University of Crete HEP Seminars


Leigh-Strassler on a spindle

Chiral magnetic effect in the quark-gluon plasma via holography

Speaker: Chris Rosen
Institution: CCTP University of Crete
Time: Tuesday 20 September 2022, 13:00
Venue: Second floor seminar room
Abstract: I describe an interesting new class of supersymmetric AdS_3 solutions in supergravity. I discuss their relevance to the Leigh-Strassler four dimensional SCFT cimpactified on a spindle.

Extreme Black Hole Anabasis

Speaker: Sergio Morales Tejera
Institution: IFT University of Madrid
Time: Tuesday 27 September 2022, 13:00
Venue: Second floor seminar room
Abstract: The Chiral Magnetic Effect (CME) has recently been under investigation in the data of the isobar run at RHIC. Understanding how the effect is realized in heavy ion collisions is affected by many difficulties. We will address one of these: the question of how long it takes for the CME current to build up in a non-equilibrium situation. This is a relevant question since the life-time of the magnetic field is limited. To this end we shall study a holographic model which allows to monitor the out-of-equilibrium evolution of relevant quantities such as pressure anisotropy and CME. We will first introduce the physics behind the CME and later focus on its holographic realisation and results.

Black hole microstate structures in string theory

Speaker: Achilleas Porfyriadis
Institution: CCTP University of Crete
Time: Tuesday 04 october 2022, 13:00
Venue: Second floor seminar room
Abstract: I introduce the notion of anabasis in the context of extremal black holes.
Speaker: Nick Warner
Institution: USC
Time: Tuesday 11 October 2022, 13:00
Venue: Webinar
Abstract: I will review the recent results in the study of microstate geometries and describe some of the future directions for this research.
Recording: The recorded talk can be found here.

Partial deconfinement

Speaker: Jack Holden
Institution: University of Southampton
Time: Tuesday 25 October 2022, 13:00
Venue: Webinar
Abstract: In large-N gauge theories, evidence has emerged recently that between confined and deconfined phases a partially-deconfined phase can appear, in which only a subset of colours deconfine. The existence of such a phase has implications for the map between degrees of freedom under gauge/gravity duality and black hole phase diagrams, where a counterpart to the partially-deconfined saddle should be present. We investigate properties of partial deconfinement on the field theory side, first considering the partially-deconfined saddle of large-N pure Yang-Mills theory. Here, the colour degrees of freedom split into confined and deconfined sectors. We argue with the use of numerical simulations that a linear confinement potential is generated in the confined sector, implying the formation of flux tubes, whereas the potential is screened in the deconfined sector and behaves instead according to the perimeter law. Furthermore, we find that the onset of partial deconfinement coincides with the breaking of chiral symmetry breaking, providing an order parameter for the partially-deconfined phase. We conjecture that partial deconfinement is accompanied by a unique signature of global symmetry breaking that can serve as an order parameter. As another, cleaner example of this, we show that CP symmetry breaking coincides precisely with the emergence of the partially-deconfined phase in supersymmetry-broken n = 1 super-Yang-Mills with a theta-angle theta = pi, for both large finite N and the formal large-N limit. Finally, we discuss consequences of these findings for holography, the QCD crossover, and the internal phase structure of neutron stars.
Recording: The recorded talk can be found here.

Bootstrapping M-theory scattering amplitude in AdS

Speaker: Himanshu Raj
Institution: IPHT
Time: Tuesday 01 November 2022, 13:00
Venue: Webinar
Abstract: Using the analytical conformal bootstrap, supersymmetric localization and AdS/CFT correspondence, we determine the complete four-point graviton scattering amplitude in the maximally supersymmetric AdS solution of M-theory upto a certain order in 1/c expansion, c being the central charge of the dual superconformal field theory. The talk will be based on the results from the recent paper 2207.11138 which builds upon several previous works including 2107.10274 and 2005.07175.
Recording: The recorded talk can be found here.

