CPT Student Seminars
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. We have funding to cover their expenses!
Organisers: James Edwards (Maths) and Tom Morgan (IPPP)
Mon 2 June 2014: Deformation quantization of non-geometric string theory
Dionysios Mylonas (Heriot-Watt)
Non-geometric spaces arise as consistent string theory backgrounds in p-form flux compactifications. In this talk I will explain how these spaces can be geometrised using membrane models. I will then show how to perform quantization using various deformation quantization techniques and discuss topics such as nonassociative field theory.
Tues 27 May 2014: Hyperbolic Monopoles
Alex Cockburn (Durham, CPT)
The worldline approach allows us to re-write quantities in a quantum field theory in terms of one dimensional quantum mechanics defined on an infinite number of worldlines. This idea will be discussed in the context of string theory and demonstrated for scalar and spinor QED.
Non-abelian monopoles in Euclidean space have been intensively studied since their discovery in the 70's, but explicit solutions are rare. This situation can be improved by moving to a hyperbolic space background, where one can exploit a connection to Euclidean instantons. I will discuss some new techniques based on this approach. The solutions include some examples with Platonic symmetry, as well as one-parameter families analogous to geodesics describing Euclidean monopole scattering.
Slides
Mon 19 May 2014: Fields, worldlines and strings
James Edwards (Durham, CPT)
The worldline approach allows us to re-write quantities in a quantum field theory in terms of one dimensional quantum mechanics defined on an infinite number of worldlines. This idea will be discussed in the context of string theory and demonstrated for scalar and spinor QED.
In my work these virtual worldlines realise an interpretation as the boundaries of string worldsheets. I will explain how the fluctuations of the gauge field can be replaced by fluctuations of these worldsheets if we allow for a contact interaction between the sheets. Finally, introducing SUSY on the worldsheets induces a fermionic theory on their boundaries. In this way QED is re-expressed in terms of interacting superstrings in such a way that the string theory evades a Weyl anomaly, producing a consistent theory for four dimensional spacetime.
A review of most of the background to my talk can be found here.
Mon 12 May 2014: Implementation of NLO Physics in SHERPA
Jennie Thompson (Durham, IPPP)
This talk looks at the current state of NLO corrections in SHERPA. I begin with an outline of a numerical NLO calculation and the techniques of precision simulations. Then I will consider the Higgs boson trilepton studies performed in ATLAS and CMS, with the signal and background simulated at NLO, with some relevant results. The final third will introduce how to extend the precision of these simulations to a greater level with EW Sudakovs, which are a very good high energy approximation to a full EW NLO calculation.
Slides
Tues 6th May 2014: Material models of dark energy.
Jonathan Pearson (Durham, CPT)
The problem of "dark energy” is rather simple: we don’t know what substances are in the Universe which could make it accelerate (or, look like its accelerating): but, we know about 70% of the Universe must be made of it. There are many scalar field and modified gravity models on the market trying to describe these observations.
In this talk, I will look at a radically different type of theory: material models of dark energy. The theory of relativistic solids is used in a cosmological context, and is built up so that the theory of a relativistic viscoelastic solid can be used as a candidate dark energy model.
The rough idea is simple: generalise Hooke’s law (built for a non-relativistic elastic solid), and make the theory relativistic. The work is based on my recent publication, arXiv 1403.1213.
Mon 28 April 2014: Dark Matter and Higgs Stability in Classically Scale Invariant Extensions of the Standard Model
Gunnar Ro (Durham, IPPP)
Dark Matter and the instability of the Higgs Potential are two of the main problems with the Standard Model. We show that the stability can be improved and that we can have viable Dark Matter candidates in a range of classically scale invariant extensions to the Standard Model with a Higgs Portal interaction. These models generate the weak scale via the Coleman-Weinberg mechanism and addresses the Standard Model naturalness problem.
