arXiv subjects

C Sivaram

Publications and source records attributed to C Sivaram.

34 records · Page 2Linked to original sources

arXiv2010

Bounds on Photon Charge from Evaporation of Massive Black Holes

Photon charge has been of interest as a phenomenological testing ground for basic assumptions in fundamental physics. There have been several constraints on the photon charge based on very different considerations. In this paper we put further limits based on the well known properties of charged black holes and their subsequent evaporation by Hawking radiation and the assumption of charge conservation over this long physical process.

physics.gen-ph↗

arXiv2010

Charged Black Holes and Constraints on Baryon Asymmetry

The no-hair theorem, which postulates that all black holes can be completely characterized by only three externally observable parameters: mass, electric charge, and angular momentum, sets constraints on both the maximal angular momentum and maximal electric charge. In this work, we would explore the consequence of these for the formation of primordial black holes in the early universe and also the formation of black holes due to collapse of dark matter configurations and how this could be used to probe the conditions in the very early universe and constrain the epoch when baryon asymmetry was established.

physics.gen-ph↗

arXiv2009

Gammaless GRBs?

The Compactness Problem in GRBs has been resolved by invoking the Lorentz factors associated with the relativistic bulk motion. This scenario applies to GRBs where sufficient energy is converted to accelerate the ejected matter to relativistic speeds. In some situations this may not be a possible mechanism. Hence the gamma rays are trapped in the region. Here we look at these possible scenarios, where the neutrino pair production process dominates, and the neutrinos are able to escape freely. This could give a scenario where release of neutrinos precedes the gamma ray emission, which is much attenuated, possibly explaining why fewer GRBs are observed than what is expected.

astro-ph.CO↗

arXiv2009

Possible Alternate Scenario for short Duration GRBs

In this paper we look at new class of objects made up entirely of dark matter particles. We look at these objects as possible candidate for short duration gamma ray bursts eliminating the baryon load problem. These could also provide a possible scenario for the formation of sub-stellar black holes, distinct from the usual Hawking black hole.

astro-ph.CO↗

arXiv2009

New Class of Dark Matter Objects and their Detection

About one-fourth of the universe is thought to consist of dark matter. Yet there is no clear understanding about the nature of these particles. Commonly discussed dark matter candidates includes the so called WIMPs or weakly interacting massive particles with masses from about 10GeV to 1TeV. These particles can gravitate to form a new class of objects in dark matter halos or around the galactic centre. We study in some detail many properties of these objects; which are dark matter dominated and bound by their self gravity; their formation and possibilities of their detection. Implications of the presence of such objects for star formation are also discussed. These objects could provide the possibility of forming primordial black holes distinct from the usual Hawking black holes and they could also provide a scenario for short duration gamma ray bursts, avoiding the baryon load problem.

astro-ph.CO↗

arXiv2009

Curvature, Phase Space, Holography and Black Hole Entropy

This paper discusses the thermodynamics of a black hole with respect to Hawking radiation and the entropy. We look at a unified picture of black hole entropy and curvature and how this can lead to the usual black hole luminosity due to Hawking radiation. It is also shown how the volume inside the horizon, apart from surface area, can play a role in understanding the Hawking flux. In addition holography also implies a phase space associated with the interior volume and this happens to be just a quantum of phase space, filled with just one photon. Generalised uncertainty principle can be incorporated in this analysis. These results hold for all black hole masses in any dimensions.

astro-ph.CO↗

arXiv2009

Relativistic Jets from Black Holes: A Unified Picture

The current understanding of the formation of powerful bi-directional jets in systems such as radio galaxies and quasars is that the process involves a supermassive black hole that is being fed with magnetized gas through an orbiting accretion disc. In this paper we discuss the dynamics of the jet powered by rotating black holes, in the presence of a magnetic field, including the scaling of the jet length and their typical time scales. We consider a unified picture covering all phenomena involving jets and rotating black holes ranging from gamma ray bursts to extragalactic jets and discuss the relevant scaling laws. We have also discussed the acceleration of the particles in jets and consequent synchrotron and inverse Compton radiations. Accelerated protons from jets as possible sources of high energy cosmic rays are also discussed.

