Faculty of Physics University of Warsaw > Events > Seminars > Exact Results in Quantum Theory

Exact Results in Quantum Theory

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join us at 14:15

Astrid Eichhorn (University of Heidelberg & University of Southern Denmark)

Frontiers of quantum gravity

I will provide an overview of two key frontiers of quantum gravity - the theoretical frontier and the observational frontier from the perspective of asymptotically safe quantum gravity and related approaches. I will highlight key open questions and potential pathways to answering them on the theory side. On the observational frontier I will present promising results on the interplay of quantum gravity with matter, including the visible as well as the dark sector of the universe. Google-Meet: https://meet.google.com/kwe-kpmi-krx

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Carlos Perez (IFT UW)

Computing the spectral action for fuzzy geometries

The attempt to path integral quantize noncommutative geometries leads to the concept of random noncommutative geometry. Feasibility, on the other hand, restricts our first attempts to the finite-dimensional arena of "fuzzy geometries" (certain finite-dimensional spectral triples we will properly introduce). The purpose of this talk is to show how random fuzzy geometries lead to random multi-matrices. The results are based on arXiv:1912.13288, which also builds on work by Barrett-Glaser (J.Phys A. 49, 2016, arXiv:1510.01377). The link to join the meeting is: https://meet.google.com/rjk-swmw-hga

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Michał Siłkowski (IFT UW)

Long-range asymptotics of exchange energy in the hydrogen molecule. Part II

Studies on exchange energy in molecular systems reach back to the early days of quantum mechanics. Its asymptotic form is known to be exponentially small for large internuclear distances. However, the prefactor and next-to-leading order term still raise controversy, even in the case of the simplest model of atom-atom interactions — the hydrogen molecule. I will summarize analytical approaches aiming to extract this asymptotics and conclude with our numerical calculations in explicitly correlated exponential basis, which resolve this controversy.
https://meet.google.com/jnt-qsco-qak?hs=122&authuser=0

join us at 14:15

Carlos Perez (IFT UW)

On random noncommutative geometry and the spectral action for fuzzy geometries

Physical systems, also classical ones, can be given an operator algebraic description: observables form a certain type of algebra (a C*-algebra) and states turn out to be given by positive linear functionals on it. I will use this argument, due to F. Strocchi, in order to physically motivate C*-algebras (which in mathematics are canonically introduced via Gelfand-Naimark theorem). These objects play a key role in Connes' spectral formalism of noncommutative geometry, which allows, among other things, for a derivationof the Standard Model lagrangian from simple data. The attempt to path integral quantize noncommutative geometries leads to the concept of random noncommutative geometry. Feasibility, on the other hand, restricts our first attempts to the finite-dimensional arena of "fuzzy geometries" (certain finite-dimensional spectral triples we will properly introduce). The purpose of this talk is to show how random fuzzy geometries are related to random multi-matrices. The results are based on arXiv:1912.13288, which also builds on work by Barrett-Glaser.
Link: https://meet.google.com/sha-kxag-sqx?hs=122

join us at 14:15

Miłosz Panfil (IFT UW)

[ON-LINE] Quantum Integrability in Condensed Matter

Quantum Integrable models play nowadays a prominent role in understanding strongly correlated low-dimensional quantum physics. The models that were once a mathematical curiosity, thanks to the advent in experimental methods, turned out to be actually useful. Their usefulness goes beyond direct modeling of physical phenomena. They also help us with understanding problems of fundamental nature, concept of thermalization being one prominent, and recently explored, example. In this talk, I will try to present the (inevitably biased) state of art on the interplay between quantum integrability and condensed matter.
meet.google.com/wvd-xsac-zms

room 1.40, Pasteura 5 at 14:15

Jan Kwapisz (IFT UW)

[ON-LINE] Asymptotyczne Bezpieczeństwo w Kwantowej Grawitacji i Fenomenologia Cząstek, Część II

[ON-LINE] Asymptotic Safety in Quantum Gravity and Phenomenology of Particles, Part II

