Prof. Yen Chin Ong (Nanjing University)

The literature is abounded with entropy functions that generalize Boltzmann-Gibbs, and in the context of black hole and cosmological horizons, they give rise to modifications of the Bekenstein-Hawking area law. This gives rise to subtleties concerning thermodynamic energy, which often is no longer equivalent to the ADM mass of the black hole. This talk will discuss how generalizing entropy may give rise to new theory of gravity in which the gravitational constant G is now area-dependent and in general, varying. Some supporting evidence for this proposal will be discussed, which include: (1) restoring the Bekenstein bound, which otherwise is grossly violated by entropy modification; (2) asymptotically safe gravity now tied to logarithmic correction of the Bekenstein-Hawking entropy; (3) GUP-like behavior for the Schwarzschild black hole without explicitly employing GUP – which may also suggest a strong connection between gravity, thermodynamics, and quantum mechanics; (4) possible theoretical basis for black hole-cosmology coupling.

Pablo A. Cano (University of Murcia)

The prediction of singularities is one of the most fundamental open problems of general relativity. While phenomenological models of singularity-free black holes have long been postulated in the literature, a dynamical theory supporting such geometries is often absent. Recently, this situation has changed thanks to the explicit construction of extensions of GR with infinite towers of higher-derivative corrections that can resolve black hole singularities in a fully dynamical way. I will review the main achievements and the status of this program and I will discuss some of the current challenges.

Oscar Varela (Utah State University)

The characterisation of the physics of the M5-brane remains an important open problem in string theory. While the superconformal field theory that resides on planar M5-brane in flat space is poorly understood, other configurations involving M5-brane wrapped on certain manifolds have well-known superconformal field theory descriptions, including class S field theories. In this talk, I will use new methods based on exceptional generalised geometry to describe the gravity duals of class S field theories, compute a universal sector of their light operator spectrum and provide, for the first time, a holographic match of their superconformal index.

Ľuboš Ravas

QFT proposes mathematical obstacles, such as a not very well-defined path integral. The Batalin–Vilkovisky formalism is a theory that aims to provide a solid mathematical grasp of QFT via geometry, homology, and homotopy. In my talk, I will provide some basics of this theory and demonstrate it on an example of su(2) forms valued in a non-specified Lie algebra. I will be using tools such as the Chevalley–Eilenberg complex, homotopy equivalence, and the homological perturbation lemma to find the classical interaction of fields in this specific example.

Nicoleta Voicu (Department of Mathematics and Computer Science, Transilvania University of Brasov, Romania)

Finsler is an extension of Riemannian one, based on a most general notion of arc length. In this talk, I will briefly review:Some key physical motivations for adopting a Finslerian model of spacetime, with emphasis on its potential to describe scenarios beyond the reach of Riemannian geometry.  The overlap between Finsler gravity and metric-affine gravity - and the way the two frameworks enrich each other. A specific Finsler gravitational model which, under cosmological symmetry, yields exponential expansion without requiring a cosmological constant or additional fields.

Davi Rodrigues

This is an introduction to symbolic tensor calculus for gravitational theories using Wolfram Language (WL) / Mathematica and the xAct. It is aimed at participants with a working knowledge of general relativity, and with some basic knowledge of Mathematica (like how to work with a notebook and function definition). The first part introduces essential WL concepts needed for tensor computations, including pattern matching, replacement rules, delayed definitions, and upvalues. The second part focuses on xAct, covering the definition of manifolds, tensors, connections, and curvature, and demonstrating workflows relevant for research in gravity. As core applications, we derive the Einstein field equations from the Einstein–Hilbert action and extend the method to quadratic curvature gravity. start time: 14:00, ONLINE: https://teams.microsoft.com/meet/37496037608184?p=ZBpPO5zZrtOGJw2AMr (join though browser)

Michele Arzano

Hopf-algebra deformations of spacetime symmetries, as they arise in models of non-commutative spacetimes, modify the very notion of how symmetries act on composite systems. I will discuss two complementary aspects of this structure, focusing on its implications for quantum dynamics and quantum information. In the first part, I show that deformed coproducts generically induce operator entanglement at the algebraic level. Using the quantum group U_q(su(2)) as a minimal and exactly solvable example, I demonstrate how a deformation that is invisible at the single-qubit level appears in the two-qubit sector through the non-cocommutativity of the coproduct. The resulting composite generators define intrinsically nonlocal unitaries whose entangling power can be computed in closed form and traced directly to their operator entanglement. This provides a concrete mechanism by which non-commutative symmetries enforce a baseline of entanglement independently of dynamics or interactions. In the second part, I critically examine claims that similar Hopf-algebra deformations of time-translation generators may lead to an intrinsic form of decoherence described by Lindblad-type evolution. By analyzing the definition of time evolution via generalized adjoint actions, I show that a consistent and physically viable formulation always leads to unitary von Neumann dynamics.

Davi Rodrigues (Universidade Federal do Espírito Santo, Vitória, Brazil)

This is an introduction to symbolic tensor calculus for gravitational theories using Wolfram Language (WL) / Mathematica and the xAct. It is aimed at participants with a working knowledge of general relativity, and with some basic knowledge of Mathematica (like how to work with a notebook and function definition). The first part introduces essential WL concepts needed for tensor computations, including pattern matching, replacement rules, delayed definitions, and upvalues. The second part focuses on xAct, covering the definition of manifolds, tensors, connections, and curvature, and demonstrating workflows relevant for research in gravity. As core applications, we derive the Einstein field equations from the Einstein–Hilbert action and extend the method to quadratic curvature gravity. The course emphasizes transparent, reproducible computations that can be adapted to general relativity and modified gravity models.

Josh O’Connor (U Mons)

Near a spacelike singularity, gravity behaves chaotically and its dynamics can be mapped to that of a particle bouncing around inside a Weyl chamber of a hyperbolic Kac-Moody algebra. We build on recent work by Perry to reformulate this in terms using twistor variables, where each geodesic between bounces is described by a constant twistor.

