Found at least 20 result(s)

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102637' style='color:#f0ad4e'>Vacua in locally de Sitter cosmologies, and how to distinguish them

Regular Seminar Jorma Louko (Nottingham U.)

at:
01:00 - 01:00
KCL Strand
room: S0.12
abstract:

de Sitter spacetime admits distinct Friedmann-Robertson-Walker foliations with cosh, sinh and exponential time evolution laws. In three or more spacetime dimensions, these foliations have respectively positive, negative and vanishing spatial curvature. In two spacetime dimensions, by contrast, there is no spatial curvature, and all three evolution laws allow spatial sections with S^1 topology and a freely specifiable spatial circumference parameter. We identify geometrically preferred quantum states for a massive scalar field on these locally de Sitter 1+1 cosmologies, some singled out by adiabatic criteria, others induced from the Euclidean vacuum by a quotient construction. We show how a comoving quantum observer, modelled as an Unruh-DeWitt detector, can distinguish these states by local measurements. (Joint work with Vladimir Toussaint, 2304.10395)

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01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 298' style='color:#f0ad4e'>Non-ergodic extended phase of the Quantum Random Energy model

regular seminar Mikhail Feigel'man (NANOCENTER Ljubljana, Slovenija and Landau ITP, Moscow, Russia)

at:
01:00 - 01:00
KCL, Strand
room: S4.23
abstract:

The concept of non-ergodicity in quantum many body systems can be discussed in the context of the wave functions of the many body system or as a property of the dynamical observables, such as time-dependent spin correlators. In the former approach the non-ergodic delocalized state is defined as the one in which the wave functions occupy a volume that scales as a non-trivial power of the full phase space. In this work we study the simplest quantum spin glass model and find that in the delocalized non-ergodic regime the spinâspin correlators decay with the characteristic time that scales as non-trivial power of the full Hilbert space volume. The long time limit of this correlator also scales as a power of the full Hilbert space volume. We identify this phase with the glass phase whilst the many body localized phase corresponds to a âhyperglassâ n which dynamics is practically absent. We discuss the implications of these findings to quantum information problems.

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01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 296' style='color:#f0ad4e'>Distribution of random quasifuchsian surfaces in 3-manifolds

regular seminar Vladimir Markovic FRS (University of Oxford)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

I will discuss the distribution of geometrically and topologically nearly geodesic random surfaces in a closed hyperbolic 3-manifold M, and describe the resulting PSL(2,R) invariant measures on the Grassmann bundle of M. (Joint work with J. Kahn and I. Smilga.)

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01.01.1970 (Thursday)

NT' style='color:#f0ad4e'>NT 292' style='color:#f0ad4e'>Internal number theory seminar: New p-adic L-functions for GSp(4)

regular seminar Nina Wawrów (KCL)

at:
01:00 - 01:00
KCL, Strand
room: S-2.08
abstract:

We will overview a construction of p-adic L-functions for GSp(4) by Loeffler-Pilloni-Skinner-Zerbes and discuss some recent work on interpolating them in a family of Hecke character twists.

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01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 257' style='color:#f0ad4e'>KCL Probability Seminar: The Critical Window for Random Graphs

regular seminar Dominic Yeo (King's College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

I will talk about the history of the Erdos-Renyi random graph model G(n,p), and its critical point, p=1/n. The critical window is a range of p, in which the largest components have the same scaling but not exactly the same distributional limit as at criticality itself. I will discuss several aspects of the behaviour of these graphs within the critical window, including a surprising connection to the mixing of random permutations.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102659' style='color:#f0ad4e'>Topology change and non-geometry at infinite distance

Exceptional Seminar Saskia Demulder (Ben Gurion U.)

at:
01:00 - 01:00
KCL Strand
room: K4.31
abstract:

The Swampland program aims at formulating a complete set of criteria in order to identify theories that can be uplifted in the UV to a theory of quantum gravity. The distance conjecture in particular diagnoses viable low energy effective theories by examining their breakdown at infinite distance in their parameter space. At the same time, infinite distance points in parameter space are naturally intertwined with string dualities and in particular T-duality. In this talk, we will show that this relation becomes much richer and intricate when the internal space is curved or supported by fluxes. Consistency of T-duality then leads us to suggest an extension to the Swampland distance conjecture. This work is in collaboration with Thomas Raml and Dieter Lüst.

