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B. Blok

Publications and source records attributed to B. Blok.

At least 55 records · Page 3Linked to original sources
arXiv2005

On the limiting behaviour of hard processes in QCD at small x

At sufficiently small $x$ where pQCD methods become insufficient we rewrote sum of dominant Feynman diagrams for single-scale hard processes in the form of the effective field theory where a quasiparticle corresponds to pQCD ladder. We explain that pQCD series are divergent at small $x$ since pQCD produces tachyon in effective field theory and because of degeneracy of vacua . Within the WKB approximation we found the hierarchy among quasiparticle interactions due to smallness of the QCD coupling constant which justifies restriction by the triple quasiparticle interaction in the Lagrangean of effective field theory. Degeneracy of vacua is removed by accounting for the classical solutions -kinks which cannot be decomposed into series over powers f $α_s$ but describe color inflation, Bose-Einstein condensation of quasiparticles. Quantum fluctuations around the WKB solution lead to the spontaneous violation of two-dimensional translation symmetry and the appearance of zero modes- ``phonons'' which are relevant for the black disc behaviour of small x processes. Account of gluon exchanges between overlapping ladders neglected in the first approximation produces a color network occupying a "macroscopic" longitudinal volume. We discuss briefly possible role of new QCD phenomena in the two-scale hard processes .

hep-ph↗
arXiv2005

On the increase with relative distances of light cone operator product of currents and related phenomena

We show that in QCD in the leading twist approximation flavor singlet light cone current-current correlators increase with distances rapidly similar to the correlator of velocities in turbulence and argue that this property is precursor of phase transitions in high energy processes . It is shown that absence of spatial oscillations of current-current correlators follows from asymptotic freedom in QCD. We discuss also influence of this new long-range interaction on the wave function of dipole in high energy DIS processes near the black disc limit.

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arXiv2004

Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes

We evaluate the coordinate space dependence of the matrix elements of the commutator of the electromagnetic and gluon currents in the vicinity of the light-cone but at large distances within the parton model, DGLAP, the resummation approaches to the small x behaviour of DIS processes, and for the Unitarity Bound. We find that an increase of the commutator with relative distance $py$ as $\propto (py)f(py,y^2=t^2-r^2)$ is the generic property of QCD at small but fixed space-time interval $y^2=t^2-r^2$ in perturbative and nonperturbative QCD regimes. We explain that the factor $py$ follows within the dipole model (QCD factorization theorem) from the properties of Lorents transformation. The increase of $f(r)$ disappeares at central impact parameters if cross section of DIS may achieve the Unitarity Limit. We argue that such long range forces are hardly consistent with thermodynamic equilibrium while a Unitarity Limit may signal equilibration. Possible implications of this new long range interaction are briefly discussed.

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arXiv2004

Coulomb scattering of quantum dipoles in QED

We calculate the total scattering cross-section of a dynamical quantum electrically neutral dipole in QED of the infinitely heavy charge and of the infinitely heavy dipole in the leading order in electromagnetic coupling constant.

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arXiv2004

Space-Time Evolution of Ultrarelativistic Quantum Dipoles in Quantum Electrodynamics

We discuss space-time evolution of ultrarelativistic quantum dipole in QED. We show that the space-time evolution can be described, in a certain approximation, by means of a regularized wave function, whose parameters are determined by the process of the dipole creation by a local current. We derive using these wave functions the dipole expansion law, that is found to coincide parametrically in the leading order with the one suggested by Farrar, Frankfurt,Liu and Strikman.

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arXiv2002

Space-Time Evolution of the Oscillator, Rapidly moving in a random media

We study the quantum-mechanical evolution of the nonrelativistic oscillator, rapidly moving in the media with the random vector fields. We calculate the evolution of the level probability distribution as a function of time, and obtain rapid level diffusion over the energy levels. Our results imply a new mechanism of charmonium dissociation in QCD media.

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arXiv1998

Parton-Hadron duality in QCD sum rules: quantum mechanical examples

Motivated by recent work on three-point QCD sum rules in heavy quark physics, we use the simple quantum mechanical models to study the basic issue of duality in three-point sum rules. We show that while in all of these models the duality in two-point sum rules works fine, the duality in three-point sum rules may be 100%- violated, leading to completely unreliable predictions for the matrix elements in question. The implications for three-point QCD sum rules are discussed. A new estimate for the parameter $λ_1$ of HQET is given.

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arXiv1997

An Illustrative Example of How Quark-Hadron Duality Might Work

We discuss the issue of the local quark-hadron duality at high energies in two- and four-dimensional QCD. A mechanism of the dynamical realization of the quark-hadron duality in two- dimensional QCD in the limit of large number of colors, N_c -> \infty, (the 't Hooft model) is considered. A similar mechanism of dynamical smearing may be relevant in four-dimensional QCD. Although particular details of our results are model-dependent, the general features of the duality implementation conjectured previously get further support.

