researchseminars.org

David Osten (Ludwig Maximilian University/Max-Planck-Institute for Physics, Munich)
2020-06-24 15:00 - 17:00 UTC | https://researchseminars.org/talk/ITMPseminar/1/
Title: Current Algebra and Generalised Geometry (https://researchseminars.org/talk/ITMPseminar/1/)
by David Osten (Ludwig Maximilian University/Max-Planck-Institute for Physics, Munich) as part of Theoretical and Mathematical Physics

Abstract
The first part of the talk will be a review of T-duality and generalised geometry in string theory. Generalised geometry is a generalisation of Riemannian geometry that captures certain 'non-geometric' backgrounds which are nevertheless well-defined in string theory. A convenient characterisation of such backgrounds is given in terms of the so-called generalised fluxes.

In the second part of the talk I want to discuss the meaning of these generalised fluxes in the worldsheet theory. There, they describe a deformation of the canonical Poisson structure -- namely the current algebra. Besides applications to magnetic backgrounds and integrable sigma models which motivated this work, the virtue of the deformed current algebra lies in the fact that it gives clear-cut routes to non-commutative and non-associative interpretations of the generalised flux backgrounds, to generalisations of T-duality and to generalisations to M-theory.

Frederic Bruenner (Vienna University of Technology (TU Wien))
2020-07-08 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/2/
Title: Gauge/gravity duality and the phenomenology of hadrons (https://researchseminars.org/talk/ITMPseminar/2/)
by Frederic Bruenner (Vienna University of Technology (TU Wien)) as part of Theoretical and Mathematical Physics

Abstract
I will give a pedagogical introduction to aspects of hadronic physics at low energy, and show how the methodology of gauge/gravity duality may be applied to certain problems arising in this context. As a concrete example, I will talk about the search for glueballs, bound states of gluons predicted by lattice gauge theory. These states have not been identified unambiguously among the hadrons we observe in collider experiments, in part due to the lack of theoretical predictions of their decay rates. I will show how gauge/gravity duality can be used to calculate glueball decay rates, and discuss potential implications.

Jose Alejandro Rosabal (Asia Pacific Center for Theoretical Physics, Pohang)
2020-07-22 11:00 - 13:00 | https://researchseminars.org/talk/ITMPseminar/3/
Title: Schwarzschild black hole thermodynamic entropy on a nice slice (https://researchseminars.org/talk/ITMPseminar/3/)
by Jose Alejandro Rosabal (Asia Pacific Center for Theoretical Physics, Pohang) as part of Theoretical and Mathematical Physics

Abstract
In this seminar I will present the calculation of the thermodynamic entropy of a Schwarzschild black hole on a nice slice. This can be seen as a warm up to address the calculation of the Von Neumann entropy for two intervals, that includes a portion of the interior of the black hole, and the Page curve. In the end I will comment on the relation between this work and some recent proposal.

Nikita Kolganov (ITMP MSU, Moscow)
2020-09-23 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/4/
Title: Constrained modified gravities: generalized unimodular gravity and beyond (https://researchseminars.org/talk/ITMPseminar/4/)
by Nikita Kolganov (ITMP MSU, Moscow) as part of Theoretical and Mathematical Physics

Abstract
In my talk, I will give you a brief introduction into modified gravity theories, and then I will proceed to particular modified gravity models, which I'm interested in. Most of the modified gravities are equivalent to the General Relativity, equipped with some additional degrees of freedom. In our case these d.o.f. are obtained by the explicit breaking of general covariance by an algebraic constraint on metric coefficients. I'm going to discuss the covariantization issue of such theories, its duality to well-known k-essence and self-gravitating media models, and applications to inflationary cosmology.

Gleb Arutyunov (University of Hamburg)
2020-09-30 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/5/
Title: Hamiltonian structures of the spin Ruijsenaars-Schneider models (https://researchseminars.org/talk/ITMPseminar/5/)
by Gleb Arutyunov (University of Hamburg) as part of Theoretical and Mathematical Physics

Abstract
TBA

Ariel Arza (ITMP MSU, Moscow)
2020-10-07 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/6/
Title: Production of massive particles from the decay of a free massless field (https://researchseminars.org/talk/ITMPseminar/6/)
by Ariel Arza (ITMP MSU, Moscow) as part of Theoretical and Mathematical Physics

Abstract
In this talk we will show, in a simple toy model (H=g\phi\chi^2), how Bose enhancement allows the decay of a massless field into massive particles. It happens due to a parametric resonance caused by a big energy density of the decaying field. I will show the instability conditions as well as the energy density threshold for the decay to occur. I will also compute the equivalent of the spontaneous decay rate.

Andrei Zotov (Steklov Mathematical Institute RAS)
2020-10-21 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/7/
Title: On double elliptic integrable system: characteristic determinant and Manakov triple (https://researchseminars.org/talk/ITMPseminar/7/)
by Andrei Zotov (Steklov Mathematical Institute RAS) as part of Theoretical and Mathematical Physics

Abstract
We discuss double elliptic integrable systems, where the dependence on the momenta of particles is elliptic. These models generalize the relativistic Ruijsenaars integrable systems, which contain trigonometric (exponential) dependence on momenta. A brief review on underlying dualities and interrelations between integrable systems will be given. We explain how to construct a kind of determinant representation for the known conservation laws. Finally, we will see that in the classical case the double elliptic models are naturally described by the Manakov L-A-B triple instead of the Lax pair

Mikhail Khlopunov (ITMP, Moscow State University)
2020-10-28 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/8/
Title: Modification of the radiation definition in odd dimensions (https://researchseminars.org/talk/ITMPseminar/8/)
by Mikhail Khlopunov (ITMP, Moscow State University) as part of Theoretical and Mathematical Physics

Abstract
In this seminar, I will discuss modification of the radiation definition for the case of odd-dimensional space-time. The standard definition of the wave zone fails in odd dimensions, due to the violation of the Huygens principle: the signal from an instantaneous flash of current reaches an observer after an interval of time required for propagation of the signal at the speed of light, but then the tail is observed endlessly; while in even-dimensional spaces an instant signal ends instantly at the observation point. The reason is that the retarded Green’s functions of the wave equation in odd dimensions has support localised not only on the light cone, but also inside it. I will discuss the covariant retarded quantities technique and Rohrlich-Teitelboim definition of the wave zone. Using this definition, the scalar radiation from a point-like charge, moving along the circular trajectory in three and five-dimensional space-times, will be computed. The obtained results will be verified by the calculations of the spectral distributions of the radiated energy, which are indifferent to the dimensionality of the space-time. Also, the contributions of the tails to the radiation will be discussed.

Alexander Zhiboedov (CERN)
2020-11-11 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/9/
Title: Event shapes, the light-ray OPE and superconvergence (https://researchseminars.org/talk/ITMPseminar/9/)
by Alexander Zhiboedov (CERN) as part of Theoretical and Mathematical Physics

Abstract
I will describe recent progress in understanding event shapes in conformal field theories. Familiar from the description of hadronic events at colliders, these observables are computed by matrix elements of the so-called light-ray operators. Characterizing the light-ray operators in a nonperturbative setting poses many theoretical challenges. I will describe some of the recently developed tools to perform computations of conformal event shapes and illustrate them using N=4 SYM. Finally, I will explain how via holography some of the basic properties of conformal event shapes lead to nontrivial sum rules obeyed by possible UV completions of general relativity.

