ELANDER Daniel
Fonction : Postdoctoral Researcher
daniel.elander
umontpellier.fr
Bureau: 37, Etg: 1, Bât: 13  Site : Campus Triolet
Domaines de Recherche:  Physique/Physique des Hautes Energies  Théorie
 Physique/Physique des Hautes Energies  Réseau
 Physique/Physique des Hautes Energies  Phénoménologie

Dernieres productions scientifiques :


The Coulomb branch of N=4 SYM and dilatonic scions in supergravity
Auteur(s): Elander D., Piai Maurizio, Roughley John
(Document sans référence bibliographique) Texte intégral en Openaccess :
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Ref Arxiv: 2103.06721
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Résumé: We find a parametrically light dilaton in special confining theories in three dimensions. Their duals form what we call a scion of solutions to the supergravity associated with the largeN limit of the Coulomb branch of the N=4 SuperYangMills (SYM) theory. The supergravity description contains one scalar with bulk mass that saturates the BreitenlohnerFreedman unitarity bound. The new solutions are defined within supergravity, they break supersymmetry and scale invariance, and one dimension is compactified on a shrinking circle, yet they are completely regular. An approximate dilaton appears in the spectrum of background fluctuations (or composite states in the confining theory), and becomes parametrically light along a metastable portion of the scion of new supergravity solutions, in close proximity of a tachyonic instability. A firstorder phase transition separates stable backgrounds, for which the approximate dilaton is not parametrically light, from metastable and unstable backgrounds, for which the dilaton becomes parametrically light, and eventually tachyonic.



Light dilaton in a metastable vacuum
Auteur(s): Elander D., Piai Maurizio, Roughley John
(Article) Publié:
Phys.rev.d, vol. 103 p.046009 (2021)
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Ref Arxiv: 2011.07049
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DOI: 10.1103/PhysRevD.103.046009
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Résumé: We identify a parametrically light dilaton by studying the perturbations of metastable vacua along a branch of regular supergravity backgrounds that are dual to fourdimensional confining field theories. The branch includes also stable and unstable solutions. The former encompass, as a special case, the geometry proposed by Witten as a holographic model of confinement. The latter approach a supersymmetric solution, by enhancing a condensate in the dual field theory. A phase transition separates the space of stable backgrounds from the metastable ones. In proximity of the phase transition, one of the lightest scalar states inherits some of the properties of the dilaton, despite not being particularly light.



Holographic models of composite Higgs in the Veneziano limit. Part I. Bosonic sector
Auteur(s): Elander D., Frigerio M., Knecht Marc, Kneur J.L.
(Article) Publié:
Jhep, vol. 03 p.182 (2021)
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Ref Arxiv: 2011.03003
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DOI: 10.1007/JHEP03(2021)182
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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 regions with a light dilaton are critically surveyed. We carefully assess the domain of validity of the holographic approach, and compare it with lattice simulations and the NambuJonaLasinio model.



Dilatonic states near holographic phase transitions
Auteur(s): Elander D., Piai Maurizio, Roughley John
(Article) Publié:
Phys.rev.d, vol. 103 p.106018 (2021)
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Ref Arxiv: 2010.04100
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DOI: 10.1103/PhysRevD.103.106018
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Résumé: The spectrum of bound states of special strongly coupled confining field theories might include a parametrically light dilaton, associated with the formation of enhanced condensates that break (approximate) scale invariance spontaneously. It has been suggested in the literature that such a state may arise in connection with the theory being close to the unitarity bound in holographic models. We extend these ideas to cases where the background geometry is nonAdS, and the gravity description of the dual confining field theory has a topdown origin in supergravity. We exemplify this programme by studying the circle compactification of Romans sixdimensional halfmaximal supergravity. We uncover a rich space of solutions, many of which were previously unknown in the literature. We compute the bosonic spectrum of excitations, and identify a tachyonic instability in a region of parameter space for a class of regular background solutions. A tachyon only exists along an energetically disfavoured (unphysical) branch of solutions of the gravity theory; we find evidence of a firstorder phase transition that separates this region of parameter space from the physical one. Along the physical branch of regular solutions, one of the lightest scalar particles is approximately a dilaton, and it is associated with a condensate in the underlying theory. Yet, because of the location of the phase transition, its mass is not parametrically small, and it is, coincidentally, the nexttolightest scalar bound state, rather than the lightest one.



Probing the holographic dilaton
Auteur(s): Elander D., Piai Maurizio, Roughley John
(Article) Publié:
Jhep, vol. 06 p.177 (2020)
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Ref Arxiv: 2004.05656
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DOI: 10.1007/JHEP06(2020)177
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Résumé: Many strongly coupled field theories admit a spectrum of gaugeinvariant bound states that includes scalar particles with the same quantum numbers as the vacuum. The challenge naturally arises of how to characterise them. In particular, how can a dilaton — the pseudoNambuGoldstone boson associated with approximate scale invariance — be distinguished from other generic light scalars with the same quantum numbers? We address this problem within the context of gaugegravity dualities, by analysing the fluctuations of the higherdimensional gravitational theory. The diagnostic test that we propose consists of comparing the results of the complete calculation, performed by using gaugeinvariant fluctuations in the bulk, with the results obtained in the probe approximation. While the former captures the mixing between scalar and metric degrees of freedom, the latter removes by hand the fluctuations that source the dilatation operator of the boundary field theory. Hence, the probe approximation cannot capture a possible light dilaton, while it should fare well for other scalar particles. We test this idea on a number of holographic models, among which are some of the best known, complete gravity backgrounds constructed within the topdown approach to gaugegravity dualities. We compute the spectra of scalar and tensor fluctuations, that are interpreted as bound states (glueballs) of the dual field theory, and we highlight those cases in which the probe approximation yields results close to the correct physical ones, as well as those cases where significant discrepancies emerge. We interpret the latter occurrence as an indication that identifying one of the lightest scalar states with the dilaton is legitimate, at least as a leadingorder approximation.

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