Slides
Mon 17rd March 2014: A Very Introductory Introduction to Higher-Spin Gauge Theory
Alex Peach (Durham, CPT)
Higher-spin gauge theories have become a lively area of research in recent years. I will try and give a very brief and pedagogical introduction to the subject, in particular talking about exactly what "higher-spin" means, how to write down free theories of higher-spin gauge fields and a brief review of some of its seductively unusual features. If the feeling takes us I might also mention something about Vasiliev theory.
Notes to accompany black-board presentation are here
Mon 10rd March 2014: Measuring W emission rate in the collinear limit at the LHC.
Petar Petrov (Durham, IPPP)
We propose a W tagging strategy when the boson is not the most energetic object in the vicinity. The method consists of a sub-structure mass reconstruction and a subsequent use of jet shapes to separate a hadronic W from the overwhelming QCD background. The Standard Model prediction is compared to different W emission rates in order to test the sensitivity of the method. The exclusion of other models is performed with a binned Log-Likelihood technique and an artificially added "systematic" error to account for experimental uncertainty.
Slides
Mon 3rd March 2014: Avoid spaghettification in Lifshitz spacetime
Yang Lei (Durham, CPT)
Lifshitz and hyperscaling violating geometries, which provide a holographic description of non-relativistic field theories, generically have a singularity in the infrared region of the geometry, where tidal forces for freely falling observers diverge, but there is a special class of hyperscaling violating geometries where this tidal force divergence does not occur. I will give a short introduction about these properties in Lifshitz spacetime and review some material in Schwarzchild black hole spacetime. Then I will show how to construct the nonsingular coordinate for hyperscaling violation spacetime.
Mon 24th Feb 2014: No more Feynman Diagrams
Daniele Galloni (Durham, IPPP)
Scattering amplitudes have recently made enormous conceptual progress, mainly by being reformulated in an intrinsically combinatorial way. Some similar formulation is likely to work with much less supersymmetry than N=4. I will quickly outline some of the excitement, reveal some of the mathematical tools that need developing, in particular on how to go beyond the current limitations, and show lots of pretty pictures.
Slides
Mon 17th Feb 2014: Calculating and Dimensionally Regularising Multi-Loop Scattering Amplitude Integrands in N=4 SYM
Tim Goddard (Durham CPT)
In the last few years there has been a departure from Feynman Integrals as the most efficient way to calculate scattering amplitudes in supersymmetric gauge theories. I will do a whiteboard talk to introduce some of the new diagrammatic methods for calculating these quantities and ask several questions such as "How easy is it to dimensionally regularise these new representations?" Then, finally, can we build these objects primarily from symmetry considerations in an algorithmic way which avoids too much effort? Pictures will be involved in more than one colour!
Mon 10th Feb 2014: Jet boosted Higgs at NNLO
Xuan Chen (Durham, IPPP)
This talk is about the current development of Higgs phenomenology study. Although the Higgs mass is now discovered around 125GeV, large theoretical uncertainty and background signals in LHC environment limit our ability to determine detailed properties of the Higgs boson. I would like to introduce boosted Higgs and its advantage in phenomenological studies. Then I will compare the two state-of-the-art methods for Next-to-Next-Leading Order calculations in Jet related processes and their applications to Jet boosted Higgs.
Slides
Mon 3rd Feb 2014: Noncommutative U(2) Instantons
Andy Iskauskas (Durham, CPT)
Topological solitons can play a part in understanding many different physical systems. In particular, the study of instantons (solitons in 5d super-Yang-Mills theory) has been conjectured to relate to the KK modes of compactified M-theory. In my talk I will provide an introduction to the framework of SU(2) commutative instantons, and outline the solutions for such a configuration in the presence of a noncommutative underlying space. Such noncommutative U(2) instantons can be seen to resolve a number of issues with the commutative framework, and provide some interesting dynamical results.