Sandipan Kundu (Johns Hopkins University)
2020-11-18 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/10/
Title: Closed strings and weak gravity condition from higher-spin causality (https://researchseminars.org/talk/ITMPseminar/10/)
by Sandipan Kundu (Johns Hopkins University) as part of Theoretical and Mathematical Physics

Abstract
I will show that metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale. Causality imposes an upper bound on the mass of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. I will argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. This implies that the gravity sector has a stringy structure with an upper bound on the string scale. Another consequence of this bound is that all metastable higher spin particles in 4d with masses below the string scale must satisfy a weak gravity condition. Moreover, these bounds also have surprising implications for large N QCD coupled to gravity.

Tim Adamo (University of Edinburgh)
2020-11-25 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/11/
Title: Scattering in chiral strong backgrounds (https://researchseminars.org/talk/ITMPseminar/11/)
by Tim Adamo (University of Edinburgh) as part of Theoretical and Mathematical Physics

Abstract
There are many reasons to be interested in quantum field theory in the presence of strong, non-perturbative background fields, but surprisingly little is known in these scenarios, especially when compared to trivial backgrounds. For instance, the full semi-classical S-matrices of gauge theory and gravity are known in a trivial background, but even for simple strong backgrounds the tree-level amplitudes of these theories have not been computed beyond four-external particles. This raises the question: are all-multiplicity formulae (and other hallmarks of the study of scattering amplitudes in recent years) inextricably tied to trivial backgrounds? In this talk, I will demonstrate that for a broad class of chiral backgrounds in four-dimensions, we can find all-multiplicity expressions for tree-level scattering amplitudes of gauge theory and gravity which are remarkably simple and clearly un-related to standard background-coupled field theory on space-time.

Konstantin Zarembo (Niels Bohr Institute, Nordita)
2020-12-02 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/12/
Title: Large-N localization and quiver CFT (https://researchseminars.org/talk/ITMPseminar/12/)
by Konstantin Zarembo (Niels Bohr Institute, Nordita) as part of Theoretical and Mathematical Physics

Abstract
The quiver CFT interpolates between N=4 SYM and N=2 super-QCD, and is dual to strings on the AdS5 x S5/Z2 orbifold. Localization of the path integral in the quiver CFT potentially gives means to test this duality rigorously. The strong-coupling solution of the localization matrix model, which I will describe, is in the remarkable qualitative agreement with the holographic dual, but is not devoid of puzzling features.

Fedor Popov (Princeton University)
2020-12-09 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/13/
Title: RG Limit Cycles and "Spooky" Fixed Points in Perturbative QFT (https://researchseminars.org/talk/ITMPseminar/13/)
by Fedor Popov (Princeton University) as part of Theoretical and Mathematical Physics

Abstract
We study quantum field theories with sextic interactions in
3−ϵ dimensions, where the scalar fields ϕab form irreducible representations under the O(N)2 or O(N) global symmetry group. We calculate the beta functions up to four-loop order and find the Renormalization Group fixed points. In an example of large N equivalence, the parent O(N)2 theory and its anti-symmetric projection exhibit identical large N beta functions which possess real fixed points. However, for projection to the symmetric traceless representation of O(N), the large N equivalence is violated by the appearance of an additional double-trace operator not inherited from the parent theory. Among the large N fixed points of this daughter theory we find complex CFTs. The symmetric traceless O(N) model also exhibits very interesting phenomena when it is analytically continued to small non-integer values of N. Here we find unconventional fixed points, which we call "spooky." They are located at real values of the coupling constants gi, but two eigenvalues of the Jacobian matrix ∂βi/∂gj are complex. When these complex conjugate eigenvalues cross the imaginary axis, a Hopf bifurcation occurs, giving rise to RG limit cycles. This crossing occurs for Ncrit≈4.475, and for a small range of N above this value we find RG flows which lead to limit cycles.

Ivo Sachs (Ludwig Maximilian University of Munich)
2020-12-16 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/14/
Title: Loops in Holography (https://researchseminars.org/talk/ITMPseminar/14/)
by Ivo Sachs (Ludwig Maximilian University of Munich) as part of Theoretical and Mathematical Physics

Abstract
A quantum field theory (QFT) in an (Anti-)de Sitter, (A-)dS space-time can be characterised by a conformal field theory (CFT) much like the S-matrix for Minkowski QFT’s. I will review how quantum loops are reflected in CFT, both in AdS and dS. The latter has a remote connection to density perturbations in the Universe.

Domenico Orlando (INFN Turin, University of Bern)
2021-01-27 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/15/
Title: The O(N) vector model at large charge: EFT, large N and resurgence (https://researchseminars.org/talk/ITMPseminar/15/)
by Domenico Orlando (INFN Turin, University of Bern) as part of Theoretical and Mathematical Physics

Abstract
I will discuss the IR fixed point of the O(N) vector model in 3 dimensions (Wilson-Fisher point) in the framework of the large charge expansion. First I will construct an EFT valid for any N, then verify the prediction of the model in the double scaling limit of large N, large charge and finally discuss the use of resurgence to extend the validity of the EFT to sectors of small charge.

Piotr Tourkine (Paris LPTHE, CERN)
2021-02-03 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/16/
Title: Scattering from production in 2d (https://researchseminars.org/talk/ITMPseminar/16/)
by Piotr Tourkine (Paris LPTHE, CERN) as part of Theoretical and Mathematical Physics

Abstract
In this seminar, I will talk about recent results about a numerical method to find unitary S-matrices. The method, based on works of Atkinson, was invented in the late 60s and was used as a proof of existence of functions that satisfy all of the S-matrix axioms in 4d. However, it was not put in practical use.
Our recent results concern the implementation of those methods for S-matrices in two dimensions, using two different iterative schemes: a fixed-point iteration and Newton's method. Those schemes iterate the unitarity and dispersion relations, and converge to solutions to the S-matrix axioms. This numerical strategy provides a solution to the problem of reconstructing the scattering amplitude starting from a given particle production probability.
After a general introduction, the talk will be focused on how we implemented the algorithms, what they converge to, and the conditions under which they converge. We will see that the question of convergence naturally connects to the recent study of the coupling maximization in the two-dimensional S-matrix bootstrap. If time allows, I'll also comment on a fractal structure which we observed to be related to the so-called CDD-ambiguities.
I'll conclude with possible future directions.

Xinan Zhou (Princeton University)
2021-02-17 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/17/
Title: Holographic correlators and emergent Parisi-Sourlas supersymmetry (https://researchseminars.org/talk/ITMPseminar/17/)
by Xinan Zhou (Princeton University) as part of Theoretical and Mathematical Physics

Abstract
In this talk, I will first review the recent progress in computing holographic four-point correlators in maximally supersymmetric CFTs. I will introduce the so-called Maximally R-symmetry Violating (MRV) limit, in which the Mellin amplitudes drastically simplify and become easy to compute. From the MRV limit, I will show that the full amplitudes can be reconstructed by using symmetries. This gives a complete answer to all tree-level four-point functions in all three maximally supersymmetric backgrounds AdS4xS7, AdS5xS5, and AdS7xS4. In the second part of my talk, I will point out that these results have surprising properties. The Mellin amplitudes exhibit an emergent dimensional reduction structure, which allows them to be expressed in terms of only scalar exchange amplitudes from lower dimensional spacetimes. I will explain that this dimensional reduction structure is closely related to a holographic realization of the Parisi-Sourlas supersymmetry.

