Pantheon SEMPARIS Le serveur des séminaires parisiens Paris

The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community.   [ More information ]


Upcoming Seminars [Next 30 ]
[ scheduler view ]

Monday 27 September 2021, 10:45 at LPTMC, salle 523 du LPTMC - Tour 12-13 Jussieu
( https://us06web.zoom.us/j/82938879975?pwd=Q3IvTmVtbFpXaVBFYVBvcDdtNzhOQT09 Meeting ID: 829 3887 9975 Passcode: 644686 )
SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.stat-mech
Alexander Hartmann ( University of Oldenburg ) Large-deviation simulations of rare non-equilibrium processes can be close to equilibrium
Abstract: Fluctuation theorems like those of Crooks or Jarzynski allow to obtain equilibrium quantities from non-equilibrium processes. For example, the distribution P(W) of the work allows to extract the free energy difference $\Delta F$ between equilibrium starting state and final state, after hypothetical final equilibration. The region of P(W) where $W\approx\Delta F$ holds is most relevant to obtain $\Delta F$. But P(W) may be extremely small in this region, which makes in the case of computer simulations sophisticated large-deviation algorithms necessary. As example, the Ising model with work performed by changing the external field is shown, where probabilities as small as $10^{-50}$ and lower must be reached. Going beyond the calculation of ΔF, we ask, how similar are the non- equilibrium processes in this rare-event tail to the equilibrium ones that determine $\Delta F$? Here, this question is investigate for the unfolding and refolding of RNA secondary structures under influence of an external force f. Indeed the extreme low-probability trajectories, which exhibit $W\approx\Delta F$ and thus contribute most to the determination of $\Delta F$ via Crooks equation, are very similar to the equilibrium trajectories.

Monday 27 September 2021, 11:00 at IAP, IAP - Salle des séminaires Évry Schatzman (and for Zoom contact fumagall@iap.fr) SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) astro-ph
Patrick Peter ( IAP / Cambridge ) Charge-velocity-dependent one-scale model for cosmic string network evolution
Abstract: The Velocity One Scale (VOS) model for cosmic string network evolution is extended to include possible currents flowing along the strings, and different regimes are shown to be present in the very simplified case of a linear equation of state. I’ll present and explain these regimes and discuss why one can conclude that in the matter-dominated era, the average current should vanish unless nonlinear effects come to dominate.

Monday 27 September 2021, 14:00 at LPNHE, Online
( We will be using Zoom for this seminar; please contact the organizers at seminaires@lpnhe.in2p3.fr for more details )
LPNHE (Séminaires du LPNHE) hep-ex
Thierry Lasserre ( CEA - IRFU ) Latest results from KATRIN on neutrino mass and the search for sterile neutrinos
Abstract: I will present the latest results from the Karlsruhe Tritium Neutrino Experiment (KATRIN). KATRIN probes the effective mass of electron anti-neutrinos via a high-precision measurement of the &#946;-decay spectrum of tritium near its endpoint at 18.6 keV. In the first campaign, KATRIN established that the effective mass of neutrinos is <1.1 eV/c2 (90% CL). In the second physics campaign, the source activity was increased by a factor of 3.8 and the background was reduced by 25% compared to the first campaign. Combining the currently available KATRIN data, we find a new upper limit on the effective neutrino mass at <0.8 eV/c2 (90% CL). Following the neutrino mass run, the KATRIN/TRISTAN project will aim to detect the signature of a sterile keV neutrino by measuring the entire tritium beta decay spectrum using an enhanced KATRIN detection and readout system.

