Ref HAL: hal-01924508_v1
Ref Arxiv: 1805.06017
DOI: 10.1063/1.5040975
WoS: 000448216600025
Ref. & Cit.: NASA ADS
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11 Citations
Résumé:

We propose a computational method to measure the configurational entropy in generic polydisperse glass-formers. In particular, our method resolves issues related to the diverging mixing entropy term due to a continuous polydispersity. The configurational entropy is measured as the difference between the well-defined fluid entropy and a more problematic glass entropy. We show that the glass entropy can be computed by a simple generalisation of the Frenkel-Ladd thermodynamic integration method, which includes permutations of the particle diameters. This approach automatically provides a physically meaningful mixing entropy, and includes contributions that are not purely vibrational. The proposed configurational entropy is thus devoid of conceptual and technical difficulties due to continuous polydispersity, while being conceptually closer and technically simpler than alternative free energy approaches.

Commentaires: 11 pages, 4 figures. Réf Journal: J. Chem. Phys. 149, 154501 (2018)

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In these lectures I will introduce and explore properties of the Renormalisation Group (RG) both in its discrete and continuous forms. Topics to be discussed include multi scale expansions, the RG, Gaussian fixed points, Wick products from the RG point of view, ultraviolet cutoff removal, flow equations and perturbative flows, trivial and non-trivial fixed points, and critical field theories. Rigorous Discrete RG analysis. I will discuss a rigorous application for a non-trivial fixed point.

Résumé:

Using dualities of string theory, I derive modular constraints onthe generating function of MSW invariants, which coincide withgeneralized Donaldson-Thomas invariants of a Calabi-Yau threefoldat the large volume attractor point in the moduli space. Thefunction is labeled by a divisor and when the divisor isirreducible, it is known to be modular. I show that in the case ofa reducible divisor, the modularity is lost, but can be restored in a non-holomorphic completion. I find a general form of thecompletion for arbitrary degree of reducibility and provide its explicit expression up to degree 5.

Résumé:

Using dualities of string theory, I derive modular constraints onthe generating function of MSW invariants, which coincide withgeneralized Donaldson-Thomas invariants of a Calabi-Yau threefoldat the large volume attractor point in the moduli space. Thefunction is labeled by a divisor and when the divisor isirreducible, it is known to be modular. I show that in the case ofa reducible divisor, the modularity is lost, but can be restored in a non-holomorphic completion. I find a general form of thecompletion for arbitrary degree of reducibility and provide its explicit expression up to degree 5.

Ref HAL: hal-01910272_v1
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PMID 29758608
DOI: 10.1103/PhysRevE.97.040601
WoS: WOS:000429636700001
30 Citations
Résumé:

We explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric and screened Coulomb interactions, respectively. In the supercooled regime, the structural relaxation time τα of both systems grows steeply with volume fraction, reminiscent of the behavior of colloidal hard spheres. Computer simulations confirm that the growth of τα on approaching the glass transition is independent of particle softness. By contrast, softness becomes relevant at very large packing fractions when the system falls out of equilibrium. In this nonequilibrium regime, τα depends surprisingly weakly on packing fraction, and time correlation functions exhibit a compressed exponential decay consistent with stress-driven relaxation. The transition to this novel regime coincides with the onset of an anomalous decrease in local order with increasing density typical of ultrasoft systems. We propose that these peculiar dynamics results from the combination of the nonequilibrium aging dynamics expected in the glassy state and the tendency of colloids interacting through soft potentials to refluidize at high packing fractions.

Ref HAL: hal-01886014_v1
Ref Arxiv: 1809.07034
Ref INSPIRE: 1694683
DOI: 10.1103/PhysRevD.98.104044
WoS: 000451337400017
Ref. & Cit.: NASA ADS
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9 Citations
Résumé:

Recent analyses [S. Nesseris et al., Phys. Rev. D 96, 023543 (2017)PRVDAQ2470-001010.1103/PhysRevD.96.023543; L. Kazantzidis and L. Pervolaropoulos, Phys. Rev. D 97, 103503 (2018)PRVDAQ2470-001010.1103/PhysRevD.97.103503] have indicated that an effective Newton’s constant Geff(z) decreasing with redshift may relieve the observed tension between the Planck15 best fit ΛCDM cosmological background (i.e., Planck15/ΛCDM) and the corresponding ΛCDM background favored by growth fσ8 and weak lensing data. We investigate the consistency of such a decreasing Geff(z) with some viable scalar-tensor models and f(R) theories. We stress that f(R) theories generically cannot lead to a decreasing Geff(z) for any cosmological background. For scalar-tensor models we deduce that in the context of a ΛCDM cosmological background, a decreasing Geff(z) is not consistent with a large Brans-Dicke parameter ωBD,0 today. This inconsistency remains and amplifies in the presence of a phantom dark energy equation of state parameter (w<-1). However, it can be avoided for w>-1. We also find that any modified gravity model with the required decreasing Geff(z) and Geff,0=G would have a characteristic signature in its growth index γ with 0.61≲γ0≲0.69 and large slopes γ0′, 0.16≲γ0′≲0.4, which is a characteristic signature of a decreasing (with z) Geff(z)