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Physique Théorique
(47) Production(s) de l'année 2024
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Effect of viscosity on wind-driven gravitation waves 
Auteur(s): Chaubet C., Kern N., Manna M.
(Article) Publié:
Physics Of Fluids, vol. 36 p.103976 (2024)
Ref HAL: hal-04773731_v1
DOI: 10.1063/5.0221941
Exporter : BibTex | endNote
Résumé: We address the question of how viscosity impacts the growth of gravitation waves, such as those on the ocean, when they are driven by wind. There is so far no general rigorous theory for this energy transfer. We extend Miles' approach [J. W. Miles, “On the generation of surface waves by shear flows,” J. Fluid Mech. 3, 185–204 (1957)], using the same logarithmic wind profile, to incorporate bulk viscosity and derive modified growth rates. Exploiting the fact that water waves fall into the “weak viscosity” regime, we produce analytical expressions for the growth rate, which we solve using the numerical method proposed by Beji and Nadaoka [“Solution of Rayleigh's instability equation for arbitrary wind profiles,” J. Fluid Mech. 500, 65–73 (2004)]. Our results confirm that corrections to the growth rates are significant for wavelengths below a meter, and for weak to modest wind strengths. We show that all wave growth is suppressed, due to viscous effects, below a critical wind strength. We also show that the wave age corresponding to a developed sea is reduced by viscosity. We quantitatively characterize the zones, in terms of wind strength and wavelength, for which the wave growth is suppressed by viscosity.
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KKLT Ex Nihilo
Auteur(s): Bena Iosif, Li Yixuan, Lüst S.
(Document sans référence bibliographique) Texte intégral en Openaccess : 
Ref HAL: hal-04771155_v1
Ref Arxiv: 2410.22400
Ref INSPIRE: 2843841
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Flux compactifications that give three- or four-dimensional Anti de Sitter vacua with a parametrically small negative cosmological constant are claimed to be ubiquitous in String Theory. However, the 1+1 and 2+1 dimensional CFT duals to such vacua should have very large central charges and rather unusual properties. We construct brane configurations that source these would-be AdS flux compactifications, and identify certain UV AdS geometries that these branes source. The central charge of the CFT duals to these UV AdS geometries place lower bounds on the absolute values of the cosmological constants of the AdS vacua. These bounds are incompatible with the scale separation needed to construct realistic cosmological models.
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Prospects for sub-EW ALP searches via $\gamma+b\bar{b}$ signatures at the LHC using jet substructure techniques
Auteur(s): Adhikary Amit, Bharucha Aoife, Feligioni Lorenzo, Frigerio M.
(Document sans référence bibliographique) 2024-10-11Texte intégral en Openaccess :
Ref HAL: hal-04745819_v1
Ref Arxiv: 2410.09033
Ref INSPIRE: 2839391
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: The current Large Hadron Collider (LHC) data show no clear indication of new physics and only incremental improvements are anticipated at the energy frontier in the near future. However, while the focus of the LHC has been on constraining TeV scale physics, new particles could still be hiding below the electroweak scale. In order to obtain sensitivity to a new light boson with couplings to SM fermions, a potentially promising decay channel, for resonances with mass $\gtrsim {\cal O}(10)$ GeV, would be the decay to $b\bar b$ pairs. The measurement of such signatures is challenging due to the trigger requirements at the LHC. In this work, we explore the LHC sensitivity to a light pseudoscalar, or axion-like particle (ALP), in the $b\bar{b}$ final state with an associated photon, using jet substructure techniques, in the mass range between 10 GeV and 100 GeV. We obtain projected exclusions on the ALP-fermion coupling in a region of phase space which has not so far been probed by direct searches. We further discuss the impact that lower trigger thresholds may have on the LHC reach.
Commentaires: 26 pages, 10 figures, 5 tables
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A single layer representation of the scattered field for multiple scattering problems
Auteur(s): Felbacq D., Gourdin A., Rousseau E.
