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Department of Physics

The Cavendish Laboratory
 

Wed 15 Jun 16:00: In Search for the Next Magic Stone

Talks - Tue, 24/05/2022 - 15:38
In Search for the Next Magic Stone

Materials demarcate periods of human civilization. The current period can be argued as defined by silicon, the magic stone that transformed the way we live. In this talk, I will discuss how the concept of quantum, and the 1st wave of quantum revolution led to the rise of silicon, integrated circuit, Silicon Valley and the information age. I will then discuss the opportunities and challenges in materials where silicon class theory fails. The focus will be on modern spectroscopy tools in aiding the development of quantum many-body theory, by testing ideas, discovering surprises and benchmarking theories, aiming at a new wave of quantum, in search for the next magic stone.

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Tue 31 May 16:00: Precision Physics with Polarised W-bosons at the LHC

Talks - Tue, 24/05/2022 - 11:45
Precision Physics with Polarised W-bosons at the LHC

The longitudinal polarisation of weak bosons originates from the Electroweak symmetry breaking mechanism and thus represents a handle on new physics. Direct observation of boson polarisation is not possible, but one finds its trace left in kinematical distributions, which we utilise to separate longitudinal and transverse modes. I will explore how W-boson polarisation is defined and can be accessed at the LHC , and present our recent studies at NNLO precision for W+j and WW processes. We will discuss the impact and effects of higher-order corrections. Finally, I will touch upon the topic of W-mass measurements in the context of its link to polarisations, and present our latest results which provide state-of-the-art theoretical input for the future mass measurements at the LHC .

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Tue 04 Oct 16:00: The search for exotic long-lived particles: illuminating a blind spot of the LHC programme

Talks - Thu, 19/05/2022 - 15:01
The search for exotic long-lived particles: illuminating a blind spot of the LHC programme

Exotic long-lived particles (LLPs) occur in many well-motivated extensions to the Standard Model (SM) of particle physics, and could explain the nature of Dark Matter (DM). However, LLPs could have been missed by the traditional LHC search programme to date due to their non-standard energy deposition patterns, which would often be thrown away as noise by standard reconstruction techniques. LLP signatures could be hiding in the “Blind Spot” of LHC searches! This talk will include a general motivation for LLP searches, and highlight the sort of signatures which are expected at CMS and ATLAS , as well as the unusual background which must be mastered. Recent examples of LLP results from the ATLAS collaboration will be used to highlight some of the novel techniques which are employed in these searches. Finally, prospects for the development of the LLP programme at CERN in coming years will be presented.

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Fri 20 May 16:00: Building blocks of the flavourful SMEFT RG

Talks - Thu, 19/05/2022 - 09:33
Building blocks of the flavourful SMEFT RG

An effective field theory’s power lies in the possibility of connecting scales through renormalisation group flow, encapsulated in the anomalous dimensions of the operators. The anomalous dimension matrix of the SMEFT encodes clues towards where to find relics of heavy new physics in data, but its unwieldy 2499×2499 size (at operator dimension six) makes it difficult to draw general conclusions. In this talk, I will review recent progress on understanding the structure of the matrix using on-shell methods. Pairing this with a flavour decomposition of the Wilson coefficient matrices, I will show that small subsystems emerge which mix almost exclusively amongst themselves. This deconstruction of the RGEs provides a first step to understanding the IR-attractive directions in the SMEFT parameter space, hence closing in on natural places for heavy new physics to make itself known.

