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Discrete symmetries in Heterotic/F-theory duality and mirror symmetry
Mirjam Cvetič, Antonella Grassi, Maximilian Poretschkin, 2017, izvirni znanstveni članek

Opis: We study aspects of Heterotic/F-theory duality for compactifications with Abelian discrete gauge symmetries. We consider F-theory compactifications on genus-one fibered Calabi-Yau manifolds with n-sections, associated with the Tate-Shafarevich group Z(n). Such models are obtained by studying first a specific toric set-up whose associated Heterotic vector bundle has structure group Z(n). By employing a conjectured Heterotic/F-theory mirror symmetry we construct dual geometries of these original toric models, where in the stable degeneration limit we obtain a discrete gauge symmetry of order two and three, for compactifications to six dimensions. We provide explicit constructions of mirror-pairs for symmetric examples with Z(2) and Z(3), in six dimensions. The Heterotic models with symmetric discrete symmetries are related in field theory to a Higgsing of Heterotic models with two symmetric abelian U(1) gauge factors, where due to the Stuckelberg mechanism only a diagonal U(1) factor remains massless, and thus after Higgsing only a diagonal discrete symmetry of order n is present in the Heterotic models and detected via Heterotic/F-theory duality. These constructions also provide further evidence for the conjectured mirror symmetry in Heterotic/F-theory at the level of fibrations with torsional sections and those with multi-sections.
Ključne besede: discrete symmetries, F-theory, string duality, superstrings, heterotic strings
Objavljeno: 08.03.2018; Ogledov: 41; Prenosov: 0
.pdf Celotno besedilo (510,30 KB)

Type II string theory on Calabi-Yau manifolds with torsion and non-Abelian discrete gauge symmetries
Volker Braun, Mirjam Cvetič, Ron Donagi, Maximilian Poretschkin, 2017, izvirni znanstveni članek

Opis: We provide the first explicit example of Type IIB string theory compactification on a globally defined Calabi-Yau threefold with torsion which results in a four-dimensional effective theory with a non-Abelian discrete gauge symmetry. Our example is based on a particular Calabi-Yau manifold, the quotient of a product of three elliptic curves by a fixed point free action of Z(2) x Z(2). Its cohomology contains torsion classes in various degrees. The main technical novelty is in determining the multiplicative structure of the (torsion part of) the cohomology ring, and in particular showing that the cup product of second cohomology torsion elements goes non-trivially to the fourth cohomology. This specifies a non-Abelian, Heisenberg-type discrete symmetry group of the four-dimensional theory.
Ključne besede: string field theory, conformal field models, string theory, discrete symmetries
Objavljeno: 08.03.2018; Ogledov: 38; Prenosov: 0
.pdf Celotno besedilo (355,78 KB)

Rotating solutions in critical Lovelock gravities
Mirjam Cvetič, Xing-Hui Feng, Hong Lü, Christopher N. Pope, 2017, izvirni znanstveni članek

Opis: For appropriate choices of the coupling constants, the equations of motion of Lovelock gravities up to order n in the Riemann tensor can be factorized such that the theories admit a single (A)dS vacuum. In this paper we construct two classes of exact rotating metrics in such critical Lovelock gravities of order n in d = 2n +1 dimensions. In one class, the n angular momenta in the n orthogonal spatial 2-planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a Kerr-Schild form, but they can then be recast in terms of Boyer-Lindquist coordinates. The other class involves metrics with only a single non-vanishing angular momentum. Again we construct them in a Kerr-Schild form, but in this case it does not seem to be possible to recast them in Boyer-Lindquist form. Both classes of solutions have naked curvature singularities, arising because of the over rotation of the configurations.
Ključne besede: astrophysics, nuclear physics
Objavljeno: 08.03.2018; Ogledov: 34; Prenosov: 1
.pdf Celotno besedilo (274,39 KB)

Attitudes toward workplace mobbing in Slovenian research organisations
Brigita Krsnik Horvat, Milan Pagon, 2012, izvirni znanstveni članek

