Found at least 20 result(s)

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 211' style='color:#f0ad4e'>TBA

journal club Schaub Vladimir (KCL)

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

Keywords:

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 200' style='color:#f0ad4e'>Asynchronous development: novel experimental designs and applications of functional data analysis

regular seminar Daphne Ezer (University of York)

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

Plants undergo several key developmental transitions, such as the decision to flower, that farmers would like to synchronise to maximise their yields. In this talk I will describe (i) a novel experimental design to understand how these transitions happen and (ii) a novel application of functional data analysis to help farmers breed more synchronised crops. To understand the biological regulation that leads to these transition points, a high temporal resolution of sampling would be required\DSEMIC however, the degree of developmental asynchrony makes such an experiment difficult to design. Instead, we sample a large collection of individual plants at the transition point and then estimate their age retroactively with a bootstrapping strategy, enabling us to order the plants along a pseudotime, giving us an unprecedented level of detail of the cascade of biological events that lead to the initiation of flowering. We then hypothesised that plants that are more sensitive to changes in day length (as occur in the spring and autumn) would have more synchronised development. Using functional data analysis approaches, we developed a predictive model of flowering synchrony on the basis of how the circadian rhythms of plants respond to changes in day length, in a population of plants with parents adapted from different latitudes. We are further adapting FDA methods to identify genetic loci that are significantly associated with these clock-related traits, which can be used to direct crop breeding for synchronised development.

Keywords:

01.01.1970 (Thursday)

AN' style='color:#f0ad4e'>AN 198' style='color:#f0ad4e'>Symmetrization inequalities on graphs

regular seminar Shubham Gupta (Imperial College London)

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

In the Euclidean space setting, symmetrization inequalities is a classical theory that has been quite useful in solving problems coming from various parts of analysis: spectral geometry, variational problems, mathematical physics, spectral theory, to name a few. In my talk, I will discuss a possible extensions of this theory to the setting of graphs. It is a fairly new topic and most of the results in the area are proved in the last two years. I will talk about these developments, connections of this theory with discrete isoperimetric inequalities, and its possible applications to problems concerning 'analysis on graphs'. The talk will be at the interface of discrete math and analysis, and will be based on a joint work with Stefan Steinerberger.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102592' style='color:#f0ad4e'>QFT in AdS instead of LSZ

Regular Seminar Balt van Rees (Ecole Polytechnique)

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

The boundary correlation functions for a quantum field theory (QFT) in a fixed antiââ¬âœde Sitter (AdS) background should reduce to S-matrix elements in the flat-space limit. We consider this procedure in detail for four-point functions. With minimal assumptions we rigorously show that the resulting S-matrix element obeys a dispersion relation, the nonlinear unitarity conditions, and the Froissart-Martin bound. QFT in AdS thus provides an alternative route to fundamental QFT results that normally rely on the LSZ axioms.

Keywords:

01.01.1970 (Thursday)

ME' style='color:#f0ad4e'>ME 205' style='color:#f0ad4e'>Maths education seminar: The King's Factor

regular seminar Dr Asuka Kumon (King's College London)

at:
01:00 - 01:00
KCL, Strand
room: K0.50
abstract:

Keywords: Outreach

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 210' style='color:#f0ad4e'>Cohomogeneity-one Lagrangian Mean Curvature Flow

regular seminar Albert Wood (King's College London)

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

Mean Curvature Flow, the negative gradient flow for the volume functional of submanifolds of Riemannian manifolds, is a well-studied field of modern geometric analysis. Of particular interest are classifications of self-similar solutions (shrinkers, expanders, and translators) and finite-time singularities\DSEMIC projects which when completed will hopefully allow one to apply the flow to prove results in Riemannian geometry and differential topology. Moreover, in a Calabi-Yau manifold the class of Lagrangian submanifolds is preserved by mean curvature flow, a fact which inspired Thomas and Yau to make influential conjectures about existence of special Lagrangians in Calabi-Yau manifolds.

In this talk, we aim to make progress towards an understanding of self-similar solutions and singularities of Lagrangian mean curvature flow, by focusing on Lagrangians in C^n that are cohomogeneity-one under the action of a compact Lie group. Interestingly, each such Lagrangian lies in a level set \mu^{-1}(c) of the moment map \mu, and mean curvature flow preserves this containment. Using this, we classify all shrinking, expanding, and translating solitons, and in the zero level set \mu^{-1}(0), we classify the Type I and Type II blowup models of LMCF singularities. Finally, given any special Lagrangian in \mu^{-1}(0), weâll show that it arises as a Type II blowup, thereby yielding infinitely many new singularity models of Lagrangian mean curvature flow.