Slides
Mon 27th Jan 2014: New Physics in $\Delta\Gamma_d$
Gilberto Tetlalmatzi-Xolocotz (Durham, IPPP)
In 2011 the D0 experiment reported a value for the dimuon asymmetry in $p\bar{p}$ collisions that deviates from the Standard Model prediction by 3.9 $\sigma$ . Recently it was suggested that the gap between theory and experiment can be reduced if the CP violation in interference between the final states of $B_{d}$ mesons decays is taken into account. It is found that the new CP violation contribution is proportional to the not yet measured decay rate difference $\Delta \Gamma_d$ of neutral $B_{d}$ particles. The main aim of this talk is to show that the SM value of $\Delta \Gamma_d$ can get a sizeable enhancement from New Physics (NP) sources without violating other experimental constraints, indeed It is found that there is room for NP induced by both $b\bar{d}\tau\bar{\tau}$ and tree level operators that can minimize the difference between the theoretical and the experimental results for observables associated with the dimuon asymmetry.
Slides
Mon 20th Jan 2014: Elegant ideas that do not work
Craig Robertson (Durham, CPT)
First I will tell you about some elegant ideas that do work: affine Toda field theory, solitons and defects. Towards the end I will stray into the dangerous territory of having my own ideas. These do not work but they're still elegant.
Slides
Mon 9th Dec 2013: An Introduction to fixed order QCD
Tom Morgan (Durham, IPPP)
This talk will serve as a very gentle introduction to fixed order QCD calculations, my target audience being researchers who do not work in QCD. I will begin by discussing the idea of 'colour decomposition' and show how we can split up a matrix element into 'leading colour' and 'subleading colour' components. From this we will see that the gluons in the 'subleading colour' contribution are abelian-like in nature.
I will then move on to demonstrating how from these matrix elements we derive meaningful IR pole structures in both real and virtual corrections to a process at Next-to leading order (NLO), resulting in the need for so called 'subtraction terms' for any fixed order calculation. Time withstanding, I hope to discuss how we can use these tools to construct Next-to Next-to leading order (NNLO) corrections to processes and the numerous difficulties that follow.
Slides
Mon 2nd Dec 2013: The super-correlator/super-amplitude duality in N=4 super-Yang-Mills theory
Reza Doobary (Durham, CPT)
Much progress has been made in understanding the structure of scattering amplitudes in N=4 SYM which ranges a broad spectrum of geometry and algebra. However, we understand a lot less about correlation functions of half-BPS operators in the same way. In this talk, I will will explain the basic formalism for computing scattering amplitudes whilst making use of Twistor geometry. I will then explain the formalism for correlation functions of half-BPS operators, in this case making use of Harmonic superspace. After this, I shall show how the duality between these two observables work, and how we might endeavour to find a correlator based on this duality. Finally I will give a brief outline of some on-going work.
Slides
Mon 25th Nov 2013: Dirac gaugino masses and duality
Daniel Busbridge (Durham IPPP)
N=1 super quantum chromodynamics provides a rich playground for a physicist. Remarkably, for a particular number of flavours and colours, the theory admits two physically equivalent descriptions often dubbed 'electric' and 'magnetic' - the first becoming strongly coupled in the infra-red whilst the second remains under perturbative control. I will begin with an introduction to this phenomena known as 'Seiberg duality.' We will then take a temporary detour to discuss some of the phenomenological advantages of a Dirac gaugino mass over the Majorana variety found in most SUSY breaking models. I will then demonstrate how most SUSY breaking operators like Majorana gaugino masses can be mapped across the Seiberg duality and explain why the same approach cannot be straightforwardly applied to Dirac mass operators. Achieving this for Dirac gauginos turns out to be much more interesting than one initially anticipates and will occupy the remainder of the discussion.
Slides
Mon 18th Nov 2013: Entanglement and holography (and firewalls).
Henry Maxfield (Durham, CPT)
Entanglement is a uniquely quantum phenomenon, and of interest to people from diverse fields such as quantum computing, solid state physics, and quantum gravity. I'll talk about what it is, how we measure it and some properties, and what happens in field theories. Then I'll describe how it is described in the framework of holographic duality, focussing in particular on how otherwise mysterious properties have simple geometric explanations. Finally, I'll change tack and describe how ideas from entanglement may be overturning paradigms in quantum gravity, via the 'firewalls' argument, with the controversial conclusion that jumping into a black hole may kill you even sooner than you might otherwise think.
