What student seminars are all about...
Student seminars are usually held on Monday afternoons, 5-6pm, in OC218 (the IPPP seminar room). Tea, coffee and biscuits are (sometimes) provided by the IPPP.
Feel free to invite a friend or collaborator from another institution to give a talk if they're in town.
Organisers: Alex Cockburn (Maths) and Alix Wilcock (Physics)
Hydrodynamics provides a description of low-energy, long-wavelength fluctuations around generic equilibrium density matrices. For decades, this theory has been studied in its own right and over the last years it has been of great renewed interest due to its holographic applications (fluid/gravity map) and its ability to describe strongly coupled systems. Although hydrodynamics is a typical example of an effective field theory, its traditional formulation is somewhat indirect and not based on the variation of an action of fundamental degrees of freedom. After explaining this fact in some detail, I will present an effective action formalism for (non-dissipative) fluid dynamics and how it can be used to gain insights into non-trivial transport phenomena, quantum anomalies, and the very nature of hydrodynamics in general.28 May 2013: Inhomogeneous phases in holography
Holography in the form of AdS/CFT provides a powerful tool for examining strongly coupled quantum field theories. This technology has been adopted to try and learn about systems in condensed matter physics, with a particular focus on systems at finite temperature and charge density. A well-studied example is holographic superconductivity, resulting from the spontaneous breaking of a boundary U(1). Another possibility is an inhomogeneous phase resulting from the spontaneous breaking of the Euclidean group of spatial symmetries. This situation is described holographically by the emergence of black branes with spatially modulated horizons. I will review the evidence for inhomogeneous black branes in holography and present their direct numerical construction.20 May 2013: Computational Neutrino Cosmology - how to simulate the 'smallest' particles in the largest lab ever
I will give a brief review on neutrino mass searches and why cosmology plays a vital part hereby followed by a more detailed discussion of my work on how to simulate the dynamics of the cosmic relic neutrino content properly to determine its distribution and impact on structure formation. Finally I will briefly discuss how this can be also used to discover/study certain new physics beyond the SM of Cosmology/PP.13 May 2013: Non-Abelian Self-Dual Strings
I will give a brief review on a theory describing multiple M5-branes, then describe its self-dual string solutions. For example, I will present their connections with magnetic monopoles. Finally I will compare the radius-transverse distance relation of self-dual strings between our results and supergravity results.7 May 2013: Hidden symmetries & gauge theories
The integral equations of electrodynamics proposed by Faraday have a fundamental role in the understanding of electromagnetic phenomena. They were proposed, of course, before Maxwell came up with the differential equations. The Yang-Mills theory appeared as a straightforward generalisation of electromagnetism for non-abelian gauge groups, and apparently only the differential equations are known. In this seminar we will discuss how to get flux-like (integral) equations for the Yang-Mills theory, and how these equations lead us to the construction of conserved charges that are invariant under any gauge transformation (which is still an open problem). This construction is inspired by the mathematical structure found in some integrable field theories in 1+1 dimensions called the zero curvature representation, and its generalisation, which requires a non-abelian formulation of Stokes' theorem in loop space. The main goal of the talk is to have fun with all these abstract ideas, but in the end we shall discuss how to get such a conserved charge for the Wu-Yang monopole.22 April 2013: Instantons, hyperbolic monopoles, and the Nahm transform
The self-dual Yang-Mills equations have long fascinated both mathematicians and physicists as 'master equations' for integrable systems. Instantons, monopoles, vortices, and kinks all arise from them via different symmetry reductions. In this talk I'll review some of the basic features of the solutions to the Yang-Mills equations in Euclidean space, as well as a mathematical transform used to construct those solutions. I'll then move from Euclidean to hyperbolic space, where I'll discuss some monopole solutions and how they relate to their Euclidean counterparts. Slides (.pdf)11 March 2013: String Theory and Gauge Fields
The connection between string theories and gauge theories runs deep and has a long history. There are many cases where a calculation in string theory can provide an answer to a problem in field theory. In this talk I will present ongoing work which reformulates Maxwell's electromagnetism as a statistical average over surfaces whose dynamics are described by a string theory with a very particular interaction. Interestingly the string theory can be evaluated in non-critical dimension because metric degrees of freedom decouple from the calculation. I will briefly explain how this idea can provide an arrow of time for classical electromagnetism and will go on to describe current work relating this theory to QED, following and extending Strassler's method of forming Wilson loops from heavy quarks. Slides (.pdf)4 March 2013: Domain Wall Skyrmions
