Seminars

The High Energy and Particle Physics group seminars are held on Tuesdays and/or Thursdays at 13:00.
Seminars with physical presence: 2nd floor of the physics department.
Online seminars on
Zoom at this link.

Seminars and recordings before 2021 can be found here.

Winter Semester

14 December, 17:30 EET (note unusual date and time)
Alex Altland (Cologne U.)
Title: TBA

Abstract: TBA

06 December, 13:00 EET
Geoffrey Compere
(ULB)
Title: TBA

Abstract: TBA

01 December, 11:00 EET (note unusual date and time)
Shigeki Sugimoto (Kyoto U.)
Title: TBA

Abstract: TBA

29 November, 13:00 EET
Prahar Mitra
(Cambridge)
Title: TBA

Abstract: TBA

24 November, 13:00 EET
Aninda Sinha (IIS, Bangalore)
Title: Positivity, low twist dominance and CSDR for CFTs

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.

16 November, 17:30 EET (note unusual date and time)
Ben Withers (Southampton)
Title: Convergence of the Fefferman-Graham expansion and complex black hole anatomy

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

15 November, 13:00 EET
Matthew Dodelson
(CERN)
Title: Orbits, scars, and supersymmetric instantons

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.

08 November, 13:30 EET (note unusual time)
Julian Sonner
(Geneva)
Title: Matrix Models for Eigenstate Thermalization with applications to holography

Abstract: TBA

01 November, 13:00 EET
Himanshu Raj
(IPHT)
Title: Bootstrapping M-theory scattering amplitude in AdS

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.

25 October, 13:00 EEST
Jack Holden
(University of Southampton)
Title: Partial deconfinement

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.

11 October, 13:00 EEST
Nick Warner
(University of Southern California)
Title: Black-Hole Microstate Structures in String Theory

Abstract: I will review the recent results in the study of microstate geometries and describe some of the future directions for this research.

04 October, 13:00 EEST
Achilleas Porfyriadis (University of Crete)
Title: TBA

Abstract: TBA

27 September, 13:00 EEST
Sergio Morales Tejera (Madrid, IFT)
Title: Chiral magnetic effect in the quark gluon plasma via holography

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.

20 September, 13:00 EEST
Chris Rosen (University of Crete)
Title: Leigh-Strassler on a spindle

Abstract: I will describe an interesting new class of supersymmetric AdS_3 solutions in supergravity.