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(156) Production(s) de l'année 2020


Holographic models of composite Higgs in the Veneziano limit: 1. Bosonic sector
Auteur(s): Elander D., Frigerio M., Knecht Marc, Kneur J.L.
(Document sans référence bibliographique) Texte intégral en Openaccess :
Ref HAL: hal03022749_v1
Ref Arxiv: 2011.03003
Ref INSPIRE: 1828484
Ref. & Cit.: NASA ADS
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Résumé: We study stronglycoupled, approximately scaleinvariant gauge theories, which develop a mass gap in the infrared. We argue that a large number of fermion flavours is most suitable to provide an ultraviolet completion for the composite Higgs scenario. The holographic approach allows to describe the qualitative features of the nonperturbative dynamics in the Veneziano limit. We introduce new bottomup holographic models, which incorporate the backreaction of flavour on the geometry, and show that this can correlate the mass gap to the scale of flavoursymmetry breaking. We compute the mass spectrum for the various composite bosonic states, and study its dependence on the scaling dimension of the symmetrybreaking operators, as well as on the number of flavours. The different possibilities for a parametricallylight dilaton are surveyed. We carefully assess the domain of validity of the holographic approach, and compare it with lattice simulations and the NambuJonaLasinio model.



Weak gravity on a $\Lambda$CDM background
Auteur(s): Gannouji Radouane, Perivolaropoulos Leandros, Polarski D., Skara Foteini
(Document sans référence bibliographique) Texte intégral en Openaccess :
Ref HAL: hal03022688_v1
Ref Arxiv: 2011.01517
Ref INSPIRE: 1827879
Ref. & Cit.: NASA ADS
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Résumé: We consider Horndeski modified gravity models obeying stability, velocity of gravitational waves $c_T$ equals $c$ and quasistatic approximation (QSA) on subhorizon scales. We assume further a $\Lambda$CDM background expansion and a monotonic evolution of the $\alpha$ functions as $\alpha_i= \alpha_{i0}~a^s$ where $i=M,B$, $a$ is the scale factor and $\alpha_{i0}$ ($\alpha_{M0}, \alpha_{B0}$), $s$ are arbitrary parameters. We show that the growth and lensing reduced (dimensionless) gravitational couplings $\mu\equiv G_{\rm growth}/G$, $\Sigma\equiv G_{\rm lensing}/G$ exhibit the following generic properties today: $\Sigma_0 < 1$ for all viable parameters, $\mu_0<1$ (weak gravity today) is favored for small $s$ while $\mu_0>1$ is favored for large $s$. We establish also the relation $\mu\geq \Sigma$ at all times. Taking into account the $f\sigma_8$ and $E_G$ data constrains the parameter $s$ to satisfy $s\lesssim 2$. Hence these data select essentially the weak gravity regime today ($\mu_0<1$) when $s<2$, while $\mu_0>1$ subsists only marginally for $s\approx 2$. We consider further the growth index $\gamma(z)$ and identify the $(\alpha_{M0},\alpha_{B0},s)$ parameter region that corresponds to specific signs of the differences $\gamma_0\gamma_0^{\Lambda CDM}$, and $\gamma_1\gamma_1^{\Lambda CDM}$, where $\gamma_0\equiv \gamma\bigl_{z=0}$ and $\gamma_1\equiv \frac{{\rm d}\gamma}{\rm d z}\bigl_{z=0}$. In this way important information is gained on the past evolution of $\mu$. We obtain in particular the signature $\gamma_0>\gamma_0^{\Lambda CDM}$ for $s<2$ in the selected weak gravity region.



Rejuvenating the structure and rheological properties of silica nanocomposites based on natural rubber
Auteur(s): Boonsomwong Kanyarat, Genix A.C., Chauveau E., Fromental J.M., DieudonneGeorge P., Sirisinha Chakrit, Oberdisse J.
(Article) Publié:
Polymer, vol. 189 p.122168 (2020)
Texte intégral en Openaccess :
Ref HAL: hal03004917_v1
Ref Arxiv: 2011.07820
DOI: 10.1016/j.polymer.2020.122168
WoS: WOS:000513011400007
Ref. & Cit.: NASA ADS
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Résumé: The antagonistic effect of processing and thermal annealing on both the filler structure and the polymer matrix is explored in polymer nanocomposites based on natural rubber with precipitated silica incorporated by coagulation from aqueous suspension followed by rollmilling. Their structure and linear and nonlinear rheology have been studied, with a particular emphasis on the effect of high temperature thermal treatment and the number of milling passes. Smallangle Xray scattering intensities show that the silica is organized in small, unbreakable aggregates containing ca. 50 primary nanoparticles, which are reorganized on a larger scale in filler networks percolating at the highest silica contents. As expected, the filler network structure is found to be sensitive to milling, more milling inducing rupture, as evidenced by the decreasing Payne effect. After thermal treatment, the nanocomposite structure is found to be rejuvenated, erasing the effect of the previous milling on the lowstrain modulus. In parallel, the dynamics of the samples described by the rheology or the calorimetric glasstransition temperature remain unchanged, whereas the natural latex polymer network structure is modified by milling towards a more fluidlike rheology, and cannot be recovered.