The results presented in this talk are contained in the preprint â˜Cohomogeneity-One Lagrangian Mean Curvature Flowâ, which is jointly written with Jesse Madnick, University of Oregon.

Keywords:

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 204' style='color:#f0ad4e'>KCL Probability Seminar: Heterogeneous diffusion: uniqueness, non-uniqueness, and selection

regular seminar Ilya Pavlyukevich (Friedrich Schiller University Jena)

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

We study solutions of the irregular Stratonovich SDE $dX = X|^\alpha \circ dB$, $\alpha\in (0, 1)$. In particular we construct solutions spending positive time in 0, describe solutions spending zero time in 0, and show how a particular physically natural solution can be singled out by means of an additional external "ambient" noise.

This talk is based on the joint works with G. Shevchenko (Kiev).

Keywords: SDE, Stratonovich, diffusion

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 191' style='color:#f0ad4e'>KCL Probability Seminar: On the convergence of the random walk Metropolis algorithm

regular seminar Sam Power (University of Bristol)

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

The Random Walk Metropolis (RWM) is a simple and enduring Markov chain-based algorithm for approximate simulation from an intractable â˜targetâ probability distribution. In this work, we study quantitatively the convergence of this algorithm, providing non-asymptotic estimates on mixing times, with explicit dependence on dimension and other problem parameters. The results hold at a reasonable level of generality, and are often sharp in a suitable sense.

The focus of the talk will be conceptual rather than technical, with an eye towards enabling intuition for i) which high-level aspects of the target distribution influence the convergence behaviour of RWM, and ii) which concrete properties must be verified in order to obtain a rigorous proof. No prior knowledge of the RWM is required from the audience.

Keywords: Metropolis algorithm, Markov chain, Random Walk

01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 214' style='color:#f0ad4e'>Quantum Entanglement in Disordered Systems: Lecture 2

regular seminar ()

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

second lecture by Prof Leonid A. Pastur

See https://dsadvancedlectures.weebly.com/

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 201' style='color:#f0ad4e'>Non-minimal coupling, negative null energy, and effective field theory

journal club Pardo Santos Diego (KCL)

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

The non-minimal coupling of scalar fields to gravity has been claimed to violate energy conditions,
leading to exotic phenomena such as traversable wormholes, even in classical theories. In this work
we adopt the view that the non-minimal coupling can be viewed as part of an effective field
theory (EFT) in which the field value is controlled by the theoryâs cutoff. Under this assumption,
the average null energy condition, whose violation is necessary to allow traversable wormholes, is
obeyed both classically and in the context of quantum field theory. In addition, we establish a type
of âœsmearedâ null energy condition in the non-minimally coupled theory, showing that the null
energy averaged over a region of spacetime obeys a state dependent bound, in that it depends on
the allowed field range. We finally motivate our EFT assumption by considering when the gravity
plus matter path integral remains semi-classically controlled.

Keywords:

01.01.1970 (Thursday)

AN' style='color:#f0ad4e'>AN 195' style='color:#f0ad4e'>Symmetrization inequalities on graphs

regular seminar Shubham Gupta (Imperial College London)

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

In the Euclidean space setting, symmetrization inequalities is a classical theory that has been quite useful in solving problems coming from various parts of analysis: spectral geometry, variational problems, mathematical physics, spectral theory, to name a few. In my talk, I will discuss a possible extensions of this theory to the setting of graphs. It is a fairly new topic and most of the results in the area are proved in the last two years. I will talk about these developments, connections of this theory with discrete isoperimetric inequalities, and its possible applications to problems concerning 'analysis on graphs'. The talk will be at the interface of discrete math and analysis, and will be based on a joint work with Stefan Steinerberger.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 102572' style='color:#f0ad4e'>Renormalization group flows in AdS and the bootstrap program

Regular Seminar Marco Meineri (U. Turin)

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

We consider the renormalization group flow of a quantum field theory (QFT) in Anti-de Sitter (AdS) space. We derive sum rules that express UV data and the energy of a chosen eigenstate in terms of the spectral densities and certain correlation functions of the theory. In two dimensions, this leads to a bootstrap setup that involves the UV central charge and may allow us to follow a Renormalization Group (RG) flow non-perturbatively by continuously varying the AdS radius. Along the way, we establish the convergence properties of the newly discovered local block decomposition, which applies to three-point functions involving one bulk and two boundary operators.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 196' style='color:#f0ad4e'>Theoretical Physics Group Seminar

regular seminar Marco Meineri (U. Turin)

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

Keywords:

01.01.1970 (Thursday)