Tim Meier (Uniwersytet w Santiago de Compostela, Hiszpania)

Integralność w ramach korespondencji AdS/CFT stanowi potężne ramy do badania teorii pola kwantowego i ich dualnych AdS przy skończonym sprzężeniu, oferując idealne pole do testowania dualności i badania nieperturbacyjnych aspektów QFT. W ostatnich latach znaczna uwaga poświęcona całkowalnym deformacjom struny AdS5, szczególnie klasie jednorodnych odkształceń Yang–Baxtera, których dualy CFT są przypuszczalnie skrzywionymi wersjami N=4 SYM. Gdy te deformacje działają na sektorze AdS tła, generycznie prowadzą do powstania nieprzemiennych teorii pola. Jednak kluczowym wyzwaniem był brak systematycznej konstrukcji niezmienniczych teorii Yanga–Millsa niezmiennych względem cechowania dla odpowiednich skrętów. W tym wystąpieniu przedstawię nowe podejście, które rozwiązuje ten problem, oferując niezmienniczą formułę nieprzemiennej teorii Yanga–Millsa dla skrętów generowanych przez transformacje skalowe i Poincaré. Te ramy otwierają drzwi do badania dualnych CFT szerokiej klasy tła AdS zdeformowanych przez Yang–Baxtera i torują drogę do głębszych testów deformacji opartych na integrowalności w AdS/CFT.

Patryk Mieszkalski (IFT)

Rachunek różniczkowy to ważne i potężne narzędzie. Jest często wykorzystywany w fizyce. Pomimo że pierwszy krok (derwacji) został zdefiniowany już w 1978 roku przez Y. Doi, w literaturze fizycznej nie ma rozważanej struktury dualnej. Chciałbym wprowadzić rachunek różniczkowy pierwszego rzędu w kontekście geometrii nieprzemiennej jako potencjalne narzędzie do rozwiązywania problemów. Jako dowód koncepcji pokażę, jak uzyskać rachunek różniczkowy pierwszego rzędu na algebrze modułowej (czasoprzestrzeń kwantowa), który jest kowariantny względem algebry Hopfa (grupa kwantowa). Pokażę procedurę na przykładzie (D+1) kappa-Minkowskiego i (D+1) kappa-Poincaré. Wprowadzenie rachunku różniczkowego i całkowego wprowadza nowe sposoby opisu czasoprzestrzeni kwantowej, które chciałbym również pokazać.

Sofia Vidal (University of Tartu)

White dwarfs are the final evolutionary stage of stars with a mass lower than approximately ten solar masses, thus about 97% of the stars in the Milky Way, and in particular, our Sun. Even though their evolution is simple in comparison to other astrophysical objects, it involves several different physical processes under extreme conditions. Hence, they present a possibility to discover new phenomena and test current physical models, including gravity theories. In this talk I will give a brief introduction to scalar-tensor theory, followed by a discussion on white dwarf structure therein as well as differences to GR. The main part of the talk will focus on a toy model describing the cooling process that determines a white dwarf’s age. Finally, I will give an outlook on ongoing and possible future work.

Otto Kong (National Central University, Taiwan)

The subject of quantum reference frame transformations gets popular lately with some interesting new theoretical developments, partly for the reason that the physics involved is becoming experimentally accessible. The position of a position eigenstate when observed from an object with `uncertainty' in position would be seen with `uncertainty'. In fact, even the existence of entanglement is reference frame-dependent. We present an improved formulation of such a transformation and give a novel way to describe exactly by `how much' the `value of the position' has changed which fully encodes all information about the changes, including the 'uncertainty' and entanglement. That is an application of the notion of noncommutative values of physical quantities we introduced to understand the reality of quantum physics and beyond. For a particle system, we have a full picture of such a symmetry of Special Quantum Relativity, together with a noncommutative geometric picture of spacetime. Deep implications on fundamental physics and quantum information science will be discussed.

Łukasz Rudnicki (Uniwersytet Gdański)

I will present two preprints [arXiv:2503.17816] and [arXiv:2503.19415], devoted to a basic equation of the form u''(x) + h(x) u(x) = 0. I will start with a discussion about generality of this equation and then introduce a family of metrics on an upper half plane, defined in terms of the function h(x). The sectional curvature of all these metrics is equal to -1, thus, they locally describe the same hyperbolic geometry. As the main result I will present a general solution of the equation in question expressed in terms of geodesic curves in the proposed two dimensional hyperbolic model. I will also show that an arbitrary pair of linearly independent solutions gives a diffeomorphism between the introduced geometry and Poincare upper half plane. In the second part I will discuss an equivalent approach in which the Riemannian geometry is replaced by an analogous Lorentzian geometry. Interestingly, it turns out that solutions of the associated Ricatti equation are at the same time geodesics in this second model. In the last part I will resort to complex Riemannian geometry with a holomorphic metric, in which I generalize previous result to the complex case with a holomorphic function h(z). Interestingly, this last geometry is locally diffeomorphic to a complex sphere with imaginary radius.

Zbigniew Haba

I shall discuss a change of variables in the functional integral in quantum field theory. I show that by means of a change of variables it is possible to derive a ground state. First, in simple models I check this option in the Hamiltonian framework. Then, I shall discuss gauge theories and gauge theories of gravity (McDowell-Mansouri). I show that an exponential of the Chern-Simons functional is the ground state. I suggest that this may also be a solution of the Wheeler-de Witt equation.

Jerzy Kowalski-Glikman

In my talk, I will begin by introducing the Universal Corner Algebra (UCA), a universal algebra of symmetries associated with corners (the boundaries of regions), within the context of classical General Relativity (GR). I will then argue that the UCA should play a role in Quantum Gravity similar to the role the Poincaré algebra plays in quantum field theory. Moving on to a two-dimensional example, I will explain how the UCA acquires a central extension in quantum theory and explore how the resulting representation theory of Quantum Corner Algebra (QCA) can be used to combine two regions into one. Additionally, I will demonstrate how these representations can be applied to compute the entanglement entropy of two regions and speculate on how this might be used to reconstruct the semiclassical spacetime. Finally, if time permits, I will briefly discuss the structure of QCA in 3 dimensions.

