Publications

2021

• Progress and Opportunities in Backward angle (u-channel) Physics
  
  • Gayoso C. Ayerbe
  • Bibrzycki Ł.
  • Diehl S.
  • Heppelmann S.
  • Higinbotham D. W.
  • Huber G. M.
  • Kay S. J. D.
  • Klein S. R.
  • Laget J. M.
  • Li W. B.
  • Mathieu V.
  • Park K.
  • Perry R. J.
  • Pire B.
  • Semenov-Tian-Shansky K.
  • Stanek A.
  • Stevens J. R.
  • Szymanowski L.
  • Weiss C.
  • Yu B. -G.
  European Journal of Physics, European Physical Society, 2021, A57, pp.342. Backward angle (u-channel) scattering provides complementary information for studies of hadron spectroscopy and structure, but has been less comprehensively studied than the corresponding forward angle case. As a result, the physics of u-channel scattering poses a range of new experimental and theoretical opportunities and questions. We summarize recent progress in measuring and understanding high energy reactions with baryon charge exchange in the u-channel, as discussed in the first backward angle (u-channel) Physics Workshop. In particular, we discuss backward angle measurements and their theoretical description via both hadronic models and the collinear factorization approach, and discuss planned future measurements of u-channel physics. Finally, we propose outstanding questions and challenges for u-channel physics.
• Transition distribution amplitudes and hard exclusive reactions with baryon number transfer
  
  • Pire B.
  • Semenov-Tian-Shansky K.
  • Szymanowski L.
  Physics Reports, Elsevier, 2021, 940, pp.1. Baryon-to-meson and baryon-to-photon transition distribution amplitudes (TDAs) arise in the collinear factorized description of a class of hard exclusive reactions characterized by the exchange of a non-zero baryon number in the cross channel. These TDAs extend the concepts of generalized parton distributions (GPDs) and baryon distribution amplitudes (DAs). In this review we discuss the general properties and physical interpretation of baryon-to-meson and baryon-to-photon TDAs. We argue that these non-perturbative objects are a convenient complementary tool to explore the structure of baryons at the partonic level. We present an overview of hard exclusive reactions admitting a description in terms of TDAs. We discuss the first signals from hard exclusive backward meson electroproduction at JLab with the 6 GeV electron beam and explore further experimental opportunities to access TDAs at JLab@12 GeV, PANDA and J-PARC.
• Necessary Conditions for a Hot Quiet Sun Atmosphere: Chromospheric Flares and Low Corona Twisted Flux Rope Eruptions
  
  • Amari Tahar
  • Luciani Jean-Francois
  • Aly Jean-Jacques
  • Canou Aurelien
  • Mikic Zoran
  • Velli Marco
  , 2021. The issue of relevant scales involved in the heating of the solar atmosphere is an important one. Since the temperature already reaches 1 MK a few megameters above the photosphere, observations made by Parker Solar Probe will be able to explore those at larger heights but only indirectly at those lower heights, where small scale coupling between sub-photospheric, chromospheric and coronal structure and dynamics occurs. While Solar Orbiter will be able to bring such observations, modeling appears a complementary interesting approach to interpret those observations Taking a sub-surface dynamo and a sharp realistic VAL- like scale profile from photosphere to corona, with a fixed temperature profile in time, we investigate the necessary conditions implied on the structures and dynamics of the atmosphere to keep this thermal structuration, as well as their implication in the energy budget of the atmosphere. Under those hypothesis we show that :i) the transverse photospheric field below 100km plays a major role; ii) an associated scale of one megameter activity naturally results to produce a zone above the photosphere with high confined electric currents, which then expands into the chromosphere and releases energy(4 500 W/m2) through small-scale eruptions driving sonic motions; iii) meso scale structuration, leads to the formation of larger coherent twisted flux ropes, and associated eruptive like activity in a way similar to large scale eruptive phenomena, as result of cancellation, emergence, and convergence motions. Finally a wave dynamics is also naturally driven in core corona associated to above 300 W/m2.
• Massive Magnetostriction of the Paramagnetic Insulator KEr(MoO4)2 via a Single‐Ion Effect
  
