UC Davis Particle Physics Seminars

Latest Episodes:

The Heart of Darkness: Neutralino Dark Matter and the Zeptobarn Scale Oct 17, 2011

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David Sanford discusses the direct detection of dark matter through its elastic scattering off nucleons as among the most promising methods for establishing the particle identity of dark matter.

Recent SUSY results in multilepton final states Oct 11, 2011

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Rob Forrest describes recent SUSY searches at CDF, emphasizing direct searches for weakly produced Charginos and Neutralinos including many recent results using the dilepton and trilepton signatures. The results represent the final and most stringent limits placed on Chargino and Neutralino mass from CDF through the end of the life of the Tevatron.

Relatively Heavy Higgs Boson in More Generic Gauge Mediation Oct 10, 2011

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Jason Evans discuss the implications of the excesses in LHC Higgs boson searches on the gauge mediated supersymmetric standard model, for the mass range 120-140 GeV. A relatively heavy lightest Higgs boson mass in this range can be reconciled with light SUSY particles, if there are additional fields which couple directly to the Higgs boson. The mass of this extra matter can be predicted rather precisely in gauge mediation for a given Higgs boson and gluino mass.

Non-standard Dark Matter Signatures at the LHC Oct 04, 2011

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Yang Bai argues that dark matter particles that have strong interactions with the Standard Model particles are not excluded by current astrophysical constraints. These dark matter particles have unique signatures at colliders; instead of missing energy, the dark matter particles produce jets. We propose a new search strategy for such strongly interacting particles by looking for a signal of two trackless jets. We show that suitable cuts can plausibly allow us to find these signals at the LHC even in early data.

Conformal Symmetry in the Bulk Oct 03, 2011

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The AdS/CFT correspondence relates bulk Einstein geometries to boundary conformal geometry. We show that bulk geometry can also be described in terms of conformal geometry. This description yields a solution generating algebra in the bulk that controls solutions to very general bulk boundary problems. Using this algebra we present a boundary conformal calculus for conformally compact manifolds.

Higgs and Jet Color-Connections Sep 27, 2011

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Jason Gallicchio discusses a new class of observables that aims to characterize the superstructure of an event, that is, features such as color flow, which are not determined by the jet four-momenta alone.

Stealth Supersymmetry Sep 20, 2011

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Jiji Fan discusses a broad class of supersymmetric models that preserve R-parity but lack missing energy signatures. These models have new light particles with weak-scale supersymmetric masses that feel SUSY breaking only through couplings to the MSSM. This small SUSY breaking leads to nearly degenerate fermion/boson pairs, with small mass splittings and hence small phase space for decays carrying away invisible energy. The simplest scenario has low-scale SUSY breaking, with missing energy only from soft gravitinos.

Generating a little hierarchy with accidental SUSY May 23, 2011

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An emergent or accidental supersymmetry is used to address the little hierarchy problem in Randall-Sundrum models by naturally generating a hierarchy between the IR scale and the electroweak scale. Supersymmetry is broken on the UV brane which triggers the stabilization of the warped extra dimension at an IR scale of order 10 TeV. This causes the first two sparticle generations to decouple, thereby avoiding the supersymmetric flavour and CP problems, while an accidental R-symmetry protects the gaugino mass. The resulting low-energy sparticle spectrum consists of stops, gauginos and Higgsinos which are sufficient to stabilize the little hierarchy between the IR scale and the electroweak scale. Introducing a singlet Higgs field on the IR brane, ameliorates the supersymmetric little hierarchy problem, and allows Higgs masses up to 300 GeV.

Interesting Results with the Invariant Mass Distribution of W + Jet Pairs at CDF May 20, 2011

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We present a study of the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb^-1. The observed distribution has an excess in the 120-160 GeV mass range which is not described by current theoretical predictions within the statistical and systematic uncertainties. In particular we will discuss the properties and the significance of this excess.

Constructing a Dynamics for Causal Sets May 17, 2011

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In the causal set approach to quantum gravity the spacetime continuum arises as an approximation to a fundamentally discrete substructure, the causal set, which is a locally finite partially ordered set. The causal set paradigm was elucidated in a classic paper by Bombelli, Lee, Meyer and Sorkin in 1987. While early kinematical results already showed promise, the program received a substantial impetus about a decade ago with the work of Rideout and Sorkin on a classical stochastic growth dynamics for causal sets. Considerable progress has been made ever since in our understanding of causal set theory while leaving undisturbed the basic paradigm. Recent highlights include a causal set expression for the Einstein-Hilbert action and the construction of a scalar field Feynman propagator on a fixed causal set.