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M. A. Braun

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

At least 73 records · Page 4Linked to original sources
arXiv2008

PT Symmetry and Hermithean Hamiltonian in the Local Supercritical Pomeron Model

The local reggeon field theory is studied perturbatively taking advantage of the PT symmetry in the Hamiltonian formulation. In the lowest non trivial order we show that the pomeron interactions renormalize the slope. In the same order we find a non local pair potential acting between pomerons, which has a singular structure. However the analysis of the scattering operator shows that at small coupling constant bound states do not appear so that the two-particle spectrum is not changed.

hep-ph↗
arXiv2008

Loops in the Reggeon model for hA scattering

Contribution of simplest loops is studied in the Local Reggeon Field Theory with a supercritical pomeron in the nuclear matter. It is shown that the latter transforms the supercritical pomeron into the subcritical. Renormalization of the intercept and difficulties related to the fact that the renormalized intercept is complex are discussed. Numerical results with the conventional parameters are reported.

hep-ph↗
arXiv2007

Nucleus-nucleus cross-sections and long-range correlations with a local supercritical pomeron

Nucleus-nucleus scattering is studied in the local Reggeon Field Theory in the quasi-classical approximation with non-eikonal boundary conditions corresponding to the Glauber picture at low energies. Comparison with the commonly used eikonal boundary conditions shows that the new conditions make both the action and nucleus-nucleus total cross-sections lower by $3÷5$ %. They also substantially change the behaviour of the solutions of the equations of motion at low energies. Using expressions for the double inclusive cross-sections derived earlier in the Reggeon Field Theory \cite{CM} long-range rapidity correlations are calculated for the RHIC and LHC energies.

hep-ph↗
arXiv2007

Boundary conditions in the QCD nucleus-nucleus scattering problem

In the framework of the effective field theory for interacting BFKL pomerons, applied to nucleus-nucleus scattering, boundary conditions for the classical field equations are discussed. Correspondence with the QCD diagrams at the boundary rapidities requires pomeron interaction with the participating nuclei to be exponential and non-local. Commonly used 'eikonal' boundary conditions, local and linear in fields, follow in the limit of small QCD pomeron-nucleon coupling. Numerical solution of the classical field equations, which sum all tree diagrams for central gold-gold scattering, demonstrates that corrected boundary conditions lead to substantially different results, as compared to the eikonal conditions studied in earlier publications. A breakdown of projectile-target symmetry for particular solutions discovered earlier in \cite{bom} is found to occur at roughly twice lower rapidity. Most important, due to a high non-linearity of the problem, the found asymmetric solutions are not unique but form a family growing in number with rapidity. The minimal value for the action turns out to be much lower than with the eikonal boundary conditions and saturates at rapidities around 10.

hep-ph↗
arXiv2007

Odderon with a running coupling constant

The running coupling is introduced into the equation for the odderon via the bootstrap relation. It is shown that the previously found odderon state with a maximal intercept, which is constructed from antisymmetric pomeron wave function, continues to exist in the running coupling case. Its intercept is found to remain equal to unity independent of the behaviour assumed for the running coupling at low momenta.

hep-ph↗
arXiv2007

On the long-range correlations in hadron-nucleus collisions

Long-range correlations between multiplicities in different rapidity windows in hadron-nucleus collisions are analyzed. After recalling the standard results in the probabilistic model, we study them in the framework of perturbative QCD. Considering interacting BFKL pomerons in the form of fan diagrams coupled to a dilute projectile, analytic estimates are done for very large rapidities. The correlation strength results weakly depending on energy and centrality or nuclear size, and generically greater than unity. Finally, we turn to the Color Glass Condensate framework. For a saturated projectile and considering the most feasible experimental situation of forward and backward rapidity windows symmetric around the center-of-mass, the resulting correlation strength turns out to be larger than unity and shows a non-monotonic behavior with increasing energy, first increasing and then decreasing to a limiting value. Its behavior with increasing centrality or nuclear size depends on the considered rapidity windows.

hep-ph↗
arXiv2007

Pomeron with a running coupling in the nucleus

The running coupling is introduced into the equation for propagation of the pomeron in the nucleus via the bootstrap relation. The resulting equation coincides with the one obtained in the colour dipole formalism by summing contributions from quark-antiquark loops, with a general choice of the regularization scheme.

hep-ph↗
arXiv2007

The Reggeon $\to$ 2 Reggeons $+$ Particle vertex in the Lipatov effective action formalism

