Y. Sobouti

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• Ph.D.
• Founder of IASBS at Institute for Advanced Studies in Basic Sciences

Singularities in Newton’s gravitation, in general relativity (GR), in Coulomb’s law, and elsewhere in classical physics, stem from two ill conceived assumptions: (a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and (b) the non-quantum assumption that these point-likes can be assigned precise coordinates a...

Singularities in Newton's gravity, in general relativity (GR), in Coulomb's law, and elsewhere in classical physics, stem from two ill conceived assumptions that, a) there are point-like entities with finite masses, charges, etc., packed in zero volumes, and b) the non-quantum assumption that these point-like entities can be assigned precise coordi...

We address three concepts. (1) The point particle assumption inherent to non-quantum physics is singular and entails divergent fields and integrals. (2) In quantum physics, electromagnetism (EM) plays an asymmetric role. It acts on quantum wave fields (wave functions) but the wave fields do not react back. We suggest to promote the one-sided action...

We envisage a black hole perturbed by a force-free magnetic field (FFMF) outside and attempt to determine its structure. We suppose the metric that describes this black hole is of the static spherical type, that is Schwarzschild, and the energy-momentum tensor emanating from an FFMF source perturbs this background metric, in this regard one can ima...

Newtonian gravity is massless and decreases as 1/r^2‎. ‎This is too fast a decline to explain the flat rotation curves of spiral galaxies‎. ‎A massive gravity field on the other hand‎, ‎has1/r behaviour and is capable of doing the job. A massive gravity can produce rotation curves flat enough to justify the observational data up to several optical...

The paper discusses global warming and its consequences. It is intended to promote public awareness on anthropogenic sources of climate change and degradation of environmental wellbeing. It is written at the invitation of the Editor of Negah-e-now, a quarterly journal in Farsi.

Two dynamical systems with same symmetry should have features in common, and as far as their shared symmetry is concerned, one may represent the other. The three light quark constituent of the hadrons, (a) have an approximate flavor SU(3)f symmetry, (b) have an exact color SU(3)c symmetry, and (c) as spin 1 2 particles, have a Lorentz SO(3, 1) symm...

In an expansion scheme in velocity space, the first order perturbations of a stellar system bear close resemblance to those of a fluid. This feature is exploited to study the structure of the Hilbert space of the linear perturbations of a stellar system, to provide a classification for the modes, and to construct ansatz for variational calculations...

We examine the wave modes in a sunspot umbra. Assuming a stratification, based on a model atmosphere in a sunspot, the normal mode spectrum is determined. The modes are classified using a scheme based on a Helmholtz decomposition of the displacements into l (longitudinal) and t (transverse) components. In certain cases these can be related to the u...

Two dynamical systems with same symmetry should have features in common, and as far as their shared symmetry is concerned, one may represent the other. The three light quark constituents of the hadrons, a) have an approximate flavor SU(3) symmetry, b) have an exact color SU(3) symmetry, and c) as spin 1/2 particles, have a Lorentz SO(3,1) symmetry....

Beginning from two simple assumptions, i) the speed of light is a universal constant, or its equivalent, the spacetime intervals are Lorentz invariant, and ii) there are mutually interacting particles, with a covariant `source-field' equation, one arrives at a class of field equations of which the standard electromagnetism (EM) and electrodynamics...

That the universal constancy of the speed of light is a logical consequence of Maxwell's equations is common knowledge. Here we show that the converse is also true. That is, electromagnetism (EM) and electrodynamics (ED) in all their details can be derived from the simple assumption that the speed of light is a universal constant. The consequences...

Allowing for virtual paths in phase space permits an extension of Hamilton’s principle of least action, of lagrangians and of hamiltonians to phase space. A subsequent canonical quantization, then, provides a framework for quantum statistical mechanics. The classical statistical mechanics and the conventional quantum mechanics emerge as special cas...

The case of a quantum two-level system coupled to a time variable magnetic field is investigated. The Schrodinger equation pertaining to the system is reduced to a second order linear equation in time and its solutions are sought by an integrating factor technique. A differential equation for the integrating factor and, therefrom, a criterion for f...

The mass of the bright M5 supergiant α1 Herculis has been estimated in a number of studies to range over wide limits of 1.7 to 15 M⊙. Here, we address this wide range of mass assessments by constraining the age, mass and nature of this interesting variable star from three independent approaches: (1) isochronal fitting of the three stars in the α He...