Tuesday 28 September 2021, 14:00 at APC, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Tina Kahniashvili ( Carnegie Mellon University and Ilia State University ) Gravitational waves from the early-universe turbulent sources
Abstract: A space-based laser interferometer, pioneered by NASA's LISA concept and now a ESA cornerstone mission, will enable direct detection of gravitational waves at lower frequencies than LIGO, without being limited by seismic noise. Perhaps the most intriguing source for LISA is the stochastic gravitational wave background produced by turbulent plasma motions in an early-universe, particularly at the electroweak energy scale. In this talk I will discuss the stochastic gravitational wave background generated from early-universe turbulence, including the effects of possible parity violation which will result in the non-zero circular polarization. Turbulent sources possibly present at the electroweak energy scales produce gravitational waves with a characteristic frequency of a millihertz, squarely in LISA's sensitivity window. I will present our recent results of direct numerical simulations to compute the net circular polarization of gravitational waves from helical (chiral) turbulent sources in the early universe for a variety of initial conditions. I will discuss the resulting gravitational wave signal assuming different turbulence genesis such as magnetically or kinetically dominant cases. Under realistic physical conditions in the early universe we have computed numerically for the first time the total polarization degree of the gravitational waves and its spectral distribution. Our major finding consists of the spectral polarization degree that strongly depends on the initial conditions. The peak of the spectral polarization degree occurs (in the wavenumber space) at twice the typical wavenumber of the source, as expected, and for the fully helical decaying turbulence, reaches its maximum (100 \%) only at the peak. In addition, we have determined the temporal evolution of the turbulent sources as well as the resulting gravitational waves, showing that the dominant contribution to the spectral energy density happens shortly after the source activation and through prolonged (slow decay) turbulence, the increase of the gravitational wave amplitude at low frequencies can be achieved. I will readdress the constraints imposed by BBN data. I will address the detection prospects through LISA for the gravitational wave signal and its net polarization. showing that the dominant contribution to the spectral energy density happens shortly after the source activation and through prolonged (slow decay) turbulence, the increase of the gravitational wave amplitude at low frequencies can be achieved. I will readdress the constraints imposed by BBN data. I will address the detection prospects through LISA for the gravitational wave signal and its net polarization. showing that the dominant contribution to the spectral energy density happens shortly after the source activation and through prolonged (slow decay) turbulence, the increase of the gravitational wave amplitude at low frequencies can be achieved. I will readdress the constraints imposed by BBN data. I will address the detection prospects through LISA for the gravitational wave signal and its net polarization.

Tuesday 28 September 2021, 14:00 at LPTHE, Library & Zoom link in comments
( https://cern.zoom.us/j/66479327749?pwd=Z1YvUUc2OWdOMk1Xc0VaSnRLVkRVdz09 Meeting ID: 664 7932 7749 Passcode: 390396 )
LPTHE-PPH (Particle Physics at LPTHE) hep-ph
Johannes Braathen ( DESY ) Precision calculations of the Higgs trilinear coupling to probe New Physics
Abstract: The Higgs trilinear coupling provides a unique opportunity to probe the structure of the Higgs sector, study the nature of the electroweak phase transition, and search for New Physics. It is known that in BSM models it can deviate significantly from its SM prediction at one loop, because of non-decoupling effects in the radiative corrections from extra scalars. One may then wonder how this result is modified at two loops, and whether new large effects may appear. In this talk, I will present recent results on the calculation of leading two-loop corrections to the Higgs trilinear coupling in a range of theories with extended scalar sectors – massive models such as the Two-Higgs-Doublet Model as well as theories with classical scale invariance. I will show that, while the two-loop corrections do not modify significantly the non-decoupling effects observed at one loop, their computation is important in view of the experimental program to precisely measure the Higgs trilinear coupling at current and future colliders.

Thursday 30 September 2021, 11:00 at IHP, Zoom
( Zoom link: https://zoom.us/j/97507124810 )
RENC-THEO (Rencontres Théoriciennes) hep-th
Eran Palti ( Ben Gourion University ) Convexity of Charged Operators in CFTs and the Weak Gravity Conjecture
Abstract: In this talk I will introduce a particular formulation of the Weak Gravity Conjecture in AdS space in terms of the self-binding energy of a particle. The holographic CFT dual of this formulation corresponds to a certain convex-like structure for operators charged under continuous global symmetries. Motivated by this, we propose a conjecture that this convexity is a general property of all CFTs, not just those with weakly-curved gravitational duals. It is possible to test this in simple CFTs, the conjecture passes all the tests performed so far. (based on 2108.04594 )

Friday 1 October 2021, 10:00 at IPHT, Amphi Bloch (hybrid; remote audience needs to register, see below)
( Remote audience needs to register at https://courses.ipht.fr/?q=en/node/271 Livestream on https://www.youtube.com/c/IPhTTV )
COURS (Cours) hep-th
Andrea Puhm ( CPHT ) Celestial holography primer
Abstract: One of the most powerful tools for understanding quantum aspects of gravity is the holographic principle, which asserts a duality between a theory of quantum gravity on a given manifold and a field theory living on its boundary. A concrete realization in spacetimes with negative curvature is the AdS/CFT correspondence, but it remains an important open question if and how the holographic principle is realized for general spacetimes. Recently, the holographic dual of quantum gravity in asymptotically flat spacetimes has been conjectured to be a codimension-two conformal field theory which lives on the celestial sphere at null infinity, aptly referred to as celestial CFT. A first hint at such a duality is the equivalence between the action of the Lorentz group and global conformal transformations on the celestial sphere. Moreover, when recast in a basis of boost eigenstates, scattering amplitudes transform as conformal correlators of primary operators in the dual celestial CFT. These celestial correlators appear to have some, but not all, of the properties of standard CFT correlators. The goal of this course will be to give an introductory guide to recent advances in celestial holography.