  • Bernáth Bence
  • Kutko Khrystyna
  • Wiedmann Steffen
  • Young Olga
  • Engelkamp Hans
  • Christianen Peter
  • Poperezhai Sergii
  • Pourovskii Leonid
  • Khmelevskyi Sergii
  • Kamenskyi Dmytro
  Advanced Electronic Materials, Wiley, 2021, 8 (3). Abstract The magnetostriction phenomenon, which exists in almost all magnetically ordered materials, is proved to have wide application potential in precision machinery, microdisplacement control, robotics, and other high‐tech fields. Understanding the microscopic mechanism behind the magnetostrictive properties of magnetically ordered compounds plays an essential role in realizing technological applications and helps the fundamental understanding of magnetism and superconductivity. In paramagnets, however, the magnetostriction is usually significantly smaller because of the magnetic disorder. Here, the observation of a remarkably strong magnetostrictive response of the insulator paramagnet KEr(MoO 4 ) 2 is reported on. Using low‐temperature magnetization and dilatometry measurements, in combination with ab initio calculations, employing a quasi‐atomic treatment of many‐body effects, it is demonstrated that the magnetostriction anomaly in KEr(MoO 4 ) 2 is driven by a single‐ion effect. This analysis reveals a strong coupling between the Er 3+ ions and the crystal lattice due to the peculiar behavior of the magnetic quadrupolar moments of Er 3+ ions in the applied field, shedding light on the microscopic mechanism behind the massive magnetostrictive response. (10.1002/aelm.202100770)
  DOI : 10.1002/aelm.202100770
• Collinear factorization of diphoton photoproduction at next to leading order
  
  • Grocholski Oskar
  • Pire Bernard
  • Sznajder Paweł
  • Szymanowski Lech
  • Wagner Jakub
  Physical Review D, American Physical Society, 2021, 104, pp.114006. We calculate in the framework of collinear factorization the amplitude for the photoproduction of a near forward large mass diphoton at leading twist and next to leading order (NLO) in alpha_s. We demonstrate the validity of factorization at this order, which was never achieved for such a reaction where the coefficient function describes a 2 to 3 hard process. While the Born order amplitude was purely imaginary and only probed the $x=\pm \xi$ cross-over line of generalized parton distributions (GPD) domain, the NLO result contains both a real and an imaginary part and probes the whole domain of definition of quark GPDs. The phenomenology of our results for medium (JLab) and higher energy (EIC) experiments will be developed in a future study.
• Intrinsically weak magnetic anisotropy of cerium in potential hard-magnetic intermetallics
  
  • Galler Anna
  • Ener Semih
  • Maccari Fernando
  • Dirba Imants
  • Skokov Konstantin P
  • Gutfleisch Oliver
  • Biermann Silke
  • Pourovskii Leonid V
  Npj Quantum Materials, Nature publishing, 2021, 6 (1). Cerium-based intermetallics are currently attracting much interest as a possible alternative to existing high-performance magnets containing scarce heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in these systems are poorly understood due to the difficulty of a quantitative description of the Kondo effect, a many-body phenomenon where conduction electrons screen out the Ce-4 f moment. Here, we show that the Ce-4 f shell in Ce–Fe intermetallics is partially Kondo screened. The Kondo scale is dramatically enhanced by nitrogen interstitials suppressing the Ce-4 f contribution to the magnetic anisotropy, in striking contrast to the effect of nitrogenation in isostructural intermetallics containing other rare-earth elements. We determine the full temperature dependence of the Ce-4 f single-ion anisotropy and show that even unscreened Ce-4 f moments contribute little to the room-temperature intrinsic magnetic hardness. Our study thus establishes fundamental constraints on the potential of cerium-based permanent magnet intermetallics. (10.1038/s41535-020-00301-6)
  DOI : 10.1038/s41535-020-00301-6
• Ferro-octupolar Order and Low-Energy Excitations in d 2 Double Perovskites of Osmium
  
