• S Biswas

Articles written in Pramana – Journal of Physics

• Dual pole eikonal ands-channel singularities

Eikonalization of dual pole amplitudes, such as the Veneziano amplitude, is shown to lead to singularities in the impact parameter plane, which, in the eikonal approximation, may be interpreted as branch points in the direct channel angular momentum plane. This result is discussed in the light of dual absorption models.

• 3He-rich solar flares

A new subgroup of3He rich solar flares is found on reanalysing the global data.3He/H ratio as a function of maximum proton flux at an energy of about 10 MeV shows a break-up of the data into two groups. The first group follows the anticorrelation of3He/H ratio with the proton flux, as expected in the plasma process acceleration models. But the second group has a constant3He/H ratio as a function of maximum proton flux. This is not in conformity with the plasma process models. But this is expected in models where the nuclear spallation reactions are responsible for the production of3He. It is also found that the same break-up into two distinct groups follows if one plots the location of the flares in the solar disc. The first group is more or less confined to the west limb of the Sun, whereas the second group is more widely spread out across the solar disk.

• Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm2 and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays.

• Confinement of tensor gluons — a classical approach

We look at the confinement of tensor gluons (fμν(c) field) in a strong gravity background and find that the strong gravity provides a trap for the confinement of colour waves of selected frequencies. We assume that the tensorfμν(c) field (mediating quanta: tensor 2+f-meson) satisfies Einstein-like equations with a cosmological constant. The colour field satisfy equations resembling Maxwell form of the linear theory of gravitation and see the effect offμν(c) field as playing the role of a medium having space dependent dielectric permeabilities. The solution of colour field equations resemble harmonic oscillator type wave functions with equispaced energy levels (no continuum) leading to confinement.

• Confinement model for quarks

A confinement model of hadron with its constituent quarks bound in a strong gravitational field is presented. The gravitational field plays the role of a medium having, as if, space dependent permeabilities from a fixed centre. The massless Dirac equation modified by the gravitational field is solved. The solution for the wavefunction of the quarks obtained shows the characteristic features of confinement, i.e., (i) wavefunction with higher energy states lying closer to the centre, (ii) equispaced energy levels without continuum, (iii) the quark orbits lying within a distance ∼ 10−14 cm, the characteristic radius of a typical hadron.

• Model of confinement

Confinement model for quarks and gluons is formulated. An attempt has been made to derive the dielectric function starting from a Lagrangian that also determines the quark and gluon field equations. Deconfinement mechanism is also discussed.

• Aharonov-Bohm effect from five dimensional space-time

We present an alternative non-quantum mechanical description of Aharonov-Bohm effect.

• Dirac equation in time dependent electric field and Robertson-Walker space-time

We show that the motion of a Dirac electron in a time dependent electromagnetic field can be considered as a motion in a dielectric medium with time dependent dielectric function. We find that this electromagnetic case is analogous to the description in Robertson-Walker (RW) space-time. We solve the Dirac equation is such a simulated space-time.

• Geometric interpretation of hadronization model

A hadronization model termed as geometric dielectric confinement model is described. The model describes the charmed meson decays quite successfully. In the model we assume that the non-abelian gauge field describing the colour force simulates the effect of a medium having space-dependent dielectric constant. The quarks produced in weak decays move in the dielectric medium such that they are free in limited region of space (r⋍0) and cannot appear as asymptotic states resulting in hadronization. It is found that the dielectric medium resembles anti-desitter microuniverse and the quarks behave essentially as free particles damped by gaussian distribution. The model reproduces from a single Lagrangian the quark motion as well as the form of dielectric function.

• Regge relation and geometrization of fundamental constant

We show that the Regge relation between angular momentum and mass is due to curved space time description of basic interactions. We try to understand the geometrization ofh ande in the light of the relation.

• WKB approximation in complex time

The WKB approximation to the one particle Schrödinger equation in time is used to obtain the wavefunction at a given point as a sum of semiclassical terms, each corresponding to a different classical trajectory (real or complex) but ending up at the same point. A method to find out reflection coefficient for processes involving one and two turning points is developed and it is shown that the semiclassical complex analysis reproduces exactly the reflection coefficient that is obtained through the exact solution of the problem. The connection between pair production and reflection amplitude is also shown. The pair production amplitude in a time dependent gravitational background is calculated and it is shown that the vacuum considered in complex trajectory WKB analysis refers to adiabatic vacuum.

