1. Discrete symmetries in Heterotic/Ftheory duality and mirror symmetryMirjam Cvetič, Antonella Grassi, Maximilian Poretschkin, 2017, izvirni znanstveni članek Opis: We study aspects of Heterotic/Ftheory duality for compactifications with Abelian discrete gauge symmetries. We consider Ftheory compactifications on genusone fibered CalabiYau manifolds with nsections, associated with the TateShafarevich group Z(n). Such models are obtained by studying first a specific toric setup whose associated Heterotic vector bundle has structure group Z(n). By employing a conjectured Heterotic/Ftheory 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 mirrorpairs 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/Ftheory duality. These constructions also provide further evidence for the conjectured mirror symmetry in Heterotic/Ftheory at the level of fibrations with torsional sections and those with multisections. Ključne besede: discrete symmetries, Ftheory, string duality, superstrings, heterotic strings Objavljeno: 08.03.2018; Ogledov: 882; Prenosov: 306 Celotno besedilo (510,30 KB) Gradivo ima več datotek! Več...

2. Type II string theory on CalabiYau manifolds with torsion and nonAbelian discrete gauge symmetriesVolker 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 CalabiYau threefold with torsion which results in a fourdimensional effective theory with a nonAbelian discrete gauge symmetry. Our example is based on a particular CalabiYau 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 nontrivially to the fourth cohomology. This specifies a nonAbelian, Heisenbergtype discrete symmetry group of the fourdimensional theory. Ključne besede: string field theory, conformal field models, string theory, discrete symmetries Objavljeno: 08.03.2018; Ogledov: 879; Prenosov: 301 Celotno besedilo (355,78 KB) Gradivo ima več datotek! Več...

3. Rotating solutions in critical Lovelock gravitiesMirjam Cvetič, XingHui 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 2planes are equal, and hence the metric is of cohomogeneity one. We construct these metrics in a KerrSchild form, but they can then be recast in terms of BoyerLindquist coordinates. The other class involves metrics with only a single nonvanishing angular momentum. Again we construct them in a KerrSchild form, but in this case it does not seem to be possible to recast them in BoyerLindquist 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: 925; Prenosov: 305 Celotno besedilo (274,39 KB) Gradivo ima več datotek! Več...

4. Wave equation for the Wu black holeTolga 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 KleinGordon 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 azimuthalangle 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: 943; Prenosov: 280 Celotno besedilo (424,79 KB) Gradivo ima več datotek! Več...

5. Vacuum polarization of STU black holes and their subtracted geometry limitMirjam 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 fourcharge 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 solutiongenerating transformation and show that the vacuum polarization stays positive throughout the interpolating solution. In the appendix we provide a closedform 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: 747; Prenosov: 276 Celotno besedilo (372,93 KB) Gradivo ima več datotek! Več...

6. Threefamily particle physics models from global Ftheory compactificationsMirjam Cvetič, Denis Klevers, Damian Kaloni Mayorga Pena, Paul Oehlmann, Jonas Reuter, 2015, izvirni znanstveni članek Opis: We construct fourdimensional, globally consistent Ftheory models with three chiral generations, whose gauge group and matter representations coincide with those of the Minimal Supersymmetric Standard Model, the PatiSalam Model and the Trinification Model. These models result from compactification on toric hypersurface fibrations X with the choice of base P3. We observe that the Ftheory 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 PatiSalam 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 HV((2,2)) (X) in each case and solve the conditions imposed by matching the M and Ftheoretical 3D ChernSimons terms. We explicitly check that the expressions found for the G(4)flux allow for a cancellation of D3brane tadpoles. We also use the integrality of 3D ChernSimons 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: 887; Prenosov: 280 Celotno besedilo (890,06 KB) Gradivo ima več datotek! Več...

7. Origin of Abelian gauge symmetries in heterotic/Ftheory dualityMirjam Cvetič, Antonella Grassi, Denis Klevers, Peng Song, Maximilian Poretschkin, 2016, izvirni znanstveni članek Opis: We study aspects of heterotic/Ftheory duality for compactifications with Abelian gauge symmetries. We consider Ftheory on general CalabiYau manifolds with a rank one MordellWeil group of rational sections. By rigorously performing the stable degeneration limit in a class of toric models, we derive both the CalabiYau geometry as well as the spectral cover describing the vector bundle in the heterotic dual theory. We carefully investigate the spectral cover employing the group law on the elliptic curve in the heterotic theory. We find in explicit examples that there are three different classes of heterotic duals that have U(1) factors in their low energy effective theories: split spectral covers describing bundles with S(U(m) x U(1)) structure group, spectral covers containing torsional sections that seem to give rise to bundles with SU(m) X Z(k) structure group and bundles with purely nonAbelian structure groups having a centralizer in E8 containing a U(1) factor. In the former two cases, it is required that the elliptic fibration on the heterotic side has a nontrivial MordellWeil group. While the number of geometrically massless U(1)'s is determined entirely by geometry on the Ftheory side, on the heterotic side the correct number of U(1)'s is found by taking into account a Stiickelberg mechanism in the lowerdimensional effective theory. In geometry, this corresponds to the condition that sections in the two half K3 surfaces that arise in the stable degeneration limit of Ftheory can be glued together globally. Ključne besede: Ftheory, string duality, superstrings, heterotic strings, Mtheory Objavljeno: 27.06.2017; Ogledov: 673; Prenosov: 293 Celotno besedilo (1,15 MB) Gradivo ima več datotek! Več...

