We are located at the 6th floor of the G.O. Jones Building on the Mile End Campus, midway between Stepney Green and Mile End Tube stations, approximately 15-20 minutes from central London on the Central or District lines. If exiting Stepney Green tube station, turn left and walk along the Mile End Road for approximately 300 metres. The G.O. Jones (Physics) building is to the right of the main college building, which is fronted by a clocktower and lawn. If exiting Mile End tube station, turn left and walk approximately 300 metres until you are opposite the main college building. A more detailed description can be found here.

`Found at least 20 result(s)`

Informal Seminar Dhritiman Nandan (University of Southampton)

at:15:30
room 610 | abstract: We consider α′ corrections to four-point correlators of half-BPS operators in N = 4 super Yang-Mills theory in the supergravity limit within the context of AdS/CFT. By demanding the correct behaviour in the flat space limit, we find that the leading (α′)^3 correction to the Mellin amplitude is fixed for arbitrary charges of the external operators. We consider double-trace operators and observe striking patterns in the α′ corrections to the spectra which hint at their common ten-dimensional origin. By extending the observed patterns and imposing them at order (α′)^5 we are able to reproduce recent results for certain correlators as well as deduce some new results. |

Journal Club Iva Lovrekovic (Imperial College)

at:14:00
room 610 | abstract: I will talk about the recent quite interesting article by Maldacena, in which he writes on the subject of the traversable wormholes. The most interesting thing that needs to be pointed out here are the way that wormholes are stabilised without the addition of the exotic matter while the theory that describes them is still Einstein gravity, with Maxwell theory and charged massless fermion, since wormholes without the addition of the exotic matter have been known in the higher derivative theories. The wormhole is made possible by fermions that give rise to negative Casimir-like energy and by being a long wormhole which does not lead to causality violations. https://arxiv.org/abs/1807.04726 |

Regular Seminar Ingo Runkel (Hamburg U.)

at:14:00
room 610 | abstract: I would like to discuss a class of three-dimensional topological field theories called Reshetikhin-Turaev theories. Examples are Chern-Simons theories with compact gauge group. There are no point-like observables in these theories, and one typically considers line-observables, called Wilson lines. However, one can also discuss observables associated to surfaces. We will see how to describe such observables in Reshetikhin-Turaev TQFTs and look at some applications. |

Regular Seminar Fei Teng (Uppsala University)

at:14:00
room G O Jones 610 | abstract: In this talk, I will connect, via tree-level double copy, any massless string amplitudes with QFT amplitudes given by Cachazo-He-Yuan (CHY) formula. This can be derived by a detailed study of integration-by-part (IBP) reduction of string integrands. As an application, we consider general multitrace integrands of heterotic string amplitudes. The new technology generates a recursive expansion of the heterotic string amplitudes in terms of those with fewer gravitons and traces, where the kinematic coefficients are building blocks for BCJ numerators of the (DF)^2+YM+phi^3 theory. Finally, we give a generic CHY integrand for multitrace (DF)^2+YM+phi^3 amplitudes, which reproduce the corresponding heterotic string amplitudes after double copy with a single-valued Z-theory. |

Journal Club Gim Seng Ng (Trinity College Dublin)

at:15:00
room G O Jones 610 | abstract: We study the leading and next-to-leading eikonal phase in the context of AdS/CFT. In the bulk side, we compute the phase shift of a highly energetic particle traveling in the background of an asymptotically AdS black hole. In the dual CFT, the phase shift is related to a four point function in the Regge limit. The black hole mass is translated to the ratio between the conformal dimension of a heavy operator and the central charge. This ratio serves as a useful expansion parameter; its power measures the number of stress tensors appearing in the intermediate channel. The leading eikonal phase shift in 4d holographic CFTs can be computed using conformal Regge theory while the computation of the next-to-leading order eikonal phase shift relies on a new universal formula for the lowest-twist OPE of double-trace stress-tensors with two scalar operators. These OPE coefficients are consistent with the second-order phase shift as well as anomalous dimensions obtained in AdS black holes in the lightcone limit. In relations to the idea of “eikonalization” of the stress-tensor sector in holographic CFTs, we comment on hints of a structure similar to the vacuum Virasoro block in 2d CFT. |

