arXiv subjects

Vikram Soni

Publications and source records attributed to Vikram Soni.

At least 19 recordsLinked to original sources

arXiv2024

Probing spherical outbursts of neutron star mergers from an equation of state with composite nucleons

We consider a variational 'crystalline' equation of state (EOS) that follows from nucleons that are chiral solitons with deep relativistic quark bound states. In this model conventional quark matter does not occur till a high density threshold at which the quark bound states in the nucleons get compressed and merge with the continuum. Once the barrier at this threshold is overcome, roughly when, $n_B \sim 1/fm^3$, we expect the 'crystalline' nuclear matter to make a sudden transition into quark matter when the EOS becomes soft through a decompression. The sudden increase in density triggers a collapse releasing large amount of gravitational potential energy that can generate a spherical outburst (or kilonova) of ejected matter.

nucl-th↗

arXiv2019

A new state of dense matter in neutron stars with nucleon structure

The existence of stars with a large mass of 2 solar masses means that the equation of state is stiff enough to provide high enough pressure at large central densities. Previous work shows that such a stiff equation of state is possible if the ground state has nucleons as its constituents. We find this to be so in a chiral soliton ( skyrmion ) model for a composite nucleon which has bound state quarks. The strong binding of the quarks in this composite nucleon is plausibly the origin of the nucleon-nucleon hard core. In this model we find a new state of superdense matter at high density which is a 'topological'cubic crystal of overlapping composite nucleons that are solitons with relativistic quark bound states. The quarks are frozen in a filled band of a unique state, which not an eigenstate of spin or isospin but an eigenstate of spin plus isospin, $ \vec S + \vec I = 0$. In this alternative model we find that all neutron stars have no regular `free'quark matter. Neutron stars whose central density crosses a threshold baryon density of approximately, $n_b \sim 1/fm^3 $, will become unstable and go through a decompression (sudden) density discontinuity to conventional quark matter. Sequentially, this contraction of the core of the star will soften the equation of state release a large amount of gravitational potential energy which can give rise to a shock wave and matter ejection. Since the merger of two neutron stars gives a compact state whose mass is larger than the allowed maximum mass, this will be followed by a jet and a short gamma ray burst while transiting into a black hole.

nucl-th↗

arXiv2019

Magnetar Crusts: Matter at $10^{15}$ Gauss

In this work we find that the at the high polar magnetic fields of magnetars, $B \sim 10^{14-15}$ G, the outermost crust ($ρ< 10^7$ gm/cc) of the star can become a transverse insulator and a filamentary crystal along the field direction. Also, the transverse conductivity in the crust goes inversely as the square of polar magnetic field (as $1/B^2$). At these high fields the transverse crustal currents associated with the polar magnetic field can then dissipate more effectively via Ohm's law.

astro-ph.HE↗

arXiv2018

Magnetar Signature - The U Curve

This work looks at some definitive signatures of magnetars, in particular of period closures accompanied by a decline of X-ray radiation in two models. We review some of the previous works which are based on the well known dynamo model in which the star is born with a period of a few milliseconds at high temperatures. In such a convection regime the dynamo mechanism can amplify the the magnetic fields to the magnetar value. This is in contrast to a screened core model which posits that a high density phase transition occurs in the inner core of magnetars that dynamically aligns all the neutron magnetic moments producing a large magnetic field in the core. The accompanying change of flux gives rise to shielding or screening currents in the surrounding high conductivity plasma that do not permit the field to exit to the surface. Ambipolar diffusion then transports the field to the crust dissipating energy in neutrinos and X-rays. The up-welling field cleaves the crust resulting in flares and X-ray radiation from ohmic dissipation in the crust till the screening currents are spent and the surface polar field attains its final value. In the dynamo model the polar magnetic field decreases with time whereas in our screened model it increases to its final value. One consequence of this is that in the latter model, as a function of time and period, the ratio of the dipole radiation loss, $\dot E$ to the X-ray luminosity, $ L_X$, is a 'U' curve, indicating that it is the exponential decline in $L_X$, that brings closure to the periods that are observed for magnetars.

astro-ph.HE↗

arXiv2015

The cosmological constant from the zero point energy of compact dimensions

We consider extra compact dimensions as the origin of a cosmological universal energy density in the regular dimensions, with only graviton fields propagating in the compact space dimensions. The quantum zero point energy originating from the finite size boundary condition in the compact dimensions can produce a constant energy density in regular $3$ space which is homogeneous and isotropic. It then makes a natural identification with the cosmological constant in conformity with the Einstein equation. It turns out that for the emergent energy density to agree with the observed value of the cosmological constant, the size/radius of compact dimension is to be of order of $10^{-2}$ cm.

