Nuclear/Particle Seminar Abstracts
Spring 2017
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The 2015 Nobel Prize in Physics was awarded for the discovery of the phenomenon of neutrino oscillations, which implies that neutrinos are not massless as we had previously believed. This raises a wealth of new and intriguing questions. What is the ordering of the neutrino mass states? Might they violate matter/antimatter symmetry? What structure, if any, does the neutrino mixing matrix have? The NOvA experiment directly addresses these questions by measuring changes undergone by a powerful neutrino beam over an 810 km baseline, from its source at Fermilab, Illinois to a huge 14 kton detector in Ash River, Minnesota. I will give a brief overview of neutrino oscillations, then present our latest results, their implications, and prospects for the future.
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The formulation of lattice field theories on curved Riemann manifolds is a difficult problem. By adopting methods from flat space lattice gauge theory, classical finite elements, and Regge Calculus, we have constructed a simplicial QFE Lagrangian for scalars and fermions. A natural first test of this method is the study of the Ising c = 1/2 CFT in two dimensions. Numerical lattice results from S2 at the Wilson-Fischer fixed point of the $\phi^4$ theory and for the free Dirac fermion will be presented and compared to analytic continuum results. The QFE method can be readily extended to radial quantization, and current results for the critical behavior of the three dimensional φ4 theory on R x S2 will be discussed.
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The Standard Model (SM) of particle physics is a spectacularly successful theory that is known to be fundamentally incomplete. The recent discovery of the Higgs boson at the Large Hadron Collider is, on one hand, the final missing piece of the SM and, on the other, a window into what lies beyond. I will discuss the motivations and experimental challenges of searching for physics beyond the SM at the LHC. Emphasis will be placed on using the Higgs boson as a probe of new physics in processes involving pairs of Higgs bosons.
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At the end of the XIX century, Lord Kelvin summarized a widespread feeling among physicists by saying that "physics is essentially complete, save for two little clouds". The "clouds" he was (apocryphally) referring to were the puzzling results from two measurements, the Michelson-Morley experiment and the Black-body spectrum, whose explanations ushered in an unprecedented era of discoveries that stretched throughout most of the XX century. After the culmination of the Standard Model in the 70's, the field of particle physics has found itself in a similar situation. Today, the "clouds" guiding the searches for physics beyond the Standard Model are issues like dark matter or the hierarchy problem. Using SUSY searches at CMS and the measurement of B->D(*)TauNu decays at BaBar as models, I will give an overview of some of the main strategies that are being followed in the quest to find new physics in the XXI century.
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The first run of the Large Hadron Collider has been a great success, most notably with the discovery of the Higgs boson. Despite the continued triumph of the Standard Model, important questions about how nature works on small scales remain unanswered. Top quarks, the most massive of all known elementary particles, play a central role in many of the extensions to the Standard Model that have been proposed to address these questions. A precise understanding of top quarks and their production and properties is therefore critical. In this talk, I will discuss the motivation and status of top quark physics at the LHC, presenting recent results from the CMS experiment. I will additionally give an outlook to the future upgrade of the LHC.
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The hypothesis of weak scale supersymmetry ameliorates the gauge hierarchy problem, yields gauge couplings consistent with grand unification, and when augmented by R-parity conservation, provides natural candidates for the observed dark matter (DM). However, experiments at the LHC have not turned up any direct evidence for the existence of superpartners, seemingly in conflict with early expectations that suggested that superymmetry would be revealed even at LEP2 or the Tevatron. We critically re-evaluate the arguments that led to these expectations and conclude that phenomenologically viable SUSY spectra with no worse that a few percent fine-tuning are perfectly possible. While no top-down model that lead to such spectra has as yet emerged, we show that it is nontheless possible to abstract many phenomenological implications of natural supersymmetry. We discuss prospects for SUSY discovery at the (high-luminosity) LHC, and argue that experiments at the proposed high energy LHC operating at 33 TeV would allow a definitive search for natural SUSY. We will also mention the complementary role of experiments at an electron-positron linear collider with a centre-of-mass energy of 600 GeV for elucidating the nature of a SUSY discovery in this framework.
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p-adic numbers are an elaboration of the arithmetic one uses to reckon days of the week. p-adic AdS/CFT is a formulation of the gauge-string duality where the conformal field theory is defined over p-adic numbers, and anti-de Sitter space is replaced by an infinite regular tree, sometimes called the Bethe lattice. I will explain this new version of AdS/CFT, illustrate with a few computations, and at the end also explain how some old ideas like Kadanoff's spin-blocking fit in elegantly to the p-adic picture.
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We discuss the different forms of the functional RG equation and their relation to each other. In particular we suggest a generalized version of the Polchinski equation as an alternative to the Wetterich equation in order to discuss Weinberg's asymptotic safety program for defining quantum gravity.
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