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Research Publications (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/213

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Author: search.filters.author.Goswami, RituparnoSubject: search.filters.subject.0206 Quantum Physics

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    Charged radiation collapse in Einstein-Gauss-Bonnet gravity
    (Springer Science and Business Media LLC, 2022-04-25) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, Rituparno
    We generalise the continual gravitational col lapse of a spherically symmetric radiation shell of matter in f ive dimensional Einstein–Gauss–Bonnet gravity to include theelectromagneticfield.Thepresenceofchargehasasignif icant effectinthecollapsedynamics.Wenotethatthereexists a maximal charge contribution for which the metric func tions in Einstein–Gauss–Bonnet gravity remain real, which is not the case in general relativity. Beyond this maximal charge the spacetime metric is complex. The final fate of col lapse for the uncharged matter field, with positive mass, is an extended, weak and initially naked central conical singular ity. With the presence of an electromagnetic field, collapse terminates with the emergence of a branch singularity sepa rating the physical spacetime from the complex region. We show that this marked difference in singularity formation is only prevalent in five dimensions. We extend our analysis to higher dimensions and show that for all dimensions N ≥ 5, charged collapse ceases with the above mentioned branch singularity. This is significantly different than the uncharged scenario where a strong curvature singularity forms post col lapse for all N ≥ 6 and a weak conical singularity forms when N =5.Acomparison with charged radiation collapse in general relativity is also given.
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    Diffusive and dynamical radiating stars with realistic equations of state
    (Springer Science and Business Media LLC, 2017-03) Brassel, Byron P.; Maharaj, Sunil D.; Goswami, Rituparno
    We model the dynamics of a spherically symmetric radiating dynamical star with three spacetime regions. The local internal atmosphere is a two-component system consisting of standard pressure-free, null radiation and an additional string fluid with energy density and nonzero pressure obeying all physically realistic energy conditions. The middle region is purely radiative which matches to a third region which is the Schwarzschild exterior. A large family of solutions to the field equations are presented for various realistic equations of state. We demonstrate that it is possible to obtain solutions via a direct integration of the second order equations resulting from the assumption of an equation of state. A comparison of our solutions with earlier well known results is undertaken and we show that all these solutions, including those of Husain, are contained in our family. We then generalise our class of solutions to higher dimensions. Finally we consider the effects of diffusive transport and transparently derive the specific equations of state for which this diffusive behaviour is possible.