Anna Horvath (HUN-REN Wigner Research Centre for Physics + Eötvös Loránd University, Budapest, Hungary)

Kaluza and Klein proposed a theory with a compactified extra dimension, which may appear in high-energy phenomena, such as nuclear reactions, strong gravitational effects, or in the presence of superdense matter. In this work, I show how astrophysical observables will be modified in the presence of extra compactified dimensions.
The interior of a compact star is modelled as a multidimensional interacting degenerate Fermi gas, embedded in a static, spherically symmetric spacetime with extra compactified spatial dimensions. The equation of state of this extreme medium is given and compared to the standard models of superdense matter. The modification of the mass-radius relation of compact stars is calculated and compared to realistic star models and astrophysical observation data. The interaction strength has been determined for this extraordinary matter. Constraints on the size of the extra dimension have been estimated based on pulsar measurements [1,2]. Strong gravitational effects may modify the phase space, thus the thermodynamics in high-energy astrophysical regimes. The generalized uncertainty principle and possible observational consequences were studied [3].

[1] A. Horváth, E. Forgács-Dajka, G.G. Barnaföldi: "Application of Kaluza-Klein Theory in Modeling Compact Stars: Exploring Extra Dimensions", MNRAS, https://doi.org/10.1093/mnras/stae2637
[2] A. Horváth, E. Forgács-Dajka, G.G. Barnaföldi: "The effect of multiple extra dimensions on the maximal mass of compact stars in Kaluza-Klein space-time", Accepted to International Journal of Modern Physics A, https://doi.org/10.1142/S0217751X25420047
[3] A. Horváth, A. Wojnar, G.G. Barnaföldi: "Uncertainty relation of a massive particle in Kaluza-Klein theory", in preparation

Anne Spiering (Humboldt University Berlin)

The pentabox and double-pentagon Feynman integrals, together with the double box, take on a central role in planar N=4 SYM theory as they form a basis for two-loop scattering in this theory. Their direct integration is challenging due to the presence of several elliptic curves. After a brief review of the one-loop case, I will present recent progress on the two-loop integrals, discussing their relation to higher-dimensional one-loop integrals and their symbol structure.

Maciej Kowalczyk

Recent observations of the cosmic microwave background evidence a notable discrepancy between the inflationary scale and the Planck scale predicted by conventional inflationary models, particularly those based on simple chaotic inflation frameworks. In this talk, I will present a proposed resolution to this conflict by introducing a slight modification to the standard general relativity framework, which naturally incorporates a cutoff scale consistent with the observations. This last scale of power suppression appears by the combined effect of the preinflationary background dynamics and an associated initial vacuum state for the cosmological perturbations which differs from the conventional Bunch-Davies state of slow-roll inflation. By choosing a vacuum based on an asymptotic diagonalization of the Hamiltonian of the perturbations, leading to a non-oscillatory primordial power spectrum, we will analytically investigate the model. I will conclude with a detailed study of several physically interesting cases.

Sylvain Lacroix (ETH Zurich)

Sigma-models are two-dimensional field theories which find applications in various domains of physics, such as string theory, holography and condensed matter. A particularly remarkable subclass of these models are the integrable ones, which possess an infinite number of symmetries / conserved charges, allowing for the derivation of exact results. Although this property is well-understood at the classical level, one of the main open challenge in the field is to prove the quantum integrability of these models by first principles, i.e. the explicit construction and the exact diagonalisation of an infinite number of commuting conserved operators at the quantum level. One of the possible approach to simplify this question is to start with the quantum integrability of the UV fixed point of these models, for which we can make use of the algebraic formalism of two-dimensional conformal field theories. In this talk I will report on work in progress with A. Molines on the application of this program to the Wess-Zumino-Novikov-Witten model and in particular on the construction of higher-spin commuting local charges in this conformal theory.

Axel Kleinschmidt, Max Planck institute for gravitational physics (Albert Einstein institute), Potsdam

Gravity-matter systems with non-abelian gauge symmetry can be constructed using the language of exceptional geometry and exceptional field theory. I will first review some general aspects of this construction and then focus on the case of two-dimensional gravity where one can construct generalizations of Jackiw-Teitelboim gravity, in particular theories that are expected to be dual holographically to the M-theory matrix model.

Glenn Barnich, Université Libre de Bruxelles

A brief review of symmetries and conservation laws in full and linearized general relativity, is followed by a general discussion of asymptotic symmetries and the properties of the associated surface charges. Selected applications in lower dimensional gravity models and in asymptotically flat general relativity at null infinity are presented.

Domenico Frattulillo, Federico II University in Naples

Quantum gravity is expected to introduce quantum aspects into the description of reference frames. Here we set the stage for exploring how quantum gravity induced deformations of classical symmetries could modify the transformation laws among reference frames in an effective regime. We invoke the quantum group SUq(2) as a description of deformed spatial rotations and interpret states of a representation of its algebra as describing the relative orientation between two reference frames. This leads to a quantization of one of the Euler angles and to the new paradigm of agency dependence: space is reconstructed as a collection of fuzzy points, exclusive to each agent, which depends on their choice of reference frame. Each agent can choose only one direction in which points can be sharp, while points in all other directions become fuzzy in a way that depends on this choice. Two agents making different choices will thus observe the same points with different degrees of fuzziness.

Michele Arzano, University of Naples

The generators of radial conformal symmetries in Minkowski space-time can be put in correspondence with generators of time evolution in conformal quantum mechanics. Within this correspondence I show that in conformal quantum mechanics the state corresponding to the inertial vacuum for a conformally invariant field in Minkowski spacetime has the structure of a thermofield double. The latter is built from a bipartite "vacuum state” corresponding to the ground state of the generators of hyperbolic time evolution. These can evolve states only within a portion of the time domain. When such generators correspond to conformal Killing vectors mapping a causal diamond in itself and generators of dilations, the temperature of the thermofield double reproduces, respectively, the diamond temperature and the Milne temperature found for massless fields in Minkowski spacetime. We calculate the entanglement entropy associated to the thermofield double states and obtain a UV divergent logarithmic behaviour analogous to known results in two-dimensional conformal field theory in which the entangling boundary is point-like.

Presentation (pdf)

Riccardo Borsato, University of Santiago de Compostela, Galician Institute of High Energy Physics

Recently, there has been a lot of progress in the construction of deformations of 2-dimensional integrable field theories that do not break the original integrity. Often, the motivation is related to the realization of such integrable models in the context of the holographic duality, thus opening the possibility to obtain exact results for gauge and gravity theories and their deformations. At the same time, the study of such deformations has led to some puzzles that force us to better understand already the undeformed models. In particular, in this talk I will explain why it is important to carefully choose the light-cone gauge (necessary to fix the reparametrisation invariance on the worldsheet of the string) in order to have a workable description of the deformed models, and I will show how inequivalent light-cone gauges are related to each other.

