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Usually, the flavour symmetry group has been an ad hoc ... [more ▼]Renormalizable SO(10) grand unified theory (GUT) models equipped with flavour symmetries are a popular framework for addressing the flavour puzzle. Usually, the flavour symmetry group has been an ad hoc choice, and no general arguments limiting this choice were known. In this paper, we establish the full list of flavour symmetry groups which may be enforced, without producing any further accidental symmetry, on the Yukawa-coupling matrices of an SO(10) GUT with arbitrary numbers of scalar multiplets in the ${\bf{10}}$, $\bar{{\bf{126}}}$, and ${\bf{120}}$ representations of SO(10). For each of the possible discrete non-Abelian symmetry groups, we present examples of minimal models which do not run into obvious contradiction with the phenomenological fermion masses and mixings. [less ▲]Detailed reference viewed: 7 (1 ULg) CP-conserving multi-Higgs model with irremovable complex coefficientsIvanov, Igor ; Silva, Joaoin Physical Review. D : Particles and Fields (2016), 93(9), 095014Models beyond the Standard Model (bSM) often involve elaborate Higgs sectors, which can be a source of CP violation. It brings up the question of recognizing in an efficient way whether a model is CP ... [more ▼]Models beyond the Standard Model (bSM) often involve elaborate Higgs sectors, which can be a source of CP violation. It brings up the question of recognizing in an efficient way whether a model is CP violating. There is a diffuse belief corroborated by all specific multi-Higgs models considered so far that the issue of explicit CP invariance can be linked to the existence of a basis in which all coefficients are real. Here, we prove that this belief is not justified. We present a CP-conserving three-Higgs-doublet model for which no real basis exists. The generalized CP symmetry of this model is of order 4, which leads to the peculiar property of the extra neutral Higgs bosons of being neither CP-even nor CP-odd but “half-odd” under this symmetry transformation. [less ▲]Detailed reference viewed: 6 (1 ULg) Quantum calculation of the Vavilov-Cherenkov radiation by twisted electronsIvanov, Igor ; Serbo, Valery; Zaytsev, Vladimirin Physical Review A (2016), 93We present a detailed quantum electrodynamical description of Vavilov-Cherenkov radiation emitted by a relativistic twisted electron in the transparent medium. Simple expressions for the spectral and ... [more ▼]We present a detailed quantum electrodynamical description of Vavilov-Cherenkov radiation emitted by a relativistic twisted electron in the transparent medium. Simple expressions for the spectral and spectral-angular distributions as well as for the polarization properties of the emitted radiation are obtained. Unlike the plane-wave case, the twisted electron produces radiation within the annular angular region, with enhancement towards its boundaries. Additionally, the emitted photons can have linear polarization not only in the scattering plane but also in the orthogonal direction. We find that the Vavilov-Cherenkov radiation emitted by an electron in a superposition of two vortex states exhibits a strong azimuthal asymmetry. Thus, the Vavilov-Cherenkov radiation offers itself as a convenient diagnostic tool of such electrons and complements the traditional microscopic imaging. [less ▲]Detailed reference viewed: 11 (2 ULg) Group-theoretic restrictions on generation of CP-violation in multi-Higgs-doublet modelsBranco, Gustavo; Ivanov, Igor in Journal of High Energy Physics [=JHEP] (2016), 2016It has been known since decades that imposing a symmetry group G on the scalar sector of multi-Higgs-doublet models has consequences for CP -violation. In all examples of two- and three-Higgs-doublet ... [more ▼]It has been known since decades that imposing a symmetry group G on the scalar sector of multi-Higgs-doublet models has consequences for CP -violation. In all examples of two- and three-Higgs-doublet models equipped with symmetries, one observes the following intriguing property: if G prevents explicit CP -violation (CPV), at least in the neutral Higgs sector, then it also prevents spontaneous CPV, and if G allows explicit CPV, then it allows for spontaneous CPV. One is led to conjecture that this is a general phenomenon. In this paper, we prove this conjecture for any rephasing symmetry