# Particle Physics

This series consists of talks in the areas of Particle Physics, High Energy Physics & Quantum Field Theory.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## Long-Lived Neutral Particles at the LHC

Friday Oct 15, 2010
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I will discuss the collider signatures of heavy, long-lived, neutral particles that decay to charged particles plus missing energy. The focus will be the case of a neutralino NLSP decaying to Z and gravitino within the context of General Gauge Mediation (based on arXiv:1006.4575). I will show that the LHC has the potential for early discovery of such a long-lived particle if its lifetime (c tau) is between about 0.1 millimeters and 100 meters. I will also discuss the use of timing and pointing measurements to fully reconstruct kinematics in events with displaced decays.

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## The flavor puzzle : Why neutrinos are different ?

Friday Sep 24, 2010
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Large mixing angles and a mild mass hierarchy are observed in neutrino oscillations, in stark contrast with the quarks and charged leptons sectors where very hierarchical masses come along with small mixings.
We review and discuss the neutrino mass patterns that are technically natural, in the context of the seesaw mechanism and with a quark-lepton unification perspective.

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## Topological defects and vacuum decay

Friday Aug 20, 2010
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False vacua in QFT are liable to undergo spontaneous decay. Slowness of quantum tunneling can however allow a long lifetime to the false vacuum state. In supersymmetric theories this is a crucial criterion for obtaining a long lived universe with spontaneously broken supersymmetry. We have explored false vacua which admit topological defects, including in a supersymmetric model with O'Rafeartaigh type supersymmetry breaking. We show that the presence of topological defects significantly alters the stability of the false vacuum.

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## Cascade supersymmetry breaking and low scale gauge mediation

Friday Jul 16, 2010
Speaker(s):

The gauge mediation models with a gravitino mass in the eV range is a
quite attractive scenario which causes no cosmological/astrophysical problems.
The model construction with such a light gravitino is, however, quite challenging
and in most cases ends up with the problems with the suppressed gaugino mass,
the vacuum instability and the Landau pole problems of the Standard Model gauge
coupling constants.

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## Rescuing the Standard Model in the case the Higgs Boson is not found

Friday May 14, 2010
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A plethora of Higgsless models have been proposed and we are in the peculiar situation where Fermilab & LHC results will be extremely interesting whether or not the Higgs boson is found. I present here a model where one of the sacred assumption of quantum field theory (renormalizability) is dropped. A precise prescription for the removal of the divergences guarantees both unitarity and predictivity. Interestingly the model is consistent if the Power counting criterion is enforced in a weak form (Weak Power Counting).

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## An Unparticle Solution to the Hierarchy Problem

Friday May 07, 2010
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The Planck-weak hierarchy is investigated in an extradimensional, soft-wall model originally proposed by Batell and Gherghetta. In this model the soft-wall is dynamically generated by background ﬁelds that, in the Einstein frame, cause the metric factor to deviate from anti-de Sitter by a power-law of the conformal coordinate. This talk will demonstrate that in order to achieve the appropriate Planck-weak hierarchy, the power of the conformal coordinate must be less than one.

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## Boosting Higgs Discovery

Friday May 07, 2010
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An enormous effort is underway to search for the Higgs boson at the LHC. One new development of the past couple of years is to look into the kinematic region where the Higgs boosted, which has led to the possibility to observe the dominant b-bar decay mode as a single "fat jet" when the Higgs is light. I'll discuss how this technique has great promise not only within the Standard Model, but potentially has even greater promise to find a light Higgs in new physics models such as supersymmetry.

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## WIMPless Dark Matter and Meson Decays with Missing Energy

Tuesday Apr 20, 2010
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WIMPless dark matter offers an attractive framework in which dark matter can be very light. We investigate the implications of such scenarios on invisible decays of bottomonium states for dark matter with a mass less than around $5 {\rm GeV}$. We relate these decays to measurements of nucleon-dark matter elastic scattering. We also investigate the effect that a coupling to $s$ quarks has on flavor changing $b\to s$ processes involving missing energy.

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## A Few Interesting Trees in the WIMP Forest

Friday Mar 26, 2010
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Gamma rays from WIMP annihilation are an important signal through which we search for non-gravitational interactions of dark matter. In particular, lines in the energy spectrum of gamma rays provide a signal which is difficult for conventional astrophysics to fake, and are thus promising despite the fact that such lines are generically expect to be suppressed, arising from one loop processes. I will discuss two theories which have an interesting family of gamma ray lines and discuss how such lines can reveal information about the WIMPs and the dark sector.

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## Gauging Baryon and Lepton Number

Friday Mar 19, 2010
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We investigate a simple theory where Baryon number (B) and Lepton number (L) are local gauge symmetries. In this theory B and L are on the same footing and the anomalies are cancelled by adding a single new fermionic generation. There is an interesting realization of the seesaw mechanism for neutrino masses. Furthermore there is a natural suppression of flavour violation in the quark and leptonic sectors since the gauge symmetries and particle content forbid tree level flavor changing neutral currents involving the quarks or charged leptons.

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## RECENT PUBLIC LECTURE

### Amanda Peet, University of Toronto and Perimeter Institute

Speaker: Amanda Peet