Conference id: 923 6907 4572

Ricardo Monteiro (Queen Mary University of London)
2021-02-24 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/18/
Title: Gravity as a double copy of gauge theory (https://researchseminars.org/talk/ITMPseminar/18/)
by Ricardo Monteiro (Queen Mary University of London) as part of Theoretical and Mathematical Physics

Abstract
Relations expressing gravity as a "double copy" of gauge theory appeared first in string theory, and have been used to compute scattering amplitudes in theories of gravity, with applications to both theory and phenomenology. I will discuss how the double copy extends to solutions to the equations of motion, including our best known black hole spacetimes, and how this story connects to the original story for scattering amplitudes.

Meeting ID: 928 8340 6261

Linus Wulff (Masaryk University)
2021-03-03 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/19/
Title: O(D,D) and string alpha'-corrections (https://researchseminars.org/talk/ITMPseminar/19/)
by Linus Wulff (Masaryk University) as part of Theoretical and Mathematical Physics

Abstract
String theory on a d-dimensional torus features an O(d,d) symmetry. It has been suggested that the low-energy effective action can be formulated with a larger O(D,D) symmetry, even before putting the theory on a torus. This approach, which goes by the name of Double Field Theory (DFT), has proven very useful. I will address the problem of constructing higher derivative invariants in this formalism. In agreement with the literature we find that a quadratic Riemann invariant can be constructed, which can account for the first alpha'-correction to the bosonic and heterotic string. However, we find that no cubic or quartic Riemann invariants can be constructed. This suggests that the quartic Riemann terms arising at order alpha'^3 in string theory do not have a DFT embedding.

Conference ID: 966 8415 0220
Passcode: [REDACTED]

Radu Roiban (Penn State University)
2021-03-10 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/20/
Title: Spinning and spinless two-particle dynamics from gravitational scattering amplitudes (https://researchseminars.org/talk/ITMPseminar/20/)
by Radu Roiban (Penn State University) as part of Theoretical and Mathematical Physics

Abstract
In the appropriate classical limit, scattering amplitude-based techniques can yield the classical interaction of massive bodies at fixed order in the post-Minkowskian expansion.

In this talk we review a framework for the construction of the two-body Hamiltonian for compact binary systems and illustrate it with state of the art results for both spinning and spinless systems. Throughout we emphasize structure of gravitational interactions and direct relations between scattering amplitudes and observables of two-particle dynamics.

Meeting ID: 933 8672 1535
Passcode: [REDACTED]

Vladimir Rosenhaus (Institute for Advanced Study, Princeton)
2021-03-17 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/21/
Title: Chaotic scattering with a highly excited string (https://researchseminars.org/talk/ITMPseminar/21/)
by Vladimir Rosenhaus (Institute for Advanced Study, Princeton) as part of Theoretical and Mathematical Physics

Abstract
Motivated by the desire to understand chaos in the S-matrix of string theory, we study tree level scattering amplitudes involving highly excited strings. While the amplitudes for scattering of light strings have been a hallmark of string theory since its early days, scattering of excited strings has been far less studied. Recent results on black hole chaos, combined with the correspondence principle between black holes and strings, suggest that the amplitudes have a rich structure. We review the procedure by which an excited string is formed by repeatedly scattering photons off of an initial tachyon. We compute the scattering amplitude of one arbitrary excited string decaying into two tachyons, and study its properties for a generic excited string. We find the amplitude is highly erratic as a function of both the precise excited string state and of the tachyon scattering angle.

Meeting ID: 936 3872 0664

Paul Heslop (Durham University)
2021-03-24 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/22/
Title: Towards the Virasoro-Shapiro Amplitude in AdS5xS5 (https://researchseminars.org/talk/ITMPseminar/22/)
by Paul Heslop (Durham University) as part of Theoretical and Mathematical Physics

Abstract
We propose a systematic procedure for obtaining all single trace 1/2-BPS correlators in N=4 super Yang-Mills corresponding to the four-point tree-level amplitude for type IIB string theory in AdS5xS5. The underlying idea is to compute generalised contact Witten diagrams coming from a 10d effective field theory on AdS5xS5 whose coefficients are fixed by the flat space Virasoro-Shapiro amplitude up to ambiguities related to commutators of the 10d covariant derivatives which require additional information such as localisation. We illustrate this procedure by computing stringy corrections to the supergravity prediction for all single trace 1/2-BPS correlators up to O(α′7), and spell out a general algorithm for extending this to any order in α′.

ID: 949 0759 4642
Passcode: [REDACTED]

Congkao Wen (Queen Mary University of London)
2021-03-31 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/23/
Title: Integrated four-point correlators in N=4 SYM (https://researchseminars.org/talk/ITMPseminar/23/)
by Congkao Wen (Queen Mary University of London) as part of Theoretical and Mathematical Physics

Abstract
In this talk, we will discuss integrated correlators of four superconformal primaries in N=4 super Yang-Mills, that are defined by integrating over spacetime coordinates of the four-point correlator with certain integration measures. The integrated correlators can be computed using supersymmetric localisation, which are expressed as N-dimensional matrix-model integrals. We will mostly focus on one of the integrated correlators. We find that this integrated correlator can be presented as a lattice sum, which makes manifest the SL(2, Z) modular invariance of N=4 SYM. Furthermore, the integrated correlator obeys a remarkable Laplace-difference equation, which relates the correlator of SU(N) theory with those of SU(N-1) and SU(N+1) theories. The expression allows us to obtain exact results of the integrated correlator in various limits. For instance, in perturbation, the expression is checked to be consistent with known results in the literature; in the large-N limit, it is shown to match with the expected results from string theory due to AdS/CFT duality

Meeting ID: 946 1044 3637
Passcode: [REDACTED]

Oleg Lunin (SUNY-Albany)
2021-04-07 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/24/
Title: Supergravity excitations of stringy geometries (https://researchseminars.org/talk/ITMPseminar/24/)
by Oleg Lunin (SUNY-Albany) as part of Theoretical and Mathematical Physics

Abstract
Motivated by the desire to understand the dynamics of light modes on various gravitational backgrounds, this talk summarizes recent results concerning properties of scalar, vector, and tensor excitations of black holes and integrable stringy geometries.

For rotating black holes and for certain Wess-Zumino-Witten models, full separability of all dynamical equations is demonstrated, and symmetries underlying this property are uncovered. For other classes of integrable backgrounds, the energy spectra of various fields are evaluated, and the algebraic constructions of the corresponding eigenfunctions are presented.

Meeting ID: 973 8330 1111
Passcode: [REDACTED]

Alexander Vikman (Institute of Physics of the Czech Academy of Sciences, Prague)
2021-04-14 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/25/
Title: Losing the trace to discover dynamical Newton or Planck constants (https://researchseminars.org/talk/ITMPseminar/25/)
by Alexander Vikman (Institute of Physics of the Czech Academy of Sciences, Prague) as part of Theoretical and Mathematical Physics

Abstract
I will discuss our recent work e-Print: 2011.07055. There we showed that promoting the trace part of the Einstein equations to a trivial identity results in the Newton constant being an integration constant. Thus, in this formulation the Newton constant is a global dynamical degree of freedom which is also a subject to quantization, quantum fluctuations and the Heisenberg uncertainty relations. This is similar to what happens to the cosmological constant in the unimodular gravity where the trace part of the Einstein equations is lost in a different way. I will consider a constrained variational formulation of these modified Einstein equations. Then, drawing on analogies with the Henneaux-Teitelboim action for unimodular gravity, I will discuss different general-covariant actions resulting in these dynamics. In this approach, it turned out that the inverse of the dynamical Newton constant is canonically conjugated to the Ricci scalar integrated over spacetime. Surprisingly, instead of the dynamical Newton constant one can formulate an equivalent theory with a dynamical Planck constant. Finally, I will show that an axion-like field can play a role not only of the cosmological constant, as in e-Print: 2001.03169, but also of the Newton constant or even of the Planck constant.

