Browsing by Author "Ganguly, Avijit K."

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Absorption of Electro-magnetic Waves in a Magnetized Medium
(2000-07-04) Ganguly, Avijit K.; Konar, Sushan
In continuation to our earlier work, in which the structure of the vacuum polarisation tensor in a medium was analysed in presence of a background electro-magnetic ﬁeld, we discuss the absorptive part of the vacuum polarization tensor. Using the real time formalism of ﬁnite temperature ﬁeld theory we calculate the absorptive part of 1-loop vacuum polarisation tensor in the weak ﬁeld limit (eB < m2 ). Estimates of the absorption probability are also made for diﬀerent physical conditions of the background medium.
Effective neutrino photon interaction in a magnetized medium
(2001-05-01) Bhattacharya, Kaushik; Ganguly, Avijit K.; Konar, Sushan
Neutrino-photon processes, forbidden in vacuum, can take place in presence of a thermal medium or an external electro-magnetic ﬁeld, mediated by the corresponding charged leptons (real or virtual). The eﬀect of a medium or an electromagnetic ﬁeld is two-fold - to induce an eﬀective ν−γ vertex and to modify the dispersion relations of all the particles involved to render the processes kinematically viable. It has already been noted that in presence of a thermal medium such an electromagnetic interaction translates into the neutrino acquiring a small eﬀective charge. In this work, we extend this concept to the case of a thermal medium in presence of an external magnetic ﬁeld and calculate the eﬀective charge of a neutrino in the limit of a weak magnetic ﬁeld. We ﬁnd that the eﬀective charge is direction dependent which is a direct eﬀect of magnetic ﬁeld breaking the isotropy of the space.
Faraday effect : A field theoretical point of view
(2015-03-01) Ganguly, Avijit K.; Konar, Sushan; Pal, Palash. B.
We analyze the structure of the vacuum polarization tensor in the presence of a background electromagnetic field in a medium. The most general gauge invariant structure contains many form factors. We use various discrete symmetries and crossing symmetry to constrain these form factors. From these symmetry arguments, we show why the vacuum polarization tensor has to be even in the background field when there is no background medium. Taking then the background field to be purely magnetic, we evaluate the vacuum polarization to linear order in it. The result shows the phenomenon of Faraday rotation, i.e., the rotation of the plane of polarization of a plane polarized light passing through this background. Finally, we calculate the amount of Faraday rotation in different kinds of media - non-relativistic, completely degenerate, and ultra-relativistic.