1. Precision magnetometry exploiting excited state quantum phase transitionsQian Wang, Ugo Marzolino, 2024, izvirni znanstveni članek Opis: Critical behaviour in phase transitions is a resource for enhanced precision metrology. The reason is that the function, known as Fisher information, is superextensive at critical points, and, at the same time, quantifies performances of metrological protocols. Therefore, preparing metrological probes at phase transitions provides enhanced precision in measuring the transition control parameter. We focus on the Lipkin-Meshkov-Glick model that exhibits excited state quantum phase transitions at different magnetic fields. Resting on the model spectral properties, we show broad peaks of the Fisher information, and propose efficient schemes for precision magnetometry. The Lipkin-Meshkov-Glick model was first introduced for superconductivity and for nuclear systems, and recently realised in several condensed matter platforms. The above metrological schemes can be also exploited to measure microscopic properties of systems able to simulate the LipkinMeshkov-Glick model. Ključne besede: magnetometry, quantum phase transitions, precision, measurements Objavljeno v DKUM: 22.08.2024; Ogledov: 62; Prenosov: 9 Celotno besedilo (1,52 MB) Gradivo ima več datotek! Več... |
2. Separability of the Dirac equation in the STU black hole spacetime : Pairwise-equal charge case studyMirjam Cvetič, M. M. Stetsko, 2023, izvirni znanstveni članek Opis: We study the separability of the Dirac equation in the background of four dimensional charged rotating asymptotically flat black hole solution of supergravity and the low energy string theory known as STU black hole. In particular, we analyze in detail the separability conditions in the pairwise equal charge STU black hole space-time [M. Cvetič and D. Youm, Phys. Rev. D 54, 2612 (1996).]. While in the latter case the minimally coupled Dirac equation is not separable, the introduction of a specific torsion term ensures the separability. The source of the torsion is the Kalb-Ramond field, which is an integral part of string theory, but further aspects of its properties and coupling to fermionic fields remain to be studied. To derive the torsion, two different approaches are used in conformally related frames, showing that the torsion is not unique. The correspondingly modified Dirac equations in the Einstein and string frames are shown to be separable. Furthermore, the massless radial and angular wave equations are examined; they show close similarity with corresponding equations for the standard Kerr background. A generalization of the Teukolsky equation for the pairwise equal case is conjectured. We also briefly analyze a technically sophisticated radial equation in the massive case. Ključne besede: quantum fields of spacetime, supergravity, curved spacetime, Dirac equation Objavljeno v DKUM: 19.07.2024; Ogledov: 165; Prenosov: 6 Celotno besedilo (373,36 KB) Gradivo ima več datotek! Več... |
3. 0-form, 1-form, and 2-group symmetries via cutting and gluing of orbifoldsMirjam Cvetič, Jonathan J. Heckman, Max Hübner, Ethan Torres, 2022, izvirni znanstveni članek Opis: Orbifold singularities of M-theory constitute the building blocks of a broad class of supersymmetric quantum field theories (SQFTs). In this paper we show how the local data of these geometries determine global data on the resulting higher symmetries of these systems. In particular, via a process of cutting and gluing, we show how local orbifold singularities encode the 0-form, 1-form, and 2-group symmetries of the resulting SQFTs. Geometrically, this is obtained from the possible singularities that extend to the boundary of the noncompact geometry. The resulting category of boundary conditions then captures these symmetries and is equivalently specified by the orbifold homology of the boundary geometry. We illustrate these general points in the context of a number of examples, including five-dimensional (5D) superconformal field theories engineered via orbifold singularities, 5D gauge theories engineered via singular elliptically fibered Calabi-Yau threefolds, as well as four-dimensional supersymmetric quantum chromodynamics-like theories engineered via M-theory on noncompact G2 spaces. Ključne besede: F-theory, compactifications, classification, singularities, instantons, geometry Objavljeno v DKUM: 06.06.2024; Ogledov: 159; Prenosov: 6 Celotno besedilo (863,93 KB) Gradivo ima več datotek! Več... |
