arXiv subjects
Publications and source records attributed to N. G. Kelkar.
We show that if we consider the full statement of Faraday's law for a closed physical circuit, the standard Maxwell's equations in the presence of electric and magnetic charges have to include in their integral form a mixed term of the form $ρ_m {\bf v}_e^{\perp}$ where $ρ_m$ is the magnetic charge density and ${\bf v}_e^{\perp}$ the perpendicular component of the velocity ${\bf v}_e$ of the electric charge.
The scattering phase shift encodes a good amount of physical information which can be used to study resonances from scattering data. Among others, it can be used to calculate the continuum density of states and the collision time in a resonant process. Whereas the first information can be employed to examine the evolution of unstable states directly from scattering data, the second one serves as a tool to detect resonances and their properties. We demonstrate both methods concentrating in the latter case on 'exotic' resonances in pi-pi and pi-K scattering.
Having successfully explored the existing relations between the S-matrix and collision times in scattering reactions to study the conventional baryon and meson resonances, the method is now extended to the exotic sector. To be specific, the collision time in various partial waves of K+ N elastic scattering is evaluated using phase shifts extracted from the K+ N --> K+ N data as well as from model dependent T-matrix solutions. We find several pentaquark resonances including some low-lying ones around 1.5 to 1.6 GeV in the P_01, P_03 and D_03 partial waves of K+ N elastic scattering.
The framework to describe natural phenomena at their basics being quantum mechanics, there exist a large number of common global phenomena occurring in different branches of natural sciences. One such global phenomenon is spontaneous quantum decay. However, its long time behaviour is experimentally poorly known. Here we show, that by combining two genuine quantum mechanical results, it is possible to infer on this large time behaviour, directly from data. Specifically, we find evidence for non-exponential behaviour of alpha decay of 8Be at large times from experiments.
Motivated by the recent experimental evidence of the exotic B = S = +1 baryonic state Theta(1540), we examine the older existing data on K+ N elastic scattering through the time delay method. We find positive peaks in time delay around 1.545 and 1.6 GeV in the D03 and P01 partial waves of K+ N scattering respectively, in agreement with experiments. We also find an indication of the J=3/2 Theta* spin-orbit partner to the Theta, in the P03 partial wave at 1.6 GeV. We discuss the pros and contras of these findings in support of the interpretation of these peaks as possible exotics.
We explore the usefulness of the existing relations between the $S$-matrix and time delay in characterizing baryon resonances in pion-nucleon scattering. We draw attention to the fact that the existence of a positive maximum in time delay is a necessary criterion for the existence of a resonance and should be used as a constraint in conventional analyses which locate resonances from poles of the $S$-matrix and Argand diagrams. The usefulness of the time delay plots of resonances is demonstrated through a detailed analysis of the time delay in several partial waves of $πN$ elastic scattering.
The usefulness of the three-body mechanism of $η$-meson production is tested by extending to high energies a recently developed two step model of the $p d \to ^3$He $η$ reaction by us, which was successful in reproducing the energy dependence of the data near threshold. The $η$ production in this model, proceeds in two steps via the $p p \to πd$ and $πN \to ηp$ reactions with the intermediate particles being off-shell. The final state interaction(FSI) is incorporated through a $T$-matrix for $η^3$He elastic scattering constructed using few body equations. In a comparison of the calculated angular distributions with some recently available data, we discover the limitations of the model at high energies.
Evidences and hints, both from the theoretical and experimental side, of exotic baryon resonances with B=S, have been with us for the last thirty years. The poor status of the general acceptance of these Z* resonances is partly due to the prejudice against penta-quark baryons and partly due to the opinion that a proof of the existence of exotic states must be rigorous. This can refer to the quality and amount of data gathered, and also to the analytical methods applied in the study of these resonances. It seems then mandatory that all possibilities and aspects be exploited. We do that by analyzing the time delay in K+ N scattering, encountering clear signals of the exotic Z* resonances close to the pole values found in partial wave analyses.