gr-qc↗

arXiv2014

The nucleon and the two solar mass neutron star

The existence of a star with such a large mass means that the equation of state is stiff enough to provide a high enough pressure up to a fairly large central densities,. Such a stiff equation of state is possible if the ground state has nucleons as its constituents. This further implies that a purely nucleon ground state may exist till about four times nuclear density which indicates that quarks in the nucleon are strongly bound and that the nucleon nucleon potential is strongly repulsive. We find this to be so in a chiral soliton model for the nucleon which has bound state quarks. We point out that this has important implications for the strong interaction $ μ_B$ vs T phase diagram.

nucl-th↗

arXiv2013

Environmental flow for Monsoon Rivers in India: The Yamuna River as a case study

We consider the flows of Monsoon Rivers in India that will permit the river to perform all its natural functions. About 80% of the total flow for Indian rivers is during the monsoon and the remaining 20% is during the non monsoon period. By carrying out a case study of the river Yamuna in Delhi we find that at least 50% of the virgin monsoon (July to September) flow is required for the transport of the full spectrum of soil particles in the river sediment. A similar flow is needed for adequate recharge of the floodplain aquifers along river. For the non monsoon period (October to June) about 60% of the virgin flow is necessary to avoid the growth of still water algae and to support river biodiversity.

physics.geo-ph↗

arXiv2012

Is the high mass binary pulsar PSR J 1614-2230 a latent magnetar?

We consider the newly found high mass and low magnetic field binary pulsar PSR J1614-2230 in a model in which magnetars owe their strong magnetic fields to a high baryon density, magnetized core. In our magnetar model all neutron stars above a certain threhold mass are magnetars. This confronts us with the very basic paradox as to why this high mass star, PSR J1614-2230, remains a pulsar and shows no magnetar characteristics. This is a star that has acquired its large mass by accretion from its binary companion over 5 gigayears. In this work we show that the maximum rate of energy gain from the strong interaction phase transition from this slow accretion does not allow for high enough interior temperature for ambipolar transport of the magnetic field to the surface of the star and thus the PSR J 1614-2230 remains latent and does not become an emergent magnetar.

astro-ph.HE↗

arXiv2012

Magnetic Moment of Constituent Fermions in Strongly Interacting Matter

We investigate the magnetic moment operator for constituent fermion masses for chirally symmetric theories. Constituent fermion masses are generated through a yukawa interaction of the fermion with a scalar (or /and psuedoscalar) field via the vacuum expectation value (VEV) of the scalar (or and psuedoscalar) field. We especially consider the high baryon density $π_0$ condensed phase, in which chiral symmetry is spontaneously broken, with space varying expectation values of the $ σ$ and $π_0$ fields. This phase has a spin polarized fermi sea as the ground state. We show that there is indeed generated a macroscopic magnetization in this phase, contrary to what one would have found, if one just used a primitive phenomenological magnetic moment formula for explicit/ current fermion masses. Furthermore, this analysis reveals that the magnetization of this state goes up as the VEV, that determines the 'mass', comes down with increasing baryon density. The consequent high magnetic field that is generated will destabilize this state at a threshold density. This is important in the context of neutron stars, as such a high density state may be responsible for very high magnetic fields in the dense core of neutron stars. This could potentially be the origin of magnetars - the stars with the largest magnetic fields in the universe.

hep-ph↗

arXiv2010

Magnetars From Magnetized Cores Created by a Strong Interaction Phase Transition

We consider a model where the strong magnetic fields of magnetars arise from a high baryon density, magnetized core. In this framework magnetars are distinguished from pulsars by their higher masses and central density. For magnetars, as core densities exceed a threshold, the strong interaction induces a phase transition to a neutral pion condensate that aligns all magnetic moments. The core magnetic field is initially shielded by the ambient high conductivity plasma. With time the shielding currents dissipate transporting the core field out, first to the crust and then breaking through the crust to the surface of the star. Recent observations provide strong support for this model which accounts for several properties of magnetars and also enables us to identify new magnetars.

astro-ph.SR↗

arXiv2007

Diversity Begets Stability in an Evolving Network

Complex evolving systems such as the biosphere, ecosystems and societies exhibit sudden collapses, for reasons that are only partially understood. Here we study this phenomenon using a mathematical model of a system that evolves under Darwinian selection and exhibits the spontaneous growth, stasis and collapse of its structure. We find that the typical lifetime of the system increases sharply with the diversity of its components or species. We also find that the prime reason for crashes is a naturally occurring internal fragility of the system. This fragility is captured in the network organizational character and is related to a reduced multiplicity of pathways between its components. This work suggests new parameters for understanding the robustness of evolving molecular networks, ecosystems, societies, and markets.