  • Mosca Dario Fiore
  • Franchini Cesare
  • Pourovskii Leonid
  Physical Review Letters, American Physical Society, 2021, 127 (23), pp.237201. (10.1103/PhysRevLett.127.237201)
  DOI : 10.1103/PhysRevLett.127.237201
• First principles study of thermal conductivity of In$_2$O$_3$ in relation to Al$_2$O$_3$, Ga$_2$O$_3$, and KTaO$_3$
  
  • Subedi Alaska
  , 2021. I use first principles calculations to investigate the thermal conductivity of $\beta$-In$_2$O$_3$ and compare the results with that of $\alpha$-Al$_2$O$_3$, $\beta$-Ga$_2$O$_3$, and KTaO$_3$. The calculated thermal conductivity of $\beta$-In$_2$O$_3$ agrees well with the experimental data obtain recently, which found that the low-temperature thermal conductivity in this material can reach values above 1000 W/mK. I find that the calculated thermal conductivity of $\beta$-Ga$_2$O$_3$ is larger than that of $\beta$-In$_2$O$_3$ at all temperatures, which implies that $\beta$-Ga$_2$O$_3$ should also exhibit high values of thermal conductivity at low temperatures. The thermal conductivity of KTaO$_3$ calculated ignoring the temperature-dependent phonon softening of low-frequency modes give high-temperature values similar that of $\beta$-Ga$_2$O$_3$. However, the calculated thermal conductivity of KTaO$_3$ does not increase as steeply as that of the binary compounds at low temperatures, which results in KTaO$_3$ having the lowest low-temperature thermal conductivity despite having acoustic phonon velocities larger than that of $\beta$-Ga$_2$O$_3$ and $\beta$-In$_2$O$_3$. I attribute this to the fact that the acoustic phonon velocities at low frequencies in KTaO$_3$ is less uniformly distributed because its acoustic phonon branches are more dispersive compared to the binary oxides, which causes enhanced momentum loss even during the normal phonon-phonon scattering processes. I also calculate thermal diffusivity using the theoretically obtained thermal conductivity and heat capacity and find that all four materials exhibit the expected $T^{-1}$ behavior at high temperatures. Additionally, the calculated ratio of the average phonon scattering time to Planckian time is larger than the lower bound of 1 that has been observed empirically in numerous other materials.
• Aspects of conformal field theories and quantum fields in AdS
  
  • Zhao Xiang
  , 2021. This thesis studies the structure and the space of conformal field theories (CFTs), and more generally various properties of conformal correlation functions. It extends into multiple directions, both perturbative and non-perturbative, local and non-local, with and without supersymmetry.The first aspect concerns the conformal correlation functions in d-dimensional spacetime and their relation to flat-space S-matrices in (d + 1)-dimensional spacetime. The connection is built up by considering a quantum field theory (QFT) in a fixed (d + 1)-dimensional Anti-de Sitter (AdS) background and sending the radius of the AdS curvature to infinity. That is, the central object to study is the flat-space limit of QFT in AdS. The analysis starts from taking the flat-space limit of the building blocks of Witten diagrams, namely the bulk-boundary and bulk-bulk propagators. This analysis leads to conjectural generic prescriptions to extracting flat-space physics from conformal correlators. Interestingly, the intuitional picture that a Witten diagram simply reduces to the corresponding Feynman diagram does not always hold and the origin of this discrepancy lies in the bulk-bulk propagators: they could have two different flat-space limits. One of the limits always exists and reduces to Feynman propagator, while the other, when present, diverges in the flat-space limit. This observation is tested by explicit examples, including four-point scalar contact, exchange and triangle Witten diagrams and the conjectures are expected to work whenever the scattering energy is large enough.The second aspect studies the classification problem of defect CFTs. The goal is to partially answer the question: given a bulk CFT and consistency conditions such as crossing symmetry and unitarity, what are the allowed conformal defects with a non-trivial coupling to the bulk? Analytic bootstrap techniques are applied to study a simplified version of this problem where in the bulk only a single free scalar field is considered. Analysis of various three-point functions among bulk and defect fields leads to the conclusion that almost all the n-point correlation functions of defect fields are completely fixed up to a potentially unfixed one-point function. This analysis also leads to an intermediate result in which it is proven that the n-point correlation functions of a conformal theory with a generalized free spectrum must be those of the generalized free field theory.The third aspect studies the interplay between analyticity in spin in CFTs and supersymmetry. Operator spectrum in a general unitary CFT is expected to be captured by a function analytic for spin L > 1, and the operators are organised into various Regge trajectories. The presence of supersymmetry in general extends the region of analyticity in spin. The 6d N = (2, 0) superconformal field theories (SCFTs) is considered as a concrete example, in which analyticity in spin is expected to hold down to L > -3. Detailed analysis of the four-point function of the the stress tensor supermultiplet uncovers an unexpected interplay between unprotected and protected multiplets: the stress tensor multiplet can be found on a long (unprotected) Regge trajectory when analytically continued to spin L = -2. In this study a general iterative bootstrap program is also established, which applies to all SCFTs that have a chiral algebra subsector. (10.70675/e33de970z2381z494dz9e04zc5128f15686a)
  DOI : 10.70675/e33de970z2381z494dz9e04zc5128f15686a
• Controlling materials with lattice vibrations
  