Meeting ID: 953 6604 7713
Passcode: [REDACTED]

Alberto Salvio (University of Rome Tor Vergata)
2021-04-21 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/26/
Title: Models for a vast energy range: particles meet gravity and cosmology (https://researchseminars.org/talk/ITMPseminar/26/)
by Alberto Salvio (University of Rome Tor Vergata) as part of Theoretical and Mathematical Physics

Abstract
I will discuss models valid over a vast energy range by following 2 strategies. In one approach (bottom-up) I will illustrate the main phenomenological aspects of a scenario where one adds to the Standard Model 3 right-handed neutrinos and an axion sector. This can account for neutrino oscillations, dark matter, baryogengesis, inflation and can also stabilize the electroweak vacuum. In another, more ambitious approach, I will talk about a scenario where all couplings flow to zero at infinite energy (total asymptotic freedom). The corresponding phenomenology of this top-down approach will also be treated.

Meeting ID: 977 1065 2931
Passcode: [REDACTED]

David Osten (ITMP MSU, Moscow)
2021-05-05 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/27/
Title: Exceptional world-volume currents and their algebras (https://researchseminars.org/talk/ITMPseminar/27/)
by David Osten (ITMP MSU, Moscow) as part of Theoretical and Mathematical Physics

Abstract
After a short review of exceptional generalised geometry I will introduce a unified setup for a duality-covariant Hamiltonian formulation of world-volume theories of objects in string and M-theory. Based on https://arxiv.org/abs/2103.03267

Meeting ID: 981 6226 4274
Passcode: [REDACTED]

Jorge Guillermo Russo (ICREA and University of Barcelona)
2021-05-12 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/28/
Title: Thermal correlators in CFT and black holes (https://researchseminars.org/talk/ITMPseminar/28/)
by Jorge Guillermo Russo (ICREA and University of Barcelona) as part of Theoretical and Mathematical Physics

Abstract
We describe the computation of thermal 2-point correlation functions in the black brane AdS5 background dual to 4d CFT's at finite temperature for operators of large scaling dimension. This gives rise to a formula that matches the expected structure from the OPE. The thermal 2-point function has an exponentiation property, whose origin we explain. We also compute the first correction to the two-point function due to graviton emission, which encodes the time travel to the black hole singularity. We will also discuss some interesting features of higher-point functions.

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Edoardo Vescovi (KTH Royal Institute of Technology, Stockholm University)
2021-05-19 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/29/
Title: Probing boundary states at finite coupling (https://researchseminars.org/talk/ITMPseminar/29/)
by Edoardo Vescovi (KTH Royal Institute of Technology, Stockholm University) as part of Theoretical and Mathematical Physics

Abstract
In this talk, we calculate exactly the correlation function of a Wilson loop operator and a local non-BPS operator in planar N=4 SYM. First, we introduce an effective theory for such observable in free theory and we reformulate the gauge-theory computation as an overlap between an energy eigenstate of a spin-chain and a matrix product state. The form of the result supports the interpretation of the correlator as an overlap between an integrable boundary state, which we determine using symmetry and integrability, and the state corresponding to the single-trace operator. Second, we explain how to formulate a non-perturbative bootstrap program based on the results obtained in this framework.

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Fedor Bezrukov (University of Manchester)
2021-05-26 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/30/
Title: Inflation and reheating with Higgs inflation and related models (https://researchseminars.org/talk/ITMPseminar/30/)
by Fedor Bezrukov (University of Manchester) as part of Theoretical and Mathematical Physics

Abstract
Using the Higgs field for inflation is an economic way to solve two problems with one scalar field -- Higgs field is require in the Standard Model, and a scalar field is the simplest method to drive inflation of the early Universe. However, consistent attempt to do this takes us to the limits of validity of the quantum field theory, and significant problems with the reheating after inflation. I’ll discuss the ways to deal with this by combining the theory with R^2 gravitational terms, and describe the highly nontrivial dynamics of the system after inflation

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Angelos Fotopoulos (Northeastern University, Boston)
2021-06-02 16:30 - 17:30 | https://researchseminars.org/talk/ITMPseminar/31/
Title: Celestial CFT Correlators and Conformal Block Decomposition (https://researchseminars.org/talk/ITMPseminar/31/)
by Angelos Fotopoulos (Northeastern University, Boston) as part of Theoretical and Mathematical Physics

Abstract
I will shortly review the connection of the Bondi-van der Burg-Metzner-Sachs (BMS) symmetry group of asymptotically flat four-dimensional spacetimes at null infinity to the S-matrix of elementary particles and gravitons.
Applying Mellin transformations to traditional, momentum space amplitudes we can compute celestial amplitudes. These are conjectured to correspond to correlators of conformal primary fields on a putative two-dimensional celestial sphere. I will elaborate on the proposal of flat holography in which four-dimensional physics is encoded in two-dimensional celestial conformal field theory (CCFT). The symmetry underlying CCFT is the extended BMS symmetry of (asymptotically) flat spacetime. I will show how to use soft and collinear theorems of Einstein-Yang-Mills theory to derive the OPEs of BMS field operators generating the symmetries of the BMS group, superrotations and supertranslations.
In the second part of my talk, time permitted, I will discuss a proposal for radial quantization of the CCFT and I will present an attempt to decompose gluon celestial amplitudes in conformal blocks. This will reveal some very interesting aspects of the Celestial CFT: the emergence of new operators in the theory and space-time scattering channels which lead to continuous complex spin primary fields. The space-time interpretation of these operators is still unclear. Moreover, CFT crossing symmetry and its relation to four-dimensional spacetime crossing symmetry of the S-matrix are some interesting open problems.

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Kristiansen Lara (University of Santiago, Chile)
2021-06-09 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/32/
Title: Integrable Systems and Spacetime Dynamics (https://researchseminars.org/talk/ITMPseminar/32/)
by Kristiansen Lara (University of Santiago, Chile) as part of Theoretical and Mathematical Physics

Abstract
It is shown that the Ablowitz-Kaup-Newell-Segur (AKNS) integrable hierarchy can be obtained as the dynamical equations of three-dimensional General Relativity with a negative cosmological constant. This geometrization of AKNS system is possible through the construction of novel boundary conditions for the gravitational field. These are invariant under an asymptotic symmetry group characterized by an infinite set of AKNS commuting conserved charges. Gravitational configurations are studied by means of $SL(2,\mathbb{R})$ conjugacy classes. Conical singularities and black hole solutions are included in the boundary conditions. Based on https://arxiv.org/abs/2104.09676

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Shota Komatsu (CERN and IAS Princeton)
2021-06-16 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/33/
Title: Comments on Large Charge and N=4 SYM (https://researchseminars.org/talk/ITMPseminar/33/)
by Shota Komatsu (CERN and IAS Princeton) as part of Theoretical and Mathematical Physics

Abstract
I will discuss three topics on the large charge limit of N=4 super Yang-Mills and its holographic dual. First, I will discuss what we can learn from holography about general structures of the large-charge expansion of SCFT with higher-rank gauge groups. Second, I will briefly discuss the double-scaling limit and their relation to the central extension of the symmetry. Third I will explain how the ideas from the large-charge expansion help to resolve confusions in the literature on the holographic computation of correlation functions of heavy operators dual to D-branes in AdS.