Terahertz probing of sunflower leaf multilayer organization
Auteur(s): Abautret Yannick, Coquillat D., Zerrad Myriam, Buet Xavier, Bendoula Ryad, Soriano Gabriel, Brouilly Nicolas, HERAN Daphné, GrezesBesset Bruno, Chazallet Frédéric, Amra Claude
(Article) Publié:
Optics Express, vol. 28 p.3501835037 (2020)
Ref HAL: hal03016956_v1
PMID 33182957
DOI: 10.1364/OE.400852
Exporter : BibTex  endNote
Résumé: We analyze the multilayer structure of sunflower leaves from Terahertz data measured in the timedomain at a ps scale. Thin film reverse engineering techniques are applied to the Fourier amplitude of the reflected and transmitted signals in the frequency range f < 1.5 Terahertz (THz). Validation is first performed with success on etalon samples. The optimal structure of the leaf is found to be a 8layer stack, in good agreement with microscopy investigations. Results may open the door to a complementary classification of leaves.



Complexity of dipolar exciton Mott transition in GaN/(AlGa)N nanostructures
Auteur(s): Chiaruttini F., Guillet T., Brimont C., Scalbert D., Cronenberger S., Jouault B., Lefebvre P., Damilano B., Vladimirova M.
(Document sans référence bibliographique) Texte intégral en Openaccess :
Ref HAL: hal03014825_v1
Ref Arxiv: 2010.08216
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: The Mott transition from a dipolar excitonic liquid to an electronhole plasma is demonstrated in a wide GaN/(Al,Ga)N quantum well at $T=7$K by means of spatiallyresolved magnetophotoluminescence spectroscopy. Increasing optical excitation density we drive the system from the excitonic state, characterized by a diamagnetic behavior and thus a quadratic energy dependence on the magnetic field, to the unbound electronhole state, characterized by a linear shift of the emission energy with the magnetic field. The complexity of the system requires to take into account both the densitydependence of the exciton binding energy and the excitonexciton interaction and correlation energy that are of the same order of magnitude. We estimate the carrier density at Mott transition as $n_\mathrm{Mott}\approx 2\times 10^{11}$cm$^{2}$ and address the role played by excitonic correlations in this process. Our results strongly rely on the spatial resolution of the photoluminescence and the assessment of the carrier transport. We show, that in contrast to GaAs/(Al,Ga)As systems, where transport of dipolar magnetoexcitons is strongly quenched by the magnetic field due to exciton mass enhancement, in GaN/(Al,Ga)N the band parameters are such that the transport is preserved up to $9$T.
Commentaires: 15 pages 13 figures



Optical properties in the infrared range of the birefringent αGeO2 single crystal
Auteur(s): Armand Pascale, Hermet P., Bantignies J.L., Haidoux Abel, Maurin D., Ménart Bertrand, Peña Alexandra, Papet Philippe
(Article) Publié:
Materials Research Bulletin, vol. 129 p.110881 (2020)
Texte intégral en Openaccess :
Ref HAL: hal02562585_v1
DOI: 10.1016/j.materresbull.2020.110881
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Résumé: The components of the frequencydependent complex refractive index were determined indirectly for the new noncentrosymmetric αGeO2 crystal using polarized Fourier transform infrared reflectivity spectra measured in the far and midinfrared spectral region at room temperature. All the longitudinal and transverseoptical infrared active modes with E and A2 symmetry, according to the D3 point group, were identified and localized within the 1001000 cm1 range in very good agreement with a previous firstprinciples based calculation. For the A2 and Etype modes, both the longitudinal and transverseoptical splitting were detected. The refractive indices no ( E⊥c) and ne (E //c) in the infrared domain present considerably higher values than the ones observed in the visible light range, and the high birefringence would find application in many optical devices.



Tailoring the viscoelasticity of polymer gels of gluten proteins through solvent quality
Auteur(s): Costanzo S., Banc A., Louhichi A., Chauveau E., Wu Baohu, Morel MarieHélène, Ramos L.
(Article) Publié:
Macromolecules, vol. 53 p.94709479 (2020)
Texte intégral en Openaccess :
Ref HAL: hal03003151_v1
Ref Arxiv: 2010.10317
DOI: 10.1021/acs.macromol.0c01466
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We investigate the linear viscoelasticity of polymer gels produced by the dispersion of gluten proteins in water:ethanol binary mixtures with various ethanol contents, from pure water to 60% v/v ethanol. We show that the complex viscoelasticity of the gels exhibits a time/solvent composition superposition principle, demonstrating the selfsimilarity of the gels produced in different binary solvents. All gels can be regarded as near critical gels with characteristic rheological parameters, elastic plateau and characteristic relaxation time, which are related one to another, as a consequence of selfsimilarity, and span several orders of magnitude when changing the solvent composition. Thanks to calorimetry and neutron scattering experiments, we evidencea cosolvency effect with a better solvation of the complex polymerlike chains of the gluten proteins as the amount of ethanol increases. Overall the gel viscoelasticity can be accounted for by a unique characteristic length characterizing the crosslink density of the supramolecular network, which is solvent compositiondependent. On a molecular level, these findings could be interpreted as a transition of the supramolecular interactions, mainly Hbonds, from intra to interchains, which would be facilitated by the disruption of hydrophobic interactions by ethanol molecules. This work provides new insight for tailoring the gelation process of complex polymer gels.