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arXiv1997

How quark hadron duality in QCD may work

We pursue the issue of the local quark-hadron duality at high energies in two- and four-dimensional QCD. A mechanism of the dynamical realization of the quark-hadron duality in two-dimensional QCD in the limit of large number of colors, $N_c \to \infty$, (the ' t Hooft model) is investigated. We argue that a similar mechanism of dynamical smearing may be relevant in four-dimensional QCD. Although particular details of our results are model-dependent (especially in the latter case), the general features of the duality implementation conjectured previously get further support.

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arXiv1997

Annihilation, Rescattering, and CP Asymmetries in B Meson Decays

A number of $B$ meson decays may proceed only through participation of the spectator quark, whether through amplitudes proportional to $f_B/m_B$ or via rescattering from other less-suppressed amplitudes. An expected hierarchy of amplitudes in the absence of rescattering will be violated by rescattering corrections. Such violations could point the way toward channels in which final-state interactions could be important. Cases in which final state phases can lead to large CP asymmetries are pointed out.

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arXiv1996

Chiral Symmetry Breaking, Duality in the \bar{Q}q Channel and b -> c anti-c s Decays

We address the issue of the quark-hadron duality in the spectral densities induced by the heavy-light quark currents anti-Q q. In the limit m_Q ->oo, m_q ->0 we observe an enhancement of the physical spectral density compared to the quark one in the scalar and axial channels, due to the Goldstone meson contributions. This may imply that the scale where duality sets in is higher in these channels than in the vector (pseudoscalar) case. Implications for the nonleptonic decays of B mesons (the b -> c anti-c s transition) are considered. We discuss in detail the decay pattern and obtain an independent estimate of the "wrong" sign D yield.

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arXiv1995

Calculation of 1/m^3 terms in the total semileptonic width of D mesons.

We calculate the 1/$m^3_c$ corrections in the inclusive semileptonic widths of $D$ mesons. We show that these are due to the novel penguin type operators that appear at this level in the transition operator. Taking into account the nonperturbative corrections leads to the predicted value of the semileptonic width significantly lower than the experimental value. The $1/m^3_c$ worsen the situation or at the very least, within uncertainty, give small contribution. We indicate possible ways out. It seems most probable that violations of duality are noticeable in the energy range characteristic to the inclusive decays in the charm family. Theoretically these deviations are related to divergence of the high-order terms in the power expansion in the inverse heavy quark mass.

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arXiv1994

Feasibility of Extracting V_td from Radiative B(B_s) Decays

We use existing measurements of $D^-\to K^{\ast0}ρ^-$ and $B\to ψ+K^\ast$, coupled with flavor independence of QCD, and with vector meson dominance to show that long distance contributions to $B\to ρ+γ$ are potentially very serious. We note that long distance (LD) contributions can be appreciably different in $B^-\to ρ^-+γ$ and $B^0\to ρ^0 (ω) +γ$. All radiative decays of $B$, $B_S$ are shown to be governed essentially by two LD and two short-distance (SD) hadronic entities. Separate measurements of $B^-\to ρ^-+γ$, $B^0\to ρ^0 (ω) +γ$, along with $B\to K^\ast +γ$ appear necessary for a meaningful extraction of \vtd. Measurements of $B_S\to ϕ+γ$ and $K^{\ast0}+γ$ could also provide very useful consistency checks.

hep-ph↗
arXiv1994

Non-Leptonic Decays of Beauty Hadrons -- from Phenomenology to Theory

`Anyone who keeps the ability to see beauty never grows old' Franz Kafka. In the last few years considerable progress has been achieved in our understanding of the decays of heavy flavour hadrons. One can now calculate inclusive transition rates in QCD proper through an expansion in inverse powers of the heavy flavour quark mass without recourse to phenomenological assumptions. The non-perturbative contributions are treated systematically in this way; they are found to produce corrections of order a few percent in beauty decays, i.e. typically somewhat smaller than the perturbative corrections. One finds, among other things: (a) The lifetime of $B^-$ mesons is predicted to be longer than that of $B^0$ mesons by several percent. (b) The QCD prediction for the semileptonic branching ratio of $B$ mesons appears to exceed present experimental values. We discuss the implications of this discrepancy. The phenomenological engineering that has been developed for the description of {\em exclusive} two-body modes of $B$ mesons has reached a mature stage and awaits more precise and detailed experimental tests. First steps towards a genuine QCD treatment of these modes are being made.

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arXiv1993

The Baffling Semileptonic Branching Ratio of $B$ Mesons

The apparent gap between the measured and the expected value for the semileptonic branching ratio of $B$ mesons has become more serious over the last year. This is due to the improved quality of the data and to the increasing maturity of the theoretical treatment of non-perturbative corrections. We discuss various theoretical options to reduce the semileptonic $B$ branching ratio; among the more spectacular resolutions of the apparent puzzle is the possibility of an unorthodox enhancement in non-perturbative corrections or even of an intervention by `New Physics'. Phenomenological implications of such scenarios are pointed out.

hep-ph↗
arXiv1992

A QCD ``Manifesto'' on Inclusive Decays of Beauty and Charm

A selfconsistent treatment of nonperturbative effects in inclusive nonleptonic and semileptonic decays of beauty and charm hadrons is presented. It is illustrated by calculating semileptonic branching ratios, lifetime ratios, radiative decay rates and the lepton spectra in semileptonic decays.

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