Linus Wulff, Mastaryk University, Brno

As a quantum theory of gravity, string theory predicts specific corrections to Einstein's theory. These corrections are in general difficult to compute. I will describe an approach that uses another characteristic feature of string theory - the existence of dualities - to constrain the form these corrections can take.

Sibylle Driezen (ETH Zurich)

Recent years have seen an upsurge of interest in deformations of two-dimensional sigma-models which preserve classical integrability when present in the original model. This property enables powerful techniques for solving these models, even in non-trivial scenarios such as at strong coupling. This talk introduces classical integrability concepts and reviews the construction of a large family of integrable deformed sigma-models. We will focus on the crucial role played by “worldsheet dualities”, which have been naturally developed within the context of string theory. In the second part of the talk, we will explore the interest of applying integrable deformations on the so-called AdS/CFT correspondence, a duality connecting highly symmetrical string theories to gauge theories. Specifically, we will focus on the “Jordanian” subclass of integrable deformations and provide insights into ongoing research in this area.

Aleksander Kozak

In my talk, I will summarize the research I conducted as a Ph.D. student at the Institute of Theoretical Physics. I will focus on the issue of conformal frames in modified gravity theories. Modified theories of gravity (or extended theories of gravity) introduce ambiguity in the description of gravitational phenomena related to the fact that there exists a multitude of conformal frames yielding - possibly - inequivalent predictions. In the literature, the most common frames are the Einstein and Jordan frames, and the issue of which one is correct remains a topic of debate. However, it was shown recently that it would be possible to construct a conformally-invariant framework for metric scalar-tensor (ST) theories of gravity. I will demonstrate that it is possible to extend the framework of conformal invariants to the case of Palatini ST theories of gravity. The connections between different versions of ST theories will also be explored. Some remarks on choosing the ‘right’ conformal frame will also be made. In the second part of my talk, I will move on to discussing applications of the invariant framework. It will be demonstrated that, in the minisuperspace formalism applied to the cosmological scenarios, the lapse function can be treated as a conformal factor, which will enable us to simplify the considerations and find integrals of motion for different theories. We will also revisit the connections between f(R) theories in different approaches and their ST representations. In the end, the conformally-invariant Tolman-Oppenheimer-Volkoff equation will be discussed.

Yuri Shtanov, Bogolyubov Institute for Theoretical Physics, Kiev, Ukraine

We discuss several facets of the metric f(R) gravity theory coupled to the Standard Model. The theory contains an extra scalar degree of freedom (the scalaron), which can be employed in several interesting ways. Firstly, if the scalaron is very heavy, it can play the role of an inflaton. In this case, a typical f(R) theory is equivalent to scalar-field models with hilltop or tabletop potentials in the Einstein frame. Inflationary evolution in such models can proceed in two alternative directions: towards the stable point at small scalar curvature describing the observable universe, or towards the asymptotic region at large scalar curvature. A universe evolving towards this asymptotically free gravity region will either run into a "Big-Rip" singularity or inflate eternally. Secondly, the scalaron in metric f(R) gravity can be a dark-matter candidate if its mass lies in the range between around 4 meV and 1.2 MeV. The scalaron manifests itself as an almost sterile cold dark matter, and one of its possible observational verifications consists in measuring specific Yukawa gravitational forces on submillimeter spatial scales. We will discuss initial conditions for the scalaron in the early universe and the role played by the Higgs field and electroweak crossover in the formation of these initial conditions. Thirdly, the scalaron in scale-invariant R^2 gravity theory can play the role of a massless dilaton breaking the scale (and electroweak) symmetry and generating the mass scale in quantum field theory. We briefly discuss this model and its fine-tuning.

MS Teams meeting

Prof. Richard Kerner, Sorbonne University, Paris

The Lagrangian of the Kaluza-Klein theory, in its simplest five-dimensional version, should include not only the scalar curvature R, but also the quadratic Gauss-Bonnet invariant. The general Lagrangian is computed and the resulting non-linear equations which generalize Maxwell's system in a quite unique way are investigated. The possibility of the existence of static solutions is presented, and the qualitative behaviour of such solutions is discussed.

Presentation (pdf)

Jorge Ovalle (Silesian University in Opava)

Although we cannot understand the true nature of singularities in the framework of GR, it is possible to evade them by following a fairly simple strategy: generate regular BHs by filling the spacetime around the central singularity with some physically reasonable source of matter (which could be consequence of some new gravitational sector). This has produced a plethora of new regular BH solutions in recent years, mainly because the matter source used to evade the central singularity can be interpreted in terms of nonlinear electrodynamics. However, all these regular BH solutions contain a Cauchy horizon, a null hyper-surface beyond which predictability breaks down, and also leads to mass inflation at the perturbative level, a pathology which occurs even in loop quantum gravity inspired models. Even though the strong cosmic censorship conjecture establish the impossibility of extending spacetime beyond this region, in this talk we show how far we can go, without invoking this conjecture, in the building of a physically reasonable black hole without a Cauchy hyper-surface. Following this reasoning, we find a black hole lacking of Cauchy horizon, asymptotically flat and satisfying either the strong or dominant energy condition. The above is possible by demanding integrable singularity for the Ricci scalar, whose direct consequence is the appearance of finite tidal forces.

Jerzy Kowalski-Glikman

In the talk, I will present a new understanding of the cosmological constant problem, built upon the realization that the vacuum energy density can be expressed in terms of a phase space volume. To this end, a UV-IR regularization is introduced, which implies a relationship between the vacuum energy and entropy. Combining this insight with the holographic bound on entropy then yields a bound on the cosmological constant consistent with observations. It follows that the universe is large, and the cosmological constant is naturally small, because the universe is filled with a large number of degrees of freedom.

Amir Khan, Max Planck Institute, Heidelberg, Germany

In this talk, I will give an overview of the general neutrino interactions, namely, vector (V), axial-vector (A), scalar (S), pseudoscalar (P), and tensor interactions (T) and their origins. I will discuss the phenomenology of the general neutrino interactions and their importance in the neutrino oscillation and absolute mass experiments, direct detection dark matter experiments and some early universe measurements. I will report recent experimental limits from different experiments. I will also briefly discuss connections between the general neutrino interactions with some simplified models.