Regular Seminar Saso Grozdanov (MIT)

at:14:00
room G O Jones 610 | abstract: Hydrodynamic excitations corresponding to sound and diffusive modes in fluids are characterised by gapless dispersion relations. In the hydrodynamic gradient expansion, their frequencies are represented by infinite power series in spatial momenta. I will discuss how the introduction of a new concept of the hydrodynamic complex spectral curve in the space of complexified frequency and spatial momentum—the concept otherwise known from algebraic geometry---can be used to prove general properties about hydrodynamics, including its finite radius of convergence. When the infinite series are resummed, they exhibit a fascinating, recently-discovered phenomenon of pole-skipping, which enables us to analyse the underlying, microscopic quantum many-body chaos in the system. Throughout my talk, I will use gauge-gravity duality as a tool to explicitly show these phenomena in holographic systems and discuss what their implications are for the dual gravity theory. |

Exceptional Seminar Andrey Gromov (Brown U.)

at:15:00
room G.O. Jones 610 | abstract: Fractional quantum Hall (FQH) states are topologically ordered. Additionally, FQH states support a collective neutral excitation known as the Girvin-MacDonald-Platzman (GMP) mode. Certain features of this mode are independent of the microscopic details. The objective of the talk is to construct an effective theory includes both topological properties and the massive GMP mode. The theory reproduces the universal properties of chiral lowest Landau level (LLL) FQH states which lie beyond the TQFT data, such as the projected static structure factor and the GMP algebra of area-preserving diffeomorphisms. The dynamics of the mode is described by a fluctuating rank-2 symmetric, positive-definite tensor, which leads to a natural geometric (or gravitational) interpretation of the GMP mode. |

Regular Seminar Michele Levi (IPhT Saclay)

at:14:00
room G O Jones 610 | abstract: This talk presents the progress made in my research via the introduction of effective field theories (EFTs) into post-Newtonian (PN) gravity. These have been put forward in the context of gravitational waves (GWs) from the compact binary inspiral. The setup and the strategy of a multi-stage EFT framework, which is deployed for the PN binary inspiral problem, is outlined. I then present in more detail the study of two effective theories at the intermediate scales of the problem. First, the EFT for a single rotating compact object is considered, from which I proceed to the EFT of a compact binary system, viewed as a composite particle with internal binding interactions. I conclude with the prospects of building on the field, and using further modern field theory insights and tools, to address the study of GWs, as well as to expand our fundamental understanding of QFTs and gravity theories at all scales. |

Regular Seminar Franz Ciceri (AEI Potsdam)

at:15:00
room G O Jones 610 | abstract: Supersymmetric extensions of conformal gravity have been known for a long time. In four dimensions, N=4 conformal supergravity is the maximally supersymmetric theory of this type. Although its field representation and the non-linear transformations rules were derived more than 30 years ago, no invariant action had been constructed so far. We present the most general class of actions which turns out to be characterised by a holomorphic function. This deviates from the non-maximally supersymmetric cases where the action is unique. Meanwhile, elaborate loop computations have indicated that N=4 Poincare supergravity diverges at four loops, and the divergence is believed to be related to the presence of a potential one-loop anomaly in the duality symmetry of the theory. We argue that one of the constructed conformal actions, after gauge fixing the conformal symmetries and carefully eliminating auxiliary fields, can be used as a finite supersymmetric counterterm that cancels the anomalous contribution of the one-loop graphs in the Poincare theory. |

Regular Seminar Jaco van Zyl (Witwatersrand U.)

at:14:00
room G O Jones 610 | abstract: The 1/2 BPS and regular LLM geometries are formed from the backreaction of a large number of D-branes on AdS_5 x S^5. The dual N=4 SYM operator to this configuration, and excitations thereof, thus lie outside of the planar limit of the theory. Explicitly the operators dual to these geometries are Schur polynomials labelled by a Young diagram with O(N^2) boxes and excitations of this configuration are restricted Schur polynomials obtained by adding boxes (and restriction labels) to this diagram. A special class of these geometries are labelled by Young diagrams with O(1) well separated corners. In the large N limit excitations localised at any one of these corners only mix with each other which is a major simplification. A recent proposal has argued that the large N dynamics of these operators is isomorphic to that of planar N=4 SYM and thus represents an integrable subsector of N=4 SYM. In this talk this proposal is reviewed and aspects of the weak and strong coupling evidence presented. |

