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Plamen P. Fiziev

Publications and source records attributed to Plamen P. Fiziev.

At least 19 recordsLinked to original sources
arXiv2019

New Results for Quasi Normal Modes of Gravitational Waves

We briefly consider the data of collaboration LIGO/VIRGO for gravitational waves (GW) and the recent observations of Event Horizon Telescope (EHT), and we discuss difficulties for finding the right theory of gravity and the nature of the observed Extremely Compact Objects (ECOs). The only undisputable way to establish existence of event horizon of ECOs, is the extraction of Quasi Normal Modes (QNMs) from the ringing phase of the sources of GW. We present our method for calculation of QNMs of GW in the Schwarzschild metric with different boundary conditions. It is based on exact solutions of the Regge-Wheeler and Zerilli equations in terms of the confluent Heun functions. We present also new numerical results of high precision ($ \geq 16$ digits) for QNM frequencies. We indicate the difficulties for comparison of theoretical results for QNMs with the observations.

gr-qc↗
arXiv2019

Schwarzschild Massive-Point-Particle Problem in Arbitrary Radial Gauge

We present, for the first time, a correct solution of the Schwarzschild Massive Point (SMP) problem in {\em arbitrary} radial gauge and formulate the strict mathematical assumptions, which are necessary and sufficient for this. In GR, there exists a two-parameter family of such exact SMP solutions to the Einstein equations, which are physically distinguishable from the well-studied one parameter family of vacuum Schwarzschild solutions related with Schwarzschild Black Holes (SBH). The obtained here SMP family of solutions is defined by positive bare mass $M_0>0$ and positive Kepler mass $M<M_0$, or, alternatively, by the standard gravitational radius $ρ_g$ and mass ratio $\varrho=M/M_0 \in (0,1)$. The metrics of spacetime have an unavoidable jump at the place of a massive point particle. We also present a proper development of the theory of distribution defined by kernels with a finite jump which appear in the solution of SMP. The specific properties of these distributions are used for work with SMP. A series of physical properties of SMP solutions are derived and commented. Our findings are important for description of Extremely Compact Objects (ECOs) studied in relation with possible echoes in Gravitational Waves (GW) recently discovered by the LIGO/VIRGO collaboration.

gr-qc↗
arXiv2019

The Era of Gravitational Astronomy and Gravitational Field of Non-Rotating Single Point Particle in General Relativity

Utilizing various gauges of the radial coordinate, we give a General Relativistic (GR) description of static spherically symmetric spacetimes with a massive point source and vacuum outside this singularity. We show that in GR there exists a two-parameter family of such solutions to the Einstein equations which are physically distinguishable and describe the gravitational field of a single massive point particle with positive proper mass $M_0$ and positive Keplerian mass $M<M_0$. In particular, we show that the widespread Hilbert form of the Schwarzschild solution, which depends only on the Keplerian mass $M$ and describes Black Holes (BH), does not solve the Einstein equations with a massive point particle stress-energy tensor. Novel normal coordinates for the gravitational field and a new physical class of gauges are proposed, thus achieving a correct description of a point mass source in GR. We also introduce a gravitational mass defect of a point particle and determine the dependence of the solutions on this mass defect. The result can be described as a change of the Newton potential $φ_{\!{}_N}=-G_{\!{}_N}M/r$ to a modified one $φ_{\!{}_G}=-G_{\!{}_N}M/ \left(r+G_{\!{}_N} M/c^2\ln{{M_0}\over M}\right)$ and the corresponding modification of the four-interval. We show that the proper 3D flat space, where these two potentials can be compared, is the tangent space above the position of the massive point source. In addition, we present invariant characteristics of the physically and geometrically different classes of spherically symmetric static spacetimes created by a point mass. Our findings are important for description of Extremely Compact Objects (ECOs) studied in relation with possible echoes in Gravitational Waves (GW) recently discovered by the LIGO/VIRGO collaboration. %

gr-qc↗
arXiv2015

A realistic model of a neutron star in minimal dilatonic gravity

We present a derivation of the basic equations and boundary conditions for relativistic static spherically symmetric stars (SSSS) in the model of minimal dilatonic gravity (MDG) which offers an alternative and simultaneous description of the effects of dark matter (DM) and dark energy (DE) using one dilaton field $Φ$. The numerical results for a realistic equation of state (EOS) MPA1 of neutron matter are presented for the first time. The three very different scales, the Compton length of the scalar field $λ_Φ$, the star's radius $r^*$, and the finite radius of the MDG Universe $r_{U}$ are a source of numerical difficulties. Owing to the introduction of a new dark scalar field $φ=\ln(1+\lnΦ)$, we have been able to study numerically an unprecedentedly large interval of $λ_Φ$ and have discovered the existence of $λ_Φ^{crit}\approx 2.1$\ km for a neutron star with MPA1 EOS. This is related to the bifurcation of the physical domain in the phase space of the system. Some novel physical consequences are discussed.

