369 research outputs found
A Gribov equation for the photon Green's function
We present a derivation of the Gribov equation for the gluon/photon Green's
function D(q). Our derivation is based on the second derivative of the
gauge-invariant quantity Tr ln D(q), which we interpret as the gauge-boson
`self-loop'. By considering the higher-order corrections to this quantity, we
are able to obtain a Gribov equation which sums the logarithmically enhanced
corrections. By solving this equation, we obtain the non-perturbative running
coupling in both QCD and QED. In the case of QCD, alpha_S has a singularity in
the space-like region corresponding to super-criticality, which is argued to be
resolved in Gribov's light-quark confinement scenario. For the QED coupling in
the UV limit, we obtain a \propto Q^2 behaviour for space-like Q^2=-q^2. This
implies the decoupling of the photon and an NJLVL-type effective theory in the
UV limit.Comment: 12 pages, 5 figures; version to be published in Eur. Phys. J.
Production of electroweak bosons in e+e- annihilation at high energies
Production of electroweak bosons in e+e- annihilation into quarks and into
leptons at energies much greater than 100 Gev is considered. We account for
double-logarithmic contributions to all orders in electroweak couplings. It is
assumed that the bosons are emitted in the multi-Regge kinematics. The explicit
expressions for the scattering amplitudes of the process are obtained. It is
shown that the cross sections of the photon and Z production have the identical
energy dependence and asymptotically their ratio depends only on the Weinberg
angle whereas the energy dependence of the cross section of the W production is
suppressed by factor s^{-0.4} compared to them.Comment: Revtex4, 16 pages, 7 figures, 2 table
Higgs and Top Quark Masses in the Standard Model without Elementary Higgs Boson
In this short note I present a simple calculation of the top quark and Higgs
masses, based on the idea that in the standard model without elementary Higgs,
the fact that the coupling becomes of the order of unity at the Landau
scale leads to spontaneous symmetry breaking and generation of
masses.Comment: 8 pages ps-file, Preprint University of Bonn, TK-94-11 (LaTeX file
using pictex-macros available on request
Nuclear effects in at small in deep inelastic scattering on Li and He
We suggest to use polarized nuclear targets of Li and He to study
nuclear effects in the spin dependent structure functions .
These effects are expected to be enhanced by a factor of two as compared to the
unpolarized targets.
We predict a significant dependence at of due to nuclear shadowing and nuclear
enhancement. The effect of nuclear shadowing at is of an
order of 16% for and 10% for
. By imposing the requirement that
the Bjorken sum rule is satisfied we model the effect of enhancement.
We find the effect of enhancement at to be of an
order of for and
for , if enhancement
occupies the region (). We predict
a 2% effect in the difference of the scattering cross sections of deep
inelastic scattering of an unpolarized projectile off Li with =3/2
and =1/2. We also show explicitly that the many-nucleon description of
deep inelastic scattering off Li becomes invalid in the enhancement region
.Comment: 29 pages, 5 figures, RevTe
EPS09 - a New Generation of NLO and LO Nuclear Parton Distribution Functions
We present a next-to-leading order (NLO) global DGLAP analysis of nuclear
parton distribution functions (nPDFs) and their uncertainties. Carrying out an
NLO nPDF analysis for the first time with three different types of experimental
input -- deep inelastic +A scattering, Drell-Yan dilepton production in
p+ collisions, and inclusive pion production in d+Au and p+p collisions at
RHIC -- we find that these data can well be described in a conventional
collinear factorization framework. Although the pion production has not been
traditionally included in the global analyses, we find that the shape of the
nuclear modification factor of the pion -spectrum at
midrapidity retains sensitivity to the gluon distributions, providing evidence
for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method
to quantify the nPDF uncertainties which originate from the uncertainties in
the data. In this method the sensitivity of to the variations of the
fitting parameters is mapped out to orthogonal error sets which provide a
user-friendly way to calculate how the nPDF uncertainties propagate to any
factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the
corresponding error sets are collected in our new release called {\ttfamily
EPS09}. These results should find applications in precision analyses of the
signatures and properties of QCD matter at the LHC and RHIC.Comment: 34 pages, 16 figures. The version accepted for publicatio
Diffractive Processes at the LHC
We consider diffractive processes which can be measured at the LHC. Analysis
of diffractive events will give unique information about the high energy
asymptotics of hadron scattering. In semihard diffraction one may study the
partonic structure of the Pomeron. Central Exclusive Diffractive production
provides a possibility to investigate the new particles (Higgs bosons, SUSY
particles,...) in an exceptionally clean environment.Comment: 12 pages, To be published in the Proc. of the Gribov-75 Memorial
Workshop, Budapest, May 200
Electroweak 2 -> 2 amplitudes for electron-positron annihilation at TeV energies
The non-radiative scattering amplitudes for electron-positron annihilation
into quark and lepton pairs in the TeV energy range are calculated in the
double-logarithmic approximation. The expressions for the amplitudes are
obtained using infrared evolution equations with different cut-offs for virtual
photons and for W and Z bosons, and compared with previous results obtained
with an universal cut-off.Comment: Revtex4, 17 pages, 7 figures. Some minor changes made, more refs
adde
Neutralino spectrum in top-down models of UHECR
We calculate the cosmic ray spectrum of ultra high energy neutralinos that
one should expect provided that the observed ultra high energy cosmic rays are
produced by the decay of superheavy particles X, M_X>10^{12} GeV, in
supersymmetric models. Our calculation uses an extended DGLAP formalism.
Forthcoming cosmic ray observatories should be able to detect these
neutralinos.Comment: 10 pages, revtex, 3 eps figures. Difference between the present work
and Montecarlo simulations clarifie
Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches
We use several diverse parameterizations of diffractive parton distributions,
extracted in leading twist QCD analyses of the HERA diffractive deep inelastic
scattering (DIS) data, to make predictions for leading twist nuclear shadowing
of nuclear quark and gluon distributions in DIS on nuclei. We find that the
HERA diffractive data are sufficiently precise to allow us to predict large
nuclear shadowing for gluons and quarks, unambiguously. We performed detailed
studies of nuclear shadowing for up and charm sea quarks and gluons within
several scenarios of shadowing and diffractive slopes, as well as at central
impact parameters. We compare these leading twist results with those obtained
from the eikonal approach to nuclear shadowing (which is based on a very
different space-time picture) and observe sharply contrasting predictions for
the size and Q^2-dependence of nuclear shadowing. The most striking differences
arise for the interaction of small dipoles with nuclei, in particular for the
longitudinal structure function F_{L}^{A}.Comment: 43 pages, 16 figures, requires JHEP style fil
Quarkonium from the Fifth Dimension
Adding fundamental matter of mass m_Q to N=4 Yang Mills theory, we study
quarkonium, and "generalized quarkonium" containing light adjoint particles. At
large 't Hooft coupling the states of spin<=1 are anomalously light (Kruczenski
et al., hep-th/0304032). We examine their form factors, and show these hadrons
are unlike any known in QCD. By a traditional yardstick they appear infinite in
size (as with strings in flat space) but we show that this is a failure of the
yardstick. All of the hadrons are actually of finite size ~ \sqrt{g^2N}/m_Q,
regardless of their radial excitation level and of how many valence adjoint
particles they contain. Certain form factors for spin-1 quarkonia vanish in the
large-g^2N limit; thus these hadrons resemble neither the observed J/Psi
quarkonium states nor rho mesons.Comment: 57 pages, LaTeX, 5 figure
- …