Found at least 20 result(s)
regular seminar He Yifei (LPENS, Paris)
at: 01:00 - 01:00 KCL, Strand room: S0.12 abstract: | We propose the Gauge Theory Bootstrap, a method to compute the pion S-matrix that describes the strongly coupled low energy physics of QCD and other similar gauge theories. The method looks for the most general S-matrix that matches at low energy the tree level amplitudes of the non-linear sigma model and at high energy, QCD sum rules and form factors. We compute pion scattering phase shifts for all partial waves with angular momentum $\ell<=3$ up to 2 GeV and calculate the low energy ChiPT coefficients. This is a theoretical/numerical calculation that uses as only data the pion mass $m_\pi$, pion decay constant $f_{\pi}$ and the QCD parameters $N_c=3$, $N_f=2$, $m_q$ and $\alpha_s$. All results are in reasonable agreement with experiment. In particular, we find the $\rho(770)$, $f_2(1270)$ and $\rho(1450)$ resonances and some initial indication of particle production near the resonances. The interplay between the UV gauge theory and low energy pion physics is an example of a general situation where we know the microscopic theory as well as the effective theory of long wavelength fluctuations but we want to solve the strongly coupled dynamics at intermediate energies. The bootstrap builds a bridge between the low and high energy by determining the consistent S-matrix that matches both and provides, in this case, a new direction to understand the strongly coupled physics of gauge theories. Based on work with Martin Kruczenski. Keywords: |
regular seminar Eamonn Postlethwaite and Ngoc Khanh Nguyen (KCL)
at: 01:00 - 01:00 KCL, Strand room: Bush House (SE) 2.10 abstract: | Ngoc Khanh Nguyen:
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journal club Andy Svesko (KCL)
at: 01:00 - 01:00 KCL, Strand room: Norfolk Building 342N abstract: | Keywords: |
regular seminar Jessica Barrett (University of Cambridge (MRC Biostatistics))
at: 01:00 - 01:00 KCL, Strand room: S5.20 abstract: | Routinely collected healthcare data is becoming more commonly used for healthcare research. The increasing availability of such data promises advantages in the shape of largescale, representative data, but also brings many challenges which require statistical innovation. I will highlight some of these promises and challenges using four examples illustrating the use of routinely collected data, including modelling lung function trajectories of cystic fibrosis patients, dynamic prediction of cardiovascular disease, multi-state modelling of multimorbidity and predicting outcomes for intensive care patients. Keywords: |
regular seminar Robert Simon (LSE)
at: 01:00 - 01:00 KCL, Strand room: S5.20 abstract: | A colouring rule is a way to colour the points x of a probability space according to the colours of finitely many measure preserving transformations
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regular seminar Dr Joan Nakato (University of Warwick)
at: 01:00 - 01:00 KCL, Strand room: UCL, Torrington Place (1-19), B09 abstract: | Although STEM programs adequately equip students with the disciplinary knowledge required for the workplace, research suggests that STEM graduates have insufficient professional competencies. Further, employers expect STEM graduates to be able to link their areas of expertise to other disciplines (Sarkar et al., 2016) so that “a subject is not divided by watertight bulkheads from all others.
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regular seminar Marta Mazzocco (University of Birmingham)
at: 01:00 - 01:00 KCL, Strand room: S4.29 abstract: | In this talk, I will explain how to apply the Fock-Goncharov construction to the representation theory of a class of algebras introduced by Etingof, Oblomkov and Rains. Keywords: |
Regular Seminar Claudia de Rham (Imperial College)
at: 01:00 - 01:00 KCL Strand room: LIMS abstract: | CANCELLED due to an unforeseen speaker emergency. Keywords: |
regular seminar Lakshmi Priya (Tel Aviv University)
at: 01:00 - 01:00 KCL, Strand room: S4.29 abstract: | I will present a simple but curious observation on the zeros of centered stationary Gaussian processes (SGP) on $\mathbb{R}$. The object of interest is
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regular seminar Alessia Annibale (KCL)
at: 01:00 - 01:00 KCL, Strand room: S4.23 abstract: | Diverse equilibrium systems with heterogeneous interactions lie at the edge of stability. Such marginally stable states are dynamically selected as the most abundant ones or as those with the largest basins of attraction. On the other hand, systems with non-reciprocal (or asymmetric) interactions are inherently out of equilibrium, and exhibit a rich variety of steady states, including fixed points, limit cycles and chaotic trajectories. How are steady states dynamically selected away from equilibrium? We address this question in a simple neural network model, with a tunable level of non-reciprocity. Our study reveals different types of ordered phases and it shows how non-equilibrium steady states are selected in each phase. In the spin-glass region, the system exhibits marginally stable behaviour for reciprocal (or symmetric) interactions and it smoothly transitions to chaotic dynamics, as the non-reciprocity (or asymmetry) in the couplings increases. Such region, on the other hand, shrinks and eventually disappears when couplings become anti-symmetric. Keywords: |
journal club Nika Sokolova (KCL)
at: 01:00 - 01:00 KCL, Strand room: Norfolk Building 342N abstract: | Keywords: |
regular seminar Megan Griffin-Pickering (UCL)
at: 01:00 - 01:00 KCL, Strand room: S5.20 abstract: | Vlasov-Poisson type systems are well established kinetic models for dilute plasma. The precise structure of the model differs according to which species of charged particle (electrons or ions) it describes, with the most well known version of the system describing electrons. The model for ions, however, has been studied only more recently, owing to an additional exponential nonlinearity in the equation for the electrostatic potential that creates several mathematical difficulties not encountered in the electron case.
