• D K CHOUDHURY

Articles written in Pramana – Journal of Physics

• SU(4), broken Zweig rule and the null plane

Using Glauber’s theory of eikonal approximation, an algebraic representation of the broken Zweig rule in the constituent quark model is obtained. Null plane language is then elaborated. It is pointed out that the exotic current associated with the disconnected quark diagrams, which break the Zweig rule, can have canonical dimension.

• Bare quark masses from the transverse cut offs ine+e interactions

From the transverse cuts off of the electron positron annihilation in the SPEAR II regime, we obtain positivity domains of bare quark masses.

• Scale breaking in neutrino scattering

We consider two types of scale breaking models—one based on asymptotically free gauge theory and the other phenomenological—which have already been fitted to the electron and muon data. Their predictions for the neutrino scattering are worked out and the sensitivity on the model parameters and the input electron data studied. The effects of scale breaking at very lowQ2 and of a finite longitudinal cross-section are incorporated in analogy withep data. The predictions are compared with the recent neutrino scattering data.

• Phenomenological structure functions and Gribov-Lipatov relation

We make an analysis of the Gribov-Lipatov relation using the phenomenological forms of the structure functionF2ep. Our analysis indicate breakdown of the relation at PETRA energies. Plausible reasons of the breakdown of Gribov-Lipatov relation are discussed together with its phenomenological form.

• An analysis of a quantum chromodynamic structure function

We obtain an approximate solution of Altarelli-Parisi equations yielding a sample of quantum chromodynamic structure function. The SLAC-MIT data are analysed with it. Possible effects of intrinsic charm and higher twist are also included. Agreement is found to be good forx⩾0.25.

• Gribov-Lipatov inequality and inclusivee+e processes

We study the inclusivee+e processes at the PETRA energy range within QCD and a fixed point theory using the phenomenological Gribov-Lipatov inequality suggested in an earlier analysis. Theoretical justification is provided within QCD and its possible implication in hadronization is discussed.

• Masses in structure functions

We derive an approximate formula for the quark mass in ξ-formalism. Using the QCD-based form of structure function, we analyse the SLAC-MIT data to estimate the experimentally allowed ranges of quark mass. The possible variation of our results with QCD cut-off parameter, gluon distribution, hard intrinsic charm component of the proton wavefunction and the higher twist effects are also discussed.

• An improved approximate solution of Altarelli-Parisi equations

We have presented here an improved solution to Altarelli-Parisi equations, and it is found to be in good agreement with SLAC-MIT data up tox⩾0.1.

• Bounds on non-leading QCD effects in a quark model for inclusive reactions

We study the possible effect of QCD in the proton wave function in a quark model for inclusive processesA+B→C+X pursued by us. The assumption is the validity of the conjecture of Lepage and Brodsky in QCD on such effects. Our results obey the perturbative expectation, |Rg tan2φ|&lt;1. Symmetric version of the model is, however, found to be at variance with most of the inclusive data as well as with some known phenomenology. If the dynamics of the underlying theory generate Regge-like symmetry breaking approximately, the model is phenomenologically viable, and the non-leading QCD effects become reasonable in size. Phenomenological necessity of the admixtures of (56, 0+)*, (70, 0+) and (56, 2+) in the nucleon wave function is also discussed in the present analysis.

• Comment on a solution of Altarelli Parisi equations

We show that the assumptions of factorizability of the structure functionF(x, t) inx andt and the equality oft evolution of the singlet and gluon distributions are not necessary to obtain the approximate solutions of Altarelli-Parisi equations derived by us recently.

• An analysis of quantum chromodynamic structure function beyond leading order

We obtain approximate solutions of Altarelli-Parisi equations beyond leading logarithmic approximation. Our results suggest quantitative utility of higher order terms in the structure function analysis of deep inelastic scattering.

• Perturbative and non-perturbative evolutions of structure functions at low-x

Approximate solutions of Altarelli-Parisi equations are obtained in low-x limit and have tested them in EMC low-x and low-Q2 data. The results are compared with the phenomenological non-perturbative evolutions. Data conform to perturbative as well as non-perturbative evolutions but do not conform to the predictions of non-linear evolution.

• Comments on structure functions at low-x

We present further analysis of the structure functions at low-x using the approximate solutions of Altarelli-Parisi equations recently reported by us. We also compare our results with non-perturbative and non-linear evolutions.

• Cross-section sum rules and inequalities in a quark model for light and heavy flavour productions

The$$qq\bar q$$ model for inclusive processes is reformulated to consider the production of heavy flavours (c, b andt) and higher order flavour exchange effects. Predictions are made in terms of sum rules and inequalities for various inclusive cross-sections. Plausible parametrization of flavour symmetry breaking is also suggested.

• Low x structure functions—HERA physics

• Perturbative and nonperturbative quark masses in structure functions

Flavour symmetry breaking is introduced in the approximate formula for quark mass reported earlier. We use SLAC-MIT as well as NMC data to estimate the up, down and strange quark masses from structure functions. Using the approximateQ2 evolutions of Altarelli-Parisi equations, we also estimate its perturbative and nonperturbative components.

• Static and dynamic properties of pseudoscalar mesons

We report the results of form factors, charge radii and decay constants of both light and heavy flavoured pseudoscalar mesons in a QCD inspired quark model. We use the quantum mechanical perturbation theory and discuss its limitations in the present problem. Several predictions are also made for bottom and top flavours.

• Static and dynamic properties of heavy light mesons in infinite mass limit

We summarize the consequences of the infinite limit of heavy quark mass in the results of form factors, charge radii and decay constants of heavy light mesons within a QCD inspired quark model recently reported.

• Root mean square radii of heavy flavoured mesons in a quantum chromodynamics potential model

We report the results of root mean square (r.m.s.) radii of heavy flavoured mesons in a QCD model with the potential $V (r) = −(4\alpha_{s}/3r) + br + c$. As the potential is not analytically solvable, we first obtain the results in the absence of confinement and Coulomb terms respectively. Confinement and Coulomb effects are then introduced successively in the approach using the Dalgarno’s method of perturbation. We explicitly consider the following two quantum mechanical aspects in the analysis: (a) The scale factor $c$ in the potential should not effect the wave function of the system even while applying the perturbation theory. (b) Choice of perturbative piece of the Hamiltonian (confinement or linear) should determine the effective radial separation between the quarks and antiquarks. The results are then compared with the available theoretical values of r.m.s. radii.

• Isgur–Wise function in a QCD-inspired potential model with WKB approximation

We use Wentzel–Kramers–Brillouin (WKB) approximation for calculating the slope and curvature of Isgur–Wise function in a QCD-inspired potential model. This work is an extension of the approximation methods to the QCD-inspired potential model. The approach hints at an effective range of distance for calculating the slope and curvature of Isgur–Wise function. Comparison is also made with those of Dalgarno method and variationallyimproved perturbation theory (VIPT) as well as other models to show the advantages of using WKB approximation.

• # Pramana – Journal of Physics

Volume 97, 2023
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019