Addressing Quantum Chromodynamics (QCD) in the infrared is a notoriously difficult task due to the size of the interaction strength. This has instigated the development of non-perturbative approaches based either on the lattice discretization and the statistical evaluation of the QCD functional integral, or on its continuum reformulation in terms of infinite hierarchies of equations. Lattice QCD provides an almost exact description of QCD that can however not be used in all situations. As for continuum approaches, even though they can be extended to these situations in principle, they very often rely on uncontrolled truncations that prevent a quantitative estimate of the error.

Over the last decades, the lattice simulation of Euclidean QCD correlators in the Landau gauge, has revealed unexpected features that shed some light on how the various QCD fields are coupled in the infrared. This allows one to envisage a "third way" into infrared QCD. In this talk, I review a ten year effort to put these ideas into solid ground, using the Curci-Ferrari action, a one-parameter model for Landau gauge-fixed QCD in the infrared. In particular, I will discuss how this approach allows one to retrieve the lattice results for the QCD correlation functions and to investigate features of the phase structure that relate to the most fundamental properties of QCD such as confinement or chiral symmetry breaking.

Although conceptually simple, the air-water interface displays complex static and dynamics properties, which become relevant when describing interfacial ion effects.

1) Different definitions of the electrostatic potential, each relevant for distinct experimental scenarios, lead to widely varying surface potential magnitudes and even different signs. Based on quantum-chemical density-functional molecular dynamics simulations, a few different surface potentials are evaluated and compared. The spatially averaged surface potential, accessible to electron holography, is dominated by the trace of the water molecular quadrupole moment and amounts to more than + 4 Volt inside the water phase, very different from results obtained with force-field water models. The surface potential inside a cavity is much smaller, less than 200 mVolt in magnitude. This is the electrochemical surface potential relevant for ion transfer reactions and ion surface adsorption. Charge transfer between water molecules leads to pronounced surface potentials as well. However, when probing electrophoresis by explicitly applying a lateral electric field, the zeta potential turns out to be zero. Thus, charge transfer between water molecules does not translate to a non-zero electrophoretic mobility at the pristine vapor-liquid water interface. [1]

2) The zeta-potential of mineral and biological surfaces can be used to characterize the specific surface affinity of ions. The non-vanishing zeta-potential of zwitterionic net-neutral phospholipid vesicles in neat water is consistently observed in experiments but not fully understood theoretically. Using atomistic molecular dynamics simulations in combination with the modified Poisson-Boltzmann equation, we study the effects of the dielectric and viscous properties of various aqueous interfaces and specific ion-surface interactions. We quantitatively reproduce and explain experimental results for the zeta-potential by using that in a thin interfacial water layer the dielectric and viscous properties are different from bulk water. For lipid membrane surfaces we need to postulate minute amounts of surface-active anionic impurities in lab water and also in the added salt. [2,3]

[1] Electrokinetic, electrochemical, and electrostatic surface potentials of the pristine water liquid–vapor interface, Maximilian R. Becker, Philip Loche and Roland R. Netz, J. Chem. Phys. 157, 240902 (2022)

[2] Interplay of Interfacial Viscosity, Specific-Ion, and Impurity Adsorption Determines Zeta Potentials of Phospholipid Membranes, Amanuel Wolde-Kidan and Roland R. Netz, Langmuir 2021, 37, 8463−8473

[3] Impurity effects at hydrophobic surfaces, Yuki Uematsu, Douwe Jan Bonthuis and Roland R. Netz, Current Opinion in Electrochemistry 2019, 13:166–173

String theory is famously known for its ability to provide an explanation for the statistical entropy of supersymmetric black holes. It consists in counting the number of brane bound states at weak gravitational coupling. At strong coupling, it has been proposed that black-hole microstates are described by solutions in string theory that do not have a horizon: This is the Fuzzball hypothesis. In the first part of the talk, I will introduce black-hole microstates in string theory and the Fuzzball proposal. In the second part, I will present some new results (based on 2211.14326 and 2202.08844) indicating the existence of horizonless solutions accounting for a finite fraction of the entropy of the three-charge black hole.

We show that mesoscopic coherent fluctuations of light propagating in random media induce fluctuating radiation forces. A hydrodynamic Langevin approach is used to describe the coherent light fluctuations, whose noise term accounts for mesoscopic coherent effects. This description—generalizable to other quantum or classical wave problems—allows us to understand coherent fluctuations as a nonequilibrium light flow, characterized by the diffusion coefficient D and the mobility σ, otherwise related by a Einstein relation. The strength of these fluctuating forces is determined by a single dimensionless and tunable parameter, the conductance gL. Orders of magnitude of these fluctuation forces are offered that show experimental feasibility.

Cosmography is the science that maps and measure the large-scale structures in the observed Universe that are built from the tug of war between gravitation and space expansion. We use the direct galaxy distances to compute the 3-dimensional peculiar/gravitational velocity field in order to reconstruct the underlying distribution of mass responsible of these motions. Filaments, walls and voids are embedded into a more global view of large gravitational watersheds delineated by empty regions. The main advantage of mapping superclusters as watershed basins is the robustness of the definition, allowing them to be used as cosmological probes. The seminar will be a journey relating the telescope campaigns, the discovery of our home supercluster « Laniakea » and the 5 newly cartographied neighbors. We will expose measurements of parameters linked to the cosmology principle of homogeneity and the gravitation law, and inform about the upcoming large surveys.

Recent advancements in both theoretical and experimental studies of out-of-equilibrium thermodynamics of quantum systems have garnered significant attention. This seminar will explore the investigation of fluctuations of heat, work, and entropy in quantum systems, which has led to a greater understanding of the emergence of thermodynamic laws and fluctuation theorems. The applications of these studies are far-reaching, including the design and analysis of quantum thermal machines such as engines and refrigerators. In the first part, I will provide an overview of recent progress in this field, including relevant experiments.