gr-qc↗
arXiv2013

Withholding Potentials, Absence of Ghosts and Relationship between Minimal Dilatonic Gravity and f(R) Theories

We study the relation between Minimal Dilatonic Gravity (MDG) and f(R) theories of gravity and establish strict conditions for their {\em global} equivalence. Such equivalence takes place only for a certain class of cosmological potentials, dubbed here {\em withholding potentials}, since they prevent change of the sign of dilaton $Φ$. The withholding property ensures the attractive character of gravity, as well as absence of ghosts and a tachyon in the gravi-dilaton sector and yields certain asymptotic of the admissible functions $f(R)$. Large classes of withholding cosmological potentials and functions $f(R)$ are found and described in detail. It is shown that the popular choices of $f(R)$ functions are not withholding ones. The particle content of the gravi-dilaton sector is found using perturbation theory around de Sitter vacuum of MDG. The graviton remains massless, since it obeys conformal invariant field equation in the de Sitter space-time. The $R/6$ term in the conformal invariant wave operator introduces a very small mass scale $m_{R} \approx 1.5 \times 10^{-38} m_e$, $m_e$ being the mass of the electron. The mass of the dilaton is much larger: $m\gtrapprox 10^{29} m_{R}$. Two new phenomena: scalaron waves and induction of gravitational waves by the scalaron field are discussed using the derived wave equations for scalaron and graviton. The MDG and f(R) theories are shown to predict physical deviations from GR. Seemingly, the MDG and f(R) theories, when globally equivalent, offer a unified description of dark energy and dark matter.

gr-qc↗
arXiv2012

Solving systems of transcendental equations involving the Heun functions

The Heun functions have wide application in modern physics and are expected to succeed the hypergeometrical functions in the physical problems of the 21st century. The numerical work with those functions, however, is complicated and requires filling the gaps in the theory of the Heun functions and also, creating new algorithms able to work with them efficiently. We propose a new algorithm for solving a system of two nonlinear transcendental equations with two complex variables based on the Müller algorithm. The new algorithm is particularly useful in systems featuring the Heun functions and for them, the new algorithm gives distinctly better results than Newton's and Broyden's methods. As an example for its application in physics, the new algorithm was used to find the quasi-normal modes (QNM) of Schwarzschild black hole described by the Regge-Wheeler equation. The numerical results obtained by our method are compared with the already published QNM frequencies and are found to coincide to a great extent with them. Also discussed are the QNM of the Kerr black hole, described by the Teukolsky Master equation.

math.NA↗
arXiv2011

Two-dimensional generalization of the Muller root-finding algorithm and its applications

We propose a new algorithm for solving a system of two nonlinear transcendental equations with two complex variables based on the Muller algorithm. The two-dimensional Muller algorithm is tested on systems of different type and is found to work comparably to Newton's method and Broyden's method in many cases. The new algorithm is particularly useful in systems featuring the Heun functions whose complexity may make the already known algorithms not efficient enough or not working at all. In those specific cases, the new algorithm gives distinctly better results than the other two methods. As an example for its application in physics, the new algorithm was used to find the quasi-normal modes (QNM) of Schwarzschild black hole described by the Regge-Wheeler equation. The numerical results obtained by our method are compared with the already published QNM frequencies and are found to coincide to a great extent with them. Also discussed are the QNM of the Kerr black hole, described by the Teukolsky Master equation.

math.NA↗
arXiv2011

The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory

We give a new theoretical basis for examination of the presence of the Kerr black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of different astrophysical objects around which astrophysical jets are typically formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei (AGN), etc. Our method is based on the study of the exact solutions of the Teukolsky master equation for electromagnetic perturbations of the Kerr metric. By imposing original boundary conditions on the solutions so that they describe a collimated electromagnetic outflow, we obtain the spectra of possible {\em primary jets} of radiation, introduced here for the first time. The theoretical spectra of primary electromagnetic jets are calculated numerically. Our main result is a detailed description of the qualitative change of the behavior of primary electromagnetic jet frequencies under the transition from the KBH to the KNS, considered here as a bifurcation of the Kerr metric. We show that quite surprisingly the novel spectra describe linearly stable primary electromagnetic jets from both the KBH and the KNS. Numerical investigation of the dependence of these primary jet spectra on the rotation of the Kerr metric is presented and discussed.

astro-ph.HE↗
arXiv2010

Exact Solutions of Teukolsky Master Equation with Continuous Spectrum

Weak gravitational, electromagnetic, neutrino and scalar fields, considered as perturbations on Kerr background satisfy Teukolsky Master Equation. The two non-trivial equations obtained after separating the variables are the polar angle equation and the radial equation. We solve them by transforming each one into the form of a confluent Heun equation. The transformation depends on a set of parameters, which can be chosen in a such a way, so the resulting equations have simple polynomial solutions for neutrino, electromagnetic, and gravitational perturbations, provided some additional conditions are satisfied. Remarkably there exists a class of solutions for which these additional conditions are the same for the two different equations for $|s|=1/2$ and $|s|=1$. As a result the additional conditions fix the dependence of the separation constant on the angular frequency but the frequency itself remains unconstrained and belongs to a continuous spectrum.

