# 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.

## 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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## A Topological Gauge Theory for Entropy and the Emergence of Hydrodynamics

Friday Nov 20, 2015
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## Confronting the strong CP problem at the LHC

Tuesday Nov 17, 2015
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We argue that solutions to the strong CP problem motivate different searches for TeV scale physics at the LHC than are currently being emphasized. We present two solutions to the strong CP problem that require the existence of new colored particles with masses below 10 TeV. New motivated searches at the LHC would provide a strong constraint on these solutions to the strong CP problem.

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## The electroweak chiral Lagrangian with a light Higgs – systematics & application

Friday Nov 13, 2015
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I consider the Standard Model as an effective field theory (EFT) at the electroweak scale $v$. At the scale $f\geq v$ I assume a new, strong interaction that breaks the electroweak symmetry dynamically. The Higgs boson arises as a composite pseudo-Nambu-Goldstone boson in these scenarios and is therefore naturally light $(m_{h}\sim v)$. Based on these assumptions and the value of $\xi=v^{2}/f^{2}$, I explain the systematics that governs the effective expansion:\\

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## What if Gravity is like QCD? -- Revisiting Quadratic Gravity in Analogy with QCD

Tuesday Nov 10, 2015
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It has been known for a long time that quadratic gravity, which generalizes Einstein gravity with quadratic curvature terms, is renormalizable and asymptotically free in the UV. However the theory is afflicted with a ghost problem if the perturbative spectrum is taken seriously. We explore the possibility that the dimensional scale of Einstein-Hilbert term is far smaller than the scale where the dimensionless gravitational couplings become strong. The propagation of the gravitational degrees of freedom can change character at this strong interaction scale.

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## Decoherence as a way to measure extremely soft collisions with Dark Matter

Friday Nov 06, 2015
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Quantum superpositions of matter are unusually sensitive to decoherence by tiny momentum transfers, in a way that can be made precise with a new diffusion standard quantum limit. Upcoming matter interferometers will produce unprecedented spatial superpositions of over a million nucleons. What sorts of dark matter scattering events could be seen in these experiments as anomalous decoherence? We show that it is extremely weak but medium range interaction between matter and dark matter that would be most visible, such as scattering through a Yukawa potential.

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## Naturalness in the Dark

Tuesday Oct 20, 2015
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The search for physics beyond the Standard Model at the LHC is largely oriented towards new particles associated with solutions to the electroweak hierarchy problem. While the precise character of these partner states may vary from model to model, they typically possess large QCD production rates favorable for detection at hadron colliders. Null results in searches for partner particles during Run 1 of the LHC have placed the idea of electroweak naturalness under increasing strain.

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## Using energy-peaks to measure (new and old) particle masses

Friday Oct 16, 2015
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I will first analytically show a simple, yet subtle "invariance" of two-body decay kinematics for the case of a massless daughter and a mother particle which is unpolarized and has a *generic* boost distribution in the laboratory frame. Namely, the laboratory frame energy distribution of the massless decay product has a peak, whose location is identical to the (fixed) energy of that particle in the rest frame of the corresponding mother particle. In turn, this value of the energy is a simple function of the other masses involved in the decay.

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## Cosmology with Goldstone bosons

Tuesday Sep 22, 2015
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I will discuss the appeal of pseudo-Goldstone bosons (pGBs) for the generation of scales in Early Universe cosmology. In particular, I will demonstrate how in Goldstone Inflation a pGB inflaton can solve the hierarchy problem of inflation (the tension between the Lyth bound and the inflationary scale as preferred by CMB anisotropies), while avoiding the problems with trans-Planckian scales that are typically associated with related models. A simple model based on the coset SU(4)/Sp(4) realises both the Higgs doublet and an inflaton singlet as Goldstone modes.

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