شمار زیادی از دانش‌پژوهان بر این باورند که زمین به طور غیر عادی گرم می‌شود و به نظر می‌رسد انسان صنعتی سده‌های نوزدهم و بیستم در این گرم شدن نقش داشته است. اقلیم سدهٔ بیست‌ویکم چه بخواهیم، چه نخواهیم با اقلیمی که انسان، جانور، و گیاه با آن انس داشته است، متفاوت خواهد بود. بسیاری از پیامدهای آن ناخوشایند خواهند بود، و بسیاری از زیست‌بوم‌های آبی و خا...

Analysis of over 15 years of V-band and Wing three filter near-IR photometry of the bright M5Ib-II supergiant has been carried out. Wavelet analysis of these data reveals that the star pulsates with several complicated oscillation modes. Different time scales of variability are identified, and with the aid of discrete Fourier analysis, depending on...

Rotation curves of spiral galaxies \emph{i}) fall off much less steeply than the Keplerian curves do, and \emph{ii}) have asymptotic speeds almost proportional to the fourth root of the mass of the galaxy, the Tully-Fisher relation. These features alone are sufficient for assigning a dark companion to the galaxy in an unambiguous way. In regions ou...

Rotation curves of spiral galaxies \emph{i}) fall off much less steeply than the Keplerian curves do, and \emph{ii}) have asymptotic speeds almost proportional to the fourth root of the mass of the galaxy, the Tully-Fisher relation. These features alone are sufficient for assigning a dark companion to the galaxy in an unambiguous way. In regions ou...

Wherever one talks of dark matter, one does so where there is an observable matter and an associated unsolved dynamical issue to be settled. We promote this observation to the status of an axiom and conjecture that there is a dark companion to every baryonic matter, subject to certain rules as regards its size, distribution. To pursue the propositi...

Flat or almost flat rotation curves of spiral galaxies can be explained by logarithmic gravitational potentials. The field equations of GR admit of spacetime metrics with such behaviors. The scenario can be interpreted either as an alternative theory of gravitation or, equivalently, as a dark matter paradigm. In the latter interpretation, one is le...

Whenever and wherever one talks of dark matter, one does so when and where there is a luminous matter and a dynamical issue to be settled. We promote this observation to the status of an axiom and assume that there is a dark companion to every luminous matter and there are orders to this companionship. To pursue the proposition in a formal and quan...

Having gained some insight into the concept of 'actual and virtual paths' in a phase-space formalism (Sobouti and Nasiri 1993 Int. J. Mod. Phys. B 7 3255, Nasiri et al 2006 J. Math. Phys. 47 092106), in the present paper we address the question of 'extended' phase-space stochastic quantization of Hamiltonian systems with first class holonomic const...

The influence of longitudinal structuring on the fast kink modes of coronal loops is investigated. Analytical dispersion relations and mode profiles are derived for the second-order ordinary differential equation governing the z- component of the perturbation in the magnetic field, $\delta B_z$. All other components are given in terms of $\delta B_...

This paper summarizes the present situation concerning astronomy in Iran. Shiraz University introduced astronomy in the mid-1960s and established the Biruni Observatory. Astronomy is also carried out at Tabriz University and in Meshed, Zanjan, Tehran, Babol and other places. The Astronomical Society of Iran is flourishing, and is about 30 years old...

Aims. We investigate the standing kink modes of a cylindrical model of coronal loops. The density is stratified along the loop axis and changes discontinuously at the surface of the cylinder. The periods and mode profiles are studies with their deviation from those of the unstratified loops. The aim is to extract information on the density scale he...

Without abstract.

Damping of MHD waves seems to play an important role in heating the solar corona. In this respect a magnetized flux tube with a specified density profile is considered and the singularity of ideal equation of motion in coronal approximation is removed by introducing the viscous and resistive damping in the tube. The resultant equations are solved b...

To explain the cosmic speed up, brought to light by the recent SNIa and CMB observations, we propose the following: (a) In a spacetime endowed with a FRW metric, we choose an empirical scale factor that best explains the observations. (b) We assume a modified gravity, generated by an unspecified field Lagrangian, f(R). (c) We use the adopted empiri...

Since the earliest identifications of the kink oscillations in coronal loops a considerable amount of data have been analysed and possible factors causing the shift in frequency and affecting the oscillation properties of the loops are investigated by different authors. Here, we use analytical and numerical methods to understand the effects of long...

We investigate the standing kink modes of a cylindrical model of coronal loops. The density is stratified along the loop axis and changes discontinuously at the surface of the cylinder. The periods and mode profiles are studies with their deviation from those of the unstratified loops. The aim is to extract information on the density scale heights...