  • Privault Gaël
  • Collet Eric
  • Lorenc Maciej
  • Chaban Ievgeniia F
  • Subedi Alaska
  • Mevellec J. Yves
  • Corraze Benoit
  • Humbert Bernard
  • Janod Etienne
  • Daro Nathalie
  • Chastanet Guillaume
  , 2021.
• Symmetry-resolved THz, IR, Raman spectroscopies and DFT studies of lattice phonon modes in the spin crossover crystal [Fe(phen)2(NCS)2]
  
  • Privault Gaël
  • Gournay Lucas
  • Mevellec J Y
  • Corraze B
  • Chaban Ievgeniia F
  • Janod E
  • Lorenc Maciej
  • Daro N
  • Chastanet G
  • Humbert B
  • Subedi A
  • Collet Eric
  , 2021.
• Statistical properties of partonic configurations and diffractive dissociation in high-energy electron-nucleus scattering
  
  • Le Anh Dung
  , 2021. In the high-energy scattering of a quark-antiquark color dipole off a hadron, the quantum states of the former are represented by a stochastic set of dipoles generated by a binary branching process, in the so-called color dipole model of quantum chromodynamics (QCD). It was found that there is a profound connection between this QCD description and the branching-diffusion processes studied in statistical physics from which different properties of the scattering in the high-energy regime are revealed. Our work in this thesis is aimed to exploit the cross-fertilization between QCD and statistical physics to study the detailed partonic content of the Fock states of a color dipole subject to high-energy evolution in the scattering off a large nucleus. We also produce predictions for diffractive dissociation in electron-ion collisions, based on the QCD dipole picture.In the first place, the scattering events of a color dipole, when parameters are set in such a way that the total cross section is small, are triggered by configurations containing large-transverse-size dipoles. The latter are due to rare partonic fluctuations, which look different as seen from different reference frames, from the rest frame of the nucleus to frames in which the rapidity is shared between the projectile dipole and the target nucleus. It turns out that the freedom to select a frame allows to deduce an asymptotic analytic expression for the rapidity distribution of the first branching of the slowest parent dipole of the set of those which scatter, which provides an estimator for the correlations of the latter. In another aspect, the study implies the importance of the characterization of particle distribution near the extremal particles, referred to as the ``tip", in the states generated by the QCD dipole branching, and more generally, by any one-dimensional branching random walk model. To this aim, we develop a Monte Carlo algorithm to generate the tip of a binary branching random walk on a real line evolving to a predefined time, which allows to study both rare and typical configurations.The above statistical description proves advantageous for calculating diffractive cross section demanding a minimal rapidity gap Y0 and the distribution of rapidity gaps Ygap in the diffractive dissociation of a small dipole off a large nucleus, in a well-defined parametric region. They are the asymptotic solutions to the Kovchegov-Levin equation, which was established more than 20 years ago to describe the diffractive dipole dissociation at high energy. Additionally, we present predictions for the distribution of rapidity gaps in realistic kinematics of future electron-ion machines, based on the numerical solutions to the original Kovchegov-Levin equation and of its next-to-leading extension taking into account the running of the strong coupling. The outcomes for the former reflect in a qualitative way our asymptotic analytical result already at rapidities accessible at future electron-ion colliders. (10.70675/55f8b5c3zbf50z441az9653z73cbb6c84750)
  DOI : 10.70675/55f8b5c3zbf50z441az9653z73cbb6c84750
• Orbital Isotropy of Magnetic Fluctuations in Correlated Electron Materials Induced by Hund’s Exchange Coupling
  
