# 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.

## 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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## The Phase Diagram of QCD: Results &amp; Challenges

Friday Mar 05, 2010
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I will review the progress made in our understanding of the QCD phase diagram within an RG approach to QCD and effective QCD models. In particular this includes a discussion of the confinement-deconfinement phase transition/cross-over, the chiral phase transition/cross-over, as well as their interrelation.

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## Sneutrino NLSP at the LHC

Friday Feb 12, 2010
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The sneutrino is a viable NLSP candidate in SUSY with gravitino LSP. In
my talk I will focus on this possibility, in particular concentrating on
the question of whether the LHC can distinguish spectra with a sneutrino
NLSP from alternatives, e.g. ones with neutralino LSP. I will show that
there are at least two different families of experimentally allowed
spectra with sneutrino NLSP which exhibit distinctive multilepton
signals. These spectra are not easy to fake within the MSSM. I will

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## Jets in Effective Field Theory

Friday Jan 29, 2010
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Final states involving hadronic jets are an important background to new physics processes in colliders, as well as a probe of QCD over a large range of energies. Because the physics of jets involves multiple energy scales, they are both complex theoretically and ideally suited to study using effective field theory techniques. In this talk I will discuss some recent progress in using effective field theory to describe the physics of jets.

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## Resonant Dark Matter

Friday Jan 15, 2010
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It is usually assumed that dark matter direct detection is sensitive to a large fraction of the dark matter (DM) velocity distribution. I will explain an alternative form of dark matter-nucleus scattering which only probes a narrow range of DM velocities due to the existence of a resonance, a DM-nucleus bound state, in the scattering - resonant dark matter (rDM). The scattering cross section becomes highly element dependent, has increased modulation and as a result can explain the DAMA/LIBRA results whilst not being in conflict with other direct detection experiments.

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## Bound states at the LHC

Tuesday Dec 15, 2009
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When a pair of particles is produced close to threshold, they may form a bound state if the potential between them is attractive. Can we use such bound states to obtain information about new colored particles at the LHC? I will discuss the relevant issues using examples from the MSSM and other beyond the standard model scenarios.

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## A Natural Higgs in the N*MSSM

Tuesday Dec 08, 2009
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Supersymmetry is a leading candidate for physics Beyond the Standard Model. However, a tree level in the Minimal Supersymmetric Standard Model the Higgs boson should be lighter than the Z boson. LEP did not discover the Higgs boson, so typically large radiative corrections are required to push the Higgs above the LEP lower limit, leading to fine tuning issues. In this talk I will describe how to avoid limits from the searches at LEP and discuss a potential early signal of a 90 GeV Higgs at the LHC.

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## Building Massless Tree Amplitudes without a Lagrangian

Wednesday Dec 02, 2009
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The BCFW recursion relations define Yang-Mills and gravity amplitudes in terms of lower-point amplitudes. I will discuss several connections between the internal consistency of this recursive definition and the allowed interactions of massless, higher-spin particles.

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## RECENT PUBLIC LECTURE

### Quantum Mechanics and Spacetime in the 21st Century

Speaker: Nima Arkani-Hamed