# HEP Young Theorists' Forum

14-15 May 2009, University College London

## Abstracts

Alphabetically by last name

Paul Archer (Sussex)
The Little Hierarchy Problem in Warped Extra Dimensions
Slides

Warped extra dimensions have provided an elegant resolution to the hierarchy problem and more generally extra dimensions have proved an integral part in many BSM scenarios. With the LHC fast approaching it would be useful to know if direct observation of extra dimensions is possible, i.e. what is the lower bound on the mass of the first Kaluza Klein state? Here I consider the bound coming from electroweak observables for a general class of warped geometries.

Jennifer Archibald (Durham)
Monte Carlo at NLO
Slides

With the advent of the LHC, and the expected statistical accuracy of the measurements conducted there, the desire for Monte Carlo generators to provide more precision in their predictions is universally acknowledged. In this talk, I shall consider motivations for the implementation of next-to-leading order matrix elements in hadronic event generators, and discuss some of the resulting complications and the tools required to overcome them.

Luke Barclay (Durham)
Black Holes, Vortices and Thermodynamics
Slides

I will briefly introduce the path integral formulation of quantum gravity in relation to black hole thermodynamics. Then there will be a short look at an Abelian Higgs vortex and its gravitational effects. Finally we will look at the thermodynamics of a system where the black hole and vortex coincide.

James Barnard (Durham)
Preserving Symmetries in Seiberg Dualities
Slides

Seiberg dualities provide a useful tool in investigating N=1 SUSY gauge theories. Often, we will want to deform a duality by adding terms to the superpotential of one of the two theories. This generally reduces the number of global symmetries in the theory and thus weakens the tests for duality. I will talk about how adding extra gauge singlets can address this problem, as well as some unexpected consequences it has in the mesons of the theory.

Andrew James Bruce (Manchester)
Higher Poisson Manifolds and higher Koszul-Schouten brackets
Slides

In recent years there has been much attention given to higher and homotopy structures in mathematics and physics. In this talk we will recall $L_{\infty}$-algebra structures and give some physically inspired geometric examples. In particular I will review the notion of a Higher Poisson manifold (A supermanifold with a "Poisson structure" that is a higher order multivector). With such a structure one associates an $L_{\infty}$-algebra on $C^{\infty}(M)$. The new content in this talk is the construction of an $L_{\infty}$-algebra on the space of differential forms, $\Omega^{*}(M)$. This generalises the Koszul--Schouten bracket of classical Poisson geometry.

Neil Butcher (Nottingham)
Topological Changing Transitions
Slides

We have investigated the possibilities presented by "topology changing transitions" and more specifically the effects of gravity upon them. Transitions offer a method of unifying the string landscape and so increasing the predictive possibilities of string theory. With the inclusion of gravity to the transition comes the possibility of black hole creation. This would act as an obstruction to the process as any black holes would mask the transition from the observer. We attempt to establish the extent of this risk and the outlook for transitions.

Gavin Cullen (Edinburgh)
Massive integrals in NLO calculations
Slides

The LHC needs theoretical predictions that are as precise as the experimental measurements. In perturbation theory this means calculating the cross section to at least Next to Leading order. The virtual part of any next to leading order calculation will involve many Feynman integrals and these are generally very time consuming to complete by hand. One of the steps towards speeding up NLO calculations is to reduce any nasty integrals appearing into a basis set of scalar integrals. I shall outline this reduction technique and highlight current work happening in this area.

Erik Gerwick (Edinburgh)
Gravitational non-linearities and a UV Completion for Kaluza Klein effective theory
blackboard talk

As a prelude I will partially rederive an old result that the consistent self coupling of a massless spin-2 particle at all orders results in Einstein's Equation. I will outline Kaluza Klein effective theory in flat extra-dimensions and mention a possible UV completion, the Asymtoptic Safety Scenario. Finally, I will argue that although UV diverges are consistently handled, the non-linearities inherent in gravity complicate our ability to derive relevant LHC observables in ADD models.

David Houseman (UCL)
Spinor geometry: the natural language for gravity
blackboard talk

The dynamical variables of spinor geometry provide an alternative formulation of classical general relativity with two clear advantages over traditional Riemannian geometry: a domain of definition which strictly implies a spacetime of Minkowski signature; and a natural coupling of the background geometry to spin-half fields. Moreover, spinor geometry offers several tantalising leads towards describing gravity as a non-abelian gauge theory with local symmetry group $SL(2, \Complex)$. These three considerations indicate spinor geometry will likely play a crucial role in a future successful theory of quantum gravity. This talk reviews the motivation and construction of spinor general relativity.