Opis: Creating a "mobbing-safe" working environment can be a real challenge; to achieve it, a better understanding of related constructs is necessary. To obtain insight into researchers' attitudes toward workplace mobbing and behavioural intentions, we used a case scenario method. The results show that respondents, on average, consider the mobbing cases presented in a questionnaire to be very serious. Their attitudes and behavioural intentions depend more on their opinion about colleagues' attitudes and related intentions and less on their own, which shows a lower integrity than desired. Low willingness to report the violator, lenient discipline sanctions and the absence of proper organisational rules create favourable conditions for workplace mobbing in Slovenian public research organisations. This paper also proposes measures based on the research findings of various authors and identifies new questions that could be addressed in further research.
Ključne besede: workplace mobbing, organisational culture, integrity, public research organisation, researcher
Objavljeno: 28.11.2017; Ogledov: 91; Prenosov: 1
.pdf Celotno besedilo (1014,04 KB)

Ivan Grohar and Oskar Dev
Franc Križnar, 2014, izvirni znanstveni članek

Opis: The new Grohar’s room in the Škofja Loka Museum that is located in a more than a thousand years old town, some kilometres northwest of Ljubljana, Slovenia, represents one of the new possibilities to popularize old local history. Ivan Grohar (1867−1911) is one of the four well-known Slovenian painters from the beginning of the 20th century, together with Rihard Jakopič, Matija Jama and Matej Sternen. These Slovenian painters are the founders of Impressionism within the modern style. Škofja Loka became the so called Slovenian “Barbizon” (i.e. French village near Fontainebleau, once the settlement of painters) and this art and old tradition inspired another Slovenian (music) artist Oskar Dev (1868−1932), who composed some of his musical works (songs and choirs) in Škofja Loka, too. His and Grohar’s period in Škofja Loka resulted in some extraordinary art works i.e. paintings and musical works. They both were inspired by the countryside that reflected on their works. This is now one of the new Slovenian’s challenges of museology and musicology in an interdisciplinary and multidisciplinary approach so the art of painting and music could be a benefit for the visitors of this and other museums.
Ključne besede: old local history, painter, composer, Impressionism, modern style, “Barbizon”, music pieces: songs and choirs, museology, musicology, Slovenian classical music, 20th century, Škofja Loka, 1905/1911
Objavljeno: 08.08.2017; Ogledov: 117; Prenosov: 6
.pdf Celotno besedilo (2,20 MB)

Parameter space for a dissipative Fermi-Ulam model
Diego F. M. Oliveira, Edson D. Leonel, 2011, izvirni znanstveni članek

Opis: The parameter space for a dissipative bouncing ball model under the effect of inelastic collisions is studied. The system is described using a two-dimensional nonlinear area-contracting map. The introduction of dissipation destroys the mixed structure of phase space of the non-dissipative case, leading to the existence of a chaotic attractor and attracting fixed points, which may coexist for certain ranges of control parameters. We have computed the average velocity for the parameter space and made a connection with the parameter space based on the maximum Lyapunov exponent. For both cases, we found an infinite family of self-similar structures of shrimp shape, which correspond to the periodic attractors embedded in a large region that corresponds to the chaotic motion.
Ključne besede: parameter space, Fermi-Ulam model, inelastic collision
Objavljeno: 03.07.2017; Ogledov: 105; Prenosov: 4
.pdf Celotno besedilo (2,84 MB)

Expanded boundary integral method and chaotic time-reversal in quatum billiards
Gregor Veble, Tomaž Prosen, Marko Robnik, 2007, izvirni znanstveni članek

Opis: We present the expanded boundary integral method for solving the planar Helmholtz problem, which combines the ideas of the boundary integral method and the scaling method and is applicable to arbitrary shapes. We apply the method to a chaotic billiard with unidirectional transport, where we demonstrate the existence of doublets of chaotic eigenstates, which are quasi-degenerate due to time-reversal symmetry, and a very particular level spacing distribution that attains a chaotic Shnirelman peak at short energy ranges and exhibits Gaussian Unitary Ensemble (GUE) like statistics for large energy ranges. We show that, as a consequence of such particular level statistics or algebraic tunnelling between disjoint chaotic components connected by time-reversal operation, the system exhibits quantum current reversals.
Ključne besede: 2D Helmholtz equation, energy spectrum, quantum billiard
Objavljeno: 03.07.2017; Ogledov: 121; Prenosov: 2
.pdf Celotno besedilo (2,90 MB)