  • Stepanov Evgeny
  • Nomura Yusuke
  • Lichtenstein Alexander
  • Biermann Silke
  Physical Review Letters, American Physical Society, 2021, 127 (20), pp.207205. (10.1103/PhysRevLett.127.207205)
  DOI : 10.1103/PhysRevLett.127.207205
• Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter
  
  • Nicolas T.
  , 2021. This paper investigates the Brillouin limit in a two species rotating collisional plasma, when the source of rotation is an orbital angular momentum carrying wave. The electric field is treated self-consistently with ion and electron radial motion. The injection of angular momentum causes radial currents leading to charge penetration and electric field build up. The electric field varies until an equilibrium with the friction forces is reached. Both collisions with neutrals and Coulomb collisions are considered. In this context, there is no collisional breakdown of the Brillouin limit, on the contrary the maximum achievable electric field decreases when the collision frequency is increased. When two species are present, one that undergoes the forcing while the second is passive, the first species is confined, while the second species can be expelled or confined depending on the charge to mass ratio and the collisionalities. Assuming equal charge numbers, if the second species is the heavy one, it is always expelled, which is a standard result. When the second species is the light one, it can also be expelled in the common case where neutral collisions dominate over Coulomb collisions, which constitutes a new result.
• Imaging the itinerant-to-localized transmutation of electrons across the metal-to-insulator transition in V O 3
  
  • Thees Maximilian
  • Lee Min-Han
  • Luca Bouwmeester Rosa
  • Rezende-Gonçalves Pedro H
  • David Emma
  • Zimmers Alexandre
  • Fortuna Franck
  • Frantzeskakis Emmanouil
  • Vargas Nicolas M
  • Kalcheim Yoav
  • Le Fèvre Patrick
  • Horiba Koji
  • Kumigashira Hiroshi
  • Biermann Silke
  • Trastoy Juan
  • Rozenberg Marcelo J
  • Schuller Ivan K
  • Santander-Syro Andrés F
  Science Advances, American Association for the Advancement of Science (AAAS), 2021, 7 (45). In solids, strong repulsion between electrons can inhibit their movement and result in a "Mott" metal-to-insulator transition (MIT), a fundamental phenomenon whose understanding has remained a challenge for over 50 years. A key issue is how the wave-like itinerant electrons change into a localized-like state due to increased interactions. However, observing the MIT in terms of the energy-and momentum-resolved electronic structure of the system, the only direct way to probe both itinerant and localized states, has been elusive. Here we show, using angleresolved photoemission spectroscopy (ARPES), that in V 2 O 3 , the temperature-induced MIT is characterized by the progressive disappearance of its itinerant conduction band, without any change in its energy-momentum dispersion, and the simultaneous shift to larger binding energies of a quasi-localized state initially located near the Fermi level. (10.1126/sciadv.abj1164)
  DOI : 10.1126/sciadv.abj1164
• Inexorable Edge Kondo Breakdown in Topological Kondo Insulators
  
  • Luo Zhihui
  • Ferrero Michel
  • Yao Dao-Xin
  • Wu Wei
  Physical Review B, American Physical Society, 2021, 104 (16), pp.L161119. Kondo breakdown is one of the most intriguing problems in strongly correlated electron systems, as it is rooted in many anomalous electron behaviors found in heavy-fermion materials. In Kondo lattice systems, Kondo breakdown can arise from either strong magnetic frustrations or critical fluctuations of collective modes. Here, we reveal a new type of Kondo breakdown with a fully different origin in interacting topological Kondo insulators. By employing numerically exact quantum Monte Carlo simulations, we show that with open boundary conditions, Kondo screening is inexorably destroyed by interaction effects on edges or corners in these systems. We argue that the Kondo breakdown is enforced by the symmetries of the system, because the ground states are symmetry protected Haldane phases. (10.1103/PhysRevB.104.L161119)
  DOI : 10.1103/PhysRevB.104.L161119
• TMDs for spin-1 hadrons
  