4. Long-range forces between nonidentical black holes with non-BPS extremal limitsSera Cremonini, Mirjam Cvetič, Christopher N. Pope, Aritra Saha, 2022, izvirni znanstveni članek Opis: Motivated by recent studies of long-range forces between identical black holes, we extend these considerations by investigating the forces between two nonidentical black holes. We focus on classes of theories where charged black holes can have extremal limits that are not BPS. These theories, which live in arbitrary spacetime dimension, comprise gravity coupled to N 2-form field strengths and (N − 1) scalar fields. In the solutions we consider, each field strength carries an electric charge. The black hole solutions are governed by the SLðN þ 1; RÞ Toda equations. In four dimensions, the black hole solutions in the SLð3; RÞ example are equivalent to the “Kaluza-Klein dyons.” We find that any pair of such extremal black holes that are not identical (up to overall scaling) will repel one another. We also show that there can exist pairs of non-extremal, nonidentical black holes which obey a zero-force condition. Finally, we find indications of similar results in the higher examples, such as SLð4; RÞ. Ključne besede: astronomy, astrophysics, black holes, spacetime dimensions Objavljeno v DKUM: 06.06.2024; Ogledov: 115; Prenosov: 3 Celotno besedilo (277,73 KB) Gradivo ima več datotek! Več... |
5. Learning Chinese in a study abroad context : the case of ritual congratulatingJuliane House, Dániel Z. Kádár, 2023, izvirni znanstveni članek Opis: In this paper, we explore how and why the realisation of the ritual act of congratulating may turn out to be challenging for foreign learners of Chinese. Congratulating and other ceremonial ritual acts are not only used when someone participates in an actual ritual event: they are also required when they are mentioned in mundane events, like casual interactions when someone talks about a family birthday or wedding. We define congratulation as an interactional move and systematically examine its conventional realisation patterns through a typology of speech acts. We approach congratulating moves by combining a speech act-anchored analysis with the field of study abroad and interaction ritual research. The results of our analysis show that various ritual occasions may trigger different types of inappropriate uses of congratulating by foreign learners of Chinese. Ključne besede: Chinese, interaction rituals, speech acts, study abroad, congratulating Objavljeno v DKUM: 20.02.2024; Ogledov: 445; Prenosov: 18 Celotno besedilo (462,61 KB) Gradivo ima več datotek! Več... |
6. Towards a Catalogue of Self-Sovereign Identity Design PatternsŠpela Čučko, Vid Keršič, Muhamed Turkanović, 2023, izvirni znanstveni članek Opis: Self-sovereign identity (SSI) is a user-centric, decentralised identity approach that provides a means for identification, authentication, and authorisation without the involvement of external entities, responsible for identity provisioning and management in current centralised and federated approaches. In general, the basic building blocks of an SSI system include decentralised identifiers, verifiable credentials, identity wallets, a verifiable data registry, and three main actors: issuer, identity holder, and verifier. Even though the SSI field is dominated by proposals, SSI systems can be implemented in different ways, which is reflected in the absence of a well-defined architecture. Thus, the best implementation is still a matter of research, the requirements of the individual system, and its field of application. However, well-designed and implemented systems are crucial to avoiding failures, speeding up the development process, ensuring high quality, and the broader adoption of SSI solutions. Hence, the main objective of this study was to identify design patterns and good practices of the SSI ecosystems by reviewing and analysing the literature, technical documentation, and existing SSI implementations. Therefore, the study is built on existing knowledge, and presents a comprehensive catalogue of thirty-five SSI design patterns that can serve as a starting point for a possible SSI system design. Ključne besede: self-sovereign identity, decentralised identity, design patterns, decentralised identifiers, verifiable credentials, blockchain, verifiable data registry, identity wallets Objavljeno v DKUM: 05.12.2023; Ogledov: 448; Prenosov: 52 Celotno besedilo (2,31 MB) Gradivo ima več datotek! Več... |