astro-ph.HE↗

arXiv2009

A Brief Overview of the Major Contribution to Physics by Landau

Lev Davidovich Landau was arguably one of the greatest and most versatile physicists. His work spans a very wide range and has had a considerable impact on all areas of physics including condensed matter physics, plasma, high energy and particle physics, fluid dynamics, astrophysics, gravitation, elasticity, etc. Along with his former fellow student, E Lifshitz, he wrote the set of a dozen volumes, the magnificent world-renowned Course of Theoretical Physics which covered topics ranging from mechanics, classical theory of fields, quantum mechanics, electrodynamics of continuous media, fluid dynamics, kinetic theory, theory of elasticity, statistical physics and more.

physics.gen-ph↗

arXiv2008

Black Holes and the LHC

The relevant physics for the possible formation of black holes in the LHC is discussed.

physics.gen-ph↗

arXiv2008

Gravitational Effects of Weak Interactions at TeV Energies

Recently there has been a lot of interest in the search for extra dimensions. If gravity propagates in extra dimensions then gravity would become as strong as other interactions. This could also lead to the production of mini black holes. Here we have discussed how even without considering extra dimensions gravitational effects of weak interactions could show up at TeV energies.

physics.gen-ph↗

arXiv2008

A Brief History of Dark Energy

Gurzadyan-Xue Dark Energy was derived in 1986 (twenty years before the paper of Gurzadyan-Xue). The paper by the present author, titled The Planck Length as a Cosmological Constant, published in Astrophysics Space Science, Vol. 127, p.133-137, 1986 contains the formula claimed to have been derived by Gurzadyan-Xue (in 2003).

physics.gen-ph↗

arXiv2008

Some Enigmatic Aspects of the Early Universe III

In the previous parts of the discussion on the same topic, various aspects of the very early universe were discussed. We discussed how inclusion of large dark energy term compensates for the net gravity. Here the discussion is taken further including the effects of charge, magnetic fields and rotation. The role of large extra dimensions under the extreme initial conditions is discussed and possible connection with the cyclic brane theory is explored. We constrain various cosmic quantities like the net charge, number density of magnetic monopoles, primordial magnetic fields, size of the extra dimensions,etc.

astro-ph↗

arXiv2008

Some Enigmatic Aspects of the Early Universe II

In a recent paper it was suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities. In this paper we extend this idea further by the inclusion of charge and spin to the system. We have also discussed other possible scenarios by which the singular state can be averted, including a temperature dependent gravitational constant. Also possible modifications in the Einstein-Hilbert action have been discussed, which can again lead to a finite maximal curvature hence avoiding a singularity.

astro-ph↗

arXiv2008

Some Enigmatic Aspects of the Early Universe

Matter collapsing to a singularity in a gravitational field is still an intriguing question. Similar situation arises when discussing the very early universe or a universe recollapsing to a singularity. It is suggested that inclusion of mutual gravitational interactions among the collapsing particles can avert a singularity and give finite value for various physical quantities like entropy, density, etc.

astro-ph↗

arXiv2008

Scaling Relations for self-Similar Structures and the Cosmological Constant

Scaling relations for the mass, angular momentum and other properties of a wide range of self-similar structures in the universe are seen to have universal features. As a consequence of the ideas elaborated in earlier papers these relations can be connected to a background constant curvature given by the cosmological constant dominating cosmical dynamics.

astro-ph↗

arXiv2007

Smashnova Model

An alternate model for gamma ray bursts is suggested. For a white dwarf (WD) and neutron star (NS) very close binary system, the WD (close to Mch) can detonate due to tidal heating, leading to a SN. Material falling on to the NS at relativistic velocities can cause its collapse to a magnetar or quark star or black hole leading to a GRB. As the material smashes on to the NS, it is dubbed the Smashnova model. Here the SN is followed by a GRB. NS impacting a RG (or RSG) (like in Thorne-Zytkow objects) can also cause a SN outburst followed by a GRB. Other variations are explored.

astro-ph↗