Meeting ID: 919 8499 0422
Passcode: [REDACTED]

Alex Buchel (Perimeter Institute)
2021-09-22 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/34/
Title: Black holes on a conifold with fluxes (https://researchseminars.org/talk/ITMPseminar/34/)
by Alex Buchel (Perimeter Institute) as part of Theoretical and Mathematical Physics

Abstract
We present a comprehensive analysis of the black holes on warped deformed conifold with fluxes in Type IIB supergravity. These black holes realize the holographic dual to thermal states of the N = 1 supersymmetric SU(N) × SU(N + M) cascading gauge theory of Klebanov et al on round S^3 . There are three distinct mass scales in the theory: the strong coupling scale Λ of the cascading gauge theory, the compactification scale µ = 1/L_3 (related to the S^3 radius L_3 ) and the temperature T of a thermal state. Depending on Λ , µ and T , there is an intricate pattern of confinement/deconfinement (Hawking-Page) and the chiral symmetry breaking phase transitions.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Eugeny Babichev (The University Paris-Saclay)
2021-09-29 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/35/
Title: Black holes in scalar-tensor theories (https://researchseminars.org/talk/ITMPseminar/35/)
by Eugeny Babichev (The University Paris-Saclay) as part of Theoretical and Mathematical Physics

Abstract
I will review black hole solutions in Horndeski theory and its extensions. For shift symmetric theories of Horndeski and beyond Horndeski theory, black holes involve several classes of nontrivial solutions: those that include, at the level of the action, a linear coupling to the Gauss-Bonnet term and those that involve time dependence in the scalar field. I will describe black hole solutions of both classes in some detail. I will also review and discuss recent results on hairy black holes in particular subclasses of the theory.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Victor Gorbenko (Stanford University)
2021-10-06 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/36/
Title: Non-perturbative gravitational effects in cosmology (https://researchseminars.org/talk/ITMPseminar/36/)
by Victor Gorbenko (Stanford University) as part of Theoretical and Mathematical Physics

Abstract
I will start with reviewing some recent progress in understanding the black hole evaporation with the help of gravitational path integral methods. It turns out that for certain observables, for example the so-called Page curve for the BH entropy, higher-topology saddle points of the gravitational path integral produce important and calculable contributions. I will then discuss potential applications of similar ideas in cosmology and when such non-perturbative effects may be relevant. Then, I will demonstrate a concrete calculation in a simple toy-model, where a bra-ket wormhole, that is a connection between the bra and the ket of the wave function of the universe arises.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Kurt Hinterbichler (Case Western Reserve University)
2021-10-13 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/37/
Title: Unitarization in Kaluza Klein theory and the Geometric Bootstrap (https://researchseminars.org/talk/ITMPseminar/37/)
by Kurt Hinterbichler (Case Western Reserve University) as part of Theoretical and Mathematical Physics

Abstract
The infinite towers of massive particles present in Kaluza Klein reductions of Einstein gravity conspire to soften the high-energy behavior of the scattering of massive spin-2 states. The mechanism by which this occurs leads to a bootstrap procedure, analogous to the conformal bootstrap, that yields new non-trivial constraints on the eigenvalue spectra of closed Einstein manifolds.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Dmitri Bykov (Steklov Mathematical Institute)
2021-10-20 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/38/
Title: Sigma models as Gross-Neveu models (https://researchseminars.org/talk/ITMPseminar/38/)
by Dmitri Bykov (Steklov Mathematical Institute) as part of Theoretical and Mathematical Physics

Abstract
I will show that there is a wide class of integrable sigma models that are exactly and explicitly equivalent to bosonic Gross-Neveu models. In full generality these are models with quiver variety phase spaces, but the familiar CP^n, Grassmannian or flag manifold sigma models belong to this class as well. This approach leads to a new take on topics such as RG (Ricci) flow, construction of integrable deformations and the inclusion of fermions. In particular, it provides a way of obtaining worldsheet SUSY theories from target space SUSY theories by means of a supersymplectic quotient.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Andrei Parnachev (Trinity College Dublin)
2021-10-27 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/39/
Title: Stress tensor and conformal correlators (https://researchseminars.org/talk/ITMPseminar/39/)
by Andrei Parnachev (Trinity College Dublin) as part of Theoretical and Mathematical Physics

Abstract
I will describe a calculation of the contributions of stress tensor composites to correlators in CFTs (in d>2) with a large number of degrees of freedom, including holographic CFTs. Implications for holography, thermalization and possible higher spin symmetries relevant for near lightcone correlators will be discussed.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Mikhail Ivanov (Princeton, IAS)
2021-11-03 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/40/
Title: Love and Naturalness (https://researchseminars.org/talk/ITMPseminar/40/)
by Mikhail Ivanov (Princeton, IAS) as part of Theoretical and Mathematical Physics

Abstract
Tidal Love numbers of a compact body capture multipole moments induced by external gravitational fields. Also they appear as Wilson coefficients in the post-Newtonian effective field theory of extended objects. It has been known for a decade that Love numbers vanish identically for black holes in four dimensions, which posed a major naturalness problem in the EFT context. In my talk, I will present a new hidden (“Love”) symmetry of black holes, which elegantly resolves this naturalness paradox.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Tommaso Macrelli (Surrey University)
2021-11-17 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/41/
Title: Colour-kinematic duality, double copy and homotopy algebras (https://researchseminars.org/talk/ITMPseminar/41/)
by Tommaso Macrelli (Surrey University) as part of Theoretical and Mathematical Physics

Abstract
While colour-kinematic duality and double copy are a well established paradigm at tree level, their loop level generalisation remained for a long time an unsolved problem. Lifting the on-shell, scattering amplitude-based description to an action-based approach, we show that a theory that exhibits tree level colour-kinematic duality can be reformulated in a way such that its loop integrands manifest colour-kinematic duality.
After a review of Batalin-Vilkovisky formalism and homotopy algebras, we discuss how these structures emerge in quantum field theory and gravity. We focus then on the application of these sophisticated mathematical tools to colour-kinematic duality and double copy, introducing an adequate notion of colour-kinematic factorisation.
This talk is based on arXiv:2007.13803 [hep-th], arXiv:2102.11390 [hep-th], arXiv:2108.03030 [hep-th].

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Hongliang Jiang (Queen Mary University)
2021-11-24 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/42/
Title: Infinite symmetries and Ward identities in celestial holography (https://researchseminars.org/talk/ITMPseminar/42/)
by Hongliang Jiang (Queen Mary University) as part of Theoretical and Mathematical Physics

Abstract
Celestial holography reformulates the scattering amplitude holographically in terms of celestial conformal field theory living at boundary null infinity, thus opening up an interesting and promising avenue towards flat holography. In this talk, I will discuss various aspects of symmetry and their implications in celestial holography. I will first discuss how to realize the global symmetry of spacetime in celestial CFT, ranging from Poincare to conformal symmetry, and further to the superconformal symmetry of N=4 SYM. Then I will study the asymptotic symmetries from the celestial conformal field theory point of view. More specifically, by focusing on the soft sector of celestial OPEs, I will derive an infinite-dimensional symmetry algebra, dubbed holography chiral algebra, in supersymmetric Einstein-Yang-Mills theory. In the case of pure Einstein gravity, the holography chiral algebra turns out to be the w_{1+∞} algebra. These infinite symmetries give rise to infinite Ward identities in celestial CFT, which are equivalent to infinite soft theorems in scattering amplitudes. Finally, I will also derive general formulae for celestial OPEs and the corresponding Ward identities arising from arbitrary cubic interactions of three spinning massless particles.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Nissan Itzhaki (Tel Aviv University)
2021-12-08 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/43/
Title: A Puncture in the Euclidean Black Hole (https://researchseminars.org/talk/ITMPseminar/43/)
by Nissan Itzhaki (Tel Aviv University) as part of Theoretical and Mathematical Physics