Wave equation for the Wu black hole
Tolga Birkandan, Mirjam Cvetič, 2014, izvirni znanstveni članek

Opis: Wu black hole is the most general solution of maximally supersymmetric gauged supergravity in D=5, containing U(1)(3) gauge symmetry. We study the separability of the massless Klein-Gordon equation and probe its singularities for a general stationary, axisymmetric metric with orthogonal transitivity, and apply the results to the Wu black hole solution. We start with the zero azimuthal-angle eigenvalues in the scalar field Ansatz and find that the residuum of a pole in the radial equation is associated with the surface gravity calculated at this horizon. We then generalize our calculations to nonzero azimuthal eigenvalues and probing each horizon singularity, we show that the residua of the singularities for each horizon are in general associated with a specific combination of the surface gravity and the angular velocities at the associated horizon. It turns out that for the Wu black hole both the radial and angular equations are general Heun's equations with four regular singularities.
Ključne besede: black holes, string theory, conformal field models, string duality
Objavljeno: 27.06.2017; Ogledov: 163; Prenosov: 3
.pdf Celotno besedilo (424,79 KB)

Vacuum polarization of STU black holes and their subtracted geometry limit
Mirjam Cvetič, G. W. Gibbons, Zain H. Saleem, Alejandro Satz, 2015, izvirni znanstveni članek

Opis: We study the vacuum polarization of a massless minimally coupled scalar field at the horizon of four-charge STU black holes. We compare the results for the standard asymptotically flat black holes and for the black holes obtained in the "subtracted limit", both in the general static case and at the horizon pole for the general rotating case. The original and the subtracted results are identical only in the BPS limit, and have opposite sign in the extremal Kerr limit. We also compute the vacuum polarization on the static solutions that interpolate between both the original and the subtracted case through a solution-generating transformation and show that the vacuum polarization stays positive throughout the interpolating solution. In the appendix we provide a closed-form solution for the Green's function on general (static or rotating) subtracted black hole geometries.
Ključne besede: black holes, supergravity, string theory, conformal field models, string duality
Objavljeno: 27.06.2017; Ogledov: 136; Prenosov: 4
.pdf Celotno besedilo (372,93 KB)

Three-family particle physics models from global F-theory compactifications
Mirjam Cvetič, Denis Klevers, Damian Kaloni Mayorga Pena, Paul Oehlmann, Jonas Reuter, 2015, izvirni znanstveni članek

Opis: We construct four-dimensional, globally consistent F-theory models with three chiral generations, whose gauge group and matter representations coincide with those of the Minimal Supersymmetric Standard Model, the Pati-Salam Model and the Trinification Model. These models result from compactification on toric hypersurface fibrations X with the choice of base P-3. We observe that the F-theory conditions on the G(4)-flux restrict the number of families to be at least three. We comment on the phenomenology of the models, and for Pati-Salam and Trinification models discuss the Higgsing to the Standard Model. A central point of this work is the construction of globally consistent G(4)-flux. For this purpose we compute the vertical cohomology H-V((2,2)) (X) in each case and solve the conditions imposed by matching the M- and F-theoretical 3D Chern-Simons terms. We explicitly check that the expressions found for the G(4)-flux allow for a cancellation of D3-brane tadpoles. We also use the integrality of 3D Chern-Simons terms to ensure that our G(4)-flux solutions are adequately quantized.
Ključne besede: black holes, supergravity, string theory, conformal field models, string duality
Objavljeno: 27.06.2017; Ogledov: 131; Prenosov: 2
.pdf Celotno besedilo (890,06 KB)

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