Matrix Models for Eigenstate Thermalization with applications to holography

Speaker: Julian Sonner
Institution: University of Geneva
Time: Tuesday 08 November 2022, 13:30
Venue: Webinar
Abstract: New connections between the behavior of matrix models and the eigenstate thermalization hypothesis will be discussed.
Recording: The recorded talk can be found here.

Orbits, scars, and supersymmetric instantons

Speaker: Matthew Dodelson
Institution: CERN
Time: Tuesday 15 November 2022, 13:00
Venue: Webinar
Abstract: I will describe recent work on the boundary interpretation of orbits around an AdS black hole. When the orbits are far away from the black hole, these orbits describe heavy-light double-twist operators in the boundary CFT. I will discuss how the dimensions of these operators can be computed exactly in terms of quasinormal modes in the bulk, using techniques from supersymmetric gauge theory. I will also explain how these results are related to the concept of quantum scars, which are eigenstates that do not obey the eigenstate thermalisation hypothesis.
Recording: The recorded talk can be found here.

Convergence of the Fefferman-Graham expansion and complex black hole anatomy

Speaker: Ben Withers
Institution: University of Southampton
Time: Wednesday 16 November 2022, 17:30
Venue: Webinar
Abstract: The AdS/CFT correspondence provides a map between data appearing in AdS gravity and CFT sources and one-point functions in the presence of sources. This data appears in a near-boundary expansion for asymptotically AdS spacetimes, the Fefferman-Graham expansion. In this talk I will discuss the large-order behaviour of the Fefferman-Graham expansion for black holes and holographic RG-flows. I will identify the physical features limiting its radius of convergence and discuss the causal structure appearing over multiple sheets of the complex Fefferman-Graham plane.
Recording: The recorded talk can be found here.

Positivity, low twist dominance and CSDR for CFTs

Speaker: Aninda Sinha
Institution: IIS Bangalore
Time: Thursday 24 Noevember 2022, 13:00
Venue: Webinar
Abstract: We consider a crossing symmetric dispersion relation (CSDR) for CFT four point correlation with identical scalar operators, which is manifestly symmetric under the cross-ratios u,v interchange. This representation has several features in common with the CSDR for quantum field theories. It enables a study of the expansion of the correlation function around u=v=1/4, which is used in the numerical conformal bootstrap program. We elucidate several remarkable features of the dispersive representation using the four point correlation function of Phi_{1,2} operators in 2d minimal models as a test-bed. When the dimension of the external scalar operator (Delta_sigma) is less than 1/2, the CSDR gets contribution from only a single tower of global primary operators with the second tower being projected out. We find that there is a notion of low twist dominance (LTD) which, as a function of Delta_sigma, is maximized near the 2d Ising model as well as the non-unitary Yang-Lee model. The CSDR and LTD further explain positivity of the Taylor expansion coefficients of the correlation function around the crossing symmetric point and lead to universal predictions for specific ratios of these coefficients. These results carry over to the epsilon expansion in 4-epsilon dimensions. We also conduct a preliminary investigation of geometric function theory ideas, namely the Bieberbach-Rogosinski bounds.
Recording: The recorded talk can be found here.

New phases of N=4 SYM

Speaker: Prahar Mitra
Institution: Cambridge
Time: Tuesday 29 November 2022, 13:00
Venue: Webinar
Abstract: We construct new static solutions to gauged supergravity that, via the AdS/CFT correspondence are dual to thermal phases in N=4 SYM at finite chemical potential. These solutions dominate the micro-canonical ensemble and are required to ultimately reproduce the microscopic entropy of AdS black holes. These are constructed in two distinct truncations of gauged supergravity and can be uplifted to solutions of type IIB supergravity. Together with the known phases of the truncation with three equal charges, our findings permit a good understanding of the full phase space of SYM thermal states with three arbitrary chemical potentials.
Recording: The recorded talk can be found here.