group G and any number of doublets. [less ▲]Detailed reference viewed: 6 (1 ULg) Tree-level metastability bounds for the most general two Higgs doublet modelIvanov, Igor ; Silva, Joãoin Physical Review. D : Particles and Fields (2015), 92Within two Higgs doublet models, it is possible that the current vacuum is not the global minimum, in which case it could possibly decay at a later stage. We discuss the tree-level conditions which must ... [more ▼]Within two Higgs doublet models, it is possible that the current vacuum is not the global minimum, in which case it could possibly decay at a later stage. We discuss the tree-level conditions which must be obeyed by the most general scalar potential in order to preclude that possibility. We propose a new procedure which is not only more general but also easier to implement than the previously published one, including CP conserving as well as CP violating scalar sectors. We illustrate these conditions within the context of the Z2 model, softly broken by a complex, CP violating parameter. [less ▲]Detailed reference viewed: 13 (2 ULg) Scattering of twisted relativistic electrons by atomsSerbo, Valery; Ivanov, Igor ; Fritzsche, Stephan et alin Physical Review A (2015), 92The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the ... [more ▼]The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams. [less ▲]Detailed reference viewed: 12 (0 ULg) Symmetry breaking patterns in 3HDMIvanov, Igor ; Nishi, Celsoin Journal of High Energy Physics [=JHEP] (2015), 15An attractive feature of New Physics models with multiple Higgs fields is that they are equipped with discrete symmetry groups in the Higgs and flavour sectors. These symmetry groups are often broken at ... [more ▼]An attractive feature of New Physics models with multiple Higgs fields is that they are equipped with discrete symmetry groups in the Higgs and flavour sectors. These symmetry groups are often broken at the global minimum of the Higgs potential, either completely or to a proper subgroup, with certain phenomenological consequences. Here, we systematically explore these symmetry breaking patterns in the scalar sector of the three-Higgs-doublet model (3HDM). We use the full list of discrete symmetry groups allowed in 3HDM, and for each group we find all possible ways it can break by the Higgs vacuum expectation value alignment. We also discuss the interplay between these symmetry groups and various forms of CP-violation in the scalar sector of 3HDM. Not only do our results solve the problem for 3HDM, but they also hint at several general features in multi-scalar sectors. [less ▲]Detailed reference viewed: 8 (0 ULg) Constraining multi-Higgs flavour modelsIvanov, Igor ; González Felipe, R.; Nishi, Celso et alin European Physical Journal C -- Particles & Fields (2014), 74To study a flavour model with a non-minimal Higgs sector one must first define the symmetries of the fields; then identify what types of vacua exist and how they may break the symmetries; and finally ... [more ▼]To study a flavour model with a non-minimal Higgs sector one must first define the symmetries of the fields; then identify what types of vacua exist and how they may break the symmetries; and finally determine whether the remnant symmetries are compatible with the experimental data. Here we address all these issues in the context of flavour models with any number of Higgs doublets. We stress the importance of analysing the Higgs vacuum expectation values that are pseudo-invariant under the generators of all subgroups. It is shown that the only way of obtaining a physical CKM mixing matrix and, simultaneously, non-degenerate and non-zero quark masses is requiring the vacuum expectation values of the Higgs fields to break completely the full flavour group, except possibly for some symmetry belonging to baryon number. The application of this technique to some illustrative examples, such as the flavour groups Delta(27), A4 and S3, is also presented. [less ▲]Detailed reference viewed: 5 (0 ULg) Forward Physics of Hadronic CollidersIvanov, Igor in Physics of Particles and Nuclei Letters (2013, December), 10(7), 739750These lectures were given at the Baikal Summer School on Physics of Elementary Particles and Astrophysics in July 2012. They can be viewed as a concise introduction to hadronic diffraction, to the physics ... [more ▼]These lectures were given at the Baikal Summer