gr-qc↗
arXiv2010

Classes of Exact Solutions to the Teukolsky Master Equation

The Teukolsky Master Equation is the basic tool for study of perturbations of the Kerr metric in linear approximation. It admits separation of variables, thus yielding the Teukolsky Radial Equation and the Teukolsky Angular Equation. We present here a unified description of all classes of exact solutions to these equations in terms of the confluent Heun functions. Large classes of new exact solutions are found and classified with respect to their characteristic properties. Special attention is paid to the polynomial solutions which are singular ones and introduce collimated one-way-running waves. It is shown that a proper linear combination of such solutions can present bounded one-way-running waves. This type of waves may be suitable as models of the observed astrophysical jets.

gr-qc↗
arXiv2009

Teukolsky-Starobinsky Identities - a Novel Derivation and Generalizations

We present a novel derivation of the Teukolsky-Starobinsky identities, based on properties of the confluent Heun functions. These functions define analytically all exact solutions to the Teukolsky master equation, as well as to the Regge-Wheeler and Zerilli ones. The class of solutions, subject to Teukolsky-Starobinsky type of identities is studied. Our generalization of the Teukolsky-Starobinsky identities is valid for the already studied linear perturbations to the Kerr and Schwarzschild metrics, as well as for large new classes of of such perturbations which are explicitly described in the present article. Symmetry of parameters of confluent Heun's functions is shown to stay behind the behavior of the known solutions under the change of the sign of their spin weights. A new efficient recurrent method for calculation of Starobinsky's constant is described.

gr-qc↗
arXiv2009

A new model of the Central Engine of GRB and the Cosmic Jets

Despite all the already existing observational data, current models still cannot explain completely the excessive energy output and the time variability of GRB. One of the reasons for this is the lack of a good model of the central engine of GRB. A major problem in the proposed models with a black hole (BH) in the center is that they don't explain the observed evidences of late time activity of the central engine. In this paper we are starting the search for a possible model of that central engine as a rotating compact body of still unknown nature. The formation of jets in the new model lies entirely on the fundamental Teukolsky Master Equation. We demonstrate that this general model can describe the formation of collimated GRB-jets of various forms. Some preliminary results are presented.

astro-ph.HE↗
arXiv2007

Exact Solutions of Regge-Wheeler Equation

The Regge-Wheeler equation describes the axial perturbations of Schwarzschild metric in linear approximation. We present its exact solutions in terms of the confluent Heun's functions, the basic properties of the general solution, novel analytical approach and numerical techniques for study of different boundary problems which correspond to quasi-normal modes of black holes and other simple models of compact objects. We depict in more detail the exact solutions of Regge-Wheeler equation in the Schwarzschild black hole interior and on Kruscal-Szekeres manifold.

gr-qc↗
arXiv2003

Schrödinger Quantization Problem and Neutron Stars

We are discussing the possibility to find a proper unique conditions for an experimental study of the Schrödinger quantization problem in the neutron stars physics. A simple toy model for physically different quantizations is formulated and a possible physical consequences are derived.

quant-ph↗
arXiv2002

Basic Principles of 4D Dilatonic Gravity and Some of Their Consequences for Cosmology, Astrophysics and Cosmological Constant Problem

We present a class of simple scalar-tensor models of gravity with one scalar field (dilaton $Φ$) and only one unknown function (cosmological potential $U(Φ)$). These models might be considered as a stringy inspired ones with broken SUSY. They have the following basic properties: 1) Positive dilaton mass, $m_Φ$, and positive cosmological constant $Λ$, define two extremely different scales. The models under consideration are consistent with the known experimental facts if $m_Φ> 10^{-3} eV$ and $Λ=Λ^{obs}\sim 10^{-56} cm^{-2}$. 2) Einstein week equivalence principle is strictly satisfied and extended to scalar-tensor theories of gravity using a novel form of principle of "constancy of fundamental constants". 3) The dilaton plays simultaneously role of inflation field and quintessence field and yields a sequential hyper-inflation with graceful exit to asymptotic de Sitter space-time which is an attractor, and is approached as $\exp(-\sqrt{3Λ^{obs}} ct/2)$. The time duration of inflation is $Δt_{infl} \sim m_Φ^{-1}$. 4) Ultra-high frequency ($ω_Φ\sim m_Φ$) dilatonic oscillations take place in asymptotic regime. 5) No fine tuning. (The Robertson-Walker solutions of general type have the above properties.) 6) A novel adjustment mechanism for cosmological constant problem seems to be possible: the huge value of cosmological constant in the stringy frame is re-scaled to its observed value by dilaton after transition to phenomenological frame.

gr-qc↗