Conventional approach to quantum mechanics in phase space, (q,p), is to take the operator based quantum mechanics of Schrodinger, or and equivalent, and assign a c-number function in phase space to it. We propose to begin with a higher level of abstraction, in which the independence and the symmetric role of q and p is maintained throughout, and at...

We propose an action-based $ f(R) $ modification of Einstein's gravity which admits of a modified Schwarzschild-deSitter metric. In the weak field limit this amounts to adding a small logarithmic correction to the newtonian potential. A test star moving in such a spacetime acquires a constant asymptotic speed at large distances. This speed turns ou...

We study the resonant absorption of MHD waves in magnetized flux tubes with a radial density inhomogeneity. Within the approximation that resistive and viscous processes are operative in thin layers surrounding the singularities of the MHD equations, we give the full spectrum of the eigenfrequencies and damping rates of the MHD quasi modes of the t...

We study the resonant absorption of MHD waves in magnetized flux tubes with a radial density inhomogeneity. Within the approximation that resistive and viscous processes are operative in thin layers surrounding the singularities of the MHD equations, we give the full spectrum of the eigenfrequencies and damping rates of the MHD quasi modes of the t...

Allowing the energy of a gravitational field to serve partially as its own source allows gravitating bodies to exhibit stronger fields, as if they were more massive. Depending on degree of compaction of the body, the field could be one to five times larger than the newtonian field. This is a comfortable range of increase in field strength and may p...

Wave transmission in low beta magnetic flux tubes has, mathematically, the same structure as the propagation of electromagnetic waves in optical fibers. In both cases the problem is reducible to a single wave equation for the longitudinal component of the perturbed field along the fiber/tube axis. We derive this equation, solve the dispersion relat...

Because of Coriolis forces equations governing the normal modes of rotating stars are quadratic in the eigenfrequency omega. Furthermore the eigendisplacement vectors have a toroidal component in the phi- direction. For axially symmetric modes; that is for the azimuthal wave number m=0 this toroidal component can be exactly expanded in terms of the...

Wave propagation in a zero-beta magnetic flux tube with a discontinuous Alfvèn speed at its surface is considered. The problem is reduced to solving a wave equation for the projection of the magnetic perturbation along the axis of the cylinder. The mathematical formalism is identical with that for the propagation of electromagnetic waves in optical...

An analysis of the toroidal modes of a rotating fluid, by means of the differential equations of motion is not readily tractable. A matrix representation of the equations in a suitable basis, however, simplifies the problem considerably and reveals many of its intricacies. Comment: 12 pages, 4 fiures, revised version to appear in A&A

The post-Newtonian approximation of the general relativistic Liouville's equation is presented. Two integrals of motion, generalizations of the classical energy and angular momentum, are obtained. Polytropic models are constructed as an application.

We use the post-Newtonian (pn) order of Liouville's equation to study the normal modes of oscillation of a spherically symmetric relativistic system. Perturbations that are neutral in Newtonian approximation develop into a new sequence of normal modes. In the first pn order; a) their frequency is an order q smaller than the classical frequencies, w...

Interaction of a stochastic background of gravitational radiation with celestial systems changes their dynamical elements in a random manner and give rise to secular changes in time. In this spirit we study the angular momentum transfer from a random background of radiation either to a rotating star or to an oscillating one. The angular momentum tr...

We use the post Newtonian (pn) order of Liouville's equation (pnl) to study the normal modes of oscillation of a relativistic system. In addition to classical modes, we are able to isolate a new class of oscillations that arise from perturbations of the space-time metric. In the first pn order; a) their frequency is an order q smaller than the clas...

The post-Newtonian approximation of general relativistic Liouville's equation is presented. Two integrals of it, generalizations of the classical energy and angular momentum, are obtained. Polytropic models are constructed as an application.

The surfaces of section in a harmonic oscillator potential, perturbed by quartic terms, are obtained analytically. A succession of action‐angle, Lissajous and Lie transformations near the 1:1 commensurability, reduces the three‐dimensional motion to a one‐dimensional one. The latter is solved in terms of Jacobi's elliptic functions. Existence condi...

There are of the order of 30 astronomers with research records and another 40-50 with substantial education in astronomy and astrophysics. Geographically, astronomical and astrophysical research is concentrated mainly at Shiraz University (cosmology and photometric observations), Sharif University of Theran (cosmology and gamma-ray astronomy), Tabr...