School on Physics of Elementary Particles and Astrophysics in July 2012. They can be viewed as a concise introduction to hadronic diffraction, to the physics of the Pomeron and related topics. [less ▲]Detailed reference viewed: 12 (0 ULg) Abelian symmetries of the N-Higgs-doublet model with Yukawa interactionsIvanov, Igor ; Nishi, Celsoin Journal of High Energy Physics [=JHEP] (2013), 2013(11), 069We investigate finite abelian groups which can represent symmetries of the N-Higgs-doublet models with quarks. We build a general formalism based on the powerful method of the Smith normal form and obtain ... [more ▼]We investigate finite abelian groups which can represent symmetries of the N-Higgs-doublet models with quarks. We build a general formalism based on the powerful method of the Smith normal form and obtain an analytic upper bound on the order of abelian symmetry groups for any N. We investigate in detail the case N = 2 and rederive known results in a more compact and intuitive fashion. We also study the NHDM with the maximal finite abelian symmetry for all small N cases up to N = 5, and show that in each case all Yukawa textures compatible with such symmetry originate from a unique basic structure. This work opens the way to a systematic exploration of phenomenology of the NHDM with a desired symmetry, and illustrates the power of the Smith normal form technique. [less ▲]Detailed reference viewed: 15 (2 ULg) Polarization radiation of vortex electrons with large orbital angular momentumIvanov, Igor ; Karlovets, Dmitryin Physical Review. A (2013), 88(4), 043840Vortex electrons—freely propagating electrons whose wave functions have helical wave fronts—could become a novel tool in the physics of electromagnetic radiation. They carry a nonzero intrinsic orbital ... [more ▼]Vortex electrons—freely propagating electrons whose wave functions have helical wave fronts—could become a novel tool in the physics of electromagnetic radiation. They carry a nonzero intrinsic orbital angular momentum (OAM) ℓ with respect to the propagation axis and, for ℓ≫1, a large OAM-induced magnetic moment μ≈ℓμB (μB is the Bohr magneton), which influences the radiation of electromagnetic waves. Here, we consider in detail the OAM-induced effects caused by such electrons in two forms of polarization radiation, namely, in Cherenkov radiation and transition radiation. Thanks to the large ℓ, we can neglect quantum or spin-induced effects, which are of the order of ℏω/Ee≪1, but retain the magnetic moment contribution ℓℏω/Ee≲1, which makes the quasiclassical approach to polarization radiation applicable. We discuss the magnetic moment contribution to polarization radiation, which has never been experimentally observed, and study how its visibility depends on the kinematical parameters and the medium permittivity. In particular, it is shown that this contribution can, in principle, be detected in azimuthally nonsymmetrical problems, for example when vortex electrons obliquely cross a metallic screen (transition radiation) or move near it (diffraction radiation). We predict a left-right angular asymmetry of the transition radiation (in the plane where the charge radiation distributions would stay symmetric), which appears due to an effective interference between the charge radiation field and the magnetic moment contribution. Numerical values of this asymmetry for vortex electrons with Ee=300 keV and ℓ=100–1000 are 0.1%–1%, and we argue that this effect could be detected with existing technology. The finite conductivity of the target and frequency dispersion play crucial roles in these predictions. [less ▲]Detailed reference viewed: 34 (4 ULg) Evading death by vacuumBarroso, Augusto; Ferreira, Pedro; Ivanov, Igor et alin European Physical Journal C -- Particles & Fields (2013), 73In the Standard Model, the Higgs potential allows only one minimum at tree level. But the open possibility that there might be two scalar doublets enriches the vacuum structure, allowing for the risk that ... [more ▼]In the Standard Model, the Higgs potential allows only one minimum at tree level. But the open possibility that there might be two scalar doublets enriches the vacuum structure, allowing for the risk that we might now be in a metastable state, which we dub the panic vacuum. Current experiments at the LHC are probing the Higgs particle predicted as a result of the spontaneous symmetry