Fall 2025
Seminars and Lectures
Jan. 3-4 2026
Introduction to Generalized and Non-invertible Symmetries
Mehmet Batu Bayındırlı | University of Minnesota
Feza Gürsey Seminar Room, North Campus, Bogazici University, 03-04.01.2026 / 18.00
Abstract of Talk
These lectures will provide a brief introduction to generalized symmetries, where, in the continuum, the ordinary symmetries are reexpressed as topological operators (or defects). This idea enables the notion of a non-invertible symmetry, where the algebra of symmetry defects corresponds to non-group structures. In the first lecture, we’ll introduce the basic definitions of generalized and higher-form symmetries and cover the 4D free Maxwell theory as an example. In the second lecture, we will go over the arguably simplest example of a non-invertible symmetry: the Kramers-Wannier duality defect in the transverse field Ising model.
Dec. 25 2025
The Kitaev Chain and Majorana Zero Modes
Mehmet Dede | Purdue University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 25.12.2025 / 18.00
Abstract of Talk
In this lecture, we introduce the Kitaev Majorana chain as a simple model of a one-dimensional topological superconductor. We derive its energy spectrum and show that the system has two distinct phases separated by a gap closing. For an open chain, we explain how Majorana zero modes appear at the ends and lead to a protected two-fold ground-state degeneracy. If time permits, we will talk about how this model relates to symmetry protected topological phases.
Dec. 18 2025
Recent Results on Input-to-State Stability Framework for Time-Delay Systems
Gökhan Göksu | Istanbul Technical University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 18.12.2025 / 18.00
Abstract of Talk
Input-to-state stability (ISS) is a concept introduced to analyze the stability of nonlinear dynamical systems under external inputs. ISS not only ensures that the system behaves stable in the absence of inputs, but also maintains this nominal behavior with deviations proportional to the input magnitude. From another perspective, small inputs lead to small steady-state errors for such systems. An important extension of ISS is the integral ISS (iISS), which relates the norm of the system trajectories to the energy of the input rather than the input amplitude. In this talk, we will first introduce the concepts and tools of ISS/iISS. We will then discuss recent developments related to these concepts in time-delay systems, emphasizing their differences from finite-dimensional systems. Next, we present new Lyapunov-Krasovskii conditions for Strong iISS, a stability concept that guarantees not only iISS but also ISS under inputs whose amplitudes are below a certain threshold. Finally, we discuss some open problems in this research area.
Nov. 27 2025
Classical Double Copy
Oğuzhan Kaşıkçı | Istanbul Technical University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 27.11.2025 / 18.00
Abstract of Talk
Nov. 21 2025
Student Seminar: ODE/IM Correspondence in 2D CFT
Şahin Çetin | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 21.11.2025 / 18.00
Abstract of Talk
Nov. 13 2025
Taniyama-Schimura
İlmar Gahramanov | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 13.11.2025 / 18.00
Abstract of Talk
Nov. 6 2025
How I learned to stop worrying and love the Schwarzian
İlmar Gahramanov | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 06.11.2025 / 18.00
Abstract of Talk
Oct. 30 2025
Combinatorial Structures in a Dubrovin-Novikov Type
İlmar Gahramanov | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 30.10.2025 / 18.00
Abstract of Talk
Oct. 24 2025
Student Seminar: Blackhole, Superradiance and Instabilities
Berkay Köktürk | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 24.10.2025 / 17.00
Abstract of Talk
This presentation explores black hole superradiance, where waves gain energy from a rotating black hole. We explain how rotation and dissipation lead to wave amplification, using the Teukolsky formalism to describe scalar and vector field behavior around Kerr black holes. Massive bosons can cause instabilities that form long-lived clouds or lead to “bosenova”-like collapses. These processes may produce observable signals such as continuous gravitational waves or missing regions in the black hole spin–mass diagram. Superradiance thus links black hole physics with searches for light particles like axions and dark photons.
Oct. 23 2025
C.N. Yang’ın anısına: 103 yıla sığdırdıkları…
İlmar Gahramanov | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 23.10.2025 / 18.00
Abstract of Talk
Oct. 16 2025
Computations with SageMath
Tolga Birkandan| İstanbul Technical University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 16.10.2025 / 18.00
Abstract of Talk
Exploring the use of the open-source symbolic computation package SageMath in general mathematical computation, general relativity calculations, and manipulation of differential forms.
Oct. 9 2025
Lie Symmetries and Analytical Solutions in Differential Equations
Cihangir Özemir| İstanbul Technical University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 9.10.2025 / 18.00
Abstract of Talk
An overview of Lie group analysis as a systematic method for studying the symmetries and exact solutions of differential equations. After outlining the general procedure for determining symmetry algebras, applications to several well-known equations including the Rosenau, Boussinesq, and nonlinear Schrödinger equations will be discussed, emphasizing the power of symmetry-based methods in mathematical physics.
Oct. 2 2025
2-Dimensional N=(0,2) Dualities
İlmar Gahramanov| Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 2.10.2025 / 18.00
Abstract of Talk
Fall 2024
Seminars, Workshop and Lectures
Oct. 21 2024
Generating Self-Similar Membrane Solutions
Jens Hoppe | Braunschweig University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 21.10.2024 / 16.00
Abstract of Talk
Several ways to reduce to a first order ODE to nonlinear PDE’s governing the relativistic motion of an axially symmetric membrane in 4 space-time dimensions, as well as examples for a previously found non-trivial transformation generating solutions, are given.
