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Ref Arxiv: 1706.04112
DOI: 10.1103/PhysRevLett.119.205501
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31 Citations
Résumé:

Marginally stable solids have peculiar physical properties that were discovered and analyzed in the context of the jamming transition. We theoretically investigate the existence of marginal stability in a prototypical model for structural glass-formers, combining analytical calculations in infinite dimensions to computer simulations in three dimensions. While mean-field theory predicts the existence of a Gardner phase transition towards a marginally stable glass phase at low temperatures, simulations show no hint of diverging timescales or lengthscales, but reveal instead the presence of sparse localized defects. Our results suggest that the Gardner transition is deeply affected by finite dimensional fluctuations, and raise issues about the relevance of marginal stability in structural glasses far away from jamming.

Commentaires: 5 pages, 3 figures. Réf Journal: Phys. Rev. Lett. 119, 205501 (2017)

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Ref Arxiv: 1704.08257
DOI: 10.1073/pnas.1706860114
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47 Citations
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Liquids relax extremely slowly upon approaching the glass state. One explanation is that an entropy crisis, due to the rarefaction of available states, makes it increasingly arduous to reach equilibrium in that regime. Validating this scenario is challenging, because experiments offer limited resolution, while numerical studies lag more than eight orders of magnitude behind experimentally-relevant timescales. In this work we not only close the colossal gap between experiments and simulations but manage to create in-silico configurations that have no experimental analog yet. Deploying a range of computational tools, we obtain four estimates of their configurational entropy. These measurements consistently confirm that the steep entropy decrease observed in experiments is also found in simulations, even beyond the experimental glass transition. Our numerical results thus extend the new observational window into the physics of glasses and reinforce the relevance of an entropy crisis for understanding their formation.

Commentaires: 4+23 pages, 3+12 figures; v2: final version, with various changes made. Data relevant to this work can be accessed at http://dx.doi.org/10.7924/G8ZG6Q9T. Réf Journal: PNAS 114, 11356-11361 (2017)

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DOI: 10.1016/j.jnoncrysol.2017.04.009
WoS: WOS:000405882900007
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6 Citations
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Polarized Raman scattering is performed in a series of sodo-silicate glasses. The Si–O–Si inter-tetrahedral angle and its distribution are extracted using a model developed previously for densified silica, and the result are compared to ab initio atomistic calculations. The two techniques reveal a reduction of the most probable angle of about 0.30°/mol% of Na2O, but the shape of the angular distributions are different. The results suggest that Raman scattering enhances a specific angular distribution of Si–O–Si bridges, likely those close to sodium atoms, highlighting local angular heterogeneities.

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DOI: 10.1088/1742-6596/880/1/012049
WoS: WOS:000412424700049
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The recently proposed renormalization group improved optimized perturbation theory is employed to evaluate the pressure of the two dimensional non linear sigma model at finite temperatures. We explicitly show how this powerful resummation method can turn the lowest (one loop) perturbative contribution to the pressure, which is not RG invariant, into a non perturbative quantity exhibiting scale invariance.

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Ref Arxiv: 1706.04529
Ref INSPIRE: 1605142
DOI: 10.1007/JHEP10(2017)002
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21 Citations
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The clockwork mechanism is a novel method for generating a large separation between the dynamical scale and interaction scale of a theory. We demonstrate how the mechanism can arise from a sequence of strongly-coupled sectors. This framework avoids elementary scalar fields as well as ad hoc continuous global symmetries, both of which are subject to serious stability issues. The clockwork factor, q, is determined by the consistency of the strong dynamics. The preserved global U(1) of the clockwork appears as an accidental symmetry, resulting from discrete or U(1) gauge symmetries, and it is spontaneously broken by the chiral condensates. We apply such a dynamical clockwork to construct models with an effectively invisible QCD axion from TeV-scale strong dynamics. The axion couplings are determined by the localisation of the Standard Model interactions along the clockwork sequence. The TeV spectrum includes either coloured hadrons or vector-like quarks. Dark matter can be accounted for by the axion or the lightest neutral baryons, which are accidentally stable.

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