  • Kumano S.
  • Song Qin-Tao
  , 2022, 37, pp.020130. Transverse-momentum-dependent parton distribution functions (TMDs) were investigated at the twists 3 and 4 for spin-1 hadrons in addition to the twist-2 ones. They were found by studying all the possible decomposition of a quark correlation function in a Lorentz-invariant way with the Hermiticity and parity invariance. The time-reversal invariance was not imposed for the TMDs due to an active role of gauge links; however, they were used for collinear parton distribution functions (PDFs) by integrating the TMDs over the transverse momentum. We found that 30 TMDs exist in the tensor-polarized spin-1 hadron at the twists 3 and 4, whereas there are 10 TMDs at the twist 2. We also showed that there are 3 collinear PDFs at the twists 3 and 4. The corresponding TMD fragmentation functions exist sat the twists 2, 3, and 4 simply by changing function names and variables. Since the time-reversal invariance is valid in the collinear PDFs, the integrals of time-reversal-odd TMDs over the transverse momentum should vanish. It leads to the sum rules $ \int d^2 k_T \, h_{1LT} (x, k_T^{\, 2}) = \int d^2 k_T g_{LT} (x, k_T^{\, 2}) = \int d^2 k_T h_{LL} (x, k_T^{\, 2}) = \int d^2 k_T h_{3LL}(x, k_T^{\, 2}) =0$ on the time-reversal odd TMDs at the twists 3 and 4.
• Useful relations and sum rules for PDFs and multiparton distribution functions of spin-1 hadrons
  
  • Kumano S.
  • Song Qin-Tao
  , 2022, 37, pp.020308. There are two types of polarizations in spin-1 hadrons, and they are vector and tensor polarizations. The latter is a unique one since it does not exist in the spin-1/2 proton. The vector-polarized PDFs are the same for both the proton and spin-1 hadrons; therefore, we mainly investigate the unique PDFs in tensor-polarized hadrons. By using the operator product expansion, the twist-3 PDF $f_{LT}$ can be expressed by two terms in the same way with $g_T$ of the proton. The first term is determined by the twist-2 PDF $f_{1LL}$ (or $b_1$) which was measured by an experiment, and the second term is expressed by twist-3 quark-gluon distributions. If we neglect the higher-twist effects, $f_{LT}$ is simply given by $f_{1LL}$, and this relation is similar to the Wandzura-Wilczek relation of $g_T$. Furthermore, a new sum rule is also obtained for $f_{2LT}=2/3 f_{LT}- f_{1LL}$, which is analogous to the Burkhardt-Cottingham sum rule, in the tensor-polarized spin-1 hadrons. In future, these interesting relations could be studied at accelerator facilities, such as the Jefferson Laboratory, the Fermilab, the nuclotron-based ion collider facility in Russia, the proposed electron-ion colliders in US and China.
• Mott insulating states with competing orders in the triangular lattice Hubbard model
  
  • Wietek Alexander
  • Rossi Riccardo
  • Šimkovic IV Fedor
  • Klett Marcel
  • Hansmann Philipp
  • Ferrero M.
  • Stoudenmire E. Miles
  • Schäfer Thomas
  • Georges Antoine
  Physical Review X, American Physical Society, 2021, 11 (4), pp.041013. The physics of the triangular lattice Hubbard model exhibits a rich phenomenology, ranging from a metal-insulator transition, intriguing thermodynamic behavior, and a putative spin liquid phase at intermediate coupling, ultimately becoming a magnetic insulator at strong coupling. In this multi-method study, we combine a finite-temperature tensor network method, minimally entangled thermal typical states (METTS), with two Green function-based methods, connected-determinant diagrammatic Monte Carlo (DiagMC) and cellular dynamical mean-field theory (CDMFT), to establish several aspects of this model. We elucidate the evolution from the metallic to the insulating regime from the complementary perspectives brought by these different methods. We compute the full thermodynamics of the model on a width-4 cylinder using METTS in the intermediate to strong coupling regime. We find that the insulating state hosts a large entropy at intermediate temperatures, which increases with the strength of the coupling. Correspondingly, and consistently with a thermodynamic Maxwell relation, the double occupancy has a minimum as a function of temperature which is the manifestation of the Pomeranchuk effect of increased localisation upon heating. The intermediate coupling regime is found to exhibit both pronounced chiral as well as stripy antiferromagnetic spin correlations. We propose a scenario in which time-reversal symmetry broken states compete with nematic, lattice rotational symmetry breaking orders at lowest temperatures. (10.1103/PhysRevX.11.041013)
  DOI : 10.1103/PhysRevX.11.041013
• String theory : Supersymmetry breaking, moduli stabilitzation and cosmological considerations
  