The baby Skyrme model is a (2+1)-dimensional theory that has topological soliton solutions. These solutions, called Skyrmions, are manifest in condensed matter systems. In this talk I shall explain how we are able to construct these Skyrmions from another type of topological soliton, domain walls. I shall then go on to examine the static solitons of this theory and finally move on to address their kinetic behaviour. Slides (.pdf) Movie 1 (.mpeg) Movie 2 (.mpeg) Movie 3 (.mpeg) Movie 4 (.mpeg) Movie 5 (.mpeg) Movie 6 (.mpeg)25 February 2013: NLO Physics with Sherpa+OpenLoops
Monte Carlo event generators have become essential in enabling theoretical predictions to be compared to experimental results. Currently there is a lot of activity in attempting to include matrix elements at NLO. The Sherpa+OpenLoops interface has been validated for a number of processes and I will present results for ttV and ttH processes using the MC@NLO method.18 February 2013: Broken Baby Skyrmions
I will start by introducing some concepts of topological solitons along with the Skyrme model and the lower dimensional baby Skyrme model. The Skyrme model can describe baryons which are described by the topological solutions of the field theory. The baby Skyrme model is a (2+1)-dimensional analogue of the Skyrme model. I will discuss a version of the baby Skyrme model in which the global O(3) symmetry is broken to the dihedral group DN. I will show that the single soliton solution is then formed of N topologically confined partons. I will also look at the N=3 and N=4 cases in more detail, numerically computing the multi-soliton solutions. It is shown that these solutions take the form of polyiamonds and polyominoes respectively (shapes formed by joining equilateral triangles/squares along their edges). I will finally look at the scattering of these solitons to see if it differs from the standard form of the theory. Slides (.pdf)11 February 2013: Is supersoft supersymmetry breaking supernatural?
The Standard Model has proved incredibly succesful to date, with essentially all experimental observations being matched by their theoretical predicitions. The observation of a Higgs-like boson with a mass of 125 GeV can be viewed (depending on taste) as a severe disagreement with Standard Model expectation, since the radiative corrections to the Higgs mass should be either be the scale of physics preventing further radiative corrections (e.g the GUT or Planck scale), or the mass of the heaviest particles in our theory (even if we have no knowledge about them at present!). Using supersymmetry as the cure, I will motivate a compelling class of 'supersoft' models that weaken current collider searches for sparticles and characteristically 'natural' spectra. I will then discuss a possible UV completion of these models.4 February 2013: SUSY Searches Reloaded
We will review some of the ingredients that go into current SUSY searches. We will discuss an often ignored approximation that is made when making such searches, which means that many results are effectively based on only leading order diagrams (with an approximate correction). Such results are still subject to sizable radiative corrections and scale variation which affect current searches. We will show how one could go beyond such approximations and make predictions for SUSY signals which are accurate up to our current ability to compute SUSY amplitudes, showing some preliminary results for the electroweak sector where constraints from the LHC are still in their early days.28 January 2013: Periodic Monopoles - Dynamics and the Dual Picture
In this talk I will discuss the Nahm transform as applied to a periodic array of magnetic monopoles. The focus will be mainly on the SU(2) monopole of charge 2. It is possible to extract geodesic submanifolds, from which we will look at the scattering of both the monopole chains and of lumps on the dual cylinder. Finally, it will be interesting to look at how the moduli space metric changes as one alters the ratio of the monopole size to the period of the chain. Slides (.pdf)21 January 2013: Hitting a Natural Higgs in Susy
I'll talk about the Higgs boson and naturalness in susy, before making precise what I call optimal naturalness. I'll introduce the NMSSM and explain its potential utility and limitations for boosting the Higgs mass naturally. Some susy collider phenomenology will be discussed, including jet substructure methods for discovering exotic Higgs decays in the NMSSM and beyond.14 January 2013: NLO calculations in SHERPA
Next to leading order QCD calculations are reviewed, and the FKS subtraction scheme discussed. The implementation of FKS subtraction in the SHERPA event generator is discussed, and some results with this implementation presented. Finally FKS subtraction is compared to other subtraction schemes.3 December 2012: Holographic Meson Condensation and Melting in N=2 Gauge Theory
Gauge/gravity duality is one of the most powerful tools to describe, for example, the field theory at strong coupling when working in the gravity theory at weak coupling. In this talk I will explain our recent work in gravity side in arXiv:1210.6188. By using the duality, the meson mass spectra were computed along with the critical isospin chemical potential. For the broken phase, we constructed the lowest energy ground state not governed by a vector meson like the other previous related models but rather by an SO(4) R-charged scalar.26 November 2012: Finding Dark Matter above the background