We investigate the possibility of the excitation of the oscillation modes of polytropic stars by gravitational waves. We decompose the displacement vector field of a normal mode into its irrotational and solenoidal components and show that the interaction with the gravitational waves takes place through the irrotational component. We calculate the...

In attempts to detect gravitational waves, the response of some celestial systems such as the earth[l] or binary systems[2] to such waves have been investigated. Following this line of thought, here we study the possibility of excitation of the oscillation modes of a polytropic star by gravitational radiation and calculate the relevant absorption c...

The stability and normal modes of oscillations of polytropic stellar systems are investigated using the symmetries of the linearized Liouville's equation. The O(3) symmetry of this linearized equation was utilized to separate the angle dependence of the eigenfunctions and hence to reduce the six dimensional phase-space problem to a two dimensional...

A dynamical symmetry group of Liouville's equation for quadratic potentials is obtained. A complete set of mutually commuting operators and the ladder operators to generate the simultaneous eigenfunctions of the set are given.

We consider the equations of general relativity in free space in the linear approximation. Non-stationary moving solutions for these equations, which are localized and have finite energy, are explicitly constructed. The energy of the localized wave is shown to be proportional to its internal frequency and can represent a massive quantum particle `m...

It is an assumption of traditional stellar dynamics that Liouville’s equation governs the time evolution of stellar systems. An inevitable consequence of such a premise is that (a) at least some modes of instability of stellar systems may be those of Liouville’s equation; and (b) stellar systems might undergo periodic changes of definite patterns i...

A systematic study of the symmetries of Liouville's equation for r-1-potential is presented. The canonical transformations in phase space which leave the hamiltonian invariant turn out to be the full symmetry transformations of Liouville's operator, as well. The symmetry group is SO(4). A maximal set of mutually commuting operators, and subsequentl...

A systematic study of the symmetries of Liouville's equation for an arbitrary potential is presented. The method is applied to the case of quadratic potentials. The symmetry group of the latter turns out to be GL(3, c) with the noncompact subgroup SL(3, c). The latter, in turn, has the subgroups SU(3), and SO(3), SO(3, 1) and SU(2, 1) of which the...

The case of a quantum two-level system coupled to a time variable magnetic field is investigated. The Schrodinger equation pertaining to the system is reduced to a second order linear equation in time and its solutions are sought by an integrating factor technique. A differential equation for the integrating factor and, therefrom, a criterion for f...

It is suggested to formulate a nonequilibrium ensemble theory by maximizing a time-integrated entropy constrained by Liouville's equation. This leads to distribution functions of the form , where g(p, q, t) is a solution of Liouville's equation. A further requirement that the entropy should be an additive functional of the integrals of Liouville's...

We examine the wave modes in a sunspot umbra. Assuming a stratification, based on a model atmosphere in a sunspot, the normal mode spectrum is determined. The modes are classified using a scheme based on a Helmholtz decomposition of the displacements into l(longitudinal) and t(transverse) components. In certain cases these can be related to the usu...

It was shown by Fabian et al. (1975) that normal modes of a binary member may be excited by the tidal effect of its companion, causing energy transfer from the orbital motion to the star. In this paper, the eigendisplacements of a normal mode are decomposed into an irrotational and a 'weighted' solenoidal component and it is shown that only the irr...

The normal modes of oscillation of a perfectly conducting and self-gravitating fluid, pervaded by a force-free magnetic field are studied. A polytropic structure is assumed for the fluid. A gauged version of the Helmholtz theorem is used to decompose the Lagrangian displacements into an irrotational and a weighted solenoidal component. The solenoid...

Exact and complete set of eigenfunctions and eigenvalues of a harmonic potential are presented. The eigenfunctions constitute three distinct sequences of analytic, coanalytic, and non analytic functions in Z = p + iq, where (q, p) are phase space coordinates. Solutions are obtained by a pair of raising and lowering operators for Liouville's equatio...

Let the linearized Liouville-Poisson equation be i∂f/∂t = A f,f = f(q, p), f, p = phase coordinates. A on f's is not a hermitian operator. However, an eigenvalue equation, A fω = ωfω, with real ω's and non-orthogonal eigenfunctions can be set up. For spherically symmetric potentials A and A2 have 0(3) symmetry. There exists an angular momentum oper...

Time-dependent solutions of Liouville's equations are constructed. From a review of existing literature on such solutions, it is concluded that the eigenfunctions of Liouville's operator are complex functions of phase coordinates in a complex Hilbert space. The latter in turn is the direct product of two Hilbert spaces, one accommodating functions...

