Ref HAL: hal-03142410_v1
DOI: 10.1103/PhysRevLett.126.066101
Exporter : BibTex | endNote

Ref HAL: hal-03138225_v1
Ref Arxiv: 2007.09418
DOI: 10.1007/s10955-021-02710-8
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

We numerically study the relaxation dynamics and associated criticality of non-Brownian frictionless spheres below jamming in spatial dimensions $d=2$, $3$, $4$, and $8$, and in the mean-field Mari-Kurchan model. We discover non-trivial finite-size and volume fraction dependences of the relaxation time associated to the relaxation of unjammed packings. In particular, the relaxation time is shown to diverge logarithmically with system size at any density below jamming, and no critical exponent can characterise its behaviour approaching jamming. In mean-field, the relaxation time is instead well-defined: it diverges at jamming with a critical exponent that we determine numerically and differs from an earlier mean-field prediction. We rationalise the finite $d$ logarithmic divergence using an extreme-value statistics argument in which the relaxation time is dominated by the most connected region of the system. The same argument shows that the earlier proposition that relaxation dynamics and shear viscosity are directly related breaks down in large systems. The shear viscosity of non-Brownian packings is well-defined in all $d$ in the thermodynamic limit, but large finite-size effects plague its measurement close to jamming.

Ref HAL: hal-03129450_v1
Ref Arxiv: 2101.08240
Ref INSPIRE: 1842071
DOI: 10.1103/PhysRevD.104.034003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

We apply the renormalization group optimized perturbation theory (RGOPT) to evaluate the quark contribution to the QCD pressure at finite temperatures and baryonic densities, at next-to-leading order (NLO). Our results are compared to NLO and state-of-the-art higher orders of standard perturbative QCD (pQCD) and hard thermal loop perturbation theory (HTLpt). The RGOPT provides an all order resummed pressure in a well-defined approximation, exhibiting a drastically better remnant renormalization scale dependence than pQCD, thanks to built-in renormalization group invariance consistency. At NLO, upon simply adding to the RGOPT-resummed quark contributions the purely perturbative NLO glue contribution, our results show a remarkable agreement with ab initio lattice simulation data for temperatures $0.25\lesssim T\lesssim 1\mathrm{GeV}$, with a remnant scale dependence drastically reduced as compared to HTLpt.

Ref HAL: hal-03125706_v1
DOI: 10.1016/j.ecss.2021.107229
Exporter : BibTex | endNote
Résumé:

Wetlands conservation and resilience capacities are key issues in many places over the globe. Understanding these issues will benefit from a precise knowledge of seagrass species occupancy and coverage over time and over space. Such information can be obtained from remote sensing images and their classification thanks to a vegetation index, to be used in a complementary manner to field work inventories. Sentinel-2 data, which are available with a frequent revisit time (<5 days) and a high spatial resolution (10m pixel size) can be used to map grassbeds at the surface or slightly below the surface of permanent lagoons, hence enabling the characterization of its seasonal dynamics, which was not possible with previous remote-sensing tools. We have proved the feasibility of such a method in the natural reserve of the Bagnas (Herault, France) where Stuckenia pectinata coverage can be tracked over a full year thanks to Sentinel-2 images and field work. Inter-annual dynamics (seasonal growth and senescence) can be mapped over time with 10m resolution and will be extended to pluriannual studies thanks to the long-term objective of the Sentinel-2 mission. This opens the way to a concerted management of natural reserves based on data analysis and field knowledge, a better understanding of seagrass coverage with fluctuating environmental conditions, and predictive mechanistic and/or stochastic models of future qualitative trends.

Ref HAL: hal-03117915_v1
Ref Arxiv: 2007.14145
DOI: 10.1103/PhysRevLett.125.268005
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

Using cyclic shear to drive a two dimensional granular system, we determine the structural char-acteristics for different inter-particle friction coefficients. These characteristics are the result of acompetition between mechanical stability and entropy, with the latter’s effect increasing with fric-tion. We show that a parameter-free maximum-entropy argument alone predicts an exponential cell order distribution, with excellent agreement with the experimental observation. We show thatfriction only tunes the mean cell order and, consequently, the exponential decay rate and the pack-ing fraction. We further show that cells, which can be very large in such systems, are short-lived,implying that our systems are liquid-like rather than glassy..

Ref HAL: hal-03115871_v1
Ref Arxiv: 2101.02124
Ref INSPIRE: 1839547
DOI: 10.1103/PhysRevD.104.L031502
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

The quark contribution to the QCD pressure, $P_q$, is evaluated up to next-to-leading order (NLO) within the renormalization group optimized perturbation theory (RGOPT) resummation approach. To evaluate the complete QCD pressure we simply add the perturbative NLO contribution from massless gluons to the resummed $P_q$. Despite this unsophisticated approximation our results for $P=P_q+P_g$ at the central scale $M\sim 2\pi T$ show a remarkable agreement with lattice predictions for $0.25\lesssim T\lesssim 1\mathrm{GeV}$. We also show that by being imbued with RG properties, the RGOPT produces a drastic reduction of the embarrassing remnant scale dependence that plagues both standard thermal perturbative QCD and hard thermal loop perturbation theory applications.

Ref HAL: hal-03087658_v1
Ref Arxiv: 2012.13947
Ref INSPIRE: 1838400
DOI: 10.1103/PhysRevD.103.115006
WoS: WOS:000661786800005
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé:

Tree-level dynamical stability of scalar field potentials in renormalizable theories can in principle be expressed in terms of positivity conditions on quartic polynomial structures. However, these conditions cannot always be cast in a fully analytical resolved form, involving only the couplings and being valid for all field directions. In this paper we consider such forms in three physically motivated models involving SU (2) triplet scalar fields: the Type-II seesaw model, the Georgi-Machacek model, and a generalized two-triplet model. A detailed analysis of the latter model allows to establish the full set of necessary and sufficient boundedness from below conditions. These can serve as a guide, together with unitarity and vacuum structure constraints, for consistent phenomenological (tree-level) studies. They also provide a seed for improved loop-level conditions, and encompass in particular the leading ones for the more specific Georgi-Machacek case. Incidentally, we present complete proofs of various properties and also derive general positivity conditions on quartic polynomials that are equivalent but much simpler than the ones used in the literature.