On Fluxed Instantons and Moduli Stabilisation in IIB Orientifolds and F-theory

We study the superpotential induced by Euclidean D3-brane instantons carrying instanton flux, with special emphasis on its significance for the stabilisation of Kahler moduli and Neveu-Schwarz axions in Type IIB orientifolds. Quite generally, once a chiral observable sector is included in the compactification, arising on intersecting D7-branes with world-volume flux, resulting charged instanton zero modes prevent a class of instantons from participating in moduli stabilisation. We show that instanton flux on Euclidean D3-branes can remove these extra zero modes and helps in reinstating full moduli stabilisation within a geometric regime. We comment also on the F-theoretic description of this effect of alleviating the general tension between moduli stabilisation and chirality. In addition we propose an alternative solution to this problem based on dressing the instantons with charged matter fields which is unique to F-theory and cannot be realised in the weak coupling limit.Comment: 9 pages in 2-column format; v2: refs adde

Fluxed M5-instantons in F-theory

We analyse the non-perturbative superpotential due to M5-brane instantons in F-theory compactifications on Calabi-Yau fourfolds. The M5 partition function is obtained via holomorphic factorisation by explicitly performing the sum over chiral 3-form fluxes. Comparison with the partition function of fluxed Euclidean D3-brane instantons in Type IIB orientifolds allows us to fix the spin structure on the intermediate Jacobian of the M5-instanton. We furthermore analyse the contribution of the M5-instanton to the superpotential in the presence of G4 gauge flux, where the superpotential is dressed with matter fields. We explicitly evaluate the pullback of G4 onto the M5-brane as a measure for the presence of charged instanton zero modes. This accounts for the M5 charge both under massless U(1)s, if present, and under what corresponds in Type II language to geometrically massive U(1)s.Comment: 47 pages. v3: refs. added, matches version published in Nuclear Physics

G_4 flux, chiral matter and singularity resolution in F-theory compactifications

We construct a set of chirality inducing G_4-fluxes in global F-theory compactifications on Calabi-Yau four-folds. Special emphasis is put on models with gauge group SU(5) x U(1)_X relevant in the context of F-theory GUT model building, which are described in terms of a U(1)-restricted Tate model. In this type of constructions, the G_4-flux arises in a manner completely analogous to the U(1)_X gauge potential. We describe in detail the resolution by blow-up of the various singularities responsible for the U(1)_X factor and the standard SU(5) gauge group and match the result with techniques applied in the context of toric geometry. This provides an explicit identification of the structure of the resolved fibre over the matter curves and over the enhancement points relevant for Yukawa couplings. The U(1)_X flux induces a chiral matter spectrum. We compute the chiral index both of SU(5) charged matter and of SU(5) singlets charged only under U(1)_X localised on curves which are not contained in the SU(5) locus. We furthermore discuss global consistency conditions such as D3-tadpole cancellation, D-term supersymmetry and Freed-Witten quantisation. The U(1)_X gauge flux is a global extension of a class of split spectral cover bundles. It constitutes an essential ingredient in the construction of globally defined F-theory compactifications with chiral matter. We exemplify this in a three-generation SU(5) x U(1)_X model whose flux satisfies all of the above global consistency conditions. We also extend our results to chiral fluxes in models without U(1) restriction.Comment: 53 pages, 2 figures; v2: details on Freed-Witten quantisation condition included, typos correcte

Gauge Fluxes in F-theory and Type IIB Orientifolds

We provide a detailed correspondence between G_4 gauge fluxes in F-theory compactifications with SU(n) and SU(n)x(1) gauge symmetry and their Type IIB orientifold limit. Based on the resolution of the relevant F-theory Tate models we classify the factorisable G_4-fluxes and match them with the set of universal D5-tadpole free U(1)-fluxes in Type IIB. Where available, the global version of the universal spectral cover flux corresponds to Type IIB gauge flux associated with a massive diagonal U(1). In U(1)-restricted Tate models extra massless abelian fluxes exist which are associated with specific linear combinations of Type IIB fluxes. Key to a quantitative match between F-theory and Type IIB is a proper treatment of the conifold singularity encountered in the Sen limit of generic F-theory models. We also shed further light on the brane recombination process relating generic and U(1)-restricted Tate models.Comment: 53 pages, 3 figures; v2: Refs added; v3: minor corrections to match version published in JHE

GUTs in Type IIB Orientifold Compactifications

We systematically analyse globally consistent SU(5) GUT models on intersecting D7-branes in genuine Calabi-Yau orientifolds with O3- and O7-planes. Beyond the well-known tadpole and K-theory cancellation conditions there exist a number of additional subtle but quite restrictive constraints. For the realisation of SU(5) GUTs with gauge symmetry breaking via U(1)_Y flux we present two classes of suitable Calabi-Yau manifolds defined via del Pezzo transitions of the elliptically fibred hypersurface P_{1,1,1,6,9}[18] and of the Quintic P_{1,1,1,1,1}[5], respectively. To define an orientifold projection we classify all involutions on del Pezzo surfaces. We work out the model building prospects of these geometries and present five globally consistent string GUT models in detail, including a 3-generation SU(5) model with no exotics whatsoever. We also realise other phenomenological features such as the 10 10 5 Yukawa coupling and comment on the possibility of moduli stabilisation, where we find an entire new set of so-called swiss-cheese type Calabi-Yau manifolds. It is expected that both the general constrained structure and the concrete models lift to F-theory vacua on compact Calabi-Yau fourfolds.Comment: 138 pages, 9 figures; v2, v3: typos corrected, one reference adde

Experimental Investigation of a SOFC Off-Gas Combustor for Hybrid Power Plant Usage with Low Heating Values Realised by Natural Gas Addition

