Papers by Michail Todorov
AIP Conference Proceedings, 2009
Multilayered long Josephson Junction Structures form an interesting physical system where both no... more Multilayered long Josephson Junction Structures form an interesting physical system where both nonlinearity and interaction between subsystems play an important role. Such systems allow to study physical effects that do not occur in single Josephson junction. The Sakai-Bodin-Pedersen model-a system of perturbed sine-Gordon equations-is used to study the dynamic states of stacks of inductively coupled long Josephson Junctions (LJJs). The corresponding static problem is numerically investigated as well. In order to study the stability of possible static solutions a Sturm-Liouville problem is generated and solved. The transitions from static to dynamic state and the scenario of these transitions are analyzed depending on the model parameters. Different physical characteristics-current-voltage characteristics, individual instant voltages and internal magnetic fields, are calculated and interpreted.
We investigate numerically models of the static spherically symmetric boson-fermion stars on the ... more We investigate numerically models of the static spherically symmetric boson-fermion stars on the scalar-tensor theory of gravity with massive dilation field. The proper mathematical model of such stars is interpreted as a nonlinear two-parametric eigenvalue problem with un unknown internal boundary. We formulate the boundary value problem in two ways and employ the continuous analogue of Newton’s method (CANM) for each of them. We obtain the behaviour of the basic geometric quantities and functions describing a dilation field and matter fields, which build the star.
Physics Letters A, 2015
We study phenomenologically by using the previously derived Landau free energy, the role of aniso... more We study phenomenologically by using the previously derived Landau free energy, the role of anisotropy in ferromagnetic superconductors UGe 2 , URhGe, and UCoGe. The three compounds are separately discussed with the special stress on UGe 2. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed.
Modern Physics Letters A, 2001
We numerically construct static and spherically symmetric electrically charged black hole solutio... more We numerically construct static and spherically symmetric electrically charged black hole solutions in Einstein–Born–Infeld gravity with massive dilaton. The numerical solutions show that the dilaton potential allows many more black hole causal structures than the massless dilaton. We find that depending on the black hole mass and charge and the dilaton mass, the black holes can have either one, two, or three horizons. The extremal solutions are also found. As an interesting peculiarity we note that there are extremal black holes with an inner horizon and with triply degenerated horizon.
Physical Review D, 2000
We study equilibrium configurations of boson stars in the framework of a class scalar-tensor theo... more We study equilibrium configurations of boson stars in the framework of a class scalar-tensor theories of gravity with massive gravitational scalar (dilaton). In particular we investigate the influence of the mass of the dilaton on the boson star structure. We find that the masses of the boson stars in presence of dilaton are close to those in general relativity and they are sensitive to the ratio of the boson mass to the dilaton mass within a typical few percent. It turns out also that the boson star structure is mainly sensitive to the mass term of the dilaton potential rather to the exact form of the potential .
Journal of Physics: Conference Series, 2013
ABSTRACT In the present paper we numerically construct new charged anti-de Sitter black holes cou... more ABSTRACT In the present paper we numerically construct new charged anti-de Sitter black holes coupled to nonlinear Born-Infeld electrodynamics within a certain class of scalar-tensor theories. The properties of the solutions are investigated both numerically and analytically. We also study the thermodynamics of the black holes in the canonical ensemble. For large values of the Born-Infeld parameter and for a certain interval of the charge values we find the existence of a first-order phase transition between small and very large black holes. An unexpected result is that for a certain small charge subinterval two phase transitions have been observed, one of zeroth and one of first order. It is important to note that such phase transitions are also observed for pure Einstein-Born-Infeld-AdS black holes.
Journal of Siberian Federal University. Mathematics & Physics
We analyze the dynamical behavior of the N-soliton train in the adiabatic approximation of the Ma... more We analyze the dynamical behavior of the N-soliton train in the adiabatic approximation of the Manakov model. The evolution of Manakov N-soliton trains is described by the complex Toda chain (CTC) which is a completely integrable dynamical model. Calculating the eigenvalues of its Lax matrix allows us to determine the asymptotic velocity of each soliton. So we describe sets of soliton parameters that ensure one of the two main types of asymptotic regimes: the bound state regime (BSR) and the free asymptotic regime (FAR). In particular we find explicit description of special symmetric configurations of N solitons that ensure BSR and FAR. We find excellent matches between the trajectories of the solitons predicted by CTC with the ones calculated numerically from the Manakov system for wide classes of soliton parameters. This confirms the validity of our model
We investigate numerically a models of the static spherically symmetric boson-fermion stars in sc... more We investigate numerically a models of the static spherically symmetric boson-fermion stars in scalar-tensor theory of gravity with massive dilaton field. The proper mathematical model of such stars is interpreted as a nonlinear two-parametric eigenvalue problem with unknown internal boundary. We employ the Continuous Analogue of Newton Method (CANM) which leads on each iteration to two separate linear boundary value
AIP Conference Proceedings, 2008
Lecture Notes in Computer Science, 2007
The textile fibers and yarns are usually modeled as one dimensional continuum of beams or as a sy... more The textile fibers and yarns are usually modeled as one dimensional continuum of beams or as a system of particles, connected by springs. The governing equation of motion of such systems has many solutions, which switch in between depending on the available energy of the system. Effective modeling of problems with bifurcations like these, applicable for more general geometries is rarely reported. In the present work we demonstrate, that using a system of particles and an appropriate change of variables, a successful time step integration either by the Leap-Frog or the Verlet algorithms is possible.