Teams link
Zoom link part 1
Zoom link part 2

Michele Arzano

The generators of radial conformal symmetries in Minkowski space-time can be put in correspondence with the generators of time evolution in conformal quantum mechanics. Within this correspondence I show that in conformal quantum mechanics the state corresponding to the inertial vacuum for a conformally invariant field in Minkowski spacetime has the structure of a thermofield double. The latter is built from a bipartite "vacuum state” corresponding to the ground state of the generators of hyperbolic time evolution. These can evolve states only within a portion of the time domain. When such generators correspond to conformal Killing vectors mapping a causal diamond in itself and generators of dilations, the temperature of the thermofield double reproduces, respectively, the diamond temperature and the Milne temperature. This result indicates that, for conformally invariant fields, the fundamental ingredient at the basis vacuum thermal effects in flat-space time is the non-eternal nature of the lifetime of observers rather than their acceleration.

dr David Osten

Typical two dimensional integrable sigma models are those which have group manifolds or Riemannian symmetric spaces, or in other words homogeneous spaces with a Z(2)-grading, as target spaces. This construction can be generalised to homogeneous spaces based on a Z(N)-grading. After a review of these sigma models and their classical integrability, I present new types of sigma models with Z(N)-symmetric homogeneous target spaces and some of their deformations. I comment on the geometric interpretation of the Z(N)-symmetry, the applicability as string sigma models and Hamiltonian integrability

Dr. Amir Khan, Max Planck Institute, Heidelberg, Germany

In this talk, I will give an overview of the general neutrino interactions, namely, vector (V), axial-vector (A), scalar (S), pseudoscalar (P), and tensor interactions (T) and their origins. I will discuss the phenomenology of the general neutrino interactions and their importance in the neutrino oscillation and absolute mass experiments, direct detection dark matter experiments and some early universe measurements. I will report recent experimental limits from different experiments. I will also briefly discuss connections between the general neutrino interactions with some simplified models.

link to the meeting

Michał Bobula

I derive a new model of black-to-white hole transition - the classical Oppenheimer-Snyder dust ball interior is modified with Loop Quantum Cosmology dynamics. I consider the rainbow metric approach for both pure dust ball collapse and the similar scenario accounting for scalar field perturbations. The collapsing matter bounces and reemerges in a new universe. Exterior geometry is extracted as well as the global causal structure of the process. I study entanglement entropy production to verify whether the black hole information paradox exists within the model.

Eric Lescano, Ruđer Bošković Institut (Zagreb, Croatia)

This talk will be about cosmology and string theory and it will have two parts. In the first one we will review the inclusion of statistical matter in Riemannian geometries. Our starting point will be the Einstein equation and we will focus on energy-momentum tensors that depend on hydrodynamics/thermodynamics variables, such as the perfect fluid. We will derive conservation laws considering relativistic kinetic theory. We will finish this part with a quick introduction to the low energy limit of string theory (supergravity) and its Double Field Theory (DFT) rewriting. In the second part of the talk we will include statistical matter in DFT (based on 2003.09588), we will construct the energy-momentum tensor for the perfect fluid in the double geometry (based on 2111.03682) and finally we will discuss about the relation between string cosmologies, DFT cosmologies and alpha'-corrections (based on 2207.04041).

Prof. Khalil Idiab, Humboldt University, Berlin

Symmetric space sigma models (SSSM) and their Yang-Baxter deformations are integrable, which makes them useful in providing exact results in the AdS/CFT correspondence. Much is known about these integrable models at classical level, but difficulties with quantization makes it hard to make general statements about their quantum integrable structure. By considering deformations of the flat space sigma model, with non semi-simple Poincaré symmetry, it turns out one can find deformed models that can be canonically quantized (plane waves), enabling future investigation of their quantum structure. As a first step, this requires extending Yang-Baxter deformations of SSSMs to cases with non semi-simple symmetry groups, this will be the main objective of the talk.

mgr Arkadiusz Bochniak, prof. Andrzej Sitarz (joint talk) (UJ)

We'll briefly review the concept of applying the construction of Connes' spectral triples to the Standard Model and gravity which goes beyond the commonly assumed product of two spectral triples. The application to the SM allows having no fermion doubling, explains naturally CP violation and no strong symmetry breaking while the gravity part leads to interesting models similar to bimetric modifications of gravity.

Prof. Richard Kerner, Sorbonne, Paris

Our aim is to derive the symmetries of the space-time, i.e. the Lorentz transformations, from symmetries of the interactions between the most fundamental constituents of matter, in particular quarks and leptons. We show how the discrete symmetries Z_2 and Z_3 combined with the superposition principle result in the SL(2, C) and SU(3) symmetries. The role of Pauli's exclusion principle in the derivation of the SL(2, C) symmetry is put forward as the source of the macroscopically observed Lorentz symmetry. Then Pauli's principle is generalized for the case of the Z_3 grading replacing the usual Z_2 grading, leading to ternary commutation relations. We present the cubic and ternary algebras which are a direct generalization of fermionic algebras with Z_3-grading replacing the usual Z_2-grading. Elementary properties and structures of such algebras are discussed, with special interest in the low-dimensional ones, with two generators only. Invariant cubic forms on Z_3-graded algebra with two generators are introduced, a possible description of the isospin. It is shown how a Z_3-graded generalization of the SL(2,C) group arises naturally as the symmetry group preserving the Z_3-graded ternary isospin algebra. Vectorial and spinorial representations of the generalized Z_3-graded. Lorentz algebra are briefly discussed.

mgr Aleksander Kozak

A class of scalar-tensor theories that unify metric, Palatini and hybrid metric-Palatini gravitational actions with nonminimal interaction is investigated from the point of view of their consistency with generalized conformal transformations. It is known that such theory can be represented on shell by a purely metric scalar-tensor theory. This extends the formalism previously introduced in our last paper [1]. Exploiting properties of the Legendre transformation, we relate some viable inflationary potentials with F(R)-gravitational Lagrangians by solving corresponding Clairaut's equation. Then for given potential function various gravitational scenarios are discussed within a metric, Palatini, as well as a hybrid metric-Palatini formulations. [1] A. Kozak and A. Borowiec, "Palatini frames in scalar-tensor theories of gravity", Eur.Phys.J. C79 (2019) no.4, 335

prof. Michele Arzano

I will show how the characteristic thermal effects that observers experience in space-times possessing an event horizon, emerge already in a simple quantum system with affine symmetry living on the real line. The derivation I will present is essentially group theoretic in nature: a thermal state emerges naturally when comparing different representations of the group of affine transformations of the real line. The freedom in the choice of different notions of translation generators is the key to the Unruh effect on the real line which I will describe.