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01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 294' style='color:#f0ad4e'>The thermodynamic cost of precision

regular seminar Francesco Coghi (Nordic Institute for Theoretical Physics (Stockholm))

at:
01:00 - 01:00
KCL, Strand
room: S4.23
abstract:

We will explore the interplay between thermodynamic cost, in terms of energy dissipated, and precision of a physical system whose only accessible information is a time series of discrete events. The analytical derivations - based on variational methods of large deviations - reveal universal bounds, extending beyond the thermodynamic uncertainty relation to diverse nonequilibrium driven systems and general time-asymmetric observables. Additionally, we will see how optimal precision saturating the bounds can be physically achieved and showcase practical applications. This includes distinguishing voluntary actions controlled by the sensorimotor cortex of rats and detecting coherence effects in atomic clocks.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102647' style='color:#f0ad4e'>Lonti: CFTs in Lorentzian signature (3/4)

Regular Seminar Petr Kravchuk (King's)

at:
01:00 - 01:00
KCL Strand
room: LIMS
abstract:

In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 270' style='color:#f0ad4e'>Non-invertible symmetries and LSM-type constraints on a tensor product Hilbert space

regular seminar Nedelin Anton (KCL)

at:
01:00 - 01:00
KCL, Strand
room: Norfolk Building 342N
abstract:

Seiberg Seifnashri & Shao
arXiv:2401.12281

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01.01.1970 (Thursday)

AN' style='color:#f0ad4e'>AN 288' style='color:#f0ad4e'>On isolated singularities and generic regularity of min-max CMC hypersurfaces

regular seminar Kobe Marshall-Stevens (UCL)

at:
01:00 - 01:00
KCL, Strand
room: S5.20
abstract:

Smooth constant mean curvature (CMC) hypersurfaces serve as effective tools to study the geometry and topology of Riemannian manifolds. In high dimensions however, one in general must account for their singular behaviour. I will discuss how such hypersurfaces are constructed via min-max techniques and some recent progress on their generic regularity, allowing for certain isolated singularities to be perturbed away.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102658' style='color:#f0ad4e'>Emergence of space and time in holography

Triangular Seminar Hong Liu (MIT)

at:
01:00 - 01:00
KCL Strand
room: S-2.23
abstract:

In holographic duality, a higher dimensional quantum gravity system is equivalent to a lower dimensional conformal field theory (CFT) with a large number of degrees of freedom. In this talk, I will introduce a framework to describe using the CFT how geometric notions in the gravity system, such as spacetime subregions, different notions of times, causal structure, and spacetime connectivity, emerge in the semi-classical limit.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102657' style='color:#f0ad4e'>Double-scaled SYK and de Sitter Holography

Triangular Seminar Vladimir Narovlansky (Princeton U.)

at:
01:00 - 01:00
KCL Strand
room: S-2.23
abstract:

Double-scaled SYK (DSSYK) is a model with interesting dynamics, and many known exact results. Yet, the gravitational behavior of the system is not fully understood. I will discuss the reasoning behind a suggested connection between DSSYK and de Sitter holography. We will mention the general form of the correspondence as well as the mapping of parameters between the two sides. On the SYK side we consider two copies of DSSYK at infinite temperature with an equal energy constraint. We will discuss explicitly the two-point function in double-scaled SYK and compare it to de Sitter.

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01.01.1970 (Thursday)

ME' style='color:#f0ad4e'>ME 289' style='color:#f0ad4e'>Embedding Climate Change in the Undergraduate Mathematics Curriculum with Student Co-Creators

regular seminar Dr Chris Sutton (Queen Mary, University of London)

at:
01:00 - 01:00
KCL, Strand
room: UCL, Torrington Place (1-19), Room 102
abstract:

This seminar will summarise a project exploring how analysis of climate change can be embedded in a range of modules including pure, applied, statistics and computing using student co-creators. We will then use this project to reflect on the potential for student co-creation in curriculum development.

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01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 287' style='color:#f0ad4e'>(Semi)classical phase-space features of quantum systems with non-Hermitian Hamiltonians

regular seminar Eva-Maria Graefe (Imperial College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.23
abstract:

While traditional quantum mechanics focusses on systems conserving energy and probability, described by Hermitian Hamiltonians, in recent decades there has been ever growing interest in the use of non-Hermitian Hamiltonians. These can effectively describe loss and gain in a quantum system. In particular systems with a certain balance of loss and gain, PT-symmetric systems, have attracted considerable attention. The realisation of PT-symmetric quantum dynamics in optical systems has opened up a whole new field of investigations.

The properties of non-Hermitian quantum systems are often less intuitive than those of conventional Hermitian systems. Here we make use of the Husimi representation in phase space to analyse dynamical and spectral features. We consider the flow of the Husimi phase-space distribution in a semiclassical limit, leading to a first order partial differential equation, that helps illuminate the foundations of the full quantum evolution. Further, we demonstrate how ingredients of the dynamics can be used to construct approximate Husimi distributions of characteristic quantum states.