Anomaly and superconnection

Speaker: Shigeki Sugimoto
Institution: Kyoto University
Time: Thursday 01 December 2022, 11:00
Venue: Webinar
Abstract: In this talk, I will discuss anomalies of fermions with spacetime-dependent masses. Using Fujikawa's method, it is found that the anomalies can be described in terms of superconnections introduced by a mathematician D. Quillen in 1985. I will explain some of the applications of our anomaly formulas to the systems with interfaces and spacetime boundaries. This talk is based on our recent paper arXvi:2106.01591, which was written in collaboration with Hayato Kanno.
Recording: The recorded talk can be found here.

Metric reconstruction from celestial multipoles

Speaker: Geoffrey Compere
Institution: ULB
Time: Tuesday 06 December 2022, 13:00
Venue: Webinar
Abstract: I will attempt to present in a pedagogical way two recent results on the structure of vacuum 4d asymptotically flat spacetimes. First, I will derive their complete set of conserved ``celestial’’ charges in the linear theory within the Bondi framework and prove their equivalence to the holomorphic basis of Freidel et al. where it was shown that the charges form the Lw_{1+\infty} algebra. I will then review elements of the post-Minkowskian formalism and explain the dictionary between the basic ingredients of the formalism, the canonical multipole moments, and the Bondi data. I will then use this dictionary to derive the complete set of conserved charges of non-radiating spacetimes, which consist of the celestial charges excluding the Newman-Penrose charges. I will show that this complete set can be alternatively described as the set of Geroch-Hansen multipole moments, the generalized BMS charges and dual supermomenta, and finally additional subleading celestial charges related to subleading memory effects.
Recording: The recorded talk can be found here.

Anomalous and axial Z' contributions to g-2

Speaker: Pascal Anastasopoulos
Institution: Vienna Uinversity
Time: Thursday 08 December 2022, 13:00
Venue: Webinar
Abstract: In this talk, we will study the effects of an anomalous Z' boson on the anomalous magnetic moment of the muon (g-2), and especially the impact of its axial coupling. We mainly evaluate the negative contribution to (g-2) of such couplings at one-loop and look at the anomalous couplings generated at two loops. We find areas of the parameter space, where the anomalous contribution becomes comparable and even dominant compared to the one-loop contribution. We show that in such cases, the cutoff of the theory is sufficiently low, so that new charged fermions can be found in the next round of collider experiments.
Recording: The recorded talk can be found here.

Semiclassical quantum chaos and two-dimensional gravity

Speaker: Alex Altland
Institution: University of Cologne
Time: Wednesday 14 December 2022, 17:30
Venue: Webinar
Abstract: Quantum chaos addresses the quantum mechanics of systems that are chaotic in the classical limit. Application fields include condensed matter physics, the physics of cold atomic and optical systems, particle physics, and gravity. Classical chaos manifests itself in the properties of phase space trajectories, quantum chaos in strong correlations of spectra. In this talk I will review how these two structures are related to each other. We will then discuss how the bridge between classical and quantum chaos has become relevant as a guiding principle in the construction of a two-dimensional holographic correspondence.
Recording: The recorded talk can be found here.

Microstates of a (non-supersymmetric) 2d Black Hole in string theory

Speaker: Panos Betzios
Institution: University of British Columbia
Time: Tuesday 20 December 2022, 13:00
Venue: Webinar
Abstract: We analyse models of Matrix Quantum Mechanics in the double scaling limit that contain non-singlet states. The finite temperature partition function of such systems contains non-trivial winding modes (vortices) and is expressed in terms of a group theoretic sum over representations. We then focus in the case when the first winding mode is dominant (model of Kazakov-Kostov-Kutasov). In the limit of large representations (continuous Young diagrams), and depending on the values of the parameters of the model such as the compactification radius and the string coupling, the dual geometric background corresponds to that of a long string (winding mode) condensate or a 2d2d (non-supersymmetric) Black Hole. In the matrix model we can tune these parameters and explore various phases and regimes. Our construction allows us to identify the origin of the microstates of these backgrounds, arising from non trivial representations, and paves the way for computing various observables on them.
Recording: The recorded talk can be found here.