Monday 4 October 2021, 11:05 at IAP, Webinar for zoom details contact fumagall@iap.fr SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) astro-ph
Syksy Räsänen ( University of Helsinki ) TBA

Monday 4 October 2021, 16:00 at LPTMC, salle 523 du LPTMC - Tour 12-13 Jussieu
( https://us06web.zoom.us/j/87875346828?pwd=eEJxcFl3WnNWMWlna3ZWTzhxS095Zz09 Meeting ID: 878 7534 6828 Passcode: 765937 )
SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat
Pierre Deplace ( ENS Lyon ) Anomalous chiral modes in 2D scattering networks
Abstract: Chiral edge states are unidirectional modes that propagate along the boundaries of two-dimensional insulators when time-reversal symmetry is broken. Their existence can be understood from topological arguments, as their number is given by a topological index of the bulk bands, the Chern number. Periodically driven quantum systems (also dubbed Floquet systems), whose evolution are dictated by a unitary operator, were surprizingly found to exhibit chiral edge states that are not always predicted by the Chern numbers. Those anomalous chiral modes have however also a topological origin, but with no counterpart in Hamiltonian (static) systems. In this talk, I will show that anomalous edge modes are actually very natural in scattering networks, and discuss why one can expect them beyond the realm of periodic driven systems. Then, I will discuss recent numerical and experimental results with microwave networks that reveal a superior robustness of edge- mediated transport in the anomalous phase than in the Chern phase.

Tuesday 5 October 2021, 10:00 at IHES, Zoom réunion
( https://indico.math.cnrs.fr/event/6791/ )
PT-IHES (Séminaire de physique théorique de l'IHES) hep-th
Yoshiko Ogata ( Univ. Tokyo ) Classification of gapped ground state phases in quantum spin systems
Abstract: Recently, classification problems of gapped ground state phases attract a lot of attention in quantum statistical mechanics. We explain about operator algebraic approach to these problems.

Tuesday 5 October 2021, 10:45 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Uri Bader ( Weizmann Institute of Science ) Algebraic Representations of Ergodic Actions (1/4)
Abstract: Ergodic Theory is a powerful tool in the study of linear groups. When trying to crystallize its role, emerges the theory of AREAs, that is Algebraic Representations of Ergodic Actions, which provides a categorical framework for various previously studied concepts and methods. Roughly, this theory extends the focus of Representation Theory from Groups to Group Actions, exploiting the tension between Ergodic Theory and Algebraic Geometry. In this series of talks I will introduce this theory and survey some of its applications, focusing on Superrigidity and Arithmeticity results.

Tuesday 5 October 2021, 14:00 at APC, seminar room 483A, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Mohammad Takook ( Kharazmi University ) From the representation of de Sitter group to the quantum field theory
Abstract: A rigorous mathematical consideration of quantum field theory in de Sitter universe is briefly presented in ambient space formalism. This formalism permit us to solve some physical and mathematical problems in de Sitter space-time. The concept of mass is defined from the light-cone propagation: massless fields or particles are propagated on the de Sitter light-cone and the massive cases are propagated inside the light-cone. In this respect, there appears a big problem of mass definition for the massless minimally coupled scalar field. This field play an important role in quantum gravity and mass generation in quantum inflationary scenario.  The classical field theory consideration is based on group theory and Lie algebra. From the Casimir operators of the de Sitter group the free field equation is derived. By using the Lie algebra of de Sitter group one-particle Hilbert state and unitary irreducible representation can be constructed and then the solution of the free field equations can be extracted. In QFT level, the field operator is defined as a map on the Fock space and then is constructed by the annihilation and creation operators on the Fock space. The free massive field operator must be transform by the unitary irreducible representation of the dS group. The act of annihilation operator on the one-particle state results to the vacuum state which must be fixed by the auxiliary condition. For the free massless field with s&#8805;1 and massless minimally coupled scalar field for obtaining a covariant quantization the field operator must be transform by an indecomposable representation of dS group. The Hilbert space of the interaction fields and the time evolution operator are the most challenging problems in de Sitter universe.