(Article) Publié:
Wave Motion, vol. p.103422 (2024)
Texte intégral en Openaccess :
Ref HAL: hal-04745663_v1
Ref Arxiv: 2309.07549
DOI: 10.1016/j.wavemoti.2024.103422
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: The scattering of scalar waves by a set of scatterers is considered. It is proven that the scattered field can be represented as an integral supported by any smooth surface enclosing the scatterers. This is a generalization of the series expansion over spherical harmonics and spherical Bessel functions for spherical geometries. More precisely, given a set of scatterers, the field scattered by any subset can be expressed as an integral over any smooth surface enclosing the given subset alone. It is then possible to solve the multiple scattering problem by using this integral representation instead of an expansion over spherical harmonics. This result is used to develop an extension of the Fast Multipole Method in order to deal with subsets that are not enclosed within non-intersecting balls.
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Inferring interphase chromosomal structure from multiplexed fluorescence in situ hybridization data: a unified picture from human and mouse cells
Auteur(s): Remini L., Segers Midas, Parmeggiani A., Carlon Enrico
(Document sans référence bibliographique) 2024-10-17
Ref HAL: hal-04741167_v1
Exporter : BibTex | endNote
Résumé: We analyze multiplexed fluorescence in situ hybridization (m-FISH) data for human and mouse cell lines. The m-FISH technique uses fluorescently-labeled single stranded probes which hybridize to specific chromosomal regions, thereby allowing the measurement of the spatial positions of up to ∼ 100 tagged sites for several thousands interphase chromosomes. Our analysis focuses on a wide range of different cell lines and two distinct organisms and provides a unified picture of chromatin structure for scales ranging from 5 kb (kilo bases) up to 2 Mb (mega bases), thus covering a genomic region of almost three orders of magnitude. Confirming recent analysis (Remini et al., Phys. Rev. E 109, 024408 ( 2024)) we show that there are two characteristic arrangements of chromatin referred to as phase α (crumpled globule) and β (looped domain) and discuss the physical properties of these phases. We show that a simple heterogeneous random walk model captures the main behavior observed in experiments and bring considerable insights on chromosomal structure.
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Noise-cancellation algorithm for simulations of Brownian particles
Auteur(s): Rusch Regina, Franosch Thomas, Jung G.
(Article) Publié:
Physical Review E, vol. 109 p.015303 (2024)
Ref HAL: hal-04735130_v1
DOI: 10.1103/PhysRevE.109.015303
Exporter : BibTex | endNote
Résumé: We investigate the usage of a recently introduced noise-cancellation algorithm for Brownian simulations to enhance the precision of measuring transport properties such as the mean-square displacement or the velocity-autocorrelation function. The algorithm is based on explicitly storing the pseudo-random numbers used to create the randomized displacements in computer simulations and subtracting them from the simulated trajectories. The resulting correlation function of the reduced motion is connected to the target correlation function up to a cross-correlation term. Using analytical theory and computer simulations, we demonstrate that the cross-correlation term can be neglected in all three systems studied in this paper. We further expand the algorithm to Monte Carlo simulations and analyze the performance of the algorithm and rationalize that it works particularly well for unbounded, weakly interacting systems in which the precision of the mean-square displacement can be improved by orders of magnitude.
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Force renormalization for probes immersed in an active bath
Auteur(s): Shea Jeanine, Jung G., Schmid Friederike
(Article) Publié:
Soft Matter, vol. 20 p.1767-1785 (2024)
Texte intégral en Openaccess :
Ref HAL: hal-04734811_v1
Ref Arxiv: 2310.02683
DOI: 10.1039/D3SM01387A
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Langevin equations or generalized Langevin equations (GLEs) are popular models for describing the motion of a particle in a fluid medium in an effective manner. Here we examine particles immersed in an inherently nonequilibrium fluid, i.e., an active bath, which are subject to an external force. Specifically, we consider two types of forces that are highly relevant for microrheological studies: A harmonic, trapping force and a constant, "drag" force. We study such systems by molecular simulations and use the simulation data to derive an effective GLE description. We find that, in an active bath, the external force in the GLE is not equal to the physical external force, but rather a renormalized external force, which can be significantly smaller. The effect cannot be attributed to the mere temperature renormalization, which is also observed.
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