dr Anna Pachoł, Queen Mary University of London

Noncommutative geometry, as the generalised notion of geometry, allows us to model the quantum gravity effects in an effective description without full knowledge of quantum gravity itself. On a curved space one must use the methods of Riemannian geometry - but in their quantum version, including quantum differentials, quantum metrics and quantum connections. The brief introduction to the general framework involving noncommutative differential graded algebra and construction of quantum Riemannian geometry elements will be provided. This framework has been applied to classification of all possible noncommutative Riemannian geometries in small dimensions (including finding explicit forms for quantum Levi-Civita connections and Riemann, Ricci and Einstein tensors), working over the field F_2 of 2 elements and with coordinate algebras up to dimension n<=3. We have found a rich moduli of examples for n=3 and top form degree 2 (providing a landscape of all reasonable up to 2D quantum geometries), including many which are not flat. Their coordinate algebras are commutative but their differentials are not. The choice of the finite field in this framework proposes a new kind of 'discretisation scheme', which we called the 'digital geometry'.

prof. L. Dąbrowski, SISSA, Trieste, Italy

By functions on a noncommutative (or `quantum') space one usually means a suitable algebra of operators. Then the smooth and metric structures can be described in terms of a spectral triple which involves an analogue of the Dirac operator. The Standard Model of fundamental particles in physics can be understood as the almost commutative geometry, the exterior part of which is the canonical spectral triple on a spin manifold and the finite inner part a quantum analogue of the de-Rham-Hodge spectral triple.

prof. Zbigniew Haba

Einstein equations with a conformally flat metric and ideal fluid source are discussed. It is shown that these equations have plane wave solutions. Scalar fields, electromagnetic plane waves and relativistic particles can be considered as the source of such an energy-momentum.

Josua Unger

In this talk I will discuss the BMS analysis of asymptotically flat spacetime, their algebraic properties and important consequences for black hole physics. The deformation by twisting of the BMS (Hopf-)algebra is presented and motivated in the context of the information loss paradox.

prof. Jerzy Kowalski-Glikman

In my talk I will present the construction of gravity Lagrangian as a sum of the topological term, the BF theory with (anti-) de Sitter gauge group and a 'constraint' term, explicitly breaking the symmetry down to local Lorentz symmetry. I will then comment on several properties of such defined theory: perturbative expansion around topological vacuum, particle(s) coupling, canonical analysis, and calculation of black hole entropy.

dr Remigiusz Durka

I offer new approach to the subject of Taub-NUT space-time supposedly possessing gravitational analog of the magnetic monopole. Starting from realizing that the source of many inconsistencies lies in neglecting the effects of the wire singularities present in that solution, I am able to explain existence of the NUT parameter by the means of quite peculiar rotation. Among many things, this leads to the consistent description of the black hole thermodynamics for the Lorentzian Taub-NUT spacetime with the essential contribution to the angular momentum and the total entropy.

prof. Jerzy Lukierski

Our next group seminar on May 21st is going to be devoted to the celebration of prof. Jerzy Lukierski birthday. We are offering short speeches, a bit of wine, some sweets, and a good deal of friendly chats. Everybody is cordially invited.

mgr Lennart Brocki

In this talk I present a recent publication by Henneaux and Troessaert in which they propose new boundary conditions for asymptotically flat spacetimes at spatial infinity and find that the conserved charges close according to the BMS algebra. Their analysis relies on the Hamiltonian formalism of general relativity and is an extension of the work done by Regge and Teitelboim in 1974, which will therefore also be summarized, and mainly differs in the choice of parity conditions. For a more complete understanding the talk will also cover some basics about the BMS Group.

mgr Lennart Brocki

In this talk I present a recent publication by Henneaux and Troessaert in which they propose new boundary conditions for asymptotically flat spacetimes at spatial infinity and find that the conserved charges close according to the BMS algebra. Their analysis relies on the Hamiltonian formalism of general relativity and is an extension of the work done by Regge and Teitelboim in 1974, which will therefore also be summarized, and mainly differs in the choice of parity conditions. For a more complete understanding the talk will also cover some basics about the BMS Group.

mgr Aleksander Kozak

Conformal transformations play an important role in the scalar-tensor theories of gravity, as they allow one to carry out calculations in a more convenient frame, simplifying the field equations. In the Palatini approach, however, the metric structure of space-time is decoupled from its affine structure, so that a transformation of the metric does not entail a corresponding change in the connection. One needs to define independent transformation for the connection, reducing to the standard formula in case the connection is Levi-Civita with respect to the metric. In my presentation, I shall introduce a scalar-tensor theory taking into account such transformation and discuss properties of the solution to the field equation for the connection. I will also introduce invariant quantities, whose functional form remains the same in every conformal frame, and show how they can be applied to analysis of possible equivalence between F(R) and scalar-tensor theories of gravity in the Palatini approach. The main part of the talk will be preceded by a short introduction to metric scalar-tensor theories and conformal transformations.

dr Tomasz Pawłowski

dr Jakub Bilski

During the seminar I will briefly introduce my idea of a canonical quantization under restrictions of general relativity. First I will show how a proper choice of canonical variables leads to the manifestly diffeomorphism invariant description of a quantum field. Next I will present a list of assumptions and simplifications that I will use in direct calculations. Then I will sketch the main steps in the derivation of quantum corrections coming from the gravitational degrees of freedom on the example of the scalar field. Discussing phenomenological applications of my result, I will consider possibilities of proving the assumptions and generalizing the simplifications from the first part of my talk.

Prof. Evgeny Ivanov

A model of the SU(2|1) supersymmetric quantum mechanics with additional semi-dynamical spin degrees of freedom is studid. The energy spectrum and the full set of physical states are found as functions of the deformation parameter m and SU(2) spin q. The states at the fixed energy levels form irreducible multiplets of the supergroup SU(2|1). The hidden superconformal symmetry OSp(4|2) of the model is revealed and shown to play a role of the spectrum-generating algebra. Some further generalizations are sketched. Based on arXiv:1710.02130 [hep-th] (in collaboration with Sergey Fedoruk and Stepan Sidorov).