7. Conference proceedings2019, zbornik recenziranih znanstvenih prispevkov na mednarodni ali tuji konferenci Opis: Konferenčni zbornik / 7. mednarodni simpozij o aplikativni elektromagnetiki SAEM 18. Mednarodni Simpozij o Aplikativni Elektromagnetiki je namenjen predstavitvi rezultatov raziskovalnega dela na različnih področjih aplikativne elektromagnetike. Simpozij je namenjen izmenjavi idej, predstavitvi dosežkov in rezultatov, zagotavljanju foruma za raziskovalce in akademike. Naše konference so znane po odprtem in prijaznem vzdušju, ki spodbuja zlasti mlade raziskovalce, da predstavijo svoje dosežke in ideje še v zgodnji fazi njihovega raziskovalnega dela. Simpozij nadaljuje tradicijo skupnih konferenc, ki so bile v preteklih letih organizirane v Makedoniji, Poljski, Sloveniji in Madžarski. Simpozij je odprt za udeležence iz vsega sveta. Letošnji simpozij je potekal med 17. in 20. junijem 2018 v Podčetrtku, Slovenija. Vsem udeležencem se zahvaljujemo za sodelovanje na mednarodnem simpoziju o Aplikativni elektromagnetiki in jih želimo uspešno akademsko kariero. Ključne besede: applied electromagnetics, electrical machinesn, electromagnetic field, electromagnetic devices, energy efficiency Objavljeno v DKUM: 04.12.2023; Ogledov: 494; Prenosov: 21 Povezava na celotno besedilo Gradivo ima več datotek! Več... Gradivo je zbirka in zajema 12 gradiv! |
8. Quadrillion F-theory compactifications with the exact chiral spectrum of the standard modelMirjam Cvetič, James Halverson, Ling Lin, Mingqiang Liu, Jianjun Paul Tian, 2019, izvirni znanstveni članek Opis: We present O(10(15)) string compactifications with the exact chiral spectrum of the standard model of particle physics. This ensemble of globally consistent F-theory compactifications automatically realizes gauge coupling unification. Utilizing the power of algebraic geometry, all global consistency conditions can be reduced to a single criterion on the base of the underlying elliptically fibered Calabi-Yau fourfolds. For toric bases, this criterion only depends on an associated polytope and is satisfied for at least O(10(15)) bases, each of which defines a distinct compactification. Ključne besede: FLUX, F-theory, string compactifications, chiral spectrum Objavljeno v DKUM: 23.10.2023; Ogledov: 489; Prenosov: 16 Celotno besedilo (184,32 KB) Gradivo ima več datotek! Več... |
9. Constraints on standard model constructions in F-theoryMirjam Cvetič, James Halverson, Ling Lin, Cody Long, 2020, izvirni znanstveni članek Opis: We argue that the following three statements cannot all be true: (i) our vacuum is a type IIB/F-theory vacuum at moderate to large h(1,1); (ii) the alpha' expansion is controlled via the supergravity approximation, a la the Kachru-Kallosh-Linde-Trivedi and Large Volume scenarios; and (iii) there are no additional gauged sectors from 7-branes. Since nearly all known globally consistent F-theory models with the exact chiral spectrum of the Standard Model and gauge coupling unification occur at moderate h(1,1), this finding calls for new moduli stabilization scenarios or/and a rich 7-brane dark sector. Ključne besede: brane worlds, compactification, string theory Objavljeno v DKUM: 23.10.2023; Ogledov: 497; Prenosov: 16 Celotno besedilo (292,32 KB) Gradivo ima več datotek! Več... |
10. Generalized Couch-Torrence symmetry for rotating extremal black holes in maximal supergravityMirjam Cvetič, Christopher N. Pope, Aritra Saha, 2020, izvirni znanstveni članek Opis: he extremal Reissner-Nordstrom black hole admits a conformal inversion symmetry, in which the metric is mapped into itself under an inversion of the radial coordinate combined with a conformal rescaling. In the rotating generalization, Couch and Torrence showed that the Kerr- Newman metric no longer exhibits a conformal inversion symmetry, but the radial equation arising in the separation of the massless Klein-Gordon equation admits a mode-dependent inversion symmetry, where the radius of inversion depends upon the energy and azimuthal angular momentum of the mode. It was more recently shown that the static four-charge extremal black holes of STU supergravity (i.e., N = 2 supergravity in four dimension coupled to three vector multiplets) admit a generalization of the conformal inversion symmetry, in which the conformally inverted metric is a member of the same four-charge black hole family but with transformed charges. In this paper we study further generalizations of these inversion symmetries, within the general class of extremal STU supergravity black holes. For the rotating black holes, where again the massless Klein-Gordon equation is separable, we show that examples with four electric charges exhibit a generalization of the Couch-Torrence symmetry of the radial equation. Now, as in the conformal inversion of the static specializations, the inversion of the radial equation maps it to the radial equation for a rotating black hole with transformed electric charges. We also study the inversion transformations for the general case of extremal Bogomol'nyi-Prasad-Sommerfield STU black holes carrying eight charges (four electric plus four magnetic), and argue that analogous generalizations of the inversion symmetries exist for both the static and the rotating cases. Ključne besede: black holes, supergravity, supersymmetry, conformal symmetry Objavljeno v DKUM: 23.10.2023; Ogledov: 562; Prenosov: 6 Celotno besedilo (287,15 KB) Gradivo ima več datotek! Več... |