Rising power demands and the increasing importance of decentralised energy production based on renewable resources require gas turbine systems with flexible energy conversion. Therefore, a suitable hybrid power plant demonstrator with a high temperature fuel cell is being set up at the German Aerospace Centre (DLR). This facility requires burner concepts for low calorific gases capable of combusting the exhaust products of the fuel cell system anode side, here referred to as SOFC (solid oxide fuel cell) off-gas. The combustor behaviour for the demonstrator system is investigated in the current work using an atmospheric combustor test rig at DLR. Additionally, a strategy for stabilisation of the flame in operating points with very low heating values (LHV) via addition of natural gas into the SOFC off-gas before entering the combustor is tested in view of expected impacts on efficiency and other critical system parameters. The combustion system is furthermore investigated in view of CO emissions

Massive Abelian Gauge Symmetries and Fluxes in F-theory

F-theory compactified on a Calabi-Yau fourfold naturally describes non-Abelian gauge symmetries through the singularity structure of the elliptic fibration. In contrast Abelian symmetries are more difficult to study because of their inherently global nature. We argue that in general F-theory compactifications there are massive Abelian symmetries, such as the uplift of the Abelian part of the U(N) gauge group on D7-branes, that arise from non-Kahler resolutions of the dual M-theory setup. The four-dimensional F-theory vacuum with vanishing expectation values for the gauge fields corresponds to the Calabi-Yau limit. We propose that fluxes that are turned on along these U(1)s are uplifted to non-harmonic four-form fluxes. We derive the effective four-dimensional gauged supergravity resulting from F-theory compactifications in the presence of the Abelian gauge factors including the effects of possible fluxes on the gauging, tadpoles and matter spectrum.Comment: 49 page

Процесс импортозамещения на предприятиях ВЭД в условиях экономических санкций и эмбарго

Дипломная работа на тему "Процесс импортозамещения на предприятиях ВЭД в условиях внешнеэкономических санкций и эмбарго". Целью исследования является раскрытие импортозамещющих процессов в условиях санкций и эмбарго на предприятиях разных отраслей промышленности. В работе рассматриваются проблемные места государственной программы импортозамещения в разных отраслях, такие как недостаточность правовой базы процесса, недоступность финансовых ресурсов для развития компаний, а также использование научного и инновационного потенциала России не в полной мере. В основной части рассмотрены проблемы и перспективы внедрения отечественных компаний аграрной, легкой и фармацевтической промышленности в импортозамещение.Diploma work on the topic "The process of import substitution in foreign trade enterprises in terms of foreign economic sanctions and embargoes." The purpose of this diploma is to disclose import-substituting processes in conditions of sanctions and embargoes at enterprises of different industries. The paper examines the problems of the state program of import substitution in various sectors, such as the lack of a legal framework for the process, the inaccessibility of financial resources for the development of companies, and the use of Russia's scientific and innovative potential is not fully realized. In the main part, problems and prospects for introducing domestic companies of the agrarian, light and pharmaceutical industries into import substitution are discussed

The effective action of D6-branes in N=1 type IIA orientifolds

We use a Kaluza-Klein reduction to compute the low-energy effective action for the massless modes of a spacetime-filling D6-brane wrapped on a special Lagrangian 3-cycle of a type IIA Calabi-Yau orientifold. The modifications to the characteristic data of the N=1 bulk orientifold theory in the presence of a D6-brane are analysed by studying the underlying Type IIA supergravity coupled to the brane worldvolume in the democratic formulation and performing a detailed dualisation procedure. The N=1 chiral coordinates are found to be in agreement with expectations from mirror symmetry. We work out the Kahler potential for the chiral superfields as well as the gauge kinetic functions for the bulk and the brane gauge multiplets including the kinetic mixing between the two. The scalar potential resulting from the dualisation procedure can be formally interpreted in terms of a superpotential. Finally, the gauging of the Peccei-Quinn shift symmetries of the complex structure multiplets reproduces the D-term potential enforcing the calibration condition for special Lagrangian 3-cycles.Comment: 48 pages, v2: typos corrected, references adde

Experimental Analysis of the Fuel Flexibility of a Jet-stabilized Micro Gas Turbine Combustor Designed for Low Calorific Gases

Fuel flexible burners are an important concept to aid in the advancement and implementation of renewable energy sources into existing infrastructure. As focus shifts from conventional to renewable fuel sources, designing gas turbines which meet both the technical and load requirements for fluctuating fuel compositions and heating values is imperative. The present work aims to study the stability and fuel flexibility of a two-stage burner, consisting of a jet-stabilized main stage and a swirl-stabilized pilot stage. Various fuel compositions, consisting of natural gas, hydrogen, carbon monoxide, carbon dioxide and nitrogen, with lower heating values ranging from 7MJ/kg to 49MJ/kg at an air preheat temperature of 873K were tested. Additionally, differing power loads (60kW to 100kW) and air-fuel equivalence ratio ranges (1.5-3.6) were examined. This study utilized OH* chemiluminescence measurements in conjunction with exhaust gas analysis of carbon monoxide and nitrogen oxide levels to assess the operation and reliability of the burner. Moreover, the experimental results are supported by steady state computational fluid dynamics simulations to provide explanation of the flame flow field characteristics and kinetics. The results indicate flame stability and low emissions levels for the majority of fuel compositions and thermal loads tested, therefore signifying high fuel flexibility of the burner. Additionally, optimal combustor operating points, which display emissions levels below the proposed German legal limits (German Federal Ministry for the Environment, 2016), were determined. Furthermore, the computational fluid dynamics simulation results indicate a good match to the experimental results, providing insight into the burner flow field characteristics and kinetics