256 research outputs found
Non-linear realisations in global and local supersymmetry
No full textIn modern physics the role of symmetries is central and, even when they are broken, their remnants can pose constraints on the interactions. In considering effective descriptions of certain physical models, the symmetry group can be indeed spontaneously broken to some subgroup, but it is still possible to write symmetry transformations which leave a given action invariant. These transformations are usually realised non-linearly on the fields, while in the unbroken regime they act linearly.
The Standard Model of particle physics can be though of as an effective theory. In this respect, beyond the Standard Model scenarios have been proposed, of which supersymmetry is one of the best motivated at present. Having been yet no direct detection in the experiments, supersymmetry is postulated to be spontaneously broken at some energy scale above the TeV. For this reason, it is important to study supersymmetry breaking mechanisms and to consider low energy effective theories with spontaneously broken and non-linearly realised supersymmetry.
An essential ingredient of this class of models is the presence of a massless goldstone fermion in the spectrum, namely a goldstino, which is associated to each broken generator.
The subject of this thesis is the construction and the study of four-dimensional effective theories with spontaneously broken and non-linearly realised global and local supersymmetry. In the first part, the global supersymmetric case is analysed. The discussion starts from the supersymmetry breaking sector, describing the goldstino and its interactions, in the case of minimal supersymmetry and it is then generalised to a generic number of spontaneously broken supersymmetry generators.
A systematic procedure is given in order to construct effective theories with non-linearly realised supersymmetry and with any desired spectrum content. In the second part of the thesis, non-linear realisations are analysed in the case of local supersymmetry, namely supergravity. The coupling of the goldstino sector to gravity is presented first and the superhiggs mechanism on a generic background is discussed. Matter couplings are then constructed in some simple examples. A new class of models is introduced in which supersymmetry is spontaneously broken and non-linearly realised already on the gravity sector. As a consequence, it is possible to construct actions in which the cosmological constant is bounded to be positive, which can be motivated for studying inflation. Two applications of non-linear realisations in local supersymmetry are discussed in detail. In the first one it is shown how to implement Kaehler invariance in a way that mimics the global supersymmetric case. In particular, the Kaehler-Hodge restriction on the scalar manifold, which is typical of supergravity, is avoided. In the second application the role of non-linear realisations in the construction of de Sitter vacua is discussed. Attention is devoted to the relationship with known de Sitter uplift constructions and with a new, recently proposed D-term in supergravity
Weak gravity versus scale separation
No full textWe give evidence that fully supersymmetric Anti-de Sitter vacua of extended
supergravity with a residual gauge group containing an abelian factor cannot be
scale separated as a consequence of the weak gravity conjecture. We prove this
for N=2 and N=8 supergravity and we explain how our argument applies also to
vacua with partially broken, but extended residual supersymmetry. We finally
discuss possible loopholes and especially how certain N=1 models can evade our
reasoning. Our results suggest that N=0,1 supersymmetry at the lagrangian level
might be the most promising chances to obtain a truly four-dimensional
effective description of quantum gravity.Comment: 23 pages, 9 tables; v2: references added, minor modifications,
published on JHE
Open-closed correspondence of K-theory and cobordism
No full textAbstract
Non-trivial K-theory groups and non-trivial cobordism groups can lead to global symmetries which are conjectured to be absent in quantum gravity. Inspired by open-closed string duality, we propose a correspondence between the two groups, which can be considered as the physical manifestation of a generalisation of the classic Conner-Floyd isomorphism. The picture is exemplified by the relations between KO-groups and Spin-cobordisms and between K-groups and Spinc-cobordisms. We suggest that global symmetries related by such an isomorphism are generically gauged. Indeed, by combining non-torsion K-theory and cobordism groups, we recover tadpole cancellation conditions well known from type I string theory and F-theory. For torsion charges, another possibility opens up.</jats:p
The supersymmetric anti-D3-brane action in KKLT
No full textThe supersymmetric anti-D3-brane action in KKLT
25 Jun 2019, 17:00
15m
500/1-001 - Main Auditorium (CERN)
Parallel Session
Speaker
Niccolo Cribiori (Vienna University of Technology)
Description
An anti-D3-brane plays a crucial role in the construction of semi-realistic cosmological models in string theory. Part of its action provides an uplift term that has been used to lift AdS solutions to phenomenological viable dS vacua in the KKLT and LVS setups. This uplift breaks supersymmetry spontaneously and it can be described in the 4d N=1 supergravity language by using non-linear supersymmetry. I will present and discuss the necessary ingredients to write down the complete 4d N=1 supergravity action for an anti-D3-brane coupled to all closed string background fields
On the dynamical origin of parameters in N=2 supersymmetry
No full textAbstract We formulate N=2 global supersymmetric Lagrangians of self-interacting vector multiplets in terms of variant multiplets, whose non-propagating fields are replaced with gauge three-forms. Setting the three-forms on-shell results in a dynamical generation of the parameters entering the scalar potential. As an application, we study how gauge three-forms may determine the partial breaking of N=2 supersymmetry and how they affect the low energy effective description
The supersymmetric anti-D3-brane action in KKLT
No full textAn anti-D3-brane plays a crucial role in the construction of semi-realistic cosmological models in string theory. Part of its action provides an uplift term that has been used to lift AdS solutions to phenomenological viable dS vacua in the KKLT and LVS setups. This uplift breaks supersymmetry spontaneously and it can be described in the 4d N=1 supergravity language by using non-linear supersymmetry. I will present and discuss the necessary ingredients to write down the complete 4d N=1 supergravity action for an anti-D3-brane coupled to all closed string background fields
The supersymmetric anti-D3-brane action in KKLT
No full textAn anti-D3-brane plays a crucial role in the construction of semi-realistic cosmological models in string theory. Part of its action provides an uplift term that has been used to lift AdS solutions to phenomenological viable dS vacua in the KKLT and LVS setups. This uplift breaks supersymmetry spontaneously and it can be described in the 4d N=1 supergravity language by using non-linear supersymmetry. I will present and discuss the necessary ingredients to write down the complete 4d N=1 supergravity action for an anti-D3-brane coupled to all closed string background fields
Supergravity EFTs and swampland constraints
No full textIn these proceedings, we review recent progress in analyzing the behavior of
lower-dimensional supergravity theories when combined with swampland
conjectures. We show that within supergravity the effectiveness and usefulness
of swampland conjectures gets amplified, existing criteria can be intertwined
and also new ones can be uncovered. Furthermore, we elaborate on some
previously unpublished work. This includes evidence for the possible existence
of a novel conjecture on Yukawa couplings and an argument to constrain large
classes of D-term inflationary models using known conjectures.Comment: 51 pages; v2: typos corrected and references added; v3: references
added. Contribution to the proceedings for Corfu Summer Institute 2022
"School and Workshops on Elementary Particle Physics and Gravity",
(CORFU2022) 28 August - 1 October 2022 Corfu, Greec
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