Abstract
We consider the backreaction of the winding zero mode on the cigar geometry. We focus on the case of the $SL(2,R)_k/U(1)$ cigar associated with e.g. the near-horizon limit of $k$ NS5 black-branes. We solve the equations of motion numerically in the large $k$ limit as a function of the amplitude of the winding mode at infinity. We find that there is a critical amplitude $C_c=\exp(-\gamma/2)$ that admits a critical solution. The exact CFT description of the $SL(2,R)_k/U(1)$ cigar, in particular the FZZ duality, fixes completely the winding amplitude. We find that in the large $k$ limit there is an exact agreement $C_c=C_{FZZ}$.
The critical solution is a cigar with a puncture at its tip; consequently, the BH entropy is carried entirely by the winding condensate. We argue that, in the Lorentzian case, the information is ejected from the black hole through this puncture.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Monica Guica (Institute of Theoretical Physics, Saclay)
2022-01-26 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/44/
Title: $J\bar T$ - deformed CFTs as non-local CFTs (https://researchseminars.org/talk/ITMPseminar/44/)
by Monica Guica (Institute of Theoretical Physics, Saclay) as part of Theoretical and Mathematical Physics

Abstract
I will start with a review of TTbar and JTbar - deformed CFTs and their holographic interpretation. I will then show that both TTbar and JTbar - deformed CFTs possess Virasoro x Virasoro symmetry. For the case of JTbar, I will discuss the classical realization of these symmetries in terms of field-dependent coordinate transformations and show how the associated generators can be used to define an analogue of "primary" operators in this non-local theory, whose correlation functions are entirely fixed in terms of those of the undeformed CFT.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

John F. Donoghue (University of Massachusetts)
2022-02-16 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/45/
by John F. Donoghue (University of Massachusetts) as part of Theoretical and Mathematical Physics

Abstract
TBA

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Barvinsky Andrei (Lebedev Institute)
2022-03-02 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/46/
Title: Horava gravity as palladium of locality, unitarity and renormalizability: methods and results (https://researchseminars.org/talk/ITMPseminar/46/)
by Barvinsky Andrei (Lebedev Institute) as part of Theoretical and Mathematical Physics

Abstract
We discuss problems of covariant renormalization of Lorentz non-invariant Horava gravity models. Projectable version of these models in generic spacetime dimensions is shown to maintain UV renormalizability, locality and unitarity, which is based on the BRST structure of renormalization in a special class of regular background covariant gauges. Renormalization group flow with the asymptotically free UV fixed point is presented in (2+1)-dimensional theory. Beta functions of (3+1)-dimensional theory are obtained by the combination of dimensional reduction and the method of universal functional traces. They feature fixed points with several candidates for asymptotic freedom and also suggest an intriguing connection between the (3+1)-dimensional Horava gravity with detailed balance and gravitational Chern-Simons/topological massive gravity.

Fernando Quevedo (Cambridge University)
2022-03-23 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/47/
Title: On moduli stabilisation, de Sitter spacetime and inflation from string compactifications (https://researchseminars.org/talk/ITMPseminar/47/)
by Fernando Quevedo (Cambridge University) as part of Theoretical and Mathematical Physics

Abstract
An overview of the different attempts to stabilise the moduli fields, measuring the size and shape of the extra dimensions in string theory, will be given. The extension of these techniques towards obtaining de Sitter spacetime and a period of early universe inflation will be highlighted, emphasizing recent progress and open challenges.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Ellis Ye Yuan (Zhejiang University)
2022-03-30 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/48/
Title: Graviton Scattering in AdS at Two Loops (https://researchseminars.org/talk/ITMPseminar/48/)
by Ellis Ye Yuan (Zhejiang University) as part of Theoretical and Mathematical Physics

Abstract
I will present a preliminary result on the third-order correction in 1/N expansion to the four-point correlator of the stress tensor multiplet in N=4 super Yang-Mills theory at large 't Hooft coupling, which corresponds to the two-loop scattering of four gravitons in the dual AdS5×S5 supergravity. This is obtained by bootstrapping an educated ansatz based on intuitions from a hidden 10-dimensionthe conformal symmetry, which I will describe in detail.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Mikhail Shaposhnikov (EPFL Lausanne)
2022-04-06 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/49/
Title: Anomaly-free scale symmetry and gravity (https://researchseminars.org/talk/ITMPseminar/49/)
by Mikhail Shaposhnikov (EPFL Lausanne) as part of Theoretical and Mathematical Physics

Abstract
What is the global symmetry of Nature? In the absence of gravity, the most obvious answer to this question is given by special relativity and is associated with the Poincare transformations. As was noted a long time ago, the free Maxwell equations have a wider symmetry group - the 15 parameters conformal invariance, containing in addition to ten Poincare generators, four special conformal transformations, and dilatations. Dilatations change the length of the rulers, while special conformal transformation can bend the lines but do not alter the angles between them. Could it be that the symmetry of all interactions is conformal? We show that conformal symmetry can be made free from the quantum anomaly only in the flat space. The presence of gravity would reduce the global symmetry group of the fundamental theory to the scale invariance only. We discuss how the effective Lagrangian respecting the scale symmetry can be used for the description of particle phenomenology and cosmology.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Barak Gabai (Harvard University)
2022-04-13 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/50/
Title: Exact quantization (https://researchseminars.org/talk/ITMPseminar/50/)
by Barak Gabai (Harvard University) as part of Theoretical and Mathematical Physics

Abstract
1d Hamiltonian problems are classically-integrable by definition. A manifestation of that is the fact that we can always use action-angle coordinates to parametrize the phase space. A generalization of the action variables to QM is not immediately obvious. In the presentation I will explain how to define rigorous quantities that can be thought of as the quantum action variables and how to write down an integral equation that determines their values, for a large class of 1d Schrodinger problems. Then, I will argue that these objects encode all of the dynamical information about the Quantum system, and explain how to extract the spectrum. The results are exact and rigorous.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Yuri Makeenko (ITEP, Moscow)
2022-04-27 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/51/
Title: How Pauli-Villars’ regularization tells the Nambu-Goto and Polyakov strings apart (https://researchseminars.org/talk/ITMPseminar/51/)
by Yuri Makeenko (ITEP, Moscow) as part of Theoretical and Mathematical Physics

Abstract
TBA

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Sergey Solodukhin (University of Tours)
2022-05-11 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/52/
Title: Quantum states and their back-reacted geometries (https://researchseminars.org/talk/ITMPseminar/52/)
by Sergey Solodukhin (University of Tours) as part of Theoretical and Mathematical Physics

Abstract
A black hole quantum state (Hartle-Hawking or Boulware) is usually defined in a fixed background of a classical black hole. In my talk I will discuss the corresponding space-time geometry when the back-reaction is taken into account. The important questions include: does the back-reacted geometry always contain a horizon?; how it depends on the choice of the quantum state?; and what is the right choice for the quantum state for the non-physical fields such as ghosts? I will answer these and other questions in the context of a two-dimensional dilaton gravity. The talk is based on a joint recent work with D. Sarkar and Y. Potaux, arXiv:2112.03855.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Dmitry Chicherin (Annecy LAPTH)
2022-05-18 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/53/
Title: Null Wilson loop with Lagrangian insertion in N=4 super Yang-Mills theory (https://researchseminars.org/talk/ITMPseminar/53/)
by Dmitry Chicherin (Annecy LAPTH) as part of Theoretical and Mathematical Physics