Mon 11th Nov 2013: Collective coordinate approximation to the scattering of solitons in the (1+1) dimensional NLS model.
Helen Baron (Durham, CPT)
We present the collective coordinate approximation to model the dynamics of two interacting nonlinear Schrodinger (NLS) solitons; and discuss the accuracy of this approximation by comparing our results to those of the full numerical simulations.
Slides
Mon 4th Nov 2013:POWHEG Method in Herwig++ for BSM Processes
Alix Wilcock (Durham, IPPP)
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 Beyond the Standard Model processes.
Slides
Mon 28 Oct 2013: Lagrangian Analysis of Magnetic Tangling
Francesca Bianchi (Durham, Mathematical Sciences)
The project aims to estimate the input of magnetic energy into the Sun’s corona using observed horizontal motions on its photospheric surface. Our study of the evolution of the field supports the idea that these motions will lead to a continuous deformation of the coronal magnetic field lines. Although the Virial Theorem relates the volume magnetic energy to that on the boundary, this would require knowledge of the vector components of the magnetic field on the photosphere. Instead, Aly has advanced a derivation of upper and lower energy bounds based only on the topology of the field.
After a discussion on how these bounds can be derived analytically, I will present the results obtained by applying them to a test case and on different sets of velocity data, showing how the movement of the footpoints of the field lines leads to a twisting of the lines in the corona and calculating bounds on the energy of the field.
Slides
Mon 21 Oct 2013: An introduction to BCFW recursion relation with colour ordered amplitudes
Simon Armstrong (Durham, IPPP)
In my project I have been using the BCFW recursion relation to calculate colour ordered spinor helicity amplitudes for quarks, gluons and higgs boson. I will introduce colour ordered amplitudes and the spinor helicity formalism using the BCFW recursion relation as an example. I will then go on to show the proof of the BCFW recursion relation and show how we can check if it can be applied to any new amplitude we want to calculate.
Slides
Mon 14 Oct 2013: Constraining properties of the dark universe Jonathan A. Pearson (Durham, CPT)
When recent observational evidence and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood "dark sector". There has been a considerable number of theoretical models constructed in an attempt to provide an "understanding" of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a "generic" way to parameterize the dark sector.
We will discuss our way of approaching this problem: constructing equations of state for perturbations. Our approach is inspired by that taken in particle physics, where the most general modifications to the standard model are written down for a given field content that is compatible with some assumed symmetries. Our emphasis is on constructing a theoretically motivated toolkit which can be used meaningfully transcribe from experimentally obtained observations into well defined statements about the allowed properties of the dark sector. It is key to use meaningful models of the perturbed universe when analysing data sets which are sensitive to the clustering of the dark sector.
I will present our observational constraints (using e.g., Planck CMB temperature and lensing, CFHTLenS data) on the parameters in the equations of state for perturbations.
Slides
Mon 07 Oct 2013: What can Direct Detection Experiments say about light Dark Matter?
Jon Davis (Durham, IPPP)
A variety of dark matter experiments seem to be universally pointing towards the presence of light Dark Matter, with a mass between approximately 5 GeV and 12 GeV. However, the XENON100 experiment stands in stark contrast, excluding the parameter space favoured by the CDMS, CoGeNT, CRESST-II and DAMA experiments. Claims have been made that such an exclusion is not so robust as previously thought, and that it is possible that the data of XENON100 in fact agree with hints of light Dark Matter. I will try to critically assess such claims. I will initially focus on the XENON100 experiment, and will discuss CoGeNT if there is time at the end.
Slides
Links to previous years' seminars: 2012/13 2011/12, 2010/11, 2009/10, 2008/09, 2004/05.
Back to the CPT seminar list.