GE' style='color:#f0ad4e'>GE 197' style='color:#f0ad4e'>Geometry Seminar: On the deformation theory of L-foliations

regular seminar Sebastián Velazquez (King's College London)

at:
01:00 - 01:00
KCL, Strand
room: S2.29
abstract:

We will review some general concepts of deformation theory. Then we will apply these ideas in order to explore the geometry of the moduli space Inv of foliations on a given variety $X$ around the points corresponding to foliations induced by Lie group actions. More precisely, let $X$ be a smooth projective variety over the complex numbers and $S(d)$ the scheme parametrizing $d$-dimensional Lie subalgebras of $H^0(X,\mathcal{T} X)$. For every $\mathfrak{g} \in S(d)$ one can consider the corresponding element $\mathcal{F}(\mathfrak{g})\in Inv$, whose generic leaf coincides with an orbit of the action of $\exp(\mathfrak{g})$ on $X$. We will show that under mild hypotheses, after taking a stratification $\coprod_i S(d)_i\to S(d)$ this assignment yields an isomorphism $\coprod_i S(d)_i\to Inv$ locally around $\mathfrak{g}$ and $\mathcal{F}(\mathfrak{g})$.

Keywords:

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 190' style='color:#f0ad4e'>KCL Probability Seminar: Cylindrical Lévy processes

regular seminar Markus Riedle (King's College London)

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

Cylindrical Lévy processes are a natural extension of cylindrical Brownian motion which has been the standard model of random perturbations of partial differential equations and other models in infinite dimensions for the last 50 years. Here, the attribute cylindrical refers to the fact that cylindrical Brownian motions are not classical stochastic processes attaining values in the underlying space but are generalised objects. The reasons for the choice of cylindrical but not classical Brownian motion can be found in the facts that there does not exist a classical Brownian motion with independent components in an infinite dimensional Hilbert space, and that cylindrical processes enable a very flexible modelling of random noise in time and space.

This talk is a very introductory presentation to cylindrical Lévy processes. We explain the difficulty to define random noises in infinite dimensions and explain the approach by cylindrical measures and cylindrical random variables, which are strongly related to other areas such as harmonic analysis and operator theory. We present some specific examples of cylindrical Lévy processes in detail and discuss their relations to other models of random perturbations in the literature. We explain how a theory of stochastic integration for cylindrical Lévy processes can be developed although standard approaches to stochastic integration cannot be applied, and how this theory can be used to derive a theory of stochastic partial differential equations driven by Cylindrical Lévy processes.

Keywords:

01.01.1970 (Thursday)

TP' style='color:#f0ad4e'>TP 203' style='color:#f0ad4e'>TBA

journal club Pethybridge Ben ()

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

Keywords:

01.01.1970 (Thursday)

ST' style='color:#f0ad4e'>ST 194' style='color:#f0ad4e'>Scalable variational Bayes inference for multivariate Hawkes processes

regular seminar Judith Rousseau (University of Oxford)

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

Multivariate nonlinear Hawkes processes are powerful models for multi-
variate point processes with excitation and inhibation phenomenon. Bayesian
nonparametric methods have been proposed and studied theoretically, showing good properties. However their implementation remain a challenge due to the complexity of the likelihood and the potentially high dimensional
space. In this work we propose a two step variational Bayes approach to
estimate both the graph of interaction and the functions of interactions. We
give theoretical guarantees to the procedure and show that it scales well for
moderately high dimensional Hawkes processes.
This is a joint work with Deborah Sulem and Vincent Rivoirard.

Keywords:

01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 187' style='color:#f0ad4e'>Disordered Systems Days at King's College London

external event ()

at:
01:00 - 01:00
KCL, Strand
room: Nash Lecture Theatre K2.31
abstract:

The Disordered Systems Group at King's College London is organising a two-day event on the physics of disorder in both the classical and quantum setting, hosting a selection of international leading experts in the field. The first day of the event will be dedicated to our dear colleague Reimer Kühn, who is retiring at the end of the current academic year. The Workshop will be an opportunity to thank Reimer for his invaluable contributions to the field and to the life of our research group. More infos at https://disorderdayskcl.weebly.com/

Keywords:

01.01.1970 (Thursday)

DS' style='color:#f0ad4e'>DS 188' style='color:#f0ad4e'>Low energy excitations of vector spin glasses

regular seminar Flavio Nicoletti (Sapienza University of Rome)

at:
01:00 - 01:00
KCL, Strand
room: S3.31
abstract:

In recent years, great efforts have been devoted to the study of the vibrational spectrum of glasses [1]. Extensive numerical data show that the density of states of several different glassy models follows a quartic law at low frequencies, with related modes spatially quasi-localised. These observations are consistent with predictions of pre-existing phenomenological theories, like the soft potential model [2], in which a glass is effectively represented as a set of interacting anharmonic oscillators.