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01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 285' style='color:#f0ad4e'>Applications of Laurent inversion to K-moduli

regular seminar Liana Heuberger (University of Bath)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

I will discuss how to use Laurent inversion, a technique coming from mirror symmetry which constructs toric embeddings, to study the local structure of the K-moduli space of a K-polystable toric Fano variety. More specifically, starting from a toric Fano 3-fold X of anticanonical volume 28 which smooths to a Fano threefold of Picard rank 4, we combine a local study of its singularities with the global deformation provided by Laurent inversion, and conclude that the K-moduli space is rational around X. This is joint work with Andrea Petracci.

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01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 256' style='color:#f0ad4e'>KCL Probability Seminar:

regular seminar Dominic Yeo (King's College London)

at:
01:00 - 01:00
KCL, Strand
room: S4.29
abstract:

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01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 286' style='color:#f0ad4e'>Advanced Lecture Series: Non-equilibrium fluctuations of interacting particle systems. Part II

regular seminar Tomohiro Sasamoto (Tokyo Institute of Technology, Japan)

at:
01:00 - 01:00
KCL, Strand
room: S4.23
abstract:

For systems in thermal equilibrium, it is well known from equilibrium statistical mechanics that fluctuations play important role, in particular in systems close to phase transitions. For non-equilibrium systems, fluctuations are
also important, giving rise to dynamical scalings, long-range correlations and capturing time reversal symmetry properties. In these two lectures we study a few aspects of non-equilibrium fluctuations by mainly treating one-dimensional systems which are analytically tractable.
We plan to cover mainly the two subjects. The first is the Kardar-Parisi-Zhang universality. We start by introducing basic models such as exclusion processes and KPZ equation. We then discuss the mapping to a problem of directed polymer in random media and exact solutions. We also discuss appearances of KPZ universality in other contexts, including anharmonic chains, random unitary circuit and quantum spin chains.
The second is the macroscopic fluctuation theory. This was introduced by a group of Jona-Lasinio et al around 2000 and has been developed since then. It is believed to describe large deviation aspects of non-equilibrium systems. Recently a few exact solutions for the MFT equations have been achieved by finding connections to classical integrable systems. We explain both basic aspects and the recent progress about the theory.

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01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102646' style='color:#f0ad4e'>Lonti: CFTs in Lorentzian signature (2/4)

Regular Seminar Petr Kravchuk (King's)

at:
01:00 - 01:00
KCL Strand
room: LIMS
abstract:

In these lectures we will discuss various aspects of conformal field theories in Lorentzian signature. First, we will study the general properties of Lorentzian correlation functions, including their global conformal structure and the relation to Euclidean correlators. We will then consider the Regge limit of correlation functions and how this limit requires the introduction of complex spin. We will define complex spin using the Lorentzian inversion formula, and interpret it in terms of non-local light-ray operators. Finally, we will discuss applications of light-ray operators to even shape observables.

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01.01.1970 (Thursday)

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 275' style='color:#f0ad4e'>Parameterizing and Simulating from Causal Models

regular seminar Robin Evans (Oxford)

at:
01:00 - 01:00
KCL, Strand
room:
abstract:

Many statistical problems in causal inference involve a probability distribution other than the one from which data are actually observed\DSEMIC as an additional complication, the object of interest is often a marginal quantity of this other probability distribution. This creates many practical complications for statistical inference, even where the problem is non-parametrically identified. In particular, it is difficult to perform likelihood-based inference, or even to simulate from the model in a general way.

We introduce the frugal parameterization, which places the causal effect of interest at its centre, and then builds the rest of the model around it. We do this in a way that provides a recipe for constructing a regular, non-redundant parameterization using causal quantities of interest. In the case of discrete variables we can use odds ratios to complete the parameterization, while in the continuous case copulas are the natural choice. Our methods allow us to construct and simulate from models with parametrically specified causal distributions, and fit them using likelihood-based methods, including fully Bayesian approaches. Our proposal includes parameterizations for the average causal effect and effect of treatment on the treated, as well as other common quantities of interest.

I will also discuss some other applications of the frugal parameterization, including to survival analysis, generative modelling, parameterizing nested Markov models, and â˜Many Dataâ: combining randomized and observational datasets in a single parametric model.

This is joint work with Vanessa Didelez (University of Bremen and BIPS), Xi Lin and Daniel Manela (both Oxford).

Reference
Evans, R.J. and Didelez, V. Parameterizing and Simulating from Causal Models (with discussion), J. Roy. Statist. Ser. B, 2024.

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