  • Coudarchet Thibaut
  , 2021. The purpose of this thesis is to explore various aspects of string theory, a unified theory of matter and all fundamental interactions including gravity. In a first chapter, we start by describing some useful key ingredients of the theory and its construction to motivate the works presented in this manuscript. We then explore three different aspects of the theory. First, a new supersymmetry-breaking mechanism in unoriented open-string models is developed. The features of this breaking are described, commented and put into perspective with other existing mechanisms. Second, one-loop masses acquired by tree-level moduli are studied in a type I string context with N=2 N=0 spontaneous breaking of supersymmetry implemented by a Scherk--Schwarz mechanism. Different strategies are followed to conclude on the stability or not at one loop of the wide variety of moduli present in the model. These strategies range from the Taylor expansion of the effective potential up to quadratic order, to the evaluation of genus-1 two-point correlation functions, through arguments arising from the duality between the heterotic and type I string. Once all the masses are computed, we give explicit models (brane configurations) where there is no instability induced at one loop and where the potential is exponentially suppressed thanks to a Bose/Fermi degeneracy at the massless level. Eventually, in heterotic string models, the backreaction of the one-loop potential generated by a spontaneous Scherk--Schwarz supersymmetry breaking on the cosmology is studied. Flat and ever-expanding solutions are looked for to establish if the classical cosmological dynamics of such solutions is perturbed or not by the one-loop quantum corrections. We then describe a new process for generating a non-relativistic dark-matter relic density in models with spontaneously broken supersymmetry and implementation of the finite temperature through compactification of the Euclidean time. (10.70675/b92feeb1zb345z4c54z920ez9ffd31bb9495)
  DOI : 10.70675/b92feeb1zb345z4c54z920ez9ffd31bb9495
• Magnetosphere-Ionosphere-Thermosphere Coupling study at Jupiter Based on Juno First 30 Orbits and Modelling Tools
  
  • Al Saati Sariah
  • Clément Noé
  • Blanc Michel
  • Wang Yuxian
  • André Nicolas
  • Louis Corentin
  • Lamy Laurent
  • Blelly Pierre‐louis
  • Louarn Philippe
  • Marchaudon Aurélie
  • Gérard Jean-Claude
  • Bonfond Bertrand
  • Grodent Denis
  • Dinelli Bianca Maria
  • Adriani Alberto
  • Mura Alessandro
  • Mauk Barry
  • Clark George
  • Allegrini Frederick
  • Bolton Scott
  , 2021, pp.EPSC2021-734. The dynamics of the Jovian magnetosphere is controlled by the complex interplay of the planet's fast rotation, its solar-wind interaction and its main plasma source at the Io torus. At the ionospheric level, these MIT coupling processes can be characterized by a set of key parameters which include ionospheric conductances, currents and electric fields, exchanges of particles along field lines and auroral emissions. Knowledge of these key parameters in turn makes it possible to estimate the net deposition/extraction of momentum and energy into/out of the Jovian upper atmosphere. In this talk we will extend to the first thirty Juno science orbits the method described in Wang et al. (JGR 2021, under review) which combines Juno multi-instrument data (MAG, JADE, JEDI, UVS, JIRAM and WAVES), adequate modelling tools and data bases to retrieve these key parameters along the Juno magnetic footprint and across the north and south auroral ovals. We will present preliminary distributions of conductances, electric currents and electric fields obtained from these orbits and will compare them with model predictions. (10.5194/espc2021-734)
  DOI : 10.5194/espc2021-734
• Evolution of Gaussian concentration bounds under diffusions
  