Oct. 18 2024
Spins, Quantum Matter and Symmetry Breaking
Ahmet Keles | Middle East Technical University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 18.10.2024/ 16.00
Abstract of Talk
Oct. 04 2024
Modern Teorik Fizik Eğitimi: Kişisel Deneyimim
Ilmar Gahramanov | Bogazici University
Feza Gürsey Seminar Room, North Campus, Bogazici University, 04.10.2024/ 16.00
Abstract of Talk
Neden Teorik Fizik: “İnsan karar vererek aşık olmaz, sadece bir bakar olmuş.” Landau-Lifshtiz: “Niçin çıktım, nasıl çıktım bunu izaha gerek yok.” Memlekette Eğitim: “Türkiye’de hiçbir başarı cezasız kalmaz.”
Sept. 12 2024
Gauge/YBE Correspondence
Masahita Yamazaki | Kavli, IPMU, University of Tokyo
Feza Gürsey Seminar Room, North Campus, Bogazici University, 12.09.2024/ 16.00
Abstract of Talk
The Gauge/YBE correspondence claims precise relations between super symmetric quiver gauge theories and integrable models, wherein statements on the one side is translated into those on the other. In this talk I will introduce the topic, starting with the basics of quantum field theories and integrable models.
July 25 2024
Confinement and Monopoles, Part II
Ege Çoban | University of Cambridge
Feza Gürsey Seminar Room, North Campus, Bogazici University, 25.07.2024/ 17.00
Abstract of Talk
Quantum Chromodynamics (QCD), a fundamental theory in particle physics, describes the strong nuclear interactions of quarks and gluons. A key feature of QCD is asymptotic freedom, where fundamental particles behave as free entities at high energies. Conversely, at low energies, particles are confined in bound states (protons, neutrons, etc.), which is sometimes referred as infrared slavery. Despite extensive study, the theoretical prediction of confinement in QCD remains elusive. However, confinement has been demonstrated in various toy models, including supersymmetric theories and QCD-like theories in non-flat spacetimes. We will focus on the Yang-Mills-Higgs model in three dimensions, where Polyakov first demonstrated confinement in 1977 through monopole condensation. We aim to understand Polyakov’s mechanism, beginning with foundational field theory concepts, path integral quantization, and approximation methods. We will then explore topological characteristics in field theory, introduce gauge theories, and present criteria for topological solutions. Later we will see the 3-dimensional SU(2) Yang-Mills-Higgs model in detail, and examine the impact of instantons on the low-energy theory. The modification of the low-energy theory due to a dilute gas of instantons will be illustrated, demonstrating the theory’s mass gap and effective potential.
July 23 2024
Confinement and Monopoles, Part I
Ege Çoban | University of Cambridge
Feza Gürsey Seminar Room, North Campus, Bogazici University, 23.07.2024/ 17.00
Abstract of Talk
Quantum Chromodynamics (QCD), a fundamental theory in particle physics, describes the strong nuclear interactions of quarks and gluons. A key feature of QCD is asymptotic freedom, where fundamental particles behave as free entities at high energies. Conversely, at low energies, particles are confined in bound states (protons, neutrons, etc.), which is sometimes referred as infrared slavery. Despite extensive study, the theoretical prediction of confinement in QCD remains elusive. However, confinement has been demonstrated in various toy models, including supersymmetric theories and QCD-like theories in non-flat spacetimes. We will focus on the Yang-Mills-Higgs model in three dimensions, where Polyakov first demonstrated confinement in 1977 through monopole condensation. We aim to understand Polyakov’s mechanism, beginning with foundational field theory concepts, path integral quantization, and approximation methods. We will then explore topological characteristics in field theory, introduce gauge theories, and present criteria for topological solutions. Later we will see the 3-dimensional SU(2) Yang-Mills-Higgs model in detail, and examine the impact of instantons on the low-energy theory. The modification of the low-energy theory due to a dilute gas of instantons will be illustrated, demonstrating the theory’s mass gap and effective potential.
July 19 2024
Spectrum Generating Algebra for Landau Levels
Todor Popov | American University, Bulgaria
Feza Gürsey Seminar Room, North Campus, Bogazici University, 19.07.2024/ 16.00
Abstract of Talk
The Landau problem and harmonic oscillator in the plane share a Hilbert space that carries the structure of Dirac’s remarkable so(2,3) representation. We show that the orthosymplectic algebra osp(1|4) is the spectrum-generating algebra for the Landau problem and, hence, for the 2D isotropic harmonic oscillator. This algebra generates a stack of Bargmann spaces in one-to-one correspondence with the Landau levels. The 2D harmonic oscillator is in duality with the 2D quantum Coulomb–Kepler systems, with the osp(1|4) symmetry broken down to the conformal symmetry so(2,3).The even so(2,3) submodule (coined Rac) generated from the ground state of zero angular momentum is identified with the Hilbert space of a 2D hydrogen atom. An odd element of the superalgebra osp(1|4) creates a pseudo-vacuum with intrinsic angular momentum 1/2 from the vacuum. The odd so(2,3)-submodule (coined Di) built upon the pseudo-vacuum is the Hilbert space of a magnetized 2D hydrogen atom: a quantum system of a dyon and an electron. Thus, the Hilbert space of the Landau problem is a direct sum of two massless unitary so(2,3) representations, namely, the Di and Rac singletons introduced by Flato and Fronsdal.
The talk is based on a recent work in collaboration with Prof. Tekin Dereli (Koç University) and my PhD student Philippe Nounahon (Institut de Mathématique et de Sciences Physiques, Porto-Novo, Bénin)
June 26 2024
Brief Introduction to Quantum Black Holes
Kirill Bazarov | MIPT
Feza Gürsey Seminar Room, North Campus, Bogazici University, 26.06.2024/ 11.00
Abstract of Talk
The goal of these lectures is to cover the main aspects of quantum effects on the black-hole back-
ground. I also tried to make the entry threshold as low as possible so that even junior students could
understand the material. In general, these lectures notes reproduce the lectures from outstanding
scientists, so please see the originals.