# 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.

## Phenomenology of semileptonic B-meson decays with form factors from lattice QCD

Tuesday Mar 08, 2016
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In this talk, I discuss several application of semileptonic B-meson form factors. Topics include the determination of $|V_{ub}|$ and $|V_{cb}|$, hints for new physics in semitauonic decays, and Standard-Model predictions for flavor-changing-neutral-current processes: $B\to P\nu\bar{\nu}$ and $B\to P\ell^+\ell^-$, where $P$ denotes a pion or kaon.

I will also cover some details of the underlying lattice-QCD calculations at a nontechnical level.

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## Exploring the Weak Gravity Conjecture

Friday Mar 04, 2016
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The Weak Gravity Conjecture (WGC), in its original form, says that given an abelian gauge theory there should be at least one charged particle whose charge is bigger than its mass in Planck units. This has surprisingly powerful implications for the possibility of large-field inflation. In this talk I will explore some of the arguments linking the WGC to inflation before taking a closer look at a different question: which version of the WGC should we be trying to prove?

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## Ultralight Axions

Tuesday Mar 01, 2016
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Axions, having a perturbative shift symmetry, can have masses much smaller than other types of particles in a technically natural way. Ultralight axions (ULAs) with m~10^{-22} eV are attractive dark matter candidates with novel properties that distinguish them from cold dark matter (CDM). A single ULA with a GUT scale decay constant provides the correct relic density without fine-tuning. Quantum gravitational effects are expected to break continuous global symmetries, and may spoil the axion potential.

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Tuesday Feb 16, 2016
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Asymptotically AdS spacetimes with reflecting boundary conditions represent a natural setting for studying superradiant instabilities of rotating or charged black holes. In the first part of this talk, I prove that all asymptotically AdS black holes with ergoregions in dimension d ≥ 4 are linearly unstable to gravitational perturbations. This proof uses the canonical energy method of Hollands and Wald in a WKB limit.

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## Electroweak Monopole - Yongmin Cho

Tuesday Feb 09, 2016

We propose the discovery of the electroweak monopole as the final test of the standard model. Unlike the Dirac's monopole in electrodynamics which is optional, the electroweak monopole must exist within the framework of the standard model because the $U(1)_{em}$ becomes non-trivial. We estimate the mass of the monopole to be around 4 to 7 TeV, and expect the production rate to be relatively large, $(1/\alpha_{em})^2$ times bigger than the WW production rate. This implies that the MoEDAL detector at LHC could have a real chance to detect it.

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## Looking for light scalar dark matter with rods and clocks

Friday Feb 05, 2016
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If the dark matter is made up of a bosonic particle, it can be ultralight, with a mass potentially much below 1 eV. Well-known DM candidates of this type include pseudoscalars like the QCD axion, and vectors such as hidden photons kinetically mixed with the Standard Model. Moduli, even-parity scalars with nonderivative couplings to the SM, can also be light dark matter. I will show that they cause tiny fractional oscillations of SM parameters, such as the electron mass and the fine-structure constant, in turn modulating length and time scales of atoms.

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## The Unnatural (or Split) Composite Higgs

Tuesday Feb 02, 2016
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A simple way to trivially satisfy precision-electroweak and flavor constraints in composite Higgs models is to require a large global symmetry breaking scale, f > 10 TeV. This leads to a tuning of order 10^-4 to obtain the observed Higgs mass, but gives rise to a 'split' spectrum where the strong-sector resonances with masses greater than 10 TeV are separated from the pseudo Nambu-Goldstone bosons, which remain near the electroweak scale. To preserve gauge-coupling unification (due to a composite top quark), the symmetry breaking scale satisfies an upper bound f

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## LHCb: Results & Prospects

Tuesday Jan 19, 2016
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The LHCb detector was designed to be the dedicated heavy-flavor physics experiment at the LHC, and has been the world's premier lab for studying processes where the net quark content changes for several years. These studies permit observing virtual contributions from beyond the SM particles up to very high mass scales, potentially (greatly) exceeding the direct reach of the LHC. I will summarize the constraints placed on high-mass BSM physics by such studies, and also highlight a few interesting anomalies.

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## Experimental Probes of Vacuum Energy

Tuesday Dec 15, 2015
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The vacuum energy changes when cosmological phase transitions take place, or in environments with high temperatures or chemical potentials. The propagation of primordial gravity waves is affected through the trace anomaly, and eras where the vacuum energy dominates can lead tofeatures in the gravity wave spectrum.

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## A Nonperturbative Regulator for Chiral Gauge Theories and Fluffy Mirror Fermions

Monday Dec 14, 2015
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I discuss a new proposal for nonperturbatively defining chiral gauge theories, something that has resisted previous attempts.

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