Grawitacja Einsteina nie może być skwantowana przy użyciu standardowych technik kwantowej teorii pola. Stąd, aby opisać grawitację na poziomie kwantowym, można albo zaproponować nową, specjalną receptę kwantyzacji. Możliwe jest także, że ogólną teorię względności należy zastąpić inną teorią, którą można właściwie skwantyzować. Jeśli pierwsza opcja jest prawdziwa, to ogólna teoria względności powinna posiadać oddziałujący stały punkt UV (jako asymptotycznie bezpieczna teoria), w następstwie czego OTW staje się fundamentalną teorią pola kwantowego dla dowolnych skal.Link do seminarium on-line: meet.google.com/rdv-omxu-vuo

join us at 14:15

Jan Kwapisz (IFT UW)

[ON-LINE] Asymptotyczne Bezpieczeństwo w Kwantowej Grawitacji i Fenomenologia Cząstek

[ON-LINE] Asymptotic Safety in Quantum Gravity and Phenomenology of Particles

Grawitacja Einsteina nie może być skwantowana przy użyciu standardowych technik kwantowej teorii pola. Stąd, aby opisać grawitację na poziomie kwantowym, można albo zaproponować nową, specjalną receptę kwantyzacji. Możliwe jest także, że ogólną teorię względności należy zastąpić inną teorią, którą można właściwie skwantyzować. Jeśli pierwsza opcja jest prawdziwa, to ogólna teoria względności powinna posiadać oddziałujący stały punkt UV (jako asymptotycznie bezpieczna teoria), w następstwie czego OTW staje się fundamentalną teorią pola kwantowego dla dowolnych skal.
Link do seminarium on-line: https://zoom.us/j/305018884

room 1.40, Pasteura 5 at 14:15

Savely Karshenboim (Ludwig Maximilian University and Pulkovo Observatory)

[ODWOŁANE] Theory of the 1s Lamb shift in hydrogen

[CANCELLED] Theory of the 1s Lamb shift in hydrogen

I will speak about recent results on the two-loop and three-loop contributions to the Lamb shift in hydrogen. In particular, I will speak about a missing term in order $\alpha^2(Z\alpha)^6m\log(Z\alpha)$, about non-logarithmic contributions in the same order, and about the estimation of the three-loop term of order $\alpha^3(Z\alpha)^5m$. Together with a recent result of Laporta of order $\alpha^4(Z\alpha)^4m$ that makes evaluation of the all $\alpha^8m$ contributions complete.

room 1.40, Pasteura 5 at 14:15

Adam Latosiński (IFT UW)

The pinch technique for Feynman diagrams. Part II

In this seminar, I'm going to present the basic ideas and methods of the so-called Pinch Technique, devised by John M. Cornwall, Joannis Papavassiliou and Daniele Binosi to deal with the lack of gauge covariance of the off-shell Green's functions in non-abelian gauge theories.

room 1.40, Pasteura 5 at 14:15

Adam Latosiński (KMMF)

The pinch technique for Feynman diagrams. Part I

room 1.40, Pasteura 5 at 14:15

Krzysztof A. Meissner (IFT UW)

Electron pairs' sliding states in superconductivity

A new mechanism of electron pairs' transport connected to high-temperature superconductivity will be described on an example of LSCO superconducting crystal.

room 1.40, Pasteura 5 at 14:15

Paweł Sznajder (IFT UW)

Velocity fluctuations and plasma like screening in sedimenting suspension

In this short talk, I will present the problem of diverging expressions for velocity fluctuations in a stationary state of uniform sedimenting suspension. Those divergencies, as suggested by Koch and Shaqfeh, can be eliminated by plasma-like screening conditions for correlation functions. Unfortunately, BBGKY hierarchy for that system derived by Cichocki and Sadlej has problem to provide solutions that obey those conditions.

room 1.40, Pasteura 5 at 14:15

Michał Tomza (IFT UW)

