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M. A. Braun

Publications and source records attributed to M. A. Braun.

135 records · Page 8Linked to original sources
arXiv1996

The EMC effect at low x in perturbative QCD

The EMC effect is studied in the perturbative QCD hard pomeron approach. In the limit $x\rightarrow 0$ and for a nucleus with a constant density the effect is found to be a function of a single variable which combines its $x$-, $Q$- and $A$-dependence. At large $Q^{2}$ the effect dies out as $\ln Q/Q$. At small but finite $x$ a change in the anomalous dimension leads to a weaker $Q$-dependence, which almost disappears as $x$ grows and the anomalous dimension becomes small. In this approach the nuclear structure function can be expressed directly in terms of the proton one. Calculations of the EMC effect on these lines give results which agree reasonably well to the existing experimental data for $x<0.05$.

hep-ph↗
arXiv1996

On the odderon intercept in perturbative QCD

Arguments are presented for the odderon intercept being exactly equal to unity. A variational method is presented based on a complete system of one-gluon functions. For the odderon, the highest intercept calculated by this method is $1-(3α_{s}/π)\,0.45$.

hep-ph↗
arXiv1996

Fusion of strings and cosmic rays at ultrahigh energies

It is shown that the fusion of strings is a source of particle production in nucleus--nucleus collisions outside the kinematical limits of nucleon--nucleon collisions. This fact, together with another effect of string fusion, the reduction of multiplicities, sheds some light on two of the main problems of ultrahigh energy cosmic rays, the chemical composition and the energy of the most energetic detected cosmic rays.

hep-ph↗
arXiv1995

The photon-photon interaction at low $x$ in the theory of reggeized gluons with a running coupling and $N_{c}\to\infty$

The forward elastic amplitude for scattering of real and weakly virtual photons is studied in the framework of the theory of reggeized gluons, with large $N_{c}$ and a running coupling constant introduced in the manner which preserves the bootstrap condition. Transition from a single to multiple pomeron exchanges is observed as $x$ gets smaller. For very low $x$ the amplitude aquires an eikonal form. The photon structure function reveals a strong violation of scaling: it grows as $Q^{2}$. As a function of $x$ it behaves as $(\ln(1/x)\ln\ln(1/x))^{2}$. Correspondingly the cross-section for physical photons grows with energy as $(\ln s\ln\ln s)^{2}$. Hadronic structure functions and cross-sections are also briefly discussed.

hep-ph↗
arXiv1994

On the Nikolaev-Zakharov-Zoller form for the BFKL pomeron

The equation proposed by N.N.Nikolaev, B.G.Zakharov and V.R.Zoller for the colour dipole cross-section is compared with the BFKL equation for the hard pomeron for the $SU(2)$ colour group. It is demonstrated that for a fixed coupling constant the difference between the two equations is due to a different manner to introduce the gluon mass.

hep-ph↗
arXiv1994

The Intercept of Symmetric Multigluon Configurations in the Variational Approach

To calculate the intercept of the multigluon system in a symmetric spatial configuration a variational method is developed based on a complete system of one-gluon functions. The method is applied to two- and three- gluon cases to compare with the known results. The convergence turns out rather slow. Ways to improve results are discussed.

hep-ph↗
arXiv1994

Pomeron with a Running Coupling Constant: Intercept and Slope

The equation for two reggeized gluons with a running QCD coupling constant, proposed earlier on the basis of the bootstrap condition, is investigated by the variational technique in the vacuum channel. The pomeron intercept and slope are calculated as a function of the infrared cutoff parameter $m$ ("the gluon mass"). The intercept depends weakly on $m$ staying in the region $0.3--0.5$ for values of $m$ in the range $0.3--1.0\ GeV$. The slope goes down from $5.0\ GeV^{-2}$ to $0.08\ GeV^{-2}$ in this range. The optimal value of $m$ seems to lie in the region $0.6--0.8\ GeV$ with the intercept $0.35$ and slope $0.35--0.15$. The character of the pomeron singularity: pole or cut, is also discussed.

hep-ph↗
arXiv1994

Reggeized Gluons with a Running Coupling Constant

The equation for two reggeized gluons in the vacuum channel is generalized to take into account the running QCD coupling constant on the basis of the bootstrap condition for gluon reggeization. Both the gluon trajectory as a function of momentum and the interaction as a function of distance grow like $\log\log$ in the ultraviolet. The resulting equation depends on the confinement region. With a simple parametrization of its influence by an effective gluon mass the pomeron intercept turns out much smaller than for a fixed coupling constant (the BFKL pomeron).

hep-ph↗