breaking. Remarkably, in the two Higgs model with a softly broken U(1) symmetry, the LHC experiments already allow to exclude many panic vacuum solutions. [less ▲]Detailed reference viewed: 11 (1 ULg) Detecting transition radiation from a magnetic momentIvanov, Igor ; Karlovets, Dmitryin Physical Review Letters (2013), 110(26), 2648015Electromagnetic radiation can be emitted not only by particle charges but also by magnetic moments and higher electric and magnetic multipoles. However, experimental proofs of this fundamental fact are ... [more ▼]Electromagnetic radiation can be emitted not only by particle charges but also by magnetic moments and higher electric and magnetic multipoles. However, experimental proofs of this fundamental fact are extremely scarce. In particular, the magnetic moment contribution has never been observed in any form of polarization radiation. Here, we propose to detect it using vortex electrons carrying large orbital angular momentum ℓ. The relative contribution of the orbital angular momentum-induced magnetic moment, ℓℏω/Ee, becomes much larger than the spin-induced contribution ℏω/Ee, and it can be observed experimentally. As a particular example, we consider transition radiation from vortex electrons obliquely incident on an interface between a vacuum and a dispersive medium, in which the magnetic moment contribution manifests itself via a left-right angular asymmetry. For electrons with Ee=300  keV and ℓ=100–1000, we predict an asymmetry of the order of 0.1%–1%, which could be measured with existing technology. Thus, vortex electrons emerge as a new tool in the physics of electromagnetic radiation. [less ▲]Detailed reference viewed: 18 (0 ULg) Metastability bounds on the two Higgs doublet modelBarroso, Augusto; Ferreira, Pedro; Ivanov, Igor et alin Journal of High Energy Physics [=JHEP] (2013), 1306In the two Higgs doublet model, there is the possibility that the vacuum where the universe resides in is metastable. We present the tree-level bounds on the scalar potential parameters which have to be ... [more ▼]In the two Higgs doublet model, there is the possibility that the vacuum where the universe resides in is metastable. We present the tree-level bounds on the scalar potential parameters which have to be obeyed to prevent that situation. Analytical expressions for those bounds are shown for the most used potential, that with a softly broken Z 2 symmetry. The impact of those bounds on the model’s phenomenology is discussed in detail, as well as the importance of the current LHC results in determining whether the vacuum we live in is or is not stable. We demonstrate how the vacuum stability bounds can be obtained for the most generic CP-conserving potential, and provide a simple method to implement them. [less ▲]Detailed reference viewed: 7 (1 ULg) Geometrical CP violation in the N-Higgs-doublet modelIvanov, Igor ; Lavoura, Luisin European Physical Journal C -- Particles & Fields (2013), 73Geometrical CP violation is a particular type of spontaneous CP violation in which the vacuum expectation values have phases which are calculable, i.e. stable against the variation of the free parameters ... [more ▼]Geometrical CP violation is a particular type of spontaneous CP violation in which the vacuum expectation values have phases which are calculable, i.e. stable against the variation of the free parameters of the scalar potential. Although originally suggested within a specific version of the three-Higgs-doublet model, it is a generic phenomenon. We investigate its viability and characteristic features in models with several Higgs doublets. Our work contains both general results and illustrative examples. [less ▲]Detailed reference viewed: 19 (0 ULg) Classification of finite reparametrization symmetry groups in the three-Higgs-doublet modelIvanov, Igor ; Vdovin, Evgenyin European Physical Journal C -- Particles & Fields (2013), 73Symmetries play a crucial role in electroweak symmetry breaking models with non-minimal Higgs content. Within each class of these models, it is desirable to know which symmetry groups can be implemented ... [more ▼]Symmetries play a crucial role in electroweak symmetry breaking models with non-minimal Higgs content. Within each class of these models, it is desirable to know which symmetry groups can be implemented via the scalar sector. In N-Higgs-doublet models, this classification problem