• WKB approximation in complex time II

The non-perturbative method, developed recently, of WKB approximation in complex time is applied to some known curved space time. Three cases namely (1) static in and out region, (2) non-static in and out region, (3) static in and non static out region are considered here. We find non-trivial particle production corresponding to the quantum vacuum definition of Castagnino and Mazzitelli.

• Particle production in curved spacetime

Particle production in curved spacetime has been discussed through the method of complex time WKB approximation. We consider Dirac equation in non-flat spacetime to understand particle production as particle-antiparticle rotation. The method is also generalized to understand particle production through parametric resonance. To understand the method of CWKB we consider particle production in Kasner spacetime as an example.

• Dirac current in expanding spacetime

We study the behaviour of Dirac current in expanding spacetime with Schrödinger and de Sitter form for the evolution of the scale-factor. The study is made to understand the particle-antiparticle rotation and the evolution of quantum vacuum leading to particle production in such spacetime.

• Starobinsky model in Schrödinger description

In the Starobinsky inflationary model inflation is driven by quantum corrections to the vacuum Einstein equation. We reduce the Wheeler-DeWitt equation corresponding to the Starobinsky model to a Schrödinger form containing time. The Schrödinger equation is solved with a Gaussian ansatz. Using the prescription for the normalization constant of the wave function given in our previous work, we show that the Gaussian ansatz demands Hawking type initial conditions for the wave function of the universe. The wormholes induce randomness in initial states suggesting a basis for time-contained description of the Wheeler-DeWitt equation.

• Stability study and time resolution measurement of straw tube detectors

Straw tube detectors are single wire proportional counters that are widely used as tracking devices. We have carried out R&D activity with a straw tube detector prototype. The aim of this work is to study the stability of the performance in terms of gain and energy resolution of these types of detectors under high rate of radiation. The gain and energy resolution of the detector are studied along with its variation with ambient temperature and pressure. X-rays from a radioactive source are used to irradiate the detector and to monitor the energy spectra simultaneously for calculating the gain. The method followed here is unique as the ageing measurements have been performed without using an accelerated particle beam or any radiation generator. The performance of a straw tube detector has been studied in a laboratory for more than 800 h at a stretch using a single sealed radioactive X-ray source with high intensity. Variation of gain and energy resolution of the straw tube detector under X-ray irradiation in Ar/CO$_2$ gas mixture (volume ratio 80/20) is discussed in this article. The gain of an aged straw depends on gas flow rate. We have estimated the time required for the gain of a straw tube detector under ageing tests to recover on increasing the gas flow rate. We have also estimated the time resolution of the straw tube detectors by using cosmic rays as the trigger for the Ar/CO$_2$ gas mixture in 70/30 volume ratio (different gas mixture was used for the measurement of the time resolution). This type of ageing and time resolution measurements in Ar/CO$_2$ gas mixture has not been reported earlier. The details of the measurement process and the experimental results are presented in this article.

• Cosmic ray flux and lockdown due to COVID-19 in Kolkata – Any correlation?

Cosmic ray muon flux is measured by the coincidence technique using plastic scintillation detectors in the High Energy Physics Detector Laboratory at Bose Institute, Kolkata. Due to the COVID-19 outbreak and nationwide complete lockdown, the laboratory was closed from the end of March 2020 till the end of May 2020. After lockdown, although the city is not in its normal state, we still were able to take data on some days. The lockdown imposed a strict restriction on the transport service other than the emergency ones and also most of the industries were shut down in and around the city. This lockdown has significant effect on the atmospheric conditions in terms of change in the concentration of air pollutants. We have measured the cosmic ray flux before and after the lockdown to observe the apparent change if any, due to change in the atmospheric conditions. In this article, we report the measured cosmic ray flux at Kolkata (22.58°N 88.42°E and 11 m above the Sea Level) along with the major air pollutants present in the atmosphere before and after the lockdown.

• # Pramana – Journal of Physics

Volume 96, 2022
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019