The vertex for gluon emission during the splitting of a reggeized gluon into two is constructed in the framework of Lipatov effective action formalism. Its reduction to a pure transverse form for the diffractive amplitude gives the standard Bartels vertex plus an additional contribution corresponding to the emission from a pointlike splitting vertex. This additional contribution turns out to be given by a longitudinal integral divergent both in the ultraviolet and infrared. A certain specific recipe for this part, including the principal value prescription for the integration, allows to eliminate this unwanted contribution.

hep-ph↗
arXiv2006

On the 'toy model" in the Reggeon field theory

The Reggeon field theory with zero transverse dimensions is studied in the Hamiltonian formulation for both sub-and supercritical pomeron. Mathematical aspects of the model, in particular the scalar products in the space of quantum states, are discussed. Relation to reaction-diffusion processes is derived in absence of pomeron merging. Numerical calculations for different parameters of the models, $α(0)-1=μ$ and the triple pomeron coupling constant $λ$, show that the triple pomeron interaction always makes amplitudes fall with rapidity irrespective of the value of the intercept. The smaller the values of the ratio $λ/μ$ the higher are rapidities $y$ at which this fall starts, so that at small values of $λ$ it begins at asymptotically high rapidities (for $λ/μ<1/4$ the fall is noticeable only at $μy>100$). No visible singularity is seen for the critical pomeron. A perturbative treatment is proposed which may be useful for more realistic models.

hep-ph↗
arXiv2006

Two-jet inclusive cross sections in heavy-ion collisions in the perturbative QCD

In the framework of perturbative QCD, double inclusive cross sections for high $p_t$ parton production in nucleus-nucleus collisions are computed with multiple rescattering taken into account. The induced long-range correlations between numbers of jets at forward and backward rapidities are found to reach $10÷20$% for light nuclei at $\sqrt{s}=200$ GeV/c and to be suppressed for heavy nuclei and LHC energies.

hep-ph↗
arXiv2006

On the inclusive gluon jet production from the triple pomeron vertex in the perturbative QCD

Single and double inclusive cross-sections for gluon jet production from within the triple pomeron vertex are studied in the reggeized gluon technique. It is shown that to satisfy the AGK rules the vertex has to be fully symmetric in all four reggeized gluons which form the two final pomerons. The single inclusive cross-sections are found for different cuttings of the triple pomeron vertex. They sum into the expression obtained by Yu.Kovchegov and K.Tuchin in the colour dipole picture. The found double inclusive cross-sections satisfy the AGK rules.

hep-ph↗
arXiv2006

Rapidity and centrality dependence in the percolating colour strings scenario

In AA collisions fusion and percolation of colour strings is studied at fixed rapidity $y$. Distribution of strings in rapidity is obtained from the observed rapidity spectra in pp collisions. For $y$-dependence of multiplicities in Au-Au collisions good agreement is obtained with the existing experimental data. Predictions for LHC energies coincide with the extrapolation of the data. Agreement with the data of the transverse momentum spectra requires introduction of quenching into the model.

hep-ph↗
arXiv2005

Conformal invariant pomeron interaction in the perurbative QCD with large N_c

An effective non-local quantum field theory is constructed, which describes interaction of pomerons in the high-coloured QCD. The theory includes both splitting and merging triple pomeron vertexes and diagrams with pomeronic loops. The Schwinger-Dyson equations for the 'physical' pomeron are written. Conformal invariance allows to reduce the theory to the old-fashioned Gribov pomeron theory with an infinite number of pomerons, one of which is supercritical.

hep-ph↗
arXiv2005

On the initial condition for evolution of the perturbative QCD Pomeron in the nucleus

It is shown that subdominant terms found in the reggeized gluon diagram technique, to be added to Pomeron fan diagrams with the 3P interaction, can be exactly taken into account by taking the initial condition for evolution in the Glauber form. This demonstrates complete equivalence of the dipole picture and the reggeized gluon approach not only on the leading level but also on the subleading level.

hep-ph↗
arXiv2005

On the inclusive gluon jet production off the nucleus in the perturbative QCD

In the perturbative QCD approach single and double inclusive cross-sections for gluon production off the nucleus are studied from the relevant reggeized gluon diagrams. Various terms corresponding to emission of gluons from the triple Pomeron vertex are found. Among them the term derived by Kovchegov and Tuchin emerges as a result of transition from the diffractive to effective high-energy vertex. However it does not exhaust all the vertex contributions to the inclusive cross-section. In the double inclusive cross-section a contribution violating naive AGK rules is found, in which one gluon is emitted from the vertex and the other from one of the Pomerons below the vertex. But then this contribution is subdominant at high energies and taking it into account seems to be questionable.

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