The Experts below are selected from a list of 960 Experts worldwide ranked by ideXlab platform
Alexander Seifert - One of the best experts on this subject based on the ideXlab platform.
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Massless spectra and gauge couplings at one-loop on non-factorisable toroidal orientifolds
Nuclear Physics B, 2018Co-Authors: Mikel Berasaluce-gonzález, Gabriele Honecker, Alexander SeifertAbstract:Abstract So-called ‘non-factorisable’ toroidal orbifolds can be rewritten in a Factorised Form as a product of three two-tori by imposing an additional shift symmetry. This finding of Blaszczyk et al. [1] provides a new avenue to ConFormal Field Theory methods, by which the vector-like massless matter spectrum – and thereby the type of gauge group enhancement on orientifold invariant fractional D6-branes – and the one-loop corrections to the gauge couplings in Type IIA orientifold theories can be computed in addition to the well-established chiral matter spectrum derived from topological intersection numbers among three-cycles. We demonstrate this framework for the Z 4 × Ω R orientifolds on the A 3 × A 1 × B 2 -type torus. As observed before for factorisable backgrounds, also here the one-loop correction can drive the gauge groups to stronger coupling as demonstrated by means of a four-generation Pati–Salam example.
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Towards Geometric D6-Brane Model Building on non-Factorisable Toroidal $\mathbb{Z}_4$-Orbifolds
Journal of High Energy Physics, 2016Co-Authors: Mikel Berasaluce-gonzález, Gabriele Honecker, Alexander SeifertAbstract:We present a geometric approach to D-brane model building on the non-factorisable torus backgrounds of $T^6/\mathbb{Z}_4$, which are $A_3 \times A_3$ and $A_3 \times A_1 \times B_2$. Based on the counting of `short' supersymmetric three-cycles per complex structure {\it vev}, the number of physically inequivalent lattice orientations with respect to the anti-holomorphic involution ${\cal R}$ of the Type IIA/$\Omega\cal{R}$ orientifold can be reduced to three for the $A_3 \times A_3$ lattice and four for the $A_3 \times A_1 \times B_2$ lattice. While four independent three-cycles on $A_3 \times A_3$ cannot accommodate phenomenologically interesting global models with a chiral spectrum, the eight-dimensional space of three-cycles on $A_3 \times A_1 \times B_2$ is rich enough to provide for particle physics models, with several globally consistent two- and four-generation Pati-Salam models presented here. We further show that for fractional {\it sLag} three-cycles, the compact geometry can be rewritten in a $(T^2)^3$ Factorised Form, paving the way for a generalisation of known CFT methods to determine the vector-like spectrum and to derive the low-energy effective action for open string states.
Federico Alberto Ceccopieri - One of the best experts on this subject based on the ideXlab platform.
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Single-diffractive Drell-Yan pair production at the LHC
The European Physical Journal C, 2017Co-Authors: Federico Alberto CeccopieriAbstract:We present predictions for single-diffractive low-mass Drell-Yan pair production in $pp$ collisions at the LHC at $\sqrt{s}=13$ TeV. Predictions are obtained adopting a Factorised Form for the relevant cross sections and are based on a new set of diffractive parton distributions resulting from the QCD analysis of combined HERA leading proton data. We discuss a number of observables useful to characterise the expected factorisation breaking effects.
Tommaso Macrì - One of the best experts on this subject based on the ideXlab platform.
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Neutrino Masses and Mixings from String Theory Instantons
Journal of High Energy Physics, 2007Co-Authors: Stefan Antusch, Luis E. Ibáñez, Tommaso MacrìAbstract:We study possible patterns of neutrino masses and mixings in string models in which Majorana neutrino masses are generated by a certain class of string theory instantons recently considered in the literature. These instantons may generate either directly the dim=5 Weinberg operator or right-handed neutrino Majorana masses, both with a certain flavour-Factorised Form. A hierarchy of neutrino masses naturally appears from the exponentially suppressed contributions of different instantons. The flavour structure is controlled by string amplitudes involving neutrino fields and charged instanton zero modes. For some simple choices for these amplitudes one finds neutrino mixing patterns consistent with experimental results. In particular, we find that a tri-bimaximal mixing pattern is obtained for simple symmetric values of the string correlators.