Abstract
Null Wilson loops in N = 4 super Yang-Mills are dual to planar scattering amplitudes. The duality holds at the level of their finite four-dimensional loop integrands as well as for the integrated observables with properly regularized infrared and cusp divergences. We consider a closely related infrared-finite four-dimensional observable which interpolates between the integrand and the fully loop-integrated quantity. It is defined as the null polygonal Wilson loop with a Lagrangian insertion normalized by the Wilson loop without insertion. Unlike the ratio and remainder functions of N = 4 super Yang-Mills amplitudes, this observable is non-trivial already at four points and it is reminiscent of finite parts of QCD amplitudes. We discuss the general structure of this n-point observable at weak coupling. At n>4, the loop corrections have rich kinematics. Indeed, there are several leading singularities and the accompanying loop functions are multivariable transcendental functions. We discuss a Grassmannian representation for the leading singularities and reveal their conformal and dual conformal symmetries. We conjecture a duality relation between the observable and the highest transcendentality piece of the planar all-plus amplitude in pure Yang-Mills theory. We test the duality using the one-loop n-point and two-loop four-point perturbative data for the observable. Relying on the duality, we predict the highest weight piece of the three-loop five-particle all-plus amplitude.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Luca Cassia (Uppsala University)
2022-05-25 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/54/
Title: q-Virasoro constraints and the algebra of Wilson loops in 3d (https://researchseminars.org/talk/ITMPseminar/54/)
by Luca Cassia (Uppsala University) as part of Theoretical and Mathematical Physics

Abstract
The BPS/CFT correspondence predicts that the partition function and other BPS observables in a 3d N=2 gauge theory can be mapped to states in a q-deformed CFT, i.e. a theory whose symmetry algebra is q-Virasoro. Following this idea, I will discuss how to derive q-Virasoro constraints for the generating function of 1/2-BPS Wilson loops for a family of 3d N=2 gauge theories.
Under certain assumptions on the Chern--Simons level and the number of flavors the constraints can be solved exactly and the solution can be recast as a "superintegrability" formula for characters of the gauge group. Moreover, I will show that the same logic can be applied to refined Chern--Simons theories and refined ABJ theories to derive formulas for refined knot invariants of the unknot. If time permits I will also discuss the symmetries of the constraints and their physical interpretation as dualities of the gauge theory. The talk is based on https://arxiv.org/abs/2007.10354 and https://arxiv.org/abs/2107.07525.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Dmitry Ponomarev (ITMP MSU, Moscow)
2022-06-01 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/55/
Title: Invariant traces of the flat space chiral higher-spin algebra as scattering amplitudes (https://researchseminars.org/talk/ITMPseminar/55/)
by Dmitry Ponomarev (ITMP MSU, Moscow) as part of Theoretical and Mathematical Physics

Abstract
We sum up two- and three-point amplitudes in the chiral higher-spin theory over helicities and find that these quite manifestly have the form of invariant traces of the flat space chiral higher-spin algebra. We consider invariant traces of products of higher numbers of on-shell higher-spin fields and interpret these as higher-point scattering amplitudes. This construction closely mimics its anti-de Sitter space counterpart, which was considered some time ago and was confirmed holographically.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Euihun Joung (Kyung Hee University, Seoul)
2022-06-08 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/56/
Title: Colorful particles and fields in low dimensions (https://researchseminars.org/talk/ITMPseminar/56/)
by Euihun Joung (Kyung Hee University, Seoul) as part of Theoretical and Mathematical Physics

Abstract
I will present a few recent applications of colorful extensions of spacetime symmetries to the theories of particles and fields in two and three dimensions. In particular, the two dimensional BF theories is shown to reduce a colorful extension of Schwarzian theory.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Vasily Maslov (ITMP MSU, Moscow)
2022-10-05 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/57/
Title: An Effective Field Theory for Large Oscillons (https://researchseminars.org/talk/ITMPseminar/57/)
by Vasily Maslov (ITMP MSU, Moscow) as part of Theoretical and Mathematical Physics

Abstract
Based on arXiv:2208.04334. We consider oscillons - localized, quasiperiodic, and extremely long-living classical solutions in models with real scalar fields. We develop their effective description in the limit of large size at finite field strength. Namely, we note that nonlinear long-range field configurations can be described by an effective complex field $\psi(t, \mathbf{x})$ which is related to the original fields by a canonical transformation. The action for $\psi$ has the form of a systematic gradient expansion. At every order of the expansion, such an effective theory has a global U(1) symmetry and hence a family of stationary nontopological solitons - oscillons. The decay of the latter objects is a nonperturbative process from the viewpoint of the effective theory. Our approach gives an intuitive understanding of oscillons in full nonlinearity and explains their longevity. Importantly, it also provides reliable selection criteria for models with long-lived oscillons. This technique is more precise in the nonrelativistic limit, in the notable cases of nonlinear, extremely long-lived, and large objects, and also in lower spatial dimensions. We test the effective theory by performing explicit numerical simulations of a (d+1)-dimensional scalar field with a plateau potential.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Sabir Ramamzanov (CEICO, Prague)
2022-10-19 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/58/
Title: Phase transitions in the dark Universe (https://researchseminars.org/talk/ITMPseminar/58/)
by Sabir Ramamzanov (CEICO, Prague) as part of Theoretical and Mathematical Physics

Abstract
Typically phase transitions are associated with a constant scale of symmetry breaking. In cosmology, however, a different situation is also natural: the expectation value of a scalar field responsible for symmetry breaking can be induced by its interactions with hot primordial plasma, in which case the expectation value decreases as the Universe cools down. This picture can be realized in a simple renormalizable and approximately scale-invariant scenario. Non-trivial time-dependence of the symmetry breaking scale enables new mechanisms of particle production at phase transitions. These particles can be considered for the role of dark matter. Another phenomenologically interesting outcome of phase transitions is formation of topological defects, which serve as a source of potentially observable gravitational waves. The latter can be used to probe the underlying model in a very weakly coupled regime inaccessible by other experiments.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Leonid Bork (ITEP, Moscow)
2022-10-26 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/59/
Title: Exact off-shell Sudakov form factor in N=4 SYM (https://researchseminars.org/talk/ITMPseminar/59/)
by Leonid Bork (ITEP, Moscow) as part of Theoretical and Mathematical Physics

Abstract
We consider the Sudakov form factor in N=4 SYM in the off-shell kinematical regime, which can be achieved by considering the theory on its Coulomb branch. We demonstrate that up two three loops both the infrared-divergent as well as the finite terms do exponentiate, with the coefficient accompanying log’s of mass determined by the octagon anomalous dimension Γ_oct. This behaviour is in strike contrast to previous conjectural accounts in the literature. Together with the finite terms we observe that up to three loops the logarithm of the Sudakov form factor is identical to twice the logarithm of the null octagon 𝕆_0, which was recently introduced within the context of integrability-based approaches to four point correlation functions with infinitely-large R-charges. The null octagon 𝕆_0 is known in a closed form for all values of the 't Hooft coupling constant and kinematical parameters. We conjecture that the relation between 𝕆_0 and the off-shell Sudakov form factor will hold to all loop orders.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Alexander Ochirov (London Institute for Mathematical Sciences)
2022-11-02 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/60/
Title: Chiral Approach to Massive Higher Spins (https://researchseminars.org/talk/ITMPseminar/60/)
by Alexander Ochirov (London Institute for Mathematical Sciences) as part of Theoretical and Mathematical Physics