We construct new numerical solutions describing charged anti-de Sitter black holes coupled to non... more We construct new numerical solutions describing charged anti-de Sitter black holes coupled to nonlinear Born-Infeld electrodynamics within a certain class of scalar-tensor theories and we study their thermodynamic phase structure. It is shown that for certain charge intervals phase transitions of zeroth and first order exist.
Journal of Computational Physics, 2001
A model of static boson-fermion star with spherical symmetry based on the scalar-tensor theory of... more A model of static boson-fermion star with spherical symmetry based on the scalar-tensor theory of gravity with massive dilaton field is investigated numerically.
Journal of Computational and Applied Mathematics, 2002
We investigate numerically a models of the static spherically symmetric boson-fermion stars in sc... more We investigate numerically a models of the static spherically symmetric boson-fermion stars in scalar-tensor theory of gravity with massive dilaton field. The proper mathematical model of such stars is interpreted as a nonlinear two-parametric eigenvalue problem with unknown internal boundary. We employ the Continuous Analogue of Newton Method (CANM) which leads on each iteration to two separate linear boundary value problems with different dimensions inside and outside the star, respectively. Along with them a nonlinear algebraic system for the spectral parameters -radius of the star Rs and quantity Ω is solved also.
Modern Physics Letters A, 2007
The no-scalar-hair conjecture rules out the existence of asymptotically flat black holes with a s... more The no-scalar-hair conjecture rules out the existence of asymptotically flat black holes with a scalar dressing for a large class of theories. No-scalar-hair theorems have been proved for the cases of neutral black holes and for charged black holes in the Maxwell electrodynamics. These theorems, however, do not apply in the case of non-linear electrodynamics. In the present work numerical solutions describing charged black holes coupled to Euler-Heisenberg type nonlinear electrodynamics in scalar-tensor theories of gravity with massless scalar field are found. In comparison to the corresponding solution in General Relativity the presented solution has a simpler causal structure the reason for which is the presence of the scalar field. The present class of black holes has a single, nondegenerate horizon, i.e., its causal structure resembles that of the Schwarzschild black hole. Pacs numbers: 4.25.Dm, 04.40.-b, 04.70.-s, 95.30.Tg, 97.60.Lf
In the present work static and spherically symmetric magnetically charged black holes coupled to ... more In the present work static and spherically symmetric magnetically charged black holes coupled to Euler-Heisenberg type non-linear electrodynamics in the scalar-tensor theories of gravity with massive scalar field are investigated numerically. For the numerical solving of the corresponding boundary-value problem with free boundary the Continuous Analogue of Newton Method is used. As a result of the numerical experiments some general
The Twelfth Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity Astrophysics and Relativistic Field Theories - Proceedings of the MG12 Meeting on General Relativity, 2012
We investigate numerically models of the static spherically symmetric boson-fermion stars on the ... more We investigate numerically models of the static spherically symmetric boson-fermion stars on the scalar-tensor theory of gravity with massive dilation field. The proper mathematical model of such stars is interpreted as a nonlinear two-parametric eigenvalue problem with un unknown internal boundary. We formulate the boundary value problem in two ways and employ the continuous analogue of Newton’s method (CANM) for each of them. We obtain the behaviour of the basic geometric quantities and functions describing a dilation field and matter fields, which build the star.
The non-existence of uncharged black holes and charged black holes in the Maxwell electrodynamics... more The non-existence of uncharged black holes and charged black holes in the Maxwell electrodynamics, with non-trivial scalar field has been proved for a large class of scalar-tensor theories. The no-scalar-hair theorems, however, do not apply in the case of non-linear electrodynamics. In the present work numerical solutions describing charged black holes coupled to Euler-Heisenberg type non-linear electrodynamics in scalar-tensor theories
The aim of the present work is to investigate numerically phases of soliton-like solutions couple... more The aim of the present work is to investigate numerically phases of soliton-like solutions coupled to non-linear electrodynamics in the scalar-tensor theories of gravity. As a result of the numerical experiments new non-unique solutions of the corresponding boundary value problem and their general properties were found.
International Journal of Modern Physics D, 2011
Born-Infeld black holes in the Scalar-Tensor Theories of Gravity, in the case of massless scalar ... more Born-Infeld black holes in the Scalar-Tensor Theories of Gravity, in the case of massless scalar field, have been recently obtained . The aim of the current paper is to study the effect from the inclusion of a potential for the scalar field in the theory, through a combination of analytical techniques and numerical methods. The black holes coupled to a massive scalar field have richer causal structure in comparison to the massless scalar field case. In the latter case, the black holes may have a second, inner horizon. The presence of potential for the scalar field allows the existence of extremal black holes for certain values of the mass of the scalar field and the magnetic (electric) charge of the black hole. The linear stability against spherically symmetric perturbations is studied. Arguments in favor of the general stability of the solutions coming from the application of the "turning point" method are also presented. * 1 The coupling between the electromagnetic field and scalar field in dilaton gravity and in STT is different. The difference between the two types of actions can be found in , for example.
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Papers by Michail Todorov