Despite strong gravitational evidence for the existence of dark matter in the Universe (from galactic to cluster scales) its nature remains largely a mystery. Yet great progress has been made in this endeavour: direct detection experiments, based on the detection of dark matter induced nuclear recoils have set progressively stronger limits on the properties of dark matter. In this talk I discuss how such experiments set limits on these properties, specifically the mass and cross section, and how they distinguish potential dark matter signals from the large background inherent with such experiments. Emphasis is placed on extracting as much information as possible from the data on the dark matter and the uncertainties involved.19 November 2012: Amplitudes from Symmetries
N=4 SYM is a highly supersymmetric, entirely massless theory. Yet given these rather unpromising physical beginnings, it is proving very popular at the moment, primarily as a testing ground for gauge theory ideas. In this talk I will introduce the theory and outline some of the most recent developments in producing amplitudes without Feynman diagrams or similarly complex computational methods. The idea being to build amplitudes simply out of symmetry considerations: cyclicity, parity, superconformal symmetry, dual conformal symmetry etc. This talk will hopefully be appropriate for people who are unaware of what the "N" in N=4 stands for, up to those who have momentum twistors coming out of their ears.12 November 2012: Antenna Subtraction in NNLO QCD
Not only can QCD elegantly describe non-abelian gauge interactions, it also has the ability to predict a huge variety of hadronic phenomena, which are continually verified by experimental data over several decades. The level of precision achieved by the LHC makes higher-order QCD calculations mandatory. Jet cross sections and their singularity structure are reviewed. I introduce Antenna Subtraction as a method of extracting IR-safe observables, and show how it can be applied to jet events relevant at hadron colliders.5 November 2012: A model for the gauge sector of multiple M5 branes
We will introduce a new model proposed recently for the gauge sector of multiple M5 branes. It admits self-duality condition as equation of motion, has full 6D Lorentz symmetry, and gives 5D YM + correction terms upon double dimensional reduction. We also find the exact self-dual string solution, which is a supportive evidence for our theory to capture some physics of M5 branes28 October 2012: POWHEG Method in Herwig++ for the Decays of Top Quarks and Supersymmetric Particles
Monte Carlo parton showers give a good description of QCD radiation in the soft and collinear regions of phase space but fail to describe high transverse momentum (hard) emissions well. One way to improve the treatment of hard emissions in the shower is by using the NLO QCD real emission matrix element coming from the hard scattering process to generate the hardest emission in the shower. This is what's done in the Positive Weight Hardest Emission Generator (POWHEG) approach. In this seminar I will introduce the POWHEG formalism and discuss it's implementation in the Herwig++ Monte Carlo generator for the decays of top quarks and supersymmetric particles.22 October 2012: The Galileon gravity dark energy model: predictions from linear perturbation theory
The Galileon gravity model is a recent member of the plethora of dark energy models proposed to explain the present accelerated expansion of the universe. From a theoretical point of view the model is interesting as its Lagrangian contains highly non-linear derivative self-couplings of a scalar field which yield nevertheless 2nd order equations of motion and should allow for a successful implementation of the Vainshtein screening mechanism to hide the modifications of gravity on local scales. Moreover, observationally the model does yield background expansion histories compatible with the data. To further understand where the Galileon model sits within the class of modified gravity theories it is important to understand the impact on the evolution of density fluctuations and formation of large scale structure. As an initial step one considers the regime where the density fluctuations are small and cosmological linear perturbation theory can be employed.15 October 2012: The holographic principle, AdS/CFT and field theory probes of bulk geometry
In this seminar, I'll talk about recent work done on the cosmological predictions in Galileon cosmologies at the linear level in perturbation theory. I'll review the main concepts and features of the Galileon model, mentioning and describing what are the best cosmological observables we can use to constraint this model and eventually distinguish it from the standard Lambda-Cold Dark Matter paradigm.
The AdS/CFT correspondence is 15 years old, and in that time it's (arguably) had much success in describing strongly-coupled QFTs using gravity. However, it's been rather quieter in the other direction, contributing little to answering the long-standing theoretical questions of quantum gravity. I'll describe some of the weirder features of quantum gravitational systems, and use these to motivate and describe the AdS/CFT correspondence. Then I'll review some recent work which aims to elucidate how gravity emerges from a lower-dimensional field theory, and asks 'How can an inhabitant of a flat world without gravity explore inside a black hole?'8 October 2012: Defects and boundaries in affine Toda field theory
The affine Toda field theories are a class of miraculous (i.e., integrable) field theories in 1+1 dimensions which generalise the sine-Gordon model. I will talk about how to enrich these models without spoiling their 'miraculosity' by adding in boundaries and/or defects. Among other things, I will attempt to convince you that integrable defects are related to the existence of solitons in these models.Links to previous years' seminars: 2011/12, 2010/11, 2009/10, 2008/09, 2004/05.
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What student seminars are all about...