Reaching the quantum regime of ultracold ion-atom collisions: theory guides experiment (part II)

room 1.40, Pasteura 5 at 14:15

Michał Dereziński (IFT UW)

Nieobciążony estymator dla regresji liniowej poprzez wyznacznikowy proces punktowy

Unbiased estimator for linear regression via a determinantal point process

Poszukiwanie nieobciążonych estymatorów dla regresji liniowej - gdzie chcemy dopasować funkcję liniową do danego zbioru pomiarów — to jedno z najstarszych zagadnień w statystyce. Klasyczne twierdzenie Gaussa-Markowa pokazuje że metoda najmniejszych kwadratów to optymalne rozwiązanie tego problemu, ale jedynie przy silnych założeniach dotyczących szumu pomiarowego. Czy jest możliwe zdefiniowanie nieobciążonego estymatora dla regresji liniowej w najogólniejszym modelu losowym bez założeń o rozkładzie szumu pomiarowego? Pokażę że jest to możliwe poprzez zastosowanie metody najmniejszych kwadratów do zbioru danych wzbogaconego o mały zestaw dodatkowych pomiarów wygenerowany przy użyciu pewnego wyznacznikowego procesu punktowego. Uzyskany w ten sposób estymator jest pierwszym użytecznym nieobciążonym estymatorem dla tego ogólnego modelu i jest on prosty do skonstruowania dla wielu praktycznych problemów. Jako przykład, zaprezentuję zastosowanie powyższych rezultatów do zagadnienia optymalnego doboru eksperymentów.

Finding unbiased estimators for linear regression — where we wish to fit a linear function to a set of noisy measurements — is one of the oldest tasks in statistics. The classical Gauss-Markov theorem shows that the least squares estimator is the optimal solution for this problem under a set of strong assumptions regarding the data and measurement noise. Is it possible to construct an unbiased estimator for general random design linear regression without any assumptions on the measurement noise? I will show that it is possible by applying the least squares estimator to the dataset augmented by a small sample of additional measurements, generated from a certain determinantal point process. The obtained estimator is the first useful unbiased estimator for random design regression, and it can be efficiently constructed in many practical settings. As an example, we will show how this technique can be utilized in the context of experimental design.

room 1.40, Pasteura 5 at 14:15

Mikołaj Misiak (IFT UW)

Effective Field Theories in R_xi gauges

In effective quantum field theories, higher-dimensional operators can affect the canonical normalization of kinetic terms at tree level. These contributions for scalars and gauge bosons should be carefully included in the gauge fixing procedure, in order to end up with a convenient set of Feynman rules. We develop such a setup for the linear R_xi-gauges. It involves a suitable reduction of the operator basis, a generalized gauge fixing term, and a corresponding ghost sector. Our approach extends previous results for the dimension-six Standard Model Effective Field Theory to a generic class of effective theories with operators of arbitrary dimension.

room 1.40, Pasteura 5 at 14:15

Jakub Jankowski (IFT UW)

Gauge/gravity duality: unification of ideas

I will review some aspects of the holographic principle and its consequences, focusing on its most famous incarnation, the AdS/CFT correspondence. This hypothesis has lead to many insights concerning the dynamics of strongly coupled Quantum Field Theory. I will review some of them, including the well known KSS bound as well as some results concerning hydrodynamization process in N=4 supersymmetric Yang-Mills theory.

room 1.40, Pasteura 5 at 14:15

prof. Witold Bardyszewski (IFT UW)

Topological phase transition in low dimensional structures

I will discuss the properties of topological insulators (TIs), existing in two-dimensional (2D) and three-dimensional (3D) material systems. In general, they are characterized by an energy gap in the bulk electronic band structure and the presence of metallic states on their surfaces or edges. Closing the bulk band gap by the surface or edge states is caused by the nontrivial topology of the bulk states, characterized by nonzero topological invariants. The examples will be narrowed to the recently discussed nitrites based quantum wells which display a behaviour surprisingly different from typical topological insulators.

