arXiv subjects

R. Bhattacharyya

Publications and source records attributed to R. Bhattacharyya.

42 records · Page 3Linked to original sources

arXiv2016

On the role of repetitive magnetic reconnections in evolution of magnetic flux-ropes in solar corona

Parker's magnetostatic theorem extended to astrophysical magnetofluids with large magnetic Reynolds number supports ceaseless regeneration of current sheets and hence, spontaneous magnetic reconnections recurring in time. Consequently, a scenario is possible where the repeated reconnections provide an autonomous mechanism governing emergence of coherent structures in astrophysical magnetofluids. In this work, such a scenario is explored by performing numerical computations commensurate with the magnetostatic theorem. In particular, the computations explore the evolution of a flux-rope governed by repeated reconnections in a magnetic geometry resembling bipolar loops of solar corona. The revealed morphology of the evolution process, including onset and ascent of the rope, reconnection locations and the associated topology of the magnetic field lines, agrees with observations, and thus substantiates physical realisability of the advocated mechanism.

astro-ph.SR↗

arXiv2011

Evolution of Currents of Opposite Signs in the Flare Productive Solar Active Region NOAA 10930

Analysis of a time series of high spatial resolution vector magnetograms of the active region NOAA 10930 available from SOT/SP on-board Hinode revealed that there is a mixture of upward and downward currents in the two foot-points of an emerging flux-rope. The flux emergence rate is almost the same in both the polarities. We observe that along with an increase in magnetic flux, the net current in each polarity increases initially for about three days after which it decreases. This net current is characterized by having exactly opposite signs in each polarities while its magnitude remains almost the same most of the time. The decrease of net current in both the polarities is due to the increase of current having a sign opposite to that of the net current. The dominant current, with same sign as the net current, is seen to increase first and then decreases during the major X-class flares. Evolution of non-dominant current appears to be a necessary condition for a flare initiation. The above observations can have a plausible explanation in terms of the superposition of two different force-free states resulting in non-zero Lorentz force in the corona. This Lorentz force then push the coronal plasma and might facilitate the magnetic reconnection required for flares. Also, the evolution of the net current is found to follow the evolution of magnetic shear at the polarity inversion line.

astro-ph.SR↗

arXiv2007

Spacetime Dependent Lagrangians and Electrogravity Duality

We apply the spacetime dependent lagrangian formalism [1] to the action in general relativity. We obtain a Barriola-Vilenkin type monopole solution by exploiting theelectrogravity duality of the vacuum Einstein equations and using a modified definition of empty space. An {\it upper bound} is obtained on the monopole mass ${\tt M}$, ${\tt M}\leq e^{(1-α)/α}/(1-α)^{2}{\tt G}$ where $α= 2k $ is the global monopole charge. Keywords: global monopole, electrogravity duality, holographic principle. PACS: 11.15.-q, 11.27.+d, 14.80.Hv, 04.

gr-qc↗

arXiv2002

String in noncommutative background: another approach

We propose a model action in 1+1 flat space-time (compact in spatial dimension) embedded in D flat space-time with a non dynamical space-time dependent two vector. For the above constrained system Dirac brackets of suitably defined co-ordinates turn out to be non zero and under specific choice of the two vector the model action reduces to a general action of open string in a noncommutative background where we find the natural embedding of the open string action of in presence of magnetic field on D-brane.

hep-th↗

arXiv2002

Spacetime Dependent Lagrangians and the Vacuum Expectation Value of the Higgs field

The spacetime dependent lagrangian formalism of references [1-2] is used to obtain a classical solution of Yang-Mills theory. This is then used to obtain an estimate of the vacuum expectation value of the Higgs field, viz. $ϕ_{a}=A/e$, where $A$ is a constant and $e$ is the Yang-Mills coupling (related to the usual electric charge). The solution can also accommodate non-commuting coordinates on the boundary of the theory which may be used to construct D-brane actions. PACS:11.15.-q ; 11.27+d ; 11.10.Ef

hep-th↗

arXiv2002

Non-singular solutions of flux branes in M-theory and attractor solutions

Here we present a class of solutions of M-theory flux branes, which are non-singular at origin. These class of solutions help us to determine the field strength at origin together with the behavior of it near origin. Further we show a way to find the attractor solutions of such flux branes.

hep-th↗