[For part I see: ibid. 210, No.1/2, 18-24 (1989; Zbl 0672.70021).] Exact and complete set of eigenfunctions and eigenvalues of a harmonic potential are presented. The eigenfunctions constitute three distinct sequences of analytic, coanalytic, and nonanalytic functions in ℤ=p+iq, where (q,p) are phase space coordinates. Solutions are obtained by a p...

It is often maintained that Antonov’s equation, a linearization of the collisionless Liouville-Boltzmann equation, governs small perturbations of a stellar system. The variational integrals resulting from Antonov’s equation are in six dimensional phase space. However, expanding the perturbations in the velocity coordinates and carrying out the inte...

It is often maintained that Antonov's equation, a linearization of the collisionless Liouville-Boltzmann equation, governs small perturbations of a stellar system. The variational integrals resulting from Antonov's equation are in six dimensional phase space. However, expanding the perturbations in the velocity coordinates and carrying out the inte...

We examine the structure of motions that can occur in a vertical magnetic flux tube with a rectangular cross-section. A polytropic stratification is assumed in the vertical direction. We use a gauged version of Helmholtz's theorem, to decompose the perturbations into an irrotational component and a solenoidal component, which we further split into...

In an expansion scheme in velocity space, the first order perturbations of a stellar system bear close resemblance to those of a fluid. This feature is exploited to study the structure of the Hilbert space of the linear perturbations of a stellar system, to provide a classification for the modes, and to provide the necessary ansatz for variational...

In an expansion scheme in velocity space, the first order perturbations of a stellar system bear close resemblance to those of a fluid. This feature is exploited to study the structure of the Hilbert space of the linear perturbations of a stellar system, to provide a classification for the modes, and to construct ansatz for variational calculations...

The Wooley (1954) and Michie-King (respectively 1963, 1967) models are among the examples analyzed in the present solution of the eigenvalue problem for the first-order radial perturbation of four energy-truncated distributions in model stellar systems. All eigenvalues obtained for all models with finite masses and radii are real, and there is no i...

Linear perturbations of stellar systems with step-like distributions of the form F(E)H(-E) are studied, where E is the energy integral, and H is Heaviside's step-function. If (1) dF/dE > 0 and (2) F|dF/dE|-1/2 = 0 at E = 0, then the operator generating the self gravitation term in Antonov's equation is positive. Then the system is stable against al...

In a convectively neutral fluid the g-modes are derived from a vector potential and the p-modes from a scalar potential. In a convectively non-neutral fluid the two potentials are coupled. For small and moderate deviations from convective neutrality, however, the solenoidal character of the g-modes and the irrotational nature of the p-modes persist...

Completeness of the sets of trial functions used in the numerical calculation of the eigenvalues and eigenvectors of the g- and p-modes of convectively neutral fluids is explicitly shown. Also, in the case of g-modes, it is proved that the eigenvectors obtained by the Rayleigh-Ritz variational method do converge to the actual eigenvectors.

The normal modes of oscillations of a rotating fluid have been expressed in terms of those of a nonrotating and convectively neutral fluid. The p-modes accept a double perturbation expansion in which the rotation and deviation of the fluid from convective neutrality are considered as two perturbation parameters. The g-modes do not yield to such a t...

The neutral g-modes of a degenerate fluid at zero temperature are analyzed. The g-modes of a degenerate fluid at finite but small temperatures are then expanded in terms of those of the zero temperature fluid. For nonrelativistic degenerate fluids it is found that (1) the g-eigenvalues are proportional to T mu(6)sub e mu(-1)sub i, where T is the in...

A perturbational-variational Rayleigh-Ritz (PV-RR) expansion scheme is developed for systematically obtaining the normal modes of small oscillations of self-gravitating fluids in perturbed configurations in powers of an external perturbing parameter that characterizes the eigenvalue equation. Some properties of the generalized perturbed eigenvalue...

Summary.. A perturbing force may remove the degeneracy of the neutral state of a convecting fluid, giving rise to a sequence of very long period oscillations. As an example it is shown that a force-free magnetic field is capable of generating pure hydromagnetic oscillations with periods of the order of Alfven crossing-times. Stability of the pertur...

A Bernoulli's integral supplemented with the equation of continuity provides a solution for the motion of gas surrounding a binary system.There exist two velocity modes whose streamlines are confined within appropriate equipotential surfaces.