8. On finiteness of type IIB compactificationsMirjam Cvetič, James Halverson, Denis Klevers, Peng Song, 2014, izvirni znanstveni članek Opis: The string landscape satisfies interesting finiteness properties imposed by supersymmetry and stringtheoretical consistency conditions. We study N = 1 supersymmetric compactifications of Type IIB string theory on smooth elliptically fibered CalabiYau threefolds at large volume with magnetized D9branes and D5branes. We prove that supersymmetry and tadpole cancellation conditions imply that there is a finite number of such configurations. In particular, we derive an explicitly computable bound on the number of magnetic flux quanta, as well as the number of D5branes, which is independent of the continuous moduli of the setup. The proof applies if a number of easy to check geometric conditions of the twofold base are met. We show that these geometric conditions are satisfied for the almost Fano twofold bases given by each toric variety associated to a reflexive twodimensional polytope as well as by the generic del Pezzo surfaces dP(n) with n = 0, ..., 8. Physically, this finiteness proof shows that there exist a finite collection of fourdimensional gauge groups and chiral matter spectra in the 4D supergravity theories realized by these compactifications. As a byproduct we explicitly construct all generators of the Kaahler cones of dP(n) and work out their relation to representation theory. Ključne besede: black holes, supergravity, string theory, conformal field models, string duality Objavljeno: 27.06.2017; Ogledov: 571; Prenosov: 72 Celotno besedilo (1,01 MB) Gradivo ima več datotek! Več...

9. Elliptic fibrations with rank three MordellWeilgroupMirjam Cvetič, Denis Klevers, Hernan Piragua, Peng Song, 2014, izvirni znanstveni članek Opis: We analyze general Ftheory compactifications with U(1)xU(1)xU(1) Abelian gauge symmetry by constructing the general elliptically fibered CalabiYau manifolds with a rank three MordellWeil group of rational sections. The general elliptic fiber is shown to be a complete intersection of two nongeneric quadrics in P3 and resolved elliptic fibrations are obtained by embedding the fiber as the generic CalabiYau complete intersection into Bl(3)P(3), the blowup of P3 at three points. For a fixed base B, there are finitely many CalabiYau elliptic fibrations. Thus, Ftheory compactifications on these CalabiYau manifolds are shown to be labeled by integral points in reflexive polytopes constructed from the nefpartition of Bl(3)P(3). We determine all 14 massless matter representations to six and four dimensions by an explicit study of the codimension two singularities of the elliptic fibration. We obtain three matter representations charged under all three U(1)factors, most notably a trifundamental representation. The existence of these representations, which are not present in generic perturbative Type II compactifications, signifies an intriguing universal structure of codimension two singularities of the elliptic fibrations with higher rank MordellWeil groups. We also compute explicitly the corresponding 14 multiplicities of massless hypermultiplets of a sixdimensional Ftheory compactification for a general base B. Ključne besede: flux compactifications, Ftheory, superstring vacua, Dbranes Objavljeno: 27.06.2017; Ogledov: 509; Prenosov: 96 Celotno besedilo (840,88 KB) Gradivo ima več datotek! Več...

10. Electrodynamics of black holes in STU supergravityMirjam Cvetič, G. W. Gibbons, Christopher N. Pope, Zain H. Saleem, 2014, izvirni znanstveni članek Opis: External magnetic fields can probe the composite structure of black holes in string theory. With this motivation we study magnetised fourcharge black holes in the STU model, a consistent truncation of maximally supersymmetric supergravity with four types of electromagnetic fields. We employ solution generating techniques to obtain Melvin backgrounds, and black holes in these backgrounds. For an initially electrically charged static black hole immersed in magnetic fields, we calculate the resultant angular momenta and analyse their global structure. Examples are given for which the ergoregion does not extend to infinity. We calculate magnetic moments and gyromagnetic ratios via Larmor's formula. Our results are consistent with earlier special cases. A scaling limit and associated subtracted geometry in a single surviving magnetic field is shown to lift to AdS(3) x S2. Magnetizing magnetically charged black holes give static solutions with conical singularities representing strings or struts holding the black holes against magnetic forces. In some cases it is possible to balance these magnetic forces. Ključne besede: black holes, supergravity, string theory, conformal field models, string duality Objavljeno: 27.06.2017; Ogledov: 556; Prenosov: 311 Celotno besedilo (563,26 KB) Gradivo ima več datotek! Več...
