling
constant \alpha_s^{NNLO}(M_Z)=0.1141(14), in fair agreement with one obtained
using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate
bosons rates calculated in the NNLO using obtained PDFs are in agreement to the
latest Run II results.Comment: 8 pages, LATEX, 2 figures (EPS
Supersymmetric Effects in Parity-Violating Deep Inelastic Electron-Nucleus Scattering
We compute the supersymmetric (SUSY) corrections to the parity-violating,
deep inelastic electron-deuteron asymmetry. Working with the Minimal
Supersymmetric Standard Model (MSSM) we consider two cases: R parity conserving
and R parity-violating. Under these scenarios, we compare the SUSY effects with
those entering other parity-violating observables. For both cases of the MSSM,
we find that the magnitude of the SUSY corrections can be as large as about 1%
and that they are strongly correlated with the effects on other
parity-violating observables. A comparison of various low-energy
parity-violating observables thus provides a potentially interesting probe of
SUSY.Comment: 12 pages, 5 figure
Mathematics for structure functions
We show some of the mathematics that is being developed for the computation
of deep inelastic structure functions to three loops. These include harmonic
sums, harmonic polylogarithms and a class of difference equations that can be
solved with the use of harmonic sums.Comment: 6 pages LaTeX, uses axodraw.sty and npb.sty (included
High precision fundamental constants at the TeV scale
This report summarizes the proceedings of the 2014 Mainz Institute for
Theoretical Physics (MITP) scientific program on "High precision fundamental
constants at the TeV scale". The two outstanding parameters in the Standard
Model dealt with during the MITP scientific program are the strong coupling
constant and the top-quark mass . Lacking knowledge on the
value of those fundamental constants is often the limiting factor in the
accuracy of theoretical predictions. The current status on and
has been reviewed and directions for future research have been identified.Comment: 57 pages, 24 figures, pdflate
Unity of elementary particles and forces for the third family
We propose a non-supersymmetric SU(5) model in which only the third family of
fermions are unified. The model remedies the non-unification of the three
Standard Model couplings in non-supersymmetric SU(5). It also provides a
mechanism for baryon number violation which is needed for the baryon asymmetry
of the Universe and is not present in the Standard Model. Current experimental
constraints on the leptoquark gauge bosons, mediating such baryon and lepton
violating interactions in our model, allow their masses to be at the TeV scale.
These can be searched for as a (b\tau) or (tt) resonance at the Large Hadron
Collider as predicted in our model.Comment: Title changed, some changes in text and figures. Published in Phys.
Lett.
A new approach to calculate the gluon polarization
We derive the Leading-Order master equation to extract the polarized gluon
distribution G(x;Q^2) = x \deltag(x;Q^2) from polarized proton structure
function, g1p(x;Q^2). By using a Laplace-transform technique, we solve the
master equation and derive the polarized gluon distribution inside the proton.
The test of accuracy which are based on our calculations with two different
methods confirms that we achieve to the correct solution for the polarized
gluon distribution. We show that accurate experimental knowledge of g1p(x;Q^2)
in a region of Bjorken x and Q^2, is all that is needed to determine the
polarized gluon distribution in that region. Therefore, to determine the gluon
polarization \deltag /g,we only need to have accurate experimental data on
un-polarized and polarized structure functions (F2p (x;Q^2) and g1p(x;Q^2)).Comment: 12 pages, 5 figure
Infrared safety of impact factors for colourless particle interactions
We demonstrate, to next-to-leading order accuracy, the cancellation of the
infrared singularities in the impact factors which arise in the QCD description
of high energy processes A + B -> A' + B' of colourless particles. We study the
example where A is a virtual photon in detail, but show that the result is true
in general.Comment: 31 pages latex including 10 figure
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