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Regular Seminar David Berenstein (UCSB)
at: 01:00 - 01:00 KCL Strand room: S0.12 abstract: | I will discuss a novel construction of field theories based on the idea that one has only a half boson degree of freedom per lattice site. Basically, instead of having a pair of canonical conjugate commuting variables at each site, one has only one degree of freedom and the non-trivial commutators arise from connections to the nearest neighbors. The construction is very similar to staggered fermions and naturally produces gapless systems with interesting topological properties. When considering gauging discrete translations on the phase space in one dimensional examples, one gets interesting critical spin chains, examples of which include the critical Ising model in a transverse magnetic field and the 3-state Potts model at criticality. I will explain how these staggered boson variables are very natural for describing non-invertible symmetries.
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regular seminar Dario Beraldo (University College London)
at: 01:00 - 01:00 KCL, Strand room: S3.31 abstract: | I will outline the recent proof of the (global, unramified) geometric Langlands conjecture, obtained in collaboration with Arinkin, Chen, Gaitsgory, Faergeman, Lin, Raskin and Rozenblyum.
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Regular Seminar Claudia de Rham (Imperial College)
at: 01:00 - 01:00 KCL Strand room: LIMS abstract: | CANCELLED due to an unforeseen speaker emergency. Keywords: |
regular seminar Leonid Pastur (King's College London)
at: 01:00 - 01:00 KCL, Strand room: S4.29 abstract: | We study the distribution of singular values for the product of random matrices related to the analysis of deep neural networks. The matrices are similar to the product of sample covariance matrices of statistics, but an important difference is that in statistics the population covariance matrices are assumed to be non-random or random but independent of the random data matrix, while now they are certain functions of the random data matrices (matrices of synaptic weights in the terminology of deep neural networks). The problem was treated recently by J. Pennington et al. assuming that the weight matrices are Gaussian and using the methods of free probability theory. Since, however, free probability theory deals with population covariance matrices that do not depend on data matrices, its applicability to this case must be justified. We use a version of the random matrix theory technique to prove the results of J. Pennington et al. in the general case where the entries of weight matrices are independent identically distributed random variables with zero mean and finite fourth
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Regular Seminar Claudia de Rham (Imperial College)
at: 01:00 - 01:00 KCL Strand room: LIMS abstract: | CANCELLED due to an unforeseen speaker emergency.
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journal club Omar Shahpo (KCL)
at: 01:00 - 01:00 KCL, Strand room: Norfolk Building 342N abstract: | Keywords: |
regular seminar Yue Zhao (University of York)
at: 01:00 - 01:00 KCL, Strand room: S5.20 abstract: | We study the estimation of partial derivatives of nonparametric regression functions with many variables, with a view to conducting a significance test for the said derivatives. Our test is based on the moment generating function of the smoothed partial derivatives of an estimator of the regression function, where the estimator is a deep neural network. We demonstrate that in the context of modelling with neural networks, derivative estimation is in fact quite different from estimating the regression function itself, and hence the smoothing operation becomes important. To conduct an effective test with predictors of high or even diverging dimension, we assume that first, the observed high-dimensional predictors arise from a factor model and that second, only the lower-dimensional but latent factors and a subset of the marginals of the high-dimensional predictors drive the regression function. Moreover, we finely adjust the regression function estimator in order to achieve the desired asymptotic normality under the null hypothesis that the partial derivative in question is zero. We demonstrate the performance of our test in simulation studies.
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regular seminar Elena Boguslavskaya (Brunel University London)
at: 01:00 - 01:00 KCL, Strand room: S5.20 abstract: | In this talk, we introduce a fractional analogue of the Wiener chaos expansion. It is important to highlight that the fractional order relates to the order of chaos decomposition elements, and not to the process itself, which continues to be the standard Wiener process. The central instrument in our fractional analogue of the Wiener chaos expansion is the function denoted as $\mathcal{H}_\alpha(x,y)$, which is referred to herein as a power-normalised parabolic cylinder function ( and is very similar to the Hermite function).
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