Natural Gauge Hierarchy in SO(10)

It is shown that a natural gauge hierarchy and doublet-triplet splitting can be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial cancellations (fine-tuning) and arbitrary forms of the superpotential are avoided, the superpotential being the most general compatible with a symmetry. It is shown by example that the Dimopoulos-Wilczek mechanism can be protected against the effects of higher-dimension operators possibly induced by Planck-scale physics. Natural implementation of the mechanism leads to an automatic Peccei-Quinn symmetry. The same local symmetries that would protect the gauge hierarchy against Planck-scale effects tend to protect the axion also. It is shown how realistic quark and lepton masses might arise in this framework. It is also argued that ``weak suppression'' of proton decay can be implemented more economically than can ``strong suppression'', offering some grounds to hope (in the context of SO(10)) that proton decay could be seen at Superkamiokande.Comment: 26 pages in plain LaTeX, 5 figures available on request, BA-94-0

Threshold Effects in Slepton-Pair Production at the LHC

We present a study of threshold resummation effects for slepton pair production at the Large Hadron Collider (LHC). After confirming the known NLO QCD corrections and generalizing the NLO SUSY-QCD corrections to the case of mixing squarks in the virtual loop contributions, we employ the Mellin N-space resummation formalism to compute logarithmically enhanced soft-gluon terms to all perturbative orders.Comment: 3 pages, 1 figure, presented at HEP 2007 (Manchester, July 2007

Anthropic tuning of the weak scale and of m_u/m_d in two-Higgs-doublet models

It is shown that in a model in which up-type and down-type fermions acquire mass from different Higgs doublets, the anthropic tuning of the Higgs mass parameters can explain the fact that the observed masses of the $d$ and $u$ quarks are nearly the same with $d$ slightly heavier. If Yukawa couplings are assumed not to "scan" (vary among domains), this would also help explain why the t quark is much heavier than the b quark. It is also pointed out that the existence of dark matter invalidates some earlier anthropic arguments against the viability of domains where the Standard Model Higgs has positive $\mu^2$, but makes other even stronger arguments possible.Comment: 31 pages, 7 figure

The anthropic principle and the mass scale of the Standard Model

In theories in which different regions of the universe can have different values of the the physical parameters, we would naturally find ourselves in a region which has parameters favorable for life. We explore the range of anthropically allowed values of the mass parameter in the Higgs potential, $\mu^2$. For $\mu^2<0$, the requirement that complex elements be formed suggests that the Higgs vacuum expectation value $v$ must have a magnitude less than 5 times its observed value. For $\mu^2>0$, baryon stability requires that $|\mu|<<M_P$, the Planck Mass. Smaller values of $|\mu^2|$ may or may not be allowed depending on issues of element synthesis and stellar evolution. We conclude that the observed value of $\mu^2$ is reasonably typical of the anthropically allowed range, and that anthropic arguments provide a plausible explanation for the closeness of the QCD scale and the weak scale.Comment: 28 pages, LaTeX. No changes from version originally submitted to archive, except that problem with figure file has been correcte

A comment on "Amplification of endpoint structure for new particle mass measurement at the LHC"

We present a comment on the kinematic variable $m_{CT2}$ recently proposed in "Amplification of endpoint structure for new particle mass measurement at the LHC". The variable is designed to be applied to models such as R-parity conserving Supersymmetry (SUSY) when there is pair production of new heavy particles each of which decays to a single massless visible and a massive invisible component. It was proposed in "Amplification of endpoint structure for new particle mass measurement at the LHC" that a measurement of the peak of the $m_{CT2}$ distribution could be used to precisely constrain the masses of the SUSY particles. We show that when Standard Model backgrounds are included in simulations, the sensitivity of the $m_{CT2}$ variable to the SUSY particle masses is more seriously impacted for $m_{CT2}$ than for other previously proposed variables.Comment: 5 page

Nonstandard order parameters and the origin of CP violation

The consideration of chirality-preserving 2-fermion order parameters may shed new light on the strong CP problem and the breakdown of flavor symmetries. We describe two situations, one having the standard KM picture for weak CP violation and another having new sources of weak CP violation.Comment: 12 pages, no figure

Can we improve the prediction of hip fracture by assessing bone structure using shape and appearance modelling?

Copyright 2013 Elsevier B.V., All rights reserved.Peer reviewedPreprin

Simulating Impacts of Extreme Weather Events on Urban Transport Infrastructure in the UK

Urban areas face many risks from future climate change and their infrastructure will be placed under more pressure due to changes in climate extremes. Using the Tyndall Centre Urban Integrated Assessment Framework, this paper describes a methodology used to assess the impacts of future climate extremes on transport infrastructure in London. Utilising high-resolution projections for future climate in the UK, alongside stochastic weather generators for downscaling, urban temperature and flooding models are used to provide information on the likelihood of future extremes. These are then coupled with spatial network models of urban transport infrastructure and, using thresholds to define the point at which systems cease to function normally, disruption to the networks can be simulated. Results are shown for both extreme heat and urban surface water flooding events and the impacts on the travelling population, in terms of both disruption time and monetary cost