nlin.AO↗

arXiv2007

A Natural Explanation for Magnetars

We explore the possibility that a magnetar may owe its strong magnetic field to a magnetized core which, as indicated by certain equations of state, may form due to phase transitions at high density mediated by strong interaction within a sufficiently massive neutron star. We argue that the field derived from such a core could explain several inferred evolutionary behaviors of magnetars.

astro-ph↗

arXiv2005

A prelude to Neutron Stars: The phase diagram of the strong interactions at finite density

We consider strong interactions at finite density in mean field theory, through an effective lagrangian that can describe both nuclear matter and quark matter. This lagrangian has three couplings that are all fixed by experiment and no other parameters. With increasing baryon density we then find the following hierarchy. At nuclear density and above we have nuclear matter with chiral spontaneous symmetry breaking (SSB), followed by the pion condensed quark matter, again with chiral SSB, albeit with a different realization and finally a transition to the diquark CFL state which also has chiral SSB (and colour SSB), with yet another realization. To one's surprise at zero temperature (in mean field theory), at any finite density chiral symmetry is never restored! We find another remarkable feature and this is that the tree level mass of the sigma particle, that is set by experiment to about 800 MeV, has a crucial and unexpected influence on the physics. Strange quark matter and strange stars are ruled out for a sigma mass above 700 MeV and neutron stars with magnetic pion condensed cores, that could provide magnetic fields of neutron stars, exist only for a small interval, between 750-850 MeV, for the sigma mass.

hep-ph↗

arXiv2005

Strong interactions at all density

We show using Mean Field Theory that the phase diagram of QCD at finite density (T=0) is such that chiral symmetry remains spontaeously broken at all density!

hep-ph↗

arXiv2003

A new window on Strange Quark Matter as the ground state of strongly interacting matter

If strange quark matter is the true ground state of matter, it must have lower energy than nuclear matter. Simultaneously, two-flavour quark matter must have higher energy than nuclear matter, for otherwise the latter would convert to the former. We show, using an effective chiral lagrangian, that the existence of a new lower energy ground state for two-flavour quark matter, the pion condensate, shrinks the window for strange quark matter to be the ground state of matter and sets new limits on the current strange quark mass.

hep-ph↗

arXiv2002

The Quark Gluon Pion Plasma

While it is commonly believed that there is a {\it direct} transition from the hadronic to a quark gluon phase at high temperature, it would be prejudicial to rule out a sequence of dynamically generated intermediate scales. Using as guide, an effective lagrangian with unconfined gluons and constituent quarks, interacting with a chiral multiplet, we examine a scenario in which the system undergoes first-order transitions at $ T_{comp}$, the compositeness scale of the pions, at $T_χ$, the scale for spontaneous chiral symmetry breaking, and at $T_c$, the confinement temperature. We find that at current energies, it is likely that the formation temperature of the plasma, $ T_0 < T_{comp} $, and that this is therefore a quark gluon pion plasma (QGPP) rather than the usual quark gluon plasma (QGP). We propose some dilepton-related signatures of this scenario.

hep-ph↗

arXiv2000

Planck Scale Physics of the Single Particle Schrödinger Equation with Gravitational Self-Interaction

We consider the modification of a single particle Schrödinger equation by the inclusion of an additional gravitational self-potential term which follows from the prescription that the' mass-density'that enters this term is given by $m |ψ(\vec {r},t)|^2$, where $ψ(\vec {r}, t)$ is the wavefunction and $m$ is the mass of the particle. This leads to a nonlinear equation, the ' Newton Schrodinger' equation, which has been found to possess stationary self-bound solutions, whose energy can be determined exactly using an asymptotic method. We find that such a particle strongly violates superposition and becomes a black hole as its mass approaches the Planck mass.

gr-qc↗

arXiv1999

A New Regime for Dense String Networks in the One Scale Model with Friction

We examine the compatibility between the one scale model with friction for the evolution of cosmic string networks with the Kibble mechanism for string network formation during a second order phase transition. We find a regime which connects (in a dramatically short time $\sim .1 t_c$) the dense string network (small network scale $L\sim 1/T_c$) created by the Kibble {\it{mechanism}} to the (dilute) Kibble {\it{regime}}(L\sim t^{3/4} in which friction dominated strings remain till times $t_*\sim (M_P/T_c)^2t_c$. The enormous loss of string length implied by this result is due to the continued dissipative motion of the string network which follows from the one scale model's identification of the typical curvature radius with the network scale and the fact that the cosmological phase transition time $t_c\sim M_{Planck}/T_c^2$ is much larger than the damping time scale $l_f\sim T_c^2/T^3$. The significant implications for string mediated Baryogenisis are also discussed briefly.

hep-ph↗