Theory Seminars Archive

Monday, November 26, 2018

Speaker: Daniel Stolarski

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: Probing Lepton Flavour Universality in Top Decays

Abstract: I will discuss a novel strategy to test lepton flavour universality (LFU) in top decays, applicable to top pair production at colliders. This proposal exploits information in kinematic distributions and mostly hinges on data-driven techniques. Based on simplified models accommodating recent hints of LFU violation in charged current B meson decays, I will show that existing LHC measurements already provide non-trivial information on the flavour structure and the mass scale of such new physics (NP). I also project that the measurements of LFU in top decays at the high-luminosity LHC could reach a precision at the percent level or below, improving the sensitivity to LFU violating NP in the top sector by more than an order of magnitude compared to existing approaches.

Monday, November 19, 2018
Speaker: David Curtin

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Cosmology and Astrophysics of the Twin Higgs

Abstract: The Twin Higgs model is an attractive solution to the little Hierarchy problem with top partners that are neutral under SM gauge charges. The framework is consistent with the null result of LHC colored top partner searches while offering many alternative discovery channels. Depending on model details, the phenomenology looks very different: either spectacular long-lived particle signals at colliders, or a plethora of unusual cosmological and astrophysical signatures via the existence of a predictive hidden sector. I will examine the latter possibility, and describe how the asymmetrically reheated Mirror Twin Higgs provides a predictive framework for a highly motivated and highly non-trivial interacting dark sector, with correlated signals in the CMB, Large Scale Structure, and direct detection searches, as well as higgs precision measurements at colliders. This provides a vivid example of the collider-cosmology complementarity, and motivates a variety of new astrophysical searches that are motivated by the hierarchy problem.

Monday, November 12, 2018

Speaker: Yongcheng Wu

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: Composite Higgs and Dark matter

Abstract: TBD

Monday, November 5, 2018

Speaker: Jack Collins

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: CWoLa Hunting: Hunting for new physics with machine learning.

Abstract: Machine learning (ML) has rapidly become a core tool for LHC physics, due to the great volume and complexity of the data that this machine collects. Given that it is not a-priori known what form new physics (if any) might take, there has been a surge of interest in the past year in approaches that would enable an ML algorithm to look for new physics directly in the LHC data without reference to any simulated signal sample. This talk will focus on a concrete example called 'CWoLa Hunting' (Classification Without Labels), in which it assumed that the signal is localized in some window in one variable (e.g. a resonance in an invariant mass) in which the background is smooth, but no additional assumptions are made about the morphology of the signal in some orthogonal set of 'auxiliary' variables. The ML algorithm searches for an unusual population of events in the signal window using these auxiliary variables. I will use as a case study a dijet resonance search in which a resonant signal might form a bump in the dijet invariant mass distribution, while the ML algorithm searches for a localized population of events with unusual jet substructure.

Monday, October 29, 2018

Speaker: Joseph Bramante

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: Asymmetric Dark Matter Exploding White Dwarfs and Converting Neutron Stars to Black Holes

Abstract: I will discuss the cosmology, couplings, and characteristics of dark matter that causes white dwarfs to explode and also form small, destructive black holes in neutron stars. Such asymmetric dark matter can be sought out with missing pulsars in the galactic center, observations of gravitational waves in conjunction with kilonovae, and a new class of astrophysical event, the " quiet kilonova."


Monday, October 15, 2018

Speaker: Alexandre Poulin

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: Modifications to the standard freeze-out picture

Abstract: Although Dark Matter (DM) makes up a significant part of the all the 
energy in the Universe, lack experimental DM measurements means that there is
 no clear path or direction for theorists. Because of this,there are many particle 
physics models and ways to theoretically produce DM, one such mechanism is 
thermal freeze-out. In this scenario, the DM was in thermal contact with the 
Standard Model and decoupled once the rate of reaction became comparable to 
the expansion rate of the Universe. This can be a complicated calculation and 
many approximations are typically made, obscuring the physics when making 
modifications to the standard picture. We will explore the concepts behind 
freeze-out in such a way that generalizations to the standard picture become 
clear, well-motivated path for continued research. We will then go down two such
 path by considering modified expansion rate and will be shown that the results 
are not obtain as simply as one would expect if they were only looking at the 
typical freeze-out equations. Next, we will look at the case with multiple DM  
species as a generalization to the single particle case revealing that general 
interactions between DM species can lead to potentially many important effects.
Monday, October 1, 2018

Speaker: Chen Sun

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: Particle Phenomenology in the Era of Gravitational Wave Astronomy

 Abstract: After the detection of black hole and neutron star binary mergers at 
LIGO/Virgo, gravitational wave becomes a new observational channel that we
didn't have access to years ago. It is an interesting question to ask what kind of
new physics this channel can probe. To answer this question, one needs to fill the
gap between the scales of the astrophysical processes and the fundamental
structures. In this talk, I will demonstrate a few ways of extracting particle
physics information directly from binary merger events of neutron stars and
boson stars, and using this information to constrain well motivated dark sectors,
such as dark gauge boson and axion like particles. A short outline of future
directions will also be discussed.


Monday, September 24, 2018

Speaker: Mustafa Bahran

Time: 2:30PM -- 3:30PM

Location: HP4351

Title: The life and death of the 17 keV neutrino


The story of the electron neutrino that has started with Pauli in 1930 continues to occupy human scientific endeavors and will do so for ever; it seems. At heart of this story are the issues of mass and mixing. Both continue to be ultra-hot topics today and for years to come both theoretically and experimentally.

This humble and simple talk will cover work done between the years 1985 and 1995 at both the university of Oklahoma and Sana’a university addressing a 17 keV massive neutrino that was first claimed in 1985 and was finally buried during the years leading to 1995. It will cover a series of papers published in Physics Letters B and Physical Review D as well as a number of conference proceedings.

The 17 keV neutrino has long been dead but issues related to new physics versus the null hypothesis remain alive particularly relevant to experimental systematic errors or theoretical corrections and thus lessons learned from its short life will be summarized.

Thursday, March 22, 2018

Speaker: Alberto Tonero

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: TBA

Abstract: TBA


Thursday, March 8, 2018
Speaker: Jay Hubisz

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Self-Organized Higgs Criticality

Abstract: I will discuss how the critical point for a Higgs sector may be made a dynamical attractor in a way that parallels similar phenomena in statistical physics such as the sand-pile model, or fault slippage in earthquakes. In this construction, a modulus field has a potential which has (meta)stable minima precisely at points where, in the low energy effective theory, the Higgs field mass is vanishing. I will discuss how quantum corrections are not expected to spoil this Higgs criticality, and how there are no ultralight particles expected, in seeming violation of expectations from naive application of effective field theory.