Panagiotis Katsaroumpas (Queen Mary)
Growing Superamplitudes 'Organically'
Slides

Identifying and measuring new physics at the Large Hadron Collider will require quantitatively reliable predictions for Standard Model background processes. New powerful on-shell techniques, that can be used in various quantum field theories, allow us to build perturbative scattering amplitudes in a recursive fashion. Maximally supersymmetric theories are the perfect lab for developing and testing these techniques while recent discoveries have revealed unexpected beauty in their amplitudes. I will present this on-shell technology, and focus on its recent generalisation to manifestly supersymmetric relations, which allow us to calculate superamplitudes more efficiently.

Liam Keegan (Edinburgh)
Walking Technicolor on the Lattice
Slides

I will briefly describe how a walking coupling, instead of the usual running coupling, may allow Technicolor models to avoid being in conflict with measured observables. I will then explain how to determine if this walking behaviour actually exists, using step scaling on the lattice.

Eoin Kerrane (Edinburgh)
The Spectrum of Non-Supersymmetric gauge theories with a non-trivial infra-red conformal fixed point
Slides

I will introduce ongoing efforts to identify the spectrum of non-supersymmetric gauge theories, which are believed to lie at or near a non-trivial infra-red fixed point, describing the motivation for these investigations and detailing how conformal or near-conformal dynamics might be manifested in the spectra of such theories when measured using lattice simulations.

Brane Tilings, M2-Branes and Chern-Simons Theories
Slides

Brane Tilings are known to describe the largest known class of SCFTs in 3+1 dimensions. There is a well established formalism to find AdS_5 x SE_5 duals to these SCFTs and to compare results on both sides. This talk extends this formalism to 2+1 dimensional SCFTs, living on the worldvolume of M2-branes, which are dual to AdS_4 x SE_7 backgrounds of M-theory. The SCFTs are quiver gauge theories with 4 supercharges (N=2 in 2+1 dimensions) and Chern-Simons couplings. They admit a moduli space of vacuum configurations which is a CY4 cone over SE_7. The talk will go over the formalism and look at several examples in detail.

John Omotani (Nottingham)
Taming the Boundaries
Slides

My aim in this talk is to explain what Heterotic M-Theory is, in particular Ian Moss's improved version. I will begin with a very brief introduction to M-Theory. I will explain, without giving much detail, how Heterotic M-Theory is constructed as supergravity on an eleven dimensional manifold with boundary, its structure being fixed by supersymmetry and anomaly cancellation. Finally I will try to indicate the difference between the original Ho?ava-Witten formulation and Ian Moss's improved version to explain why I am working on the latter fourteen years after Ho?ava and Witten's original paper.

Alkistis Pourtsidou (Nottingham)
Cosmic (Super)strings
Slides

Cosmic strings are topological defects arising in gauge theories. Originally, they were thought to be a possible alternative to inflation for explaining the inhomogeneities responsible for structure. This idea was abandoned after they failed to produce the correct CMB power spectrum. However, interest in cosmic strings is renewed since it was realized that they may also arise in models of brane inflation. These cosmic superstrings can be stable, observable and distinguishable from gauge strings. Thus, they may provide a window to string theory through cosmology.

Johannes Schmude (Swansea)
The mathematics of string duals with backreacting, smeared flavor
blackboard talk

In the context of gauge/string duality, the construction of string duals with backreacting flavors has been an area of ongoing interest. While the flavoring procedure is conceptually rather straightforward, one does often encounter increasingly complex technical difficulties. In this talk we will review the problem and show how the application of mathematical tools known to phenomenologists helps simplifying such difficulties considerably.

Ross Stanley (Swansea)
The Refractive Index of Curved Spacetime
Slides

This work considers the way that quantum loop effects modify the propagation of light in curved space. The refractive index for QED is calculated. It is shown how the low frequency phase velocity can be greater than c, but causality is respected in the sense that retarded Green functions vanish outside the lightcone. An overview of phenomenology'' of the refractive index is then presented for black holes, FRW universes and gravitational waves. In some cases, some of the polarization states propagate with a refractive index having a negative imaginary part indicating a potential breakdown of the optical theorem in curved space and possible instabilities.

Dylan Tanner (Kings)
A New Approach to String Cosmology
Slides

The usual approach in string cosmology consists of canceling one-loop beta functions corresponding to Weyl invariance and then solving a set of differential equations involving the background fields to produce equations of motion for fields in target space-time. Our new approach involves devising and solving similarly Weyl invariant bosonic string equations in a non-perturbative (or exact) manner. Such an approach may be interesting in a high-curvature early universe environment where the behaviour of higher perturbative orders may not be well understood. The method is briefly outlined along with some potential cosmological implications such as optical anisotropy.

Mitsuo Tsumagari (Nottingham)
Q-Balls
Slides

We will explore the history of Q-balls (non-toplogical solitons) which exist in many phenomenological and super-symmetric models: polynomial, Graviy-mediated, and Gauge-mediated models, and we then will discuss their stability and dynamics with our analytical and numerical results published in [arxiv: 0905.0125, 0805.3233].

Last updated: 11 May 2009