In this presentation we discuss the theory of spin glasses as a first-principle theory for glassy excitations. We consider spin glass models with vector unit spins, both in the mean field case and in the diluted case, with and without the action of a random external field at zero temperature. In the mean field case, the Hessian of the energy function is an instance of the Deformed Wigner ensemble [3], with gapless spectra extending down to zero energy. Matrices of this ensemble can feature density of states with power-law lower tails and localized eigenvectors at the edges of the spectrum: we found that in the passage from a stable to a marginally stable phase, the system undergoes a delocalization transition in its softest modes [4, 5].In the diluted case, we considered a random regular graph as underlying interaction network. We find by means of numerical simulations that the density of states follows the quartic law, as observed in finite-dimensional glasses. The related modes are localized, but can feature non-trivial topological patterns, such as modes made of localization cores scattered far-apart from each other. Lacking a theoretical argument that establishes a connection between the properties of low energy excitations and the emergence of marginal stability, we study numerically the topological properties of soft modes against the onset of the spin glass transition in a field [6].


[1] E Lerner and E Bouchbinder. J. Chem. Phys. 155.20, 200901 (2021).
[2] VL Gurevich, DA Parshin and HR Schober. Phys. Rev. B 67.9, 094293 (2003).
[3] JO Lee and K Schnelli. Probab. Theory Relat. Fields 164.1-2, 165 (2016).
[4] S Franz, F Nicoletti, G Parisi, F Ricci-Tersenghi. SciPost Physics 12.1, 016 (2022).
[5] S Franz, F Nicoletti and F Ricci-Tersenghi. J. Stat. Mech. Theory Exp. 2022.5, 053302 (2022).
[6] F Nicoletti. âœLow energy excitations of vector spin glassesâ, PhD Thesis. Link: https://theses.hal.science/tel-04144692.

Keywords: spin glasses, density of states

01.01.1970 (Thursday)

PR' style='color:#f0ad4e'>PR 186' style='color:#f0ad4e'>Directional gradient estimates on the Lévy-Itô space

regular seminar Stefan Geiss (University of Jyväskylä (Finland) )

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

Assume a pure jump L\'evy process $X=(X_t)_{t\in [0,T]}$ with L\'evy measure $\nu$ and a Borel function $f:\rm{\bf R} \to \rm{\bf R}$ with $f(x+X_s)\in L_1$ for $(s,x)\in [0,T]\times \rm{\bf R}$. Define $F:[0,T]\times \rm{\bf R}\to \rm{\bf R}$ by
$F(t,x) := E f(x+X_{T-t})$ and the vector-valued gradient \[ D_J F:[0,T) \times \rm{\bf R} \to L_0(\rm{\bf R}\setminus \{0\} )
\quad \mbox{by} \quad
D_J F(t,x) := \left \{ z \mapsto \frac{F(t,x+z) - F(t,x)}{z} \right \} \] known from Malliavin calculus and non-local PDEs. If $\rho$ is a finite Borel measure on $\rm{\bf R}$ sharing the small ball estimate $\rho([-r,r])\le c r^\varepsilon$ for some $\varepsilon \ge 0$ and if the coupling property $\| P_{z+X_s} - P_{X_s}\|_{TV} \le d |z| s^{-\frac{1}{\beta}}$ holds for some $\beta \in (0,2]$, then in \cite{1} we prove \[ \left \| (T-t)^\alpha \sup_{x\not = 0} \left | \int_{\rm{\bf R}\setminus \{0\}} (\partial_J F(t,x))(z) d\rho(z)
\right | \right \|_{L_q((0,T],\frac{d t}{T-t})}
\le C \| f \|_{{\rm Hoel}_{\eta,q}},\] where $f$ belongs to the Besov space ${\rm Hoel}_{\eta,q}(\rm{\bf R})$ with $(\eta,q)\in (0,1-\varepsilon)\times [1,\infty]$, $X\subseteq L_{\eta+\gamma}$ for some $\gamma>0$, and for $\alpha:= \frac{1-(\varepsilon+\eta)}{\beta}>0$.
The exponent $\alpha$ is best possible. The estimate applies to stable like processes. Applications to the predictable representation property on the L\'evy-It\^o space and the path-regularity of the gradient $D_JF$ are given.


\begin{thebibliography}{9}
\bibitem{1} S.~Geiss and T.~Nguyen:
On Riemann-Liouville type operators, BMO, gradient estimates in the L\'evy-It\^o space, and approximation,
arXiv:2009.00899.\smallskip
\end{thebibliography}

Keywords: