Student seminars are usually held on Monday afternoons, 5-6pm, in OC218 (the IPPP seminar room). Tea, coffee and biscuits are provided by the IPPP.
Feel free to invite a friend or collaborator from another institution to give a talk if they're in town.
3 February 2020 17:00 in OC218
This talk discusses on how to identify events with fatjets from charming Higgs decays, H→cc, at the LHC. To reduce the overwhelmingly large backgrounds and to reduce false positives, we consider applying a combination of jet shape observables and imaging techniques, using a selection of neural network architectures.
27 January 2020 17:00 in OC218
In recent years it has become increasingly apparent that the study of BPS states is highly applicable not only to physics but several areas of mathematics as well. For example, BPS states are important objects in black hole physics, homological mirror symmetry and enumerative geometry. It is therefore important that we develop an efficient method of calculating the BPS states of a theory. This is made more complicated by the fact that the BPS spectrum discontinuously varies upon crossing certain surfaces in parameter space- giving rise to the so called 'wall-crossing phenomenon'. In this talk we develop the method of BPS quivers which gives us a way to understand all the BPS chambers of a theory in a purely combinatorial way.
20 January 2020 17:00 in OC218
On-shell diagrams are a useful tool for calculating and manipulating amplitudes. For N=4 SYM, they can be used to recurse amplitudes to all loop orders but their application to supergravity is less clear.
I will review how to calculate tree level amplitudes in these theories using recursion relations and on-shell diagrams. I'll then look at what they can tell us about 1-loop amplitudes and their leading singularities, hinting at possible new expressions for n-point MHV supergravity amplitudes at 1-loop.
9 December 2019 17:00 in OC218
In this talk I will give an introduction to B-meson mixing, focusing on the determination of non-perturbative input through HQET sum rules. I will demonstrate how the sum rule works and then highlight the advantages of using it over alternative methods, i.e Lattice QCD, in the context of the bag parameter. Finally, I will illustrate the importance of mixing constraints for the determination of the CKM matrix and in testing the Standard Model.
25 November 2019 17:00 in OC218
In this talk we will derive an expression for conserved charges in Lovelock anti–de Sitter gravity for solutions having k-fold degenerate vacua, making manifest a link between the degeneracy of a given vacuum and the nonlinearity of the energy formula. The level of degeneracy fixes the relevant order in the curvature where the mass of a black hole solution is contained. As a matter of fact, the full charge can be consistently truncated and expressed in terms of powers of the Weyl tensor. This may be interpreted as a natural generalization of the Ashtekar-Magnon-Das formula for any Lovelock-AdS gravity theories.
18 November 2019 17:00 in OC218
I will review a technique to obtain analytical spinor-helicity rational coefficients for loop amplitudes from floating-point numerical evaluations, with explicit examples for QCD processes. Afterwards, I will discuss the Cachazo-He-Yuan formalism for massless scattering. I will show how arbitrary-precision numerical solutions of the scattering equations lead to compact analytical tree-level amplitudes in a variety of theories, including the first complete set of five-point (DF)^2 amplitudes.
11 November 2019 17:00 in OC218
Compact stellar objects such as white dwarfs (WDs) have been proposed as potential probes to set constraints on dark matter (DM) particles. When DM scatters off nuclei, kinetic energy is transferred to the star that can give rise to an observational signal. Previous works did not consider relativistic effects on the calculation of the DM capture rate in WDs. However, since WDs are very dense objects, these effects can lead to sizeable corrections to the DM scattering cross-section. We present preliminary results of such computation and also study the impact of the inner structure and finite temperature of these stars on the DM capture rate.
4 November 2019 17:00 in OC218
The 2D Yang-Mills theory is an example of a quantum field theory which can be solved exactly without resorting to perturbation theory. ‘Solving’ the theory means finding an exact expression for the partition function of the theory on a Riemann surface Σ of genus g and area A. The free 2D Yang-Mills theory partition function only depends on A and g, and not the special geometry of Σ, so in the zero area limit it is a topological quantum field theory. I will calculate the partition function by first considering the theory on a cylinder in the Hamiltonian formulation. Then, once we have the partition function on a cylinder, I will use the ‘gluing rule’ to find the partition function on a Riemann surface of genus g.
28 October 2019 17:00 in OC218
Lifetimes are among the most fundamental properties of elementary particles. Our project aims to carry out a precise determination of the lifetime ratio τ(Bs) / τ(Bd), which happens to be very sensitive to higher power corrections because of multiple cancellations arising. A comprehensive study of this observable could then provide a unique way to test the theoretical framework and indirectly constrain the size of possible new physics contributions. In this talk I will present the status of our project with some preliminary results.
21 October 2019 17:00 in OC218
Meson decay rates are often difficult to calculate using QCD, especially in the case of high spin mesons. However, the problem may instead be studied by modelling the meson as a string in an holographic background. Recent work suggests that the problem may be further simplified by Wick rotating the time coordinate of the spacetime and using an instanton method. This talk will demonstrate a simple example of how to build this model, starting with a simple toy 2D flat spacetime example, before moving on to a more realistic example in Sakai Sugimoto spacetime for zero temperature. A possible extension to finite temperature will also be discussed.
14 October 2019 17:00 in OC218
We highlight that the anomalous orbits of Trans-Neptunian Objects (TNOs) and an excess in microlensing events in the 5-year OGLE dataset can be simultaneously explained by a new population of astrophysical bodies with mass several times that of Earth. We take these objects to be primordial black holes (PBHs) and point out the orbits of TNOs would be altered if one of these PBHs was captured by the Solar System, inline with the Planet 9 hypothesis. Capture of a free floating planet is a leading explanation for the origin of Planet 9 and we show that the probability of capturing a PBH instead is comparable. The observational constraints on a PBH in the outer Solar System significantly differ from the case of a new ninth planet. This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH.
What student seminars are all about...