Remigiusz Durka

The subject of the talk will concern a recent work of D. Palumbo https://arxiv.org/abs/1610.04734. It introduces interesting model of three dimensional topological insulators in the presence of the electromagnetic field, which results from the Chern-Simons theory with the gauge connection that takes values in the Maxwell algebra. The final action written in terms of the dreibein, spin connection and electromagnetic gauge potential leads to a description of the Hall conductance, the torsional Hall viscosity, and novel non-minimal coupling between the abelian gauge field and curved background, which resemble the relativistic version of the Wen-Zee term.

Prof. David Blaschke (Rostock University)

We show that within a recently developed nonlocal chiral quark model the critical density for a phase transition to color superconducting quark matter under neutron star conditions can be low enough for these phases to occur in compact star configurations with masses below 1.3M_sun. We study the cooling of these objects in isolation for different values of the gravitational mass and argue that, if the quark matter phase would allow unpaired quarks, the corresponding hybrid stars would cool too fast. The comparison with observational data puts tight constraints on possible color superconductiong quark matter phases. Possible candidates with diquark gaps of the order 10keV - 1MeV such as the "2SC+X" and the color spin locking (CSL) phase are presented.

mgr Artur Pietrykowski

Powszechnie wiadomo, iż kwantowa Ogólna Teoria Względności jest teorią perturbacyjnie nierenormalizowalną. Uwzględnienie pól materii w procesie kwantyzacji nie zmienia tego rezultatu. Nadto wykazano brak istnienia poprawek grawitacyjnych do stałych sprzężenia w teoriach z cechowaniem na poziomie jednopętlowym. Niemniej podejście do grawitacji Einsteinowskiej jako do niskoenergetycznej teorii efektywnej pozwoliło odkryć, iż jest ona teorią nieperturbacyjnie renormalizowalną. Ów kontekst motywuje ponowne rozpatrzenie wpływu fluktuacji grawitacyjnych na stałe sprzężenia w teoriach z cechowaniem, którym to zagadnieniem zajęli się P.S. Robinson i F. Wilczek. Wyniki ich badań wskazują na obeceność takich poprawek, których uwzględnienie w konsekwencji prowadzi do obniżenia skali unifikacji oddziaływań oraz do asymptotycznej swobody dla stałych sprzężenia. Jednakże istnienie poprawek, jak wynika z rachunków przeprowadzonych przez prelegenta, okazuje się być zależne od wyboru cechowania. Omówienie zarysowanych zagadnień stanowić będzie treść wystąpienia.

prof. Piotr Małecki IFJ w Krakowie

Prof. Bernd Schroers

In 2+1 dimensions Eintein's theory of gravity can be formulated as a gauge group with the Poincare group as the gauge group. In my talk I will explain how to introduce point particles and how to model universes with boundaries in the Chern-Simons formulation. I will also sketch how the (finite dimensional) phase space of the theory can be parametrised and how its symplectic structure can be computed. I will end with remarks about the quantisation of the theory, in particular the role played by quantum groups.

dr Cezary Juszczak

We Wrocławskiej grupie neutrinowej powstaje od kilku lat generator oddziaływań neutrin z jądrami atomowymi. Omówię jego obecny status, zadania na najbliższą przyszłość - w szczególności projekt implementacji kaskady jądrowej, oraz porównam z konkurencyjnymi generatorami.

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Katarzyna Imiłkowska

W referacie zostaną przedstawione główne postulaty teorii z dwoma niezależnymi od obserwatora skalami. Podane zostaną najważniejsze motywacje doświadczalne i teoretyczne skłaniające do zajmowania się taką teorią, m.in. zostanie omówiony paradoks GZK oraz przedstawiona zostanie kontrakcja grupy SO_q(3,1) w granicy płaskiej czasoprzestrzeni.

prof. Jakub Rembieliński

Referat dotyczy opisu zmodyfikowanego doświadczenia Einsteina-Podolskiego-Rosena-Bohma (korelacje dziwności zamiast korelacji spinu). Do liczenia korelacji itp. wykorzystuję opis cząstek niestabilnych jako kwantowych układów otwartych.

dr Dariusz Prorok

Globalne obserwable to obserwable charakteryzujące całość produkcji cząstek w danym zderzeniu. Są to tzw. energia poprzeczna i całkowita ilość cząstek naładowanych. W pierwszej części referatu przedstawię jak "dopasowuje" się pewien model statystyczny (czyli wartości jego parametrów) do danych doświadczalnych dotyczących zidentyfikowanych cząstek, głównie pionów, kaonów oraz protonów/antyprotonów. W drugiej części zaprezentuję przewidywania na energię poprzeczną i całkowitą ilości cząstek naładowanych uzyskane w tak "dopasowanym" modelu dla konkretnych eksperymentów w RHIC-u.

mgr Paulina Suchanek

Teoria Liouville może być skwantowana jako 2 wymiarowa konforemna teoria pola. Dzięki własności konforemnej niezmienniczości teorie tego typu można całkowicie scharakteryzować za pomocą spektrum tzw. pól pierwotnych oraz ich trójpunktowych funkcji korelacji. Na seminarium przedstawię sposób konstrukcji trójpunktowej funkcji korelacji w teorii Liouville w ramach podejścia operatorowego.

mgr Dariusz Tryniecki

Zgodnie z rozpowszechnioną obecnie opinią , teoria grawitacji oparta na działaniu Hilberta-Einsteina powinna być traktowana jako pierwszy wyraz rozwinięcia efektywnej teorii grawitacji. O wyrazach wyższego rzędu wiemy, iż powinny być zbudowane z odpowiednich członów krzywiznowych, na które (w każdym rzędzie rozwinięcia) składać się mają wyrazy określonego typu, R^{0}_{\mu\nu}. Zadaniem o podstawowym znaczeniu jest zatem próba przeanalizowania wpływu wyższych członów krzywiznowych na charakterystyki fizyki czarnych dziur. W moim wystąpieniu skoncentruję się na trzech konkretnych zagadnieniach: 1) iteracyjnym rozwiązaniu opisującym elektrycznie naładowaną i statyczną czarną dziurę w kwadratowej grawitacji, kładąc szczególny nacisk na przypadek ekstremalny. Można pokazać , że położenie horyzontu zdarzeń jest wówczas dane przez r+=|e|. 2) Obliczeniu poprawki pierwszego rzędu dla rozwiązania sprzężonych równań kwadratowej grawitacji i nieliniowej elektrodynamiki, z rozwiązaniem zerowego rzędu podanym przez Ayona-Beato i Garci i przez Bronnikowa. Pokażę, iż rozwiązanie pierwszego rzędu jest również regularne. 3) Konstrukcji i (perturbacyjnym) rozwiązaniu równań z wyższymi członami krzywiznowymi w D-wymiarowej czasoprzestrzeni.