Regular Seminar Rohini Godbole (Indian Institute of Science)

at:15:00
room G O Jones 610 | abstract: After a summary of current status of experimental results in particle physics, including the presentation of what I call the LHC paradox, I will discuss briefly how colliders were indispensible in arriving at this point of the journey. After this I would discuss what the next steps are: as to where do we go from here in the story of collider physics. If time is left, I will discuss some of the issues that the future colliders can address , by taking examples from the known unknowns, viz. in the framework of particular BSM models and also the unknown unknowns viz the model independent approach. |

Regular Seminar Simone Giacomelli (Oxford)

at:14:00
room G O Jones 610 | abstract: In this seminar I will discuss a recently-found class of RG flows in four dimensions exhibiting enhancement of supersymmetry in the infrared, which provides a lagrangian description of several strongly-coupled N=2 SCFTs. The procedure involves starting from a N=2 SCFT, coupling a chiral multiplet in the adjoint representation of the global symmetry to the moment map of the SCFT and turning on a nilpotent expectation value for this chiral. We show that, combining considerations based on 't Hooft anomaly matching and basic results about the N=2 superconformal algebra, it is possible to understand in detail the mechanism underlying this phenomenon and formulate a simple criterion for supersymmetry enhancement. |

Regular Seminar Anatoly Konechny (Heriot-Watt University)

at:14:00
room G.O. Jones 610 | abstract: Renormalisation group (RG) interfaces were introduced by I. Brunner and D. Roggenkamp in 2007. To construct such an interface consider perturbing a UV fixed point, described by a conformal field theory (CFT), by a relevant operator on a half space. Renormalising and letting the resulting QFT flow along the RG flow we obtain a conformal interface between the UV and IR fixed point CFTs. Although enjoying a full conformal symmetry this interface carries information about the RG flow it originated from. In this talk I will consider a rather special case of the RG interface between two boundary conditions of a 2D CFT which is obtained from a boundary RG flow interpolating between two conformal boundary conditions. This interface is zero-dimensional and is thus described by a local boundary-condition changing operator. I investigate its properties in concrete models and formulate a number of general conjectures that can help charting phase diagrams of boundary RG flows. |

Regular Seminar Matthew Roberts (Imperial)

at:14:00
room G O Jones 610 | abstract: We construct new supersymmetric solutions of 11D supergravity, preserving 1/4 of the supersymmetry, that are dual to the ABJM Chern-Simons-matter theory deformed by mass terms which depend on one spatial direction. The BPS equations boil down to solving the Helmholtz equation on the complex plane giving rise to rich classes of new solutions. In particular, the construction gives rise to infinite classes of new supersymmetric “boomerang” RG flows, as well as generalising other previously known solutions. |

Regular Seminar David Berenstein (UC Santa Barbara)

at:14:00
room G O Jones 610 | abstract: I will describe simple models of holography that can display some of the thermodynamics associated to small black holes. These phenomena include negative specific heat and localization on additional dimensions of the geometry. I will also explain how the dynamics of these states should naturally be thought of as partial deconfinement on a submatrix set of degrees of freedom of the model. |

Regular Seminar Massimo Bianchi (Roma Tor Vergata)

at:14:00
room G O Jones 610 | abstract: Ultra-planckian collisions represent a fertile arena where to test quantum theories of gravity such as string theory. Glimpses of black hole formation and evaporation can be taken. For suitably defined infrared-safe observables, we show that the `classicalization' approach to high-multiplicity processes agrees with the ACV approach based on the resummation of ladder diagrams. Since a significant fraction of energy is lost in gravitational bremsstrahlung, we re-derived the zero-frequency limit (ZFL) of the GW flux using soft graviton theorems at leading order and compute the corrections at sub- and sub-sub-leading order. For massless two-particle elastic collisions the former is shown to vanish, while the latter takes an explicit expression which is checked against a simple tree-level process.However, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs resummation, an unphysical IR singularity occurs due to the infinite Coulomb phase. We briefly discuss a recent proposal as how to deal with these divergences and find agreement with the eikonal approach. |