Tuesday 5 October 2021, 17:30 at DPT-PHYS-ENS, Amphi Jaurès - Ecole normale supérieure 29 rue d'Ulm 75005 PARIS COLLOQUIUM-ENS (Colloquium of the Physics Department of ENS) physics
Florian Marquardt ( Max Planck Institute, Erlangen ) How a physical system can be turned into a self-learning machine
Abstract: Machine learning using artifical neural networks is revolutionizing many areas of science and technology. This increases the urgency for exploring alternatives to artificial neural networks running on digital hardware. These alternatives might eventually be faster and/or more power-efficient. With this in mind, we ask the question whether one can identify a general principle that would enable a nonlinear physical system to become a self-learning machine - i.e. a physical information-processing device where internal degrees of freedom self-adjust by physical interactions to learn a desired input-output relation. In this talk, I will present our recent idea on how this might be achieved for arbitrary time-reversal-invariant Hamiltonian systems. I will introduce the principle of 'Hamiltonian Echo Backpropagation', and demonstrate how efficient learning could be possible in a wide class of physical systems. See: Self-learning Machines based on Hamiltonian Echo Backpropagation, Victor Lopez-Pastor, Florian Marquardt, arXiv 2103.04992 (2021)

Wednesday 6 October 2021, 14:30 at LPENS, L367 FORUM-ENS (Forum de Physique Statistique @ ENS) cond-mat.soft
Valerio Sorichetti ( LPTMS ) Fluctuations control the assembly kinetics of semiflexible filaments
Abstract: The problem of irreversible polymerization is fundamental for its many applications to different fields, from material science to biology. In living cells, cytoskeletal filaments grow and bundle together, forming complex networks. Since the assembly and bundling of these filaments often involve energies of the order of hundreds or thousands of $k T$, the final structure of the network will be heavily influenced by the kinetics of these processes (Kayser et al., Soft Matter, 2012, 8, 8873). Approaches based on equilibrium physics are therefore bound to fail when studying the structural and mechanical properties of such networks, and approaches that explicitly considers the kinetics are necessary. We extend a previously developed theoretical framework (De Gennes, J. Chem. Phys., 1982, 76, 3316) to study how the average length $L$ of a system of semiflexible filaments that anneal irreversibly via end-to-end reactions increases with time. We find that filament assembly is controlled by the short-time transversal fluctuations, which lead to a linear growth of $L$ with time. We perform the same calculations also for perfectly rigid rods, which have no transversal fluctuations modes, showing that in this case L increases only as the square root of time. Finally, we compare our theoretical predictions with molecular dynamics simulations of particles that aggregate irreversibly into semiflexible filaments with a tunable persistence length, finding an excellent agreement with the theoretical predictions.

Thursday 7 October 2021, 10:45 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Uri Bader ( Weizmann Institute of Science ) Algebraic Representations of Ergodic Actions (2/4)
Abstract: Ergodic Theory is a powerful tool in the study of linear groups. When trying to crystallize its role, emerges the theory of AREAs, that is Algebraic Representations of Ergodic Actions, which provides a categorical framework for various previously studied concepts and methods. Roughly, this theory extends the focus of Representation Theory from Groups to Group Actions, exploiting the tension between Ergodic Theory and Algebraic Geometry. In this series of talks I will introduce this theory and survey some of its applications, focusing on Superrigidity and Arithmeticity results.

Thursday 7 October 2021, 11:00 at LPTHE, bibliothèque du LPTHE, tour 13-14, 4eme étage SEM-DARBOUX (Séminaire Darboux - physique théorique et mathématiques) hep-th
Tomoyuki Arakawa ( RIMS Kyoto ) TBA

Thursday 7 October 2021, 15:00 at LPTM, Distanciel TEAMS SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) physics.bio-ph
Alex Leow ( School of Public Health / Psychiatric Institute (SPHPI) , U.Ill. Chicago, USA ) The human brain as a dynamic system: things I learned about the brain through the lens of statistical physics.
Abstract: In this talk I would like to share some self-reflections, as a computational person at heart while also practicing medicine as part of my job description, attempting to understand the human mind using hard sciences. To illustrate my point we will discuss the idea of the human connectome (a complete diagram of human brain connectivity on a mesoscale) as informed using modern magnetic resonance (MR) techniques of diffusion-weighted MR imaging and resting-state functional MRI. I will discuss in detail our team's ongoing research efforts that leverage fundamental principles of modern physics first discovered in statistical and thermal physics (e.g., the maximum entropy principle, Boltzmann distribution, etc.), in the hope of stimulating interest among researchers from different disciplines to work together towards a better understanding of the human brain, arguably the very core of human experience.

