Annual Report 2009.pdf - School of Physics - University of Melbourne

group reports& publicationstheoretical particle physics (TPP)Prof Ray VolkasResearch highlights for 2009 include the continuingdevelopment of “soft wall” models as wellas work on Higgsless models of electroweaksymmetry breaking by ARC Federation FellowProfessor Tony Gherghetta In work with Kapustaand Kelley from the University of Minnesota,Gherghetta adapted the soft wall idea in a waythat would permit insights into how quantumchromodynamics binds quarks and gluons intohadrons. Because this binding involves extremelystrong forces, it is notoriously difficult to solve therequired field equations to extract observablessuch as hadron masses. By exploiting a dualitybetween extra-dimensional theories and theoriesinvolving strong interactions (the Maldacenaconjecture), Gherghetta and collaborators wereable to obtain reasonable results for importantquantities such as the hadron masses. Ina separate paper with Sword, also from theUniversity of Minnesota, Gherghetta used softwallideas to understand the origin of quark andlepton families and masses. Finally in work withCui at Harvard and Wells at CERN, a model ofcomposite W,Z bosons was constructed satisfyingelectroweak precision tests. In this model massis generated, not by the Higgs mechanism, butinstead by strong dynamics of a new force.Dr Nicole Bell has for some time been exploringthe nature of dark matter by looking in a modelindependentway at constraints on its propertiesimposed by astrophysical and cosmologicalobservations. In 2009, her attention turned to thepossibility that dark matter may consist of a verylong-lived particle that decays over a cosmologicaltime scale into a daughter dark matter particle ofslightly smaller mass. Working with her studentAhmad Galea and new research fellow Dr KalliopiPetraki, she began a detailed study of constraintson such decays. This work will be reported onfurther in 2010. Also on the dark matter front,research fellow Dr Robert Foot continued hisinvestigations of the possibility that the dark matteris “mirror matter”. Mirror matter is a hypotheticalset of particles and forces that essentially duplicatethe known particles and forces. Mirror protonsand mirror electrons are stable particles, so mirroratoms constitute dark matter candidates. Footexamined this hypothesis in the light of newexperimental results from the DAMA/Libra andCDMS collaborations.48Professor Ray Volkas continued his research ondomain-wall brane models. Two pieces of workcompleted in 2009 were a study with Chkareuli(Tbilisi) and Kobakhidze of domain-wall solutionsusing vector fields rather than scalar fields, andthe development of a new kind of grand-unifieddomain-wall brane model with his student JayneThompson. On-going work with student BenCallen on the flavour problem in models of thistype will be discussed more fully in the 2010report.There were a number of personnel changesin 2009. It was with great pleasure that wewelcomed Dr Kalliopi Petraki as a research fellowspecialising in astroparticle physics to the group.Petraki completed her PhD under Professor AlexKusenko at UCLA, and Melbourne is her firstpostdoc. Two PhD students graduated: DamienGeorge and Sandy Law, who were both supervisedby Prof Ray Volkas. George is now a postdoc atNikhef, the Netherlands institute for high energyphysics, in Amsterdam. Law also moved onto a postdoc position, at Chung Yuan ChristianUniversity in Taiwan. We continue to enjoy thecontributions of Drs Robert Foot, Benedict vonHarling, Archil Kobakhidze and Nicholas Setzer aspostdocs. Visitors to the group included ProfessorJ. L. Chkareuli from Tbilisi, Georgia, and ProfessorEmilian Dudas from the Ecole Polytechnique inParis.From 18-20 November, the group hosted theCosPA 2009 International Symposium onCosmology and Particle Astrophysics, one of anannual series of conferences in the Asia-Pacificregion. Approximately 50 participants camefrom Asia-Pacific regions such as mainlandChina, Japan, Korea, New Zealand and Taiwan,plus several participants from other institutionsin Australia, with good representation also fromthe US. Professor Sean Carroll of the CaliforniaInstitute of Technology delivered a very wellreceived and attended public lecture on the originof the arrow of time as part of the conference.www.physics.unimelb.edu.au