CPT Student Seminars 2009-2010
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After a brief overview of the properties of integrable models and the S-matrix I will introduce a boundary to the model and talk about how integrability can be preserved with appropriate boundary conditions. This leads to so called 'boundary S-matrix equations'. The techniques and equations derived in general are applied to and solved in the Ising model at the free fermion point (i.e. a theory of free Majorana fermions) with a variety of boundary conditions. Slides (.pdf)
In this talk, I will introduce the Mixmaster Universe and discuss my very new results of geodesics "bouncing" off the t=0 singularity. No previous knowledge necessary (except a small amount of GR).
I will first review some of the interesting properties of plane wave spacetimes. Then I'll briefly discuss the issue of variational principles in gravity, before setting up a well-defined action principle for asymptotically plane wave spacetimes. I shall then consider black objects in plane wave backgrounds. We shall find a class of black string solutions with some unusual properties which imply that the space of asymptotically plane wave solutions is restricted. If time permits I will show that it is not possible to find black hole solutions in these backgrounds, which is a counter-example to a conjecture of Emparan et. al. Finally, we will discuss the implications of these results on the issue of holography for plane waves.
I will be disscussing the sine-Gordon equation modified by the presence of an extended, spacially dependent 'defect' term. In particular I am interested in how this set up may be exploited to create breathers in the lab.
Sine-Gordon theory is the prototypical 1+1 dim integral model, containing a sector of stable, finite energy excitations - the solitons. The O(3) sigma model is another relatively simple such model. In 1976, the same year the Eurovision Song Contest was won by Brotherhood of Man, Pohlmeyer showed that for every solution of the one there exists a solution of the other, but for some reason it appears no one explored this explicitly until 2006. I shall describe the map, it's relevance to AdS/CFT, and my work on elucidating the map when the theory has a boundary. I'll talk about some classical string theoretical calculations if there's time.
The neutrino oscillation experiments prove that neutrinos have non-zero mass. However, they are not able to give information on the absolute scale of neutrino masses. Also, the oscillation cannot clarify the nature of neutrino - what kind of particle it is. Thus we need to study double beta decay to know more about neutrinos. I shall briefly introduce neutrinoless double beta decay, and discuss the destructive interference effects between light neutrino and heavy neutrino exchange in the double beta decay.
The AdS/CFT correspondence is getting old - it's had to branch out. In this talk I will discuss a recent example of this rebranding: the modelling of the superconductor phase transition. Despite the simplified setup I will describe, this story may also have something to say about the problem of black hole microstate counting.
In this seminar I will briefly describe the effective charges method and explain how event shape moments from LEP can be used to find alpha_s(M_z). I will show some of my results, and talk about how we might understand them from their perturbative expansions.
Scattering amplitudes in N=4 SYM are known to be almost, but not quite, invariant under generators of the super-conformal symmetry. The symmetry is broken at tree level by the holomorphic anomaly. At higher loops it is also broken by the conformal anomaly. A recent paper proposes how generators of the super-conformal symmetry may be 'deformed' to make the symmetry exact at tree level and I also discuss the dual-superconformal symmetry and Yangians which has recently been used to constrain amplitudes at 1-loop.
In the age of hadronic colliders it is necessary to study QCD scattering and jet physics. Jet cross sections will be reviewed with a discussion on their soft and collinear singularity structure. The "antenna subtraction" method will be introduced and how this is used to extract IR safe jet observables will be explained schematically. The technique will be discussed in the context of current work on two jet production from quark-antiquark initial states.
This talk will focus on two-dimensional conformal field theories with boundaries, a subject of interest in Condensed Matter Physics and String Theory. In particular I'll discuss the origin and application of the 'g-function', and highlight it as an important tool in the the study of boundary CFTs appearing as fixed points in the RG flows of certain QFTs.
We will soon have LHC data, and will need NLO precision to understand and use them. I present GOLEM, an automated tool for efficient calculation of one-loop Feynman diagrams.
We embed a holographic model of an U(1) charged fluid with Galilean invariance in string theory and calculate its specific heat capacity and Prandtl number. Such theories are generated by a R-symmetry twist along a null direction of a N=1 superconformal theory. We study the hydrodynamic properties of such systems employing ideas from the fluid-gravity correspondence.
Given the potential precision of future LHC cross section measurements and the need to reliably predict the (possibly minute) cross sections of some BSM processes for comparison, it is an absolute necessity to include NLO QCD corrections in any cross section prediction for the LHC. We will give an overview of how this is done in Herwig++ by sketching how the dipole subtraction method is used to compute the NLO cross section numerically (despite the appearance of divergences in intermediate steps) and how this is implemented in Herwig++ using the POWHEG method. This will lead to NLO cross section predictions for an E_6 GUT Z' model and for mSUGRA slepton pair production.
After talking about the motivations for considering two Higgs doublet models (2HDM), I will discuss the custodial symmetry in the standard model and its generalization to 2HDM's. Next, I will show how the interplay between this generalized custodial symmetry and CP symmetry leads to interesting phenomenology. Finally, different methods for computing the mass spectrum of the several Higgs bosons will be considered.
We begin by reviewing dualities in string theory and how the five superstring theories unify in the eleventh dimension. The basics about branes will be discussed and how they can be coupled to a background field. We shall then discuss the worldvolume $\mathcal{N}=8$ theory of multiple M2-branes known as Bagger-Lambert theory, then showing how one can can couple this to a background $C$-field. We shall then describe how an M5-brane can end on a stack of M2-branes via the Basu-Harvey equation, then we shall demonstrate how one can generalise this to include fluxes in the case of M2-branes with a boundary.
Cosmic strings, generic in popular inflationary models, may be detected by the current generation of gravitational wave detectors. The main source of gravitational wave emission is from an event called a 'cusp'. It is important to model these events in order to recognise them. We study the signal in the case of the existence of extra dimensions, and find that overall it is much smaller. I will try to explain the results (without going into too much maths)!