dr hab. Paweł Rudawy (Instytut Astronomii)

Rozbłyski słoneczne, protuberancje, koronalne wyrzuty materii i wiele innych zjawisk i procesów obserwowanych w atmosferze Słońca (od chromosfery do korony), powstaje w wyniku oddziaływania plazmy z polem magnetycznym. Słońce jest jedynym obiektem, w którym - w pewnym zakresie - możemy bezpośrednio obserwować oddziaływania plazma-pole w warunkach niemożliwych do odtworzenia w laboratorium a typowych dla innych obiektów astronomicznych. Dane uzyskiwane z takich obserwacji mają ogromne znaczenie dla badań procesów fizyki wysokich energii (np. generacji energii w wyniku kontrolowanej syntezy termonuklearnej). W ramach referatu zostaną przedstawione: a) standardowy model Słońca wraz z zagadnieniem generacji pola magnetycznego w procesie a-d dynama; b) ogólna charakterystyka zjawisk oddziaływania plazmy z polem magnetycznym w atmosferze Słońca wraz z cyklicznością występowania tych zjawisk; c) charakterystyka rozblysków słonecznych wraz ze standardowym modelem rozbłysku; d) wybrane wyniki badań rozbłysków słonecznych z wykorzystaniem spektrografu MSDP oraz Maszyny Pulsarowej.

dr Artur Duda

Zostanie przedstawiona przeprowadzona przez Nonakę i Osakawę (Ch. Nonaka, M. Asakawa, Physical Review C, vol. 71, 044904). analiza ewolucji hydrodynamicznej w pobliżu punktu krytycznego na diagramie fazowym QCD. W oparciu o założenie, że krytyczny punkt końcowy (CEP) występujący na diagramie QCD należy do tej samej klasy uniwersalności co występujący w trójwymiarowym modelu Isinga przeanalizowane będzie zachowanie takich parametrów jak gęstość entropii oraz gęstość liczby barionowej. Przedstawione zostaną dla tego modelu trajektorie izentropowe oraz obserwowany dla nich efekt ogniskowania, porównam je też z przewidywaniami modelu "bag-plus-excluded". Będzie dokonana analiza zachowania prędkości dźwięku dla trajektorii izentropowych dla różnych wartości parametrów. Przedstawię porównanie z danymi eksperymentalnymi.

dr hab. Marek Mozrzymas

Znaczenie w fizyce operatorów tensorowych związanych z grupami i algebrami Liego skłania do rozważenia koncepcji operatorów tensorowych dla algebr kwantowych i ogólnie algebr Hopfa. W niniejszym wykładzie podana zostanie ogólna definicja operatora tensorowego w reprezentacjach dowolnej algebry Hopfa. Definicja ta opiera się na podstawowy w algebrze pojęciu homomorfizmu i jakkolwiek wydaje się być abstakcyjna to w przypadku klasycznych struktur grup i algebr Liego so(3) staje się klasyczną definicją Wignera i Racaha. W ramach tej definicji można, przy pewnych założeniach udowodnić twierdzenie Wignera-Eckarta dla operatorów tensorowych dowolnej algebry Hopfa. W tym ogólnym podejściu dowód twierdzenia Wignera-Eckarta opiera się na klasycznym lemacie Schura. Jako przykład omówione zostaną operatory tensorowe dla kwantowej algebry Uq[su(2)], które można traktować jako deformację klasycznych operatorów tensorowych pojawiającyh się np. w mechanice kwantowej.

prof. dr hab. Ludwik Turko

Symulacje sieciowe chromodynamiki kwantowej pozwoliły w ostatnich trzech latach na uzyskanie wyników, które dają ilościowy opis struktury fazowej materii hadronowej. Dotyczy to rodzaju przejścia fazowego oraz wyznaczania parametrów krytycznych. Przedmiotem seminarium jest omówienie metodologii sieciowej oraz porównanie wyników otrzymanych na sieci z przewidywaniami statystycznego bootstrapu oraz modelu termicznego.

mgr Artur Ankowski

Jednym z podejść do opisu jądra w oddziaływaniach neutrin jest formalizm funkcji spektralnej. Przybliżę na czym on polega, pokażę najprostszą metodę liczenia funkcji spektralnej. Uzasadnię dlaczego istotne znaczenie w fizyce neutrin ma argon i pokażę że przekroje czynne otrzymywane w tym podejściu różnią się od przekrojów gazu Fermiego.

mgr Izabella Próchnicka

Po wstępie dotyczącym opisu grawitacji w modelu wszechświata na branie ("brane world scenario") zostanie omówiony model 5-wymiarowej grawitacji Einsteina sprzężonej kowariantnie z 3-braną. Na 3-branie zostanie wprowadzone także indukowane działanie Einsteina-Hilberta. W przybliżeniu biliniowym do działania zostanie przebadany problem bezmasowości pola grawitacyjnego na branie.

Prof. Yen Chin Ong (Nanjing University)

The literature is abounded with entropy functions that generalize Boltzmann-Gibbs, and in the context of black hole and cosmological horizons, they give rise to modifications of the Bekenstein-Hawking area law. This gives rise to subtleties concerning thermodynamic energy, which often is no longer equivalent to the ADM mass of the black hole. This talk will discuss how generalizing entropy may give rise to new theory of gravity in which the gravitational constant G is now area-dependent and in general, varying. Some supporting evidence for this proposal will be discussed, which include: (1) restoring the Bekenstein bound, which otherwise is grossly violated by entropy modification; (2) asymptotically safe gravity now tied to logarithmic correction of the Bekenstein-Hawking entropy; (3) GUP-like behavior for the Schwarzschild black hole without explicitly employing GUP – which may also suggest a strong connection between gravity, thermodynamics, and quantum mechanics; (4) possible theoretical basis for black hole-cosmology coupling.