Using the concept of collision time (time delay) introduced by Eisenbud and Wigner and its connection to on-shell intermediate unstable states, we study mesonic resonances in pi-pi and pi-K scattering. The time-delay method proves its usefulness by revealing the spectrum of the well-known rho- and K*-mesons and by supporting some speculations on rho-mesons in the 1200 MeV region. We use this method further to shed some light on more speculative meson resonances, among others the enigmatic scalars. We confirm the existence of chiralons below 1 GeV in the unflavoured and strange meson sector.
We evaluate the time delay in some of the established resonance regions of $πN$ elastic scattering. In addition to the positive peaks corresponding to resonances, we identify broad regions of negative time delay or time advancement which restrict the energy ranges within which the resonances can be located.
A detailed study of the effect of the $η$-nucleus final state interaction (FSI) in the $p d \to ^3$He$ η$ reaction close to threshold is presented. The FSI is incorporated through a T-matrix for $η^3$He elastic scattering, constructed using few body equations. This T-matrix accounts for off-shell and binding effects in $η$-nucleus scattering. The energy dependence of the data on the $p d \to ^3$He$ η$ reaction near threshold is reproduced only after including the FSI. The off-shell and binding effects in $η^3$He scattering are found to be important. Given the uncertainty in the knowledge of the elementary $η$-nucleon interaction, the sensitivity of the $ p d \to ^3$He$ η$ cross section to different prescriptions of the elementary t-matrix, $t_{ηN \to ηN}$ is also discussed.
We present a model for the structure of the pion. Based on ideas of a recently developed statistical model of the nucleon, we assume the pion to be a gas of partons. The finite-size corrections (FSC) are incorporated through two parameters. Using the same two FSC parameters for the proton and pion we reproduce quantitatively the data on $π^- N \to μ^+ μ^- X$ Drell-Yan production and valence quark distribution of the pion.
We present calculations of the invariant mass spectra of the $Λ$p system for the exclusive $p p \to K^+ Λp$ reaction with the aim of studying the final state interaction between the $Λ$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Λp$ interaction is incorporated through an off-shell t-matrix for the $Λp \to Λp$ scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the $Λ$ and $Σ$ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
We present a physical model for polarized and unpolarized structure functions and parton density functions (PDFs) of the proton and the neutron. It reproduces the data on F_2^p(x,Q^2) for 0.00001<x<1 and 2.5<Q^2<5000 GeV^2, F_2^p(x)-F_2^n(x), F_2^n(x)/F_2^p(x), xg(x), dbar(x)-ubar(x), d(x)/u(x), the Gottfried sum, the fractional momentum of charged partons and the polarized structure functions g_1^{p,n}(x), at various Q^2. We present for the first time, proton and neutron PDFs which do not assume charge symmetry. Contrary to the common practice, we explain polarized and unpolarized data with a single model.
The weak production of Lambdas in nucleon-nucleon scattering is studied in a meson-exchange framework. The weak transition operator for the $NN \to N Λ$ reaction is identical to a previously developed weak strangeness-changing transition potential $ΛN \to NN$ that describes the nonmesonic decay of hypernuclei. The initial $NN$ and final $YN$ state interaction has been included by using realistic baryon-baryon forces that describe the available elastic scattering data. The total and differential cross sections as well as the parity-violating asymmetry are studied for the reaction $pn \to pΛ$. These observables are found to be sensitive to the choice of the strong interaction potential and the structure of the weak transition potential.
With the advent of high precision proton accelerators, such as COSY in Jülich, or with medium energy accelerators like RCNP at Osaka, it may become possible to perform a direct study of the strangeness changing hadronic $np \to Λp$ process. In this work we study this reaction using a one-meson-exchange weak potential and realistic $NN$ and $YN$ strong interactions to distort both the initial $np$ and the final $Λp$ states. The calculated cross sections are very sensitive to the different mesons included in the weak transition, as well as to the strong $YN$ interaction model that generates the distorted final state.
We calculate cross sections for coherent pion production in nuclei induced by neutrinos and antineutrinos of the electron and muon type. The analogies and differences between this process and the related ones of coherent pion production induced by photons, or the (p,n) and $(^3 He, t)$ reactions are discussed. The process is one of the several ones occurring for intermediate energy neutrinos, to be considered when detecting atmospheric neutrinos. For this purpose the results shown here can be easily extrapolated to other energies and other nuclei.