was solved only for N=2 doublets. Very recently, we suggested a method to classify all realizable finite symmetry groups of Higgs-family transformations in the three-Higgs-doublet model (3HDM). Here, we present this classification in all detail together with an introduction to the theory of solvable groups, which play the key role in our derivation. We also consider generalized-CP symmetries, and discuss the interplay between Higgs-family symmetries and CP-conservation. In particular, we prove that presence of the $Z_4$ symmetry guarantees the explicit CP-conservation of the potential. This work completes classification of finite reparametrization symmetry groups in 3HDM. [less ▲]Detailed reference viewed: 17 (0 ULg) Geometric minimization of highly symmetric potentialsDegée, Audrey ; Ivanov, Igor ; Keus, Venus in Journal of High Energy Physics [=JHEP] (2013), 2013In non-minimal Higgs mechanisms, one often needs to minimize highly symmetric Higgs potentials. Here we propose a geometric way of doing it, which, surprisingly, is often much more efficient than the ... [more ▼]In non-minimal Higgs mechanisms, one often needs to minimize highly symmetric Higgs potentials. Here we propose a geometric way of doing it, which, surprisingly, is often much more efficient than the usual method. By construction, it gives the global minimum for any set of free parameters of the potential, thus offering an intuitive understanding of how they affect the vacuum expectation values. For illustration, we apply this method to the S_4 and A_4-symmetric three-Higgs-doublet models. We find that at least three recent phenomenological analyses of the A_4-symmetric model used a local, not the global minimum. We discuss coexistence of minima of different types, and comment on the mathematical origin of geometrical CP-violation and on a new symmetry linking different minima. [less ▲]Detailed reference viewed: 37 (4 ULg) Symmetries in multi-Higgs-doublet modelsIvanov, Igor ; Vdovin, Evgenyin AIP Conference Proceedings (2013)We report the recent progress in understanding of symmetries which can be implemented in the scalar sector of electroweak symmetry breaking models with several Higgs doublets. In particular we present the ... [more ▼]We report the recent progress in understanding of symmetries which can be implemented in the scalar sector of electroweak symmetry breaking models with several Higgs doublets. In particular we present the list of finite reparametrization symmetry groups which can appear in the three-Higgs-doublet models. [less ▲]Detailed reference viewed: 16 (1 ULg) Probing the phase of the elastic $pp$ scattering amplitude with vortex proton beamsIvanov, Igor in AIP Conference Proceedings (2013)We show that colliding vortex proton beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the scattering amplitude changes with the scattering angle. In ... [more ▼]We show that colliding vortex proton beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the scattering amplitude changes with the scattering angle. In elastic $pp$ scattering, this will open a novel way to measure the parameter $\rho(t)$ and probe the real part of the Pomeron. [less ▲]Detailed reference viewed: 11 (1 ULg) Discrete symmetries in the three-Higgs-doublet modelIvanov, Igor ; Vdovin, Evgenyin Physical Review. D : Particles and Fields (2012), 86(9), 0950305N-Higgs-doublet models (NHDM) are among the most popular examples of electroweak symmetry breaking mechanisms beyond the Standard Model. Discrete symmetries imposed on the NHDM scalar potential play a ... [more ▼]N-Higgs-doublet models (NHDM) are among the most popular examples of electroweak symmetry breaking mechanisms beyond the Standard Model. Discrete symmetries imposed on the NHDM scalar potential play a pivotal role in shaping the phenomenology of the model, and various symmetry groups have been studied so far. However, in spite of all efforts, the classification of finite Higgs-family symmetry groups realizable in NHDM for any N>2 is still missing. Here, we solve this problem for the three-Higgs-doublet model by making use of Burnside’s theorem and other results from pure finite group theory which are rarely exploited in physics. Our method and results can also be used beyond high-energy physics, for example, in the study of possible symmetries in three-band superconductors. [less ▲]Detailed reference viewed: 14 (3 ULg) 1 2 3