Ref HAL: hal-03090752_v1
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The standard lore has it that supersymmetry breaking in the visible sector is always soft when mediated by gravity from a hidden sector of Supergravity.Correspondingly, the associated generic forms of the superpotential and Kahler potential have long been the basis for the construction of consistent low energy susy models. In this talk we report on the existence of a whole class of new forms, equally consistent for low energy susy model building, but exhibiting hard susy breaking on top of the usual soft one. Moreover, these new forms require Standard Model gauge singlet chiral superfields displaying specific structures and flat directions. We discuss briefly the possible phenomenological spin-offs regarding the 125GeV Higgs fine-tuning issues and the (so far) non-discovery of susy particles, as well as next-to-minimal susy inflationary model-building. (based on G. Moultaka, M.R. de Traubenberg & D. Tant, Int.J.Mod.Phys. A34 (2019) no.01, 1950004, and work in progress).

Ref HAL: hal-02550157_v1
Ref INSPIRE: 1789740
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I discuss the infrared mass spectrum of strongly-coupled gauge theories, thatinduce the Higgs as a composite pseudo-Nambu-Goldstone boson. The set ofcomposite states accompanying the Higgs is determined by the symmetries of thetheory. Here we estimate their mass spectrum by non-perturbative techniquesinspired by QCD, as well as by exploiting gauge-gravity duality. 1 CompositeHiggs: motivations and relevant energy scales As the Large Hadron Collider (LHC)did not find new states significantly coupled to the Standard Model (SM) belowthe TeV scale, any SM extension by such heavy states suffers from a littlehierarchy problem, as the mass of the scalar Higgs boson lies close to the 100GeV scale. Still, some SM extensions have the potential to address the bighierarchy between the TeV scale and the Planck scale. One possibility is toavoid elementary scalar fields, and assume the observed Higgs is a compositeobject, with a compositeness scale f 1 TeV. This scenario requires a strongly-coupled sector, whose spectrum generically includes several additional compositestates besides the Higgs. The mass of the lowest-lying states cannot exceed ∼4πf , and some could be significantly lighter and within the LHC reach. Definitepredictions for the mass spectrum require to specify the strongly-coupled theoryin the ultraviolet (UV). Here we will assume it is a gauge theory of fermions,that confines in the infrared. We will estimate its mass spectrum in some well-defined approximations, by employing non-perturbative techniques inspired by QCD1) , as well as gauge-gravity duality techniques 2). In models where the Higgsis a pseudo-Nambu-Goldstone boson (pNGB) the electroweak scale, v 246 GeV, isinduced in two steps. The theory has a global (flavour) symmtry G F , that isspontaneously broken to a subgroup H F at the scale f. The electroweak symmetrySU (2) L × U (1) Y is embedded in 91

Ref HAL: hal-02302945_v1
Ref Arxiv: 1908.08363
Ref INSPIRE: 1750592
DOI: 10.1103/PhysRevD.100.114006
WoS: 000499979100004
Ref. & Cit.: NASA ADS
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2 Citations
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We apply the renormalization group optimized perturbation theory (RGOPT) to evaluate the QCD (matter) pressure at the two-loop level considering three flavors of massless quarks in a dense and cold medium. Already at leading order (αs0), which builds on the simple one loop (RG resummed) term, our technique provides a nontrivial nonperturbative approximation which is completely renormalization group invariant. At the next-to-leading order the comparison between the RGOPT and the perturbative QCD predictions shows that the former method provides results which are in better agreement with the state-of-the-art higher order perturbative results, which include a contribution of order αs3ln2αs. At the same time one also observes that the RGOPT predictions are less sensitive to variations of the arbitrary MS¯ renormalization scale than those obtained with perturbative QCD. These results indicate that the RGOPT provides an efficient resummation scheme which may be considered as an alternative to lattice simulations at high baryonic densities.

Ref HAL: hal-02302374_v1
DOI: 10.1002/andp.201800486
WoS: WOS:000471714300003
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The screened Coulomb potential plays a crucial role in the binding energies of excitons in a thin dielectric slab. The asymptotic behavior of this potential is studied when the thickness of the slab is very small as compared to the exciton Bohr radius. A regularized expression is given and the exact effective 2D potential is derived. These expressions may be useful for the computation of the exciton binding energy in 2D or quasi‐2D materials.

Ref HAL: hal-02266321_v1
Ref Arxiv: 1908.00117
Ref INSPIRE: 1747566
DOI: 10.1103/PhysRevD.100.083503
WoS: 000488510300002
Ref. & Cit.: NASA ADS
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1 Citation
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We perform here a global analysis of the growth index γ behavior from deep in the matter era till the far future. For a given cosmological model in general relativity (GR) or in modified gravity, the value of γ(Ωm) is unique when the decaying mode of scalar perturbations is negligible. However, γ∞, the value of γ in the asymptotic future, is unique even in the presence of a non-negligible decaying mode today. Moreover, γ becomes arbitrarily large deep in the matter era. Only in the limit of a vanishing decaying mode do we get a finite γ, from the past to the future in this case. We find further a condition for γ(Ωm) to be monotonically decreasing (or increasing). This condition can be violated inside GR for varying wDE though generically γ(Ωm) will be monotonically decreasing (like ΛCDM), except in the far future and past. A bump or a dip in Geff can also lead to a significant and rapid change in the slope dγdΩm. On a ΛCDM background, a γ substantially lower (higher) than 0.55 with a negative (positive) slope reflects the opposite evolution of Geff. In Dvali-Gabadadze-Porrati (DGP) models, γ(Ωm) is monotonically increasing except in the far future. While DGP gravity becomes weaker than GR in the future and wDGP→-1, we still get γ∞DGP=γ∞ΛCDM=23. In contrast, despite GeffDGP→G in the past, γ does not tend to its value in GR because dGeffDGPdΩm|-∞≠0.

Ref HAL: hal-02114493_v1
Ref Arxiv: 1904.11906
DOI: 10.1007/JHEP08(2019)070
WoS: WOS:000483191300001
Ref. & Cit.: NASA ADS
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1 Citation
Résumé:

We analyze a bi-gravity model based on the first order formalism, having as fundamental variables two tetrads but only one Lorentz connection. We show that on a large class of backgrounds its linearization agrees with general relativity. At the non-linear level, additional degrees of freedom appear, and we reveal the mechanism hiding them around the special backgrounds. We further argue that they do not contain a massive graviton, nor the Boulware-Deser ghost. The model thus propagates only one graviton, whereas the nature of the additional degrees of freedom remains to be investigated. We also present a foliation-preserving deformation of the model, which keeps all symmetries except time diffeomorphisms and has three degrees of freedom.

Commentaires: 29 pages

Ref HAL: hal-02884268_v1
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