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Tue 24 May 16:00: Colour meets Flavour: QCD contributions to the decay of heavy hadrons

Talks - Thu, 12/05/2022 - 08:12
Colour meets Flavour: QCD contributions to the decay of heavy hadrons

Lifetimes of heavy hadrons are determined experimentally very precisely by now. On the theoretical side, the total decay width, namely the inverse of the lifetime, can be systematically computed in the framework of the heavy quark expansion (HQE) in terms of a series expansion in inverse powers of the heavy quark mass mQ. The applicability of the HQE strongly relies on the assumption that mQ is much larger than the typical hadronic scale, and in order to obtain precise theoretical predictions it is crucial to have good control on higher power corrections. In this talk, I will discuss the computation of the Darwin operator contribution, which corresponds to corrections of order mQ^{-3} in the HQE and review the current theoretical status for quantities like B and D mesons lifetime and mixing. Finally, by comparing precise measurements with the corresponding HQE predictions, it is possible to constrain the parameter space for new physics models that might e.g. explain the B anomalies.

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Thu 19 May 16:00: Is wood a material?

Talks - Tue, 10/05/2022 - 16:58
Is wood a material?

The seminar will critically examine the various ways in which the mechanical properties of wood have been understood. Much understanding of wood’s elastic and inelastic properties is based on models developed for homogeneous materials. But wood’s cellular and fibrous nature means that its mechanical properties depend on the size of the test specimen. A more complete understanding of wood’s mechanical properties must take account of it being in some sense intermediate between a material and a structure.

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Wed 11 May 16:00: Dynamic Behaviour of Concrete materials in Underground Engineering.

Talks - Tue, 10/05/2022 - 14:08
Dynamic Behaviour of Concrete materials in Underground Engineering.

This talk will cover research that I have undertaken as part of my PhD project, using a novel triaxial Hopkinson bar system. This has been combined with diagnostics such as acoustic emission, DIC , synchrotron based x-ray tomography and numerical modelling to gain insight into the fracture properties of concrete and geological materials.

Please note that if you do not have card access to the Cavendish Laboratory, you will need to arrive at Reception in the Bragg Building by 16.00 at the very latest. We will not have anyone waiting there to let you in after that time.

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Thu 09 Jun 14:00: Title to be confirmed

Talks - Mon, 09/05/2022 - 22:40
Title to be confirmed

Abstract not available

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Wed 11 May 16:00: Dynamic Behaviour of Concrete materials in Underground Engineering.

Talks - Mon, 09/05/2022 - 16:19
Dynamic Behaviour of Concrete materials in Underground Engineering.

This talk will cover research that I have undertaken as part of my PhD project, using a novel triaxial Hopkinson bar system. This has been combined with diagnostics such as acoustic emission, DIC , synchrotron based x-ray tomography and numerical modelling to gain insight into the fracture properties of concrete and geological materials.

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Tue 31 May 16:00: TBC

Talks - Mon, 09/05/2022 - 12:28
TBC

Abstract not available

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Tue 24 May 16:00: TBC

Talks - Mon, 09/05/2022 - 12:28
TBC

Abstract not available

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Fri 13 May 16:00: Putting SMEFT Fits to Work: Lessons from Matching Simple Models

Talks - Mon, 09/05/2022 - 08:22
Putting SMEFT Fits to Work: Lessons from Matching Simple Models

The Standard Model Effective Field Theory (SMEFT) has become the preferred tool for parameterizing potential beyond the Standard Model physics effects in precision measurements at the LHC . While the observation of a nonzero operator coefficient in the SMEFT would be a clear sign of new physics, gleaning information about the nature of the underlying model at the high scale presents a number of challenges. In this talk, I will discuss recent progress in using SMEFT fits to LHC and electroweak precision data to constrain the parameters of simple extensions of the Standard Model, focusing in particular on the examples of a singlet scalar, a right-handed top partner, and a 2HDM. Focusing on these simple extensions allows us to study the process of extracting limits from SMEFT fits in detail, including the effects of running between the matching scale and the weak scale, the impact of one loop matching contributions, and the relative importance of dimension-8 operators. Including dimension-8 operators highlights interesting subtleties in the matching procedure that can affect the interpretation of SMEFT fit results.

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Tue 21 Jun 14:00: Title to be confirmed

Talks - Sat, 07/05/2022 - 15:19
Title to be confirmed

Abstract not available

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Thu 19 May 14:00: Theories of Cross phenomena and Zentropy

Talks - Sat, 07/05/2022 - 15:16
Theories of Cross phenomena and Zentropy

Cross phenomena, representing responses of a system to external stimuli, are ubiquitous from quantum to macro scales. Through flux equations based on the combined law of thermodynamics, theory of cross phenomena is developed and applied to thermoelectricity, thermodiffusion, diffusion, electromigration, electrocaloric and electromechanical effects, and thermal expansion. It is shown that the coefficient matrix connecting the driving forces and the fluxes is intrinsically diagonal, and thus symmetrical in accordance with Onsager’s reciprocal relations (https://doi.org/10.1080/21663831.2022.2054668). In order to predict the emergent cross phenomena, the zentropy theory is developed to represent the total entropy of a system (macrostate) by a nested formula with two portions: the weighted average of the entropies of statistically significant configurations of the system (microstates) and the statistical distribution of the microstates in the system. It is shown that when the microstates are represented by mixed quantum states, the free energy of each microstate should be used in their partition functions instead of internal energy commonly used in the literature (https://doi.org/10.1007/s11669-022-00942-z).

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Thu 26 May 14:00: Photon-Instanton Collider Implemented by a Superconducting Circuit: Splitting a Single Photon

Talks - Fri, 06/05/2022 - 14:59
Photon-Instanton Collider Implemented by a Superconducting Circuit: Splitting a Single Photon

How would our world look like if the fine structure constant α were of order unity? While in our small α world an atom excited to the first excited state has negligible probability of decaying to the ground state while emitting more than a single photon, such processes are important in a large α world, making photon frequency conversion effective in the single-photon regime. We show how such behavior can be realized in a superconducting circuit QED system, where a transmon, which serves as an artificial atom, is galvanically coupled to a high-impedance Josephson junction array, which acts as a waveguide for microwave photons with a high effective α. Instantons (phase slips) that occur in the transmon interact with the microwave photons, and lead to inelastic scattering probabilities which approach unity and greatly exceed the effect of the quartic anharmoncity of the Josephson potential [1]. The instanton-photon cross section is calculated using a novel formalism which allows to directly observe the dynamical properties of the instantons, and should be useful in other quantum field theoretical contexts. The calculated inelastic decay rates compare well with recent measurements from the Manucharyan group at Maryland [2]. I will also show how this effects can be used to shed a single-photon light on the Bulgadaev-Schmid superconductor-to-insulator transition in the transmon, which has been the center of a recent controversy.

References:

[1] Photon-instanton collider implemented by a superconducting circuit, A. Burshtein, R. Kuzmin, V. E. Manucharyan, and M. Goldstein, Phys. Rev. Lett. 126 137701 (2021).

[2] Photon decay in circuit quantum electrodynamics, R. Kuzmin, N. Grabon, N. Mehta, A. Burshtein, M. Goldstein, M. Houzet, L. I. Glazman, and V. E. Manucharyan, Phys. Rev. Lett. 126, 197701 (2021).

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Fri 03 Jun 16:00: Anja Butter - TBA

Talks - Tue, 03/05/2022 - 09:13
Anja Butter - TBA

The seminar will take place via Zoom here.

Abstract: TBA

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Thu 26 May 16:00: Alloy design against fatigue?

Talks - Fri, 29/04/2022 - 11:53
Alloy design against fatigue?

Better understanding of dislocation plasticity leads to the prospect of alloy design against the initiation of fatigue cracks. First thoughts on this will be aired.

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Thu 26 May 16:00: Alloy design against fatigue

Talks - Fri, 29/04/2022 - 10:46
Alloy design against fatigue

Better understanding of dislocation plasticity leads to the prospect of alloy design against the initiation of fatigue cracks. First thoughts on this will be aired.

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Fri 20 May 16:00: Sophie Renner - TBA

Talks - Thu, 28/04/2022 - 11:34
Sophie Renner - TBA

Abstract not available

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