Mikel Berasaluce-gonzález - One of the best experts on this subject based on the ideXlab platform.
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Massless spectra and gauge couplings at one-loop on non-factorisable toroidal orientifolds
Nuclear Physics B, 2018Co-Authors: Mikel Berasaluce-gonzález, Gabriele Honecker, Alexander SeifertAbstract:Abstract So-called ‘non-factorisable’ toroidal orbifolds can be rewritten in a Factorised Form as a product of three two-tori by imposing an additional shift symmetry. This finding of Blaszczyk et al. [1] provides a new avenue to ConFormal Field Theory methods, by which the vector-like massless matter spectrum – and thereby the type of gauge group enhancement on orientifold invariant fractional D6-branes – and the one-loop corrections to the gauge couplings in Type IIA orientifold theories can be computed in addition to the well-established chiral matter spectrum derived from topological intersection numbers among three-cycles. We demonstrate this framework for the Z 4 × Ω R orientifolds on the A 3 × A 1 × B 2 -type torus. As observed before for factorisable backgrounds, also here the one-loop correction can drive the gauge groups to stronger coupling as demonstrated by means of a four-generation Pati–Salam example.
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Towards Geometric D6-Brane Model Building on non-Factorisable Toroidal $\mathbb{Z}_4$-Orbifolds
Journal of High Energy Physics, 2016Co-Authors: Mikel Berasaluce-gonzález, Gabriele Honecker, Alexander SeifertAbstract:We present a geometric approach to D-brane model building on the non-factorisable torus backgrounds of $T^6/\mathbb{Z}_4$, which are $A_3 \times A_3$ and $A_3 \times A_1 \times B_2$. Based on the counting of `short' supersymmetric three-cycles per complex structure {\it vev}, the number of physically inequivalent lattice orientations with respect to the anti-holomorphic involution ${\cal R}$ of the Type IIA/$\Omega\cal{R}$ orientifold can be reduced to three for the $A_3 \times A_3$ lattice and four for the $A_3 \times A_1 \times B_2$ lattice. While four independent three-cycles on $A_3 \times A_3$ cannot accommodate phenomenologically interesting global models with a chiral spectrum, the eight-dimensional space of three-cycles on $A_3 \times A_1 \times B_2$ is rich enough to provide for particle physics models, with several globally consistent two- and four-generation Pati-Salam models presented here. We further show that for fractional {\it sLag} three-cycles, the compact geometry can be rewritten in a $(T^2)^3$ Factorised Form, paving the way for a generalisation of known CFT methods to determine the vector-like spectrum and to derive the low-energy effective action for open string states.
M. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Lattice vibration spectra. Part LXXXVI. Infrared and Raman spectra of baryte-type TlClO4, TlBF4, and NH4BF4 single crystals and of11B-enriched NH4BF4
Journal of Alloys and Compounds, 1996Co-Authors: H. D. Lutz, J. Himmrich, M. SchmidtAbstract:Polarised infrared reflection spectra of TlClO4, TlBF4 and NH4BF4 single-crystal plates were recorded and analysed for the frequencies of the transversal and longitudinal optical zone-centre phonon modes and other oscillator parameters by using the three-parameter (dielectric sum function) and the four-parameter (Factorised Form) oscillator-fit methods. In addition, single-crystal Raman spectra of the title compounds and the spectra of polycrystalline samples including those of11B-enriched NH4BF4 were monitored. The obtained spectra are assigned and discussed with respect to (i) splitting of the respective modes due to all10B/11B isotope substitution, long-range Coulomb forces (TO/LO), distortion of the anionic units (site group), and dynamic interaction (Davydov), (ii) phase transition to the cubic high-temperature polymorphs, and (iii) change of bonding (including effective charges) on going from both the thallium to the alkali-metal compounds and from perchlorates to tetrafluoroborates.