  • Chazottes J.-R
  • Collet P.
  • Redig F
  Markov Processes And Related Fields, Polymat Publishing Company, 2021, 27 (5). We study the behavior of the Gaussian concentration bound (GCB) under stochastic time evolution. More precisely, in the context of Markovian diffusion processes on $\mathbb{R}^d$ we prove in various settings that if we start the process from an initial probability measure satisfying GCB, then at later times GCB holds, and estimates for the constant are provided. Under additional conditions, we show that GCB holds for the unique invariant measure. This gives a semigroup interpolation method to prove Gaussian concentration for measures which are not available in explicit form. We also consider diffusions ``coming down from infinity'' for which we show that, from any starting measure, at positive times, GCB holds. Finally we consider non-Markovian difussion processes with drift of Ornstein Uhlenbeck type, and general bounded predictable variance.
• Topological proximity effect in bilayer systems and stochastic approach to interacting topological phases
  
  • Klein Philipp Wilhelm
  , 2021. He past decades have shown great progress in the description of phases of quantum matter beyond the Ginzburg-Landau paradigm. Among the most crucial developments was von Klitzings experimental observation of the quantum Hall effect. It was then Haldane who developed a simple, elegant model - the prototypical model of a Chern insulator - that exhibits a quantum Hall effect without the necessity of an applied external magnetic field. The, almost twenty years after Haldane seminal paper, Kane and Mele described the Quantum Spin Hall Effect (QSHE).In this thesis, we explore the rich phenomenology of the Haldane honeycomb model as well as the Kane-Mele model in a context of novel interfaces and interaction effects. First we study the Haldane-graphene bilayer model and reveal an intriguing proximity effect that allows to induce a topological index into the bulk of graphene. We explore in detail the rich phenomenology of this system. Importantly, we present experimental protocols designed to reveal the effects. In particular, we propose a generalized Haldane bilayer model that is designed to observe the topological proximity effect in a cold atom experimental setup.Furthermore, we study the Haldane honeycomb model with nearest neighbor interactions. We develop a stochastic decoupling scheme, compute the Mott transition line supported with iDMRG calculations and confirm the first order nature of the phase transition by means of Ginzburg-Landau arguments. Then, we propose a new quantity dubbed extit{stochastic Chern number} which provides a measure for the topology in the system in the presence of strong correlations. We utilize the dichroism of light to build a bridge in quantifying excited quasi particles and show an analogy between interaction induced particle-hole pairs and temperature effects.Finally, we study the Mott transition in the Kane-Mele-Hubbard model by applying our variational stochastic decomposition scheme. We compare two kinds of mean field theories where one of them provides a closed analytic expression for the Mott transition line. (10.70675/67702c5dz4d7dz4f43za7f5zecc9da77b765)
  DOI : 10.70675/67702c5dz4d7dz4f43za7f5zecc9da77b765
• Deciphering the role of multiple scatterings and time delays in the in-medium emission process
  
  • Andres Carlota
  • Apolinario Liliana
  • Dominguez Fabio
  • Martinez Marcos Gonzalez
  • Salgado Carlos A.
  , 2022, PANIC2021, pp.252. In this work we use the all-order resummed solution of the BDMPS-Z spectrum to shed light on the dynamics that controls the in-medium radiation process for each kinematical regime. We find that multiple scatterings are essential to correctly describe the radiation process both in the low and mid-energy regime, while in the high-energy region one single hard scattering is enough. Furthermore, we compute the all-order spectrum when the medium is produced with a time delay with respect to the hard process in which the parent parton was created. The propagation of the hard parton through vacuum before the medium formation induces extra medium-induced radiation which might have impact on phenomenological analyses. (10.22323/1.380.0252)
  DOI : 10.22323/1.380.0252
• Strongly-correlated bosons in optical quasicrystals
  
  • Sanchez-Palencia Laurent
  , 2021.