room 1.40, Pasteura 5 at 14:15

Alexander Stottmeister (University of Münster)

Operator-algebraic construction of 1+1-dimensional gauge theory and Jones’ unitary actions of Thompson’s groups

I will present some recent joint work with A. Brothier on the construction of a 1+1-dimensional gauge theory by operator-algebraic methods. The construction aims at providing a continuum-limit field algebra starting from a lattice formulation. Furthermore, I will explain how the categorical construction of representations of Thompson’s groups by Jones leads to an automorphic action of said groups on an intermediate field algebra — the semi-continuum field algebra. Supplementing the latter with a state, one expects from a renormalization group perspective to arrive at a notion of continuum field algebra. I will discuss the type of this limit w.r.t. a natural class of states.

room 1.40, Pasteura 5 at 14:15

Michał Tomza (IFT UW)

Reaching the quantum regime of ultracold ion-atom collisions: theory guides experiment

Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics. Reaching the ultracold s-wave quantum regime is one of the most important challenges in this field at the moment. Unfortunately, the lowest attainable temperatures in experiments using the Paul ion trap are limited by the possible rf-field-induced heating related to the micromotion. In my seminar, I will present how in collaboration with experimental groups from Amsterdam and Stuttgart we have overcome this limitation and how electronic structure theory and exact nuclear dynamics simulations guided and explained experimental efforts.

room 1.40, Pasteura 5 at 14:15

Jakub Jankowski (IFT UW)

Physicist's view on resurgence

Perturbative expansions are ubiquitous in physics, often resulting inasymptotic series with zero radius of convergence. In order for theassociated observables to become nonperturbatively well-defined oneneeds to use theory of resurgence. In this seminar, I will give anincomers view on the theory of resurgence functions illustrating basicconcepts with simplest examples. Some applications in physics will beshortly reviewed.

room 1.40, Pasteura 5 at 14:15

Piotr Sułkowski2 (IFT UW)

Strings, knots, quivers, and hypergeometric functions, part II

I will present the relationship between a wide class of amplitudes in topological string theory and quiver representation theory. For a given string theory model, we find its dual description in terms of effective spacetime theory, or supersymmetric quantum mechanics, whose interactions are succinctly encoded in a quiver graph. This relation, in various more specific situations, leads to very interesting mathematical and physics statements. For example, for topological string configurations related to knots, the quiver point of view enables one to prove some old conjectures about knot invariants and leads to new knot invariants. On the other hand, we show that amplitudes in topological strings on toric Calabi-Yau manifolds without compact four-cycles, which take the form of q-hypergeometric functions, can be also encoded in some quiver. This leads to interesting new statements about hypergeometric functions and their q-analogs. In this talk, I will summarize these relations and discuss prospects for future work.

room 1.40, Pasteura 5 at 14:15

Piotr Sułkowski (IFT UW)

Strings, knots, quivers, and hypergeometric functions

I will present the relationship between a wide class of amplitudes intopological string theory and quiver representation theory. For agiven string theory model, we find its dual description in terms ofeffective spacetime theory, or supersymmetric quantum mechanics, whoseinteractions are succinctly encoded in a quiver graph. This relation,in various more specific situations, leads to very interestingmathematical and physics statements. For example, for topologicalstring configurations related to knots, the quiver point of viewenables to prove some old conjectures about knot invariants and leadsto new knot invariants. On the other hand, we show that amplitudes intopological strings on toric Calabi-Yau manifolds without compactfour-cycles, which take the form of q-hypergeometric functions, can bealso encoded in some quiver. This leads to interesting new statementsabout hypergeometric functions and their q-analogs. In this talk, Iwill summarize these relations and discuss prospects for future work.

room 1.40, Pasteura 5 at 14:15

prof. Witold Bardyszewski (IFT UW)

Topological phase transition in low dimensional structures

room 1.40, Pasteura 5 at 14:15

no seminar

Pierwsze z seminariów odbędzie się 11.10.

The seminar series will start 11.10.