Fall 2025

Seminars and Lectures

Introduction to Generalized and Non-invertible Symmetries

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.


The Kitaev Chain and Majorana Zero Modes

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.


Recent Results on Input-to-State Stability Framework for Time-Delay Systems

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.


Classical Double Copy

Abstract of Talk


Student Seminar: ODE/IM Correspondence in 2D CFT

Abstract of Talk


Taniyama-Schimura

Abstract of Talk


How I learned to stop worrying and love the Schwarzian

Abstract of Talk


Combinatorial Structures in a Dubrovin-Novikov Type

Abstract of Talk


Student Seminar: Blackhole, Superradiance and Instabilities

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.


C.N. Yang’ın anısına: 103 yıla sığdırdıkları…

Abstract of Talk


Computations with SageMath

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.


Lie Symmetries and Analytical Solutions in Differential Equations

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.


2-Dimensional N=(0,2) Dualities

Abstract of Talk

Fall 2024

Seminars, Workshop and Lectures

Generating Self-Similar Membrane Solutions

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.


Spins, Quantum Matter and Symmetry Breaking

Abstract of Talk


Modern Teorik Fizik Eğitimi: Kişisel Deneyimim

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.”


Gauge/YBE Correspondence

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.


Confinement and Monopoles, Part II

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.


Confinement and Monopoles, Part I

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.


Spectrum Generating Algebra for Landau Levels

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)


Brief Introduction to Quantum Black Holes

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.