Friday 8 October 2021, 15:00 at CPHT, Salle Louis Michel Batiment 6 COURS (Cours) hep-th
Tasos Petkou On scale, conformal and Weyl invariance in QFT
Abstract: Scale, conformal and Weyl invariance play a central role in Quantum Field Theories, and they are omnipresent in AdS/CFT correspondence. Through various examples I will review various issues and possible misconceptions regarding the interrelationships between these three important notions and connect them to some recent investigations.

Monday 11 October 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) astro-ph
Julian Rey ( IFT - Madrid ) TBA

Monday 11 October 2021, 13:30 at LPENS, Salle Djebar - 29 rue d'Ulm LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Loïc Lanco ( Centre de Nanosciences et de Nanotechnologies, C2N ) Controlling the interaction between (single) spins and (single) photons

Tuesday 12 October 2021, 10:45 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Uri Bader ( Weizmann Institute of Science ) Algebraic Representations of Ergodic Actions (3/4)
Abstract: Ergodic Theory is a powerful tool in the study of linear groups. When trying to crystallize its role, emerges the theory of AREAs, that is Algebraic Representations of Ergodic Actions, which provides a categorical framework for various previously studied concepts and methods. Roughly, this theory extends the focus of Representation Theory from Groups to Group Actions, exploiting the tension between Ergodic Theory and Algebraic Geometry. In this series of talks I will introduce this theory and survey some of its applications, focusing on Superrigidity and Arithmeticity results.

Tuesday 12 October 2021, 14:00 at APC, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Joonas Hirvonen ( University of Helsinki ) Effective field theory approach to thermal bubble nucleation
Abstract: The possibility of observing a stochastic gravitational wave background originating from a cosmological first-order phase transition elicits interest in studying the transitions. Currently, a limiting factor in accurately determining the gravitational wave spectrum from an underlying microphysical model is the calculation of the nucleation rate. I will discuss recent work in which we have proposed a new effective field theory (EFT) framework for determining the thermal nucleation rate in high-temperature QFTs. Typical issues encountered in thermal nucleation calculations (double counting fluctuations, stray imaginary parts and diverging derivative expansions) arise due to an inconsistent treatment of nucleating bubbles. Using the EFT framework, we are able to create an effective description for the length scale of the nucleating bubbles and hence treat the nucleating bubbles consistently, resolving the aforementioned issues. In addition, the framework provides a clear physical picture of the process by making a connection to classical nucleation theory by Langer.

Thursday 14 October 2021, 10:45 at IHES, Amphithéâtre Léon Motchane
( Cours de l'IHES )
MATH-IHES (TBA) math
Uri Bader ( Weizmann Institute of Science ) Algebraic Representations of Ergodic Actions (4/4)
Abstract: Ergodic Theory is a powerful tool in the study of linear groups. When trying to crystallize its role, emerges the theory of AREAs, that is Algebraic Representations of Ergodic Actions, which provides a categorical framework for various previously studied concepts and methods. Roughly, this theory extends the focus of Representation Theory from Groups to Group Actions, exploiting the tension between Ergodic Theory and Algebraic Geometry. In this series of talks I will introduce this theory and survey some of its applications, focusing on Superrigidity and Arithmeticity results.

Thursday 14 October 2021, 14:00 at LPTMC, Jussieu campus INSP 22-23 3rd floor room 317
( https://us06web.zoom.us/j/84591143939 ID de réunion : 845 9114 3939 Code secret : 541621 )
SEM-EXCEP (Séminaire exceptionel) cond-mat.mes-hall
Clément Tauber ( IRMA Strasbourg ) Topological indices for shallow-water waves
Abstract: In this talk, I will apply tools from topological insulators to a fluid dynamics problem: the rotating shallow- water wave model with odd viscosity. The bulk-edge correspondence explains the presence of remarquable stable waves propagating towards the east along the equator and observed in some Earth oceanic layers. The odd viscous term is a small-scale regularization that provides a well defined Chern number for this continuous model where momentum space is unbounded. Equatorial waves then appear as interface modes between two hemispheres with a different topology. However, in presence of a sharp boundary there is a surprising mismatch in the bulk-edge correspondence: the number of edge modes depends on the boundary condition. I will explain the origin of such a mismatch using scattering theory and Levinson’s theorem. This talk is based on a series of joint works with Pierre Delplace, Antoine Venaille, Gian Michele Graf and Hansueli Jud.

