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10 Citations
Résumé:

One of the most remarkable predictions to emerge out of the exact infinite-dimensional solution of the glass problem is the Gardner transition.Although this transition was first theoretically proposed a generation ago for certain mean-field spin glass models, its materials relevance wasonly realized when a systematic effort to relate glass formation and jamming was undertaken. A number of nontrivial physical signaturesassociated with the Gardner transition have since been considered in various areas, from models of structural glasses to constraint satisfactionproblems. This perspective surveys these recent advances and discusses the novel research opportunities that arise from them.

Commentaires: 17 pages, 9 figures. Réf Journal: J. Chem. Phys. 151, 010901 (2019)

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Ref Arxiv: 1908.00117
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DOI: 10.1103/PhysRevD.100.083503
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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.

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Ref Arxiv: 1903.02778
DOI: 10.1103/PhysRevB.99.224425
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2 Citations
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We present the full phase diagram of the dumbbell model of spin ice as a function of temperature, chemical potential and staggered chemical potential which breaks the translational lattice symmetry in favour of charge crystal ordering. We observe a double winged structure with five possible phases, monopole fluid (spin ice), fragmented single monopole crystal phases and double monopole crystal, the zinc blend structure. Our model provides a skeleton for liquid-liquid phase transitions and for the winged structures observed for itinerant magnets under pressure and external field. We relate our results to recent experiments on Ho$_2$Ir$_2$O$_7$ and propose a wide ranging set of new experiments that exploit the phase diagram, including high pressure protocols, dynamical scaling of Kibble-Zurek form and universal violations of the fluctuation-dissipation theorem.

Commentaires: 14 pages, 14 figures. Réf Journal: Phys. Rev. B 99, 224425 (2019)

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I'll present a new model inspired by ghost-free bigravity. Despite involving two metrics as the usual bigravity models, it describes only one gravitational interaction. Expanded around a large class of backgrounds, the model propagates a single massless graviton. At non-linear level it has 6 additional degrees of freedom, but they contain neither massive graviton, nor the Boulware-Deser ghost. Thus, the model represents an interesting modification of general relativity which might be relevant for cosmology.

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DOI: 10.1088/1742-5468/ab1910
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39 Citations
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It was recently demonstrated that a simple Monte Carlo (MC) algorithm involving the swap of particle pairs dramatically accelerates the equilibrium sampling of simulated supercooled liquids. We propose two numerical schemes integrating the efficiency of particle swaps into equilibrium molecular dynamics (MD) simulations. We first develop a hybrid MD/MC scheme combining molecular dynamics with the original swap Monte Carlo. We implement this hybrid method in LAMMPS, a software package employed by a large community of users. Secondly, we define a continuous time version of the swap algorithm where both the positions and diameters of the particles evolve via Hamilton's equations of motion. For both algorithms, we discuss in detail various technical issues as well as the optimisation of simulation parameters. We compare the numerical efficiency of all available swap algorithms and discuss their relative merits.

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DOI: 10.1103/PhysRevLett.122.255502
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We show numerically that a three-dimensional model for structural glass displays aging, rejuvenation, and memory effects when subjected to a temperature cycle. These effects indicate that the free energy landscape of structural glasses may possess the complex hierarchical structure that characterizes materials such as spin and polymer glasses. We use the theoretical concept of marginal stability to interpret our results, and explain in which physical conditions a complex aging dynamics can emerge in dense supercooled liquids, paving the way for future experimental studies of complex aging dynamics in colloidal and granular glasses.

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Ref Arxiv: 1902.08580
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15 Citations
Résumé:

Despite the diversity of materials designated as active matter, virtually all active systems undergo a form of dynamic arrest when crowding and activity compete, reminiscent of the dynamic arrest observed in colloidal and molecular fluids undergoing a glass transition. We present a short perspective on recent and ongoing efforts to understand how activity competes with other physical interactions in dense systems. We first review recent experimental work on active materials that uncovered both classic signatures of glassy dynamics and intriguing novel phenomena at large density. We introduce a minimal model of self-propelled particles where the competition between interparticle interactions, crowding, and self-propulsion can be studied in great detail. We discuss more complex models that include some additional, material-specific ingredients. We end with some general perspectives on dense active materials, suggesting directions for future research, in particular for theoretical work.

Commentaires: 16 pages, 8 figures. Réf Journal: J. Chem. Phys. 150, 200901 (2019)