In the latter part of the presentation, I will focus on the functioning and performance of an endoreversible Otto cycle with a harmonically confined Bose gas as the working medium. The engine's operation will be analyzed in three different regimes: the Bose-Einstein condensate (BEC) phase, the normal phase, and across the BEC-normal phase transition, during each cycle. The BEC phase's unique properties provide for an enhanced engine performance, such as increased power output and higher efficiency at maximum power.

This contribution promises to be an informative and insightful discussion of recent advancements in quantum thermodynamics and their applications.


References:
[1] N. M. Myers, F. J. Peña, O. Negrete, P. Vargas, G. De Chiara, S. Deffner, New J. Phys. 24, 025001 (2022)

The mechanism and driving forces of chromosome segregation in the bacterial cell cycle of E. coli is one of the least understood events in its life cycle [1,2,3]. Using principles of entropic repulsion between DNA-polymer loops confined in a cylinder, we use Monte carlo simulations to show that the segregation is spontaneously enhanced by the adoption of a certain DNA-polymer architecture as replication progresses. Secondly, the chosen polymer-topology ensures its self-organization along the cell axis while segregation is in progress, such that various chromosomal segments (loci) get spatially localized as seen in-vivo [4]. The evolution of loci positions match the corresponding experimentally reported results for E.coli using FISH [5]. Additionally, the contact map generated using our bead-spring model [4] reproduces the four macro-domains of the experimental Hi-C maps [6]. We modify the architecture by adding just four crosslinks at specific positions along the chain contour in 500 monomer bead-spring ring polymer, which represents the choromosome. After replication of our model-polymer, we obtain two 500-monomer ring polymers, which spontaneously get segregated and organized by virtue of their polymer topology. Thus we have proposed a framework which reconciles many spatial organizational aspects of E. coli chromosome as seen in-vivo, and provides a consistent mechanistic understanding of the process underlying segregation. Certain proteins are expected to contribute to change the DNA-polymer architecture. We also observe quantitative match of FISH data [7] and HiC data [3] for another bacteria C.crescentus where we use another polymer topology [8]. We have extended our studies to investigate chromosome organization in fast growth conditions for E.coli [9]. We have investigated a host of polymer topologies to develop understanding of how polymer topologies effect organization and segregation forces in cylindrical confinement. [1] Jay K. Fisher, Aude Bourniquel, G. Witz, B. Weiner, M. Prentiss, and Nancy Kleckner.


[1] Cell, 153(4):882–895, (2013).
[2] A. Japaridze, C. Gogou, J. W. J. Kerssemakers, H. M. Nguyen, Cees Dekker. Journal : Nature Communications, 11(1), (2020).
[3] Virginia S. Lioy, Ivan Junier, and F. Boccard. Ann. Rev. of Microbiology, 75(1), (2021).
[4] Polymer architecture orchestrates the segregation and spatial organization of replicating E.coli chromosomes in slow growth. D. Mitra, S. Pande, Apratim Chatterji. Soft Matter, 18, 5615-5631 (2022)
[5] J. Cass, N.J. Kuwada, B. Traxler, P.A.Wiggins: Biophys. Journal . 110 (12):2597-260 (2016)
[6] T. B. K. Le, M. V. Imakaev, L. A. Mirny and M. T. Laub, Science, 342, 731–734 (2013).
[7] P.H. Viollier, M. Thanbichler, P.T. McGrath, L.West, M.Meewan, H.H. Mcadams, Lucy Shapiro. Journal: PNAS, 101 (25) 9257 (2004)
[8] Topology-driven spatial organization of ring polymers under confinement Authors: D. Mitra, S. Pande, Apratim Chatterji. Phys. Rev. E, 106, 054502 (2022).
[9] Entropy mediated organization of E.coli chromosome in fast growth conditions. Shreerang Pande, Debarshi Mitra, Apratim Chatterji. arXiv:2304.02275

Gene expression is the process of protein synthesis inside living cells that happens via two steps: transcription (genetic code is copied to mRNA) and translation ( protein is produced from mRNA ). The levels of mRNA and proteins can exhibit remarkable variation across genetically identical cells even under the same external environment due to inherent stochastic chemical reactions that occur in low molecular numbers.

Transcription factor proteins (TFs) that regulate the transcription process by binding to their specific regulatory sites, can also bind to a wide range of genomic sites with high affinity. Binding to such “decoys” has been mostly ignored in the past in the context of their regulatory roles. We investigate how the decoy binding can affect the stochastic gene expression for oscillatory and non-oscillatory gene expressions using linear noise approximation, stability analysis, and kinetic monte carlo simulations. Our study shows decoy can be crucial to regulating stochastic gene expression dynamics.

Reference:
1) Enhancement of gene expression noise from transcription factor binding to genomic decoy sites, S Dey, M Soltani, and A Singh, Scientific Report (2020)

2) Diverse role of decoys on emergence and precision of oscillations in a biomolecular clock, Biophysical Journal, S Dey and A Singh (2021)

In this seminar, I will discuss the state of searches for WIMP particles, in the minimal dark matter (MDM) scenario. Good prospects for the discovery of MDM could be offered by a future muon collider. In particular, there would be the unique possibility of discovering the 5-plet MDM through the detection of its bound state. At the first stage of operation of a multi-TeV muon collider, the 5-plet MDM can be discovered directly via the resonant production of the neutral component of the bound state (via an on-peak search) or, in a complementary way, through the W associated production of the charged components (via an above-threshold analysis). The W associated production proves to be in general a very efficient way to test charged resonances.