Monday 18 October 2021, 11:00 at IAP, Webinar for zoom details contact fumagall@iap.fr SEM-GRECO (Séminaire du GReCO : groupe de GRavitation et COsmologie à l'IAP) astro-ph
Julien Larena ( University of Cape Town ) TBA

Monday 18 October 2021, 13:30 at LPENS, Salle Djebar - 29 rue d'Ulm LPENS-MDQ (Séminaire Matériaux et Dispositifs Quantiques du LPENS) cond-mat
Michele Filippone ( CEA Grenoble ) TBA

Monday 18 October 2021, 14:30 at IHES, Amphithéâtre Léon Motchane PT-IHES (Séminaire de physique théorique de l'IHES) hep-th
Ritam Sinha ( Hebrew University Jerusalem ) The Bi-conical Vector Model at 1/N
Abstract: We study finite N aspects of the O(m) × O(N-m) vector model with quartic interactions in general 2 &#8804; d &#8804; 6 spacetime dimensions. This model has recently been shown to display the phenomenon of persistent symmetry breaking at a perturbative Wilson-Fisher-like fixed point in d=4-&#949; dimensions. The large rank limit of the bi-conical model displays a conformal manifold and a moduli space of vacua. We find a set of three double trace scalar operators that are respectively irrelevant, relevant and marginal deformations of the conformal manifold in general d. We calculate the anomalous dimensions of the single and multi-trace scalar operators to the first sub-leading order in the large rank expansion. The anomalous dimension of the marginal operator does not vanish in general, indicating that the conformal manifold is lifted at finite N. In the case of equal ranks we are able to derive explicitly the scaling dimensions of various operators as functions of only d.

Tuesday 19 October 2021, 14:00 at APC, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Ville Vaskonen ( Institut de Física d'Altes Energies ) Gravitational wave probes of primordial black holes
Abstract: The dawn of gravitational wave (GW) astronomy has enabled new probes of dark matter. In particular, the formation and abundance of primordial black holes (PBHs) can be probed through GWs. In this talk I will discuss different ways how GW observations can be used to probe PBHs and I will review the implications of LIGO-Virgo observations on PBHs.

Tuesday 26 October 2021, 14:00 at APC, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Alexander Jenkins ( King's College London ) Two recent topics in gravitational-wave cosmology: Binary resonance searches and nonlinear memory from cosmic strings
Abstract: In the first half of this talk, I will discuss how binary systems can be used as dynamical detectors of gravitational waves (GWs). Since the passage of GWs through a binary perturbs the trajectories of the two bodies, we can infer the presence of a GW signal by searching for changes in the binary's orbital parameters. In the presence of a stochastic GW background (SGWB) these changes accumulate over time, causing the binary orbit to execute a random walk through parameter space. I will present a powerful new formalism for calculating the full statistical evolution of a generic binary system in the presence of a SGWB, capturing all six of the binary's orbital parameters, and will show how this formalism can be applied to timing of binary pulsars and lunar laser ranging to set powerful upper limits on the SGWB spectrum in the microHz band between LISA and PTAs. In the second half of this talk, I will discuss the nonlinear GW memory effect---a fascinating prediction of general relativity, in which oscillatory GW signals are generically accompanied by a monotonically-increasing strain which persists in the detector long after the signal has passed. I will present the first-ever calculations of the nonlinear memory signal associated with GW bursts from cusps and kinks on cosmic string loops, which are an important target for current and future GW observatories. Surprisingly, the cusp GW signal diverges for sufficiently large loops when all memory contributions are included, which I argue is due to a breakdown in the weak-field treatment of GW emission from the cusp. This implies that previously-neglected strong gravity effects play an important role near cusps, although the exact mechanism by which they cure the divergence is not currently understood. I will argue that one possible resolution is for these cusps to collapse to form primordial black holes.

Tuesday 2 November 2021, 14:00 at APC, contact roperpol@apc.in2p3.fr for Zoom meeting details APC-TH (Seminar of the theory group of APC) gr-qc
Salome Mtchedlidze ( Ilia State University ) Evolution and signatures of primordial magnetic fields

seminars from series at institute
in subject with field matching

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