Abstract
Quantum field theory of higher-spin particles is a formidable subject, where preserving the physical number of degrees of freedom in the Lorentz-invariant way requires a host of auxiliary fields. They can be chosen to have a rich gauge-symmetry structure, but introducing consistent interactions in such approaches is still a non-trivial task, with massive higher-spin Lagrangians specified only up to three points. In this talk, I will discuss a new, chiral description for massive higher-spin particles, which in four spacetime dimensions allows to do away with the unphysical degrees of freedom. This greatly facilitates the introduction of consistent interactions. I will concentrate on three theories, in which higher-spin matter is coupled to electrodynamics, non-Abelian gauge theory or gravity. These theories are currently the only examples of consistently interacting field theories with massive higher-spin fields.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Francois Rondeau (the Sorbonne)
2022-11-09 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/61/
Title: Intersecting D-brane models and the anomalous magnetic moment of the muon (https://researchseminars.org/talk/ITMPseminar/61/)
by Francois Rondeau (the Sorbonne) as part of Theoretical and Mathematical Physics

Abstract
The anomalous magnetic moment of the muon ($(g-2)_{\mu}$) might be one of the most promising signals of new physics beyond the Standard Model (SM). The theoretical calculation predicts a value smaller than the experimental measurement from the Brookhaven National Laboratory and Fermilab experiments, with a standard deviation of $4.7\sigma$. This talk will discuss recently proposed solutions to this discrepancy in the framework of low mass scale strings, large extra dimensions and intersecting D-brane physics.

After reminding some basic aspects of intersecting D-brane models, and in particular how the SM of particle physics can be obtained in this framework, we will present two proposals able to explain (part of) the observed discrepancy. They are based on the contributions to the $(g-2)_{\mu}$ coming from the Kaluza-Klein (KK) states of the lepton number gauge boson, corresponding to an open string tied to a leptonic $U(1)$ brane, as well as from light scalars corresponding to the first stringy excitations of an open string stretched between two D-branes intersecting with an ultra-small angle. In both cases, we show that there is a region of the parameter space compatible with the current experimental bounds, where these states can provide significant contributions to the $(g-2)_{\mu}$, and fully or partially bridge the gap in the observed discrepancy. We then build the minimal D-brane configurations able to realise these two proposals.

The talk is based on 2110.01247, 2112.07587 and 2209.11152.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Alexey Litvinov (Landau ITP, Chernogolovka)
2022-11-16 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/62/
Title: R-matrix formulation of affine Yangian of $\hat{gl}(1|1)$ and integrable systems of N=2 superconformal field theory (https://researchseminars.org/talk/ITMPseminar/62/)
by Alexey Litvinov (Landau ITP, Chernogolovka) as part of Theoretical and Mathematical Physics

Abstract
We study N=2 superconformal field theory and define the R-matrix which acts as an intertwining operator between different realisations of N=2W -algebras of type A. Using the R-matrix we define RLL algebra and relate it to current realisation of affine Yangian of $\hat{gl}(1|1)$. We also derive Bethe ansatz equations for the spectrum of integrals of motion.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Yuya Kusuki (Caltech and Wako, RIKEN)
2022-11-23 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/63/
Title: AdS/BCFT from Bootstrap: Construction of Gravity with particle & brane (https://researchseminars.org/talk/ITMPseminar/63/)
by Yuya Kusuki (Caltech and Wako, RIKEN) as part of Theoretical and Mathematical Physics

Abstract
We consider gravity with branes and massive particles, which has many unclear aspects. For example, we do not know how to understand some problematic configurations, like brane self-intersections, negative tension branes, and spinning particles interacting with branes. We address these issues through AdS/BCFT. We solve a related conformal bootstrap and show that the self-intersection can be avoided by the black hole formation. We also reveal how to resolve the other problems in AdS/BCFT using the bootstrap.
In the later part, we give the resolution of the same problems from the gravity side. For this purpose, we develop a simple way to construct gravity with branes and particles by cutting and pasting. The solution from this construction tells us how to resolve the issues from the gravity side, which is completely consistent with the CFT result.
As a bonus, we find a refined formula for the holographic Rényi entropy, which appears to be crucial to correctly reproduce the boundary entropy term. We also find a holographic dual of boundary primaries.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Carlo Heissenberg (Uppsala University and NORDITA)
2022-11-30 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/64/
Title: Angular Momentum Loss Due to Tidal Effects in the Post-Minkowskian Expansion (https://researchseminars.org/talk/ITMPseminar/64/)
by Carlo Heissenberg (Uppsala University and NORDITA) as part of Theoretical and Mathematical Physics

Abstract
The steadily increasing sensitivity of gravitational-wave measurements challenges the state of the art of precision calculations for gravitational collisions. In this context, scattering amplitudes have contributed to the advance of the precision frontier in the Post-Minkowskian (PM) expansion, based on successive approximations labeled by powers of Newton's constant G and valid for generic velocities. In this talk, based on arXiv:2210.15689, I will illustrate the calculation of tidal corrections to the loss of angular momentum in a two-body collision at leading Post-Minkowskian order from an amplitude-based approach. The eikonal operator allows us to efficiently combine elastic and inelastic amplitudes, and captures both the contributions due to genuine gravitational-wave emissions and those due to the static gravitational field. We calculate the former by harnessing powerful collider-physics techniques such as reverse unitarity, thereby reducing them to cut two-loop integrals. For the latter, we can employ the results of arXiv:2203.11915 where static-field effects were calculated for generic gravitational scattering events using the leading soft graviton theorem.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Anton Pribytok (Trinity College, Dublin)
2022-12-07 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/65/
Title: Automorphic symmetry and AdS String novel integrable deformations (https://researchseminars.org/talk/ITMPseminar/65/)
by Anton Pribytok (Trinity College, Dublin) as part of Theoretical and Mathematical Physics

Abstract
We address the new structures arising in quantum and string integrable theories, as well as construct a method to find them. Initially we implement the automorphic symmetries on periodic lattice systems and exploit properties of an integrable hierarchy. This prescription is first applied for potentially new sl_2 sector, Generalised Hubbard type classes and more. We then construct a boost recursion for systems with R-/S-matrices that exhibit arbitrary spectral dependence, which is also an apparent property of the scattering in AdS integrable backgrounds. The generalised bottom-up approach based on coupled differential systems is derived to resolve for R-matrices exactly. In addition, one can isolate a special class of models (non-difference form) that provide a new structure consistently arising in AdS_{3} and AdS_{2} string backgrounds. These classes can be proven to be represented as deformations of the AdS_{2,3} models, which satisfy free fermion, constraint, braiding unitarity, crossing and exhibit deformed algebraic structure that shares certain properties with AdS_3xSˆ3xMˆ4 and AdS_2xSˆ2xTˆ6 models. A related discussion on further investigation of AdS_3 free fermion property, TBA finite size corrections and GSE will be provided.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]

Dionysios Anninos (King’s College London)
2022-12-14 15:00 - 17:00 | https://researchseminars.org/talk/ITMPseminar/66/
Title: Finite Features in Holography (https://researchseminars.org/talk/ITMPseminar/66/)
by Dionysios Anninos (King’s College London) as part of Theoretical and Mathematical Physics

Abstract
We consider theories of gravity where a more "finite" holographic theory is relevant. From a Lorentzian perspective we comment on properties of gravity in the presence of finite timelike boundaries, and holographic realisations. Time permitting, we also discuss Euclidean gravity on manifolds with no boundary, like Euclidean de Sitter.

Meeting ID: 815 0976 8678
Passcode: [REDACTED]
