Theory Seminars Archive

Thursday, April 6, 2017

Speaker: Masha Baryakhtar

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Searching for Ultralight Particles with Black Holes and Gravitational Waves

Abstract:

The LIGO detection of gravitational waves has opened a new window on the universe. I will discuss how the process of superradiance, combined with gravitational wave measurements, makes black holes into nature's laboratories to search for new light bosons, from axions to dark photons. When a bosonic particle's Compton wavelength is comparable to the horizon size of a black hole, superradiance of these bosons into bound "Bohr levels" extracts energy and angular momentum from the black hole. The occupation number of the levels grows exponentially and the black hole spins down. One candidate for such an ultralight boson is the QCD axion with decay constant above the GUT scale. Current black hole spin measurements disfavor a factor of 30 (>100) in axion (vector) mass; future measurements can provide evidence of a new boson. Particles transitioning between levels and annihilating to gravitons may produce thousands of monochromatic gravitational wave signals, and turn LIGO into a particle detector.

Thursday, March 23, 2017

Speaker: Sean Tulin

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Dark matter self-interactions and small scale structure

 Abstract: Astrophysical observations of the structure of galaxies and clusters are no longer simply proving the existence of dark matter (DM), but have sharpened into a tool probing the particle physics of DM. I review small scale structure anomalies for cold DM and their possible implications for DM physics, such as the existence of forces in the dark sector. New results on cluster scales provide a new important handle for constraining DM's interactions, its mass, and the mass of dark mediator particles. I discuss how self-interactions arise in particle physics models and are complementarity with other types of dark matter searches.

Thursday, March 16, 2017

Speaker: Antonio Delgado

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Searching for compressed spectra

Abstract: I will present two scenarios where standard searches for SUSY at the LHC
are not very efficient because the mass splitting between the LSP and the NLSP
is small and therefore there is not a lot of MET in the events. I will then use different
observables to be able to improve the reach of the LHC in this kind of situations.
Thursday, March 9, 2017

Speaker: Yuhsin Tsai

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Probing dark showers at the LHCb

Abstract: Dark shower is a generic feature of the Hidden Valley (HV)
model, which produces bound states with a high multiplicity, low
masses, and long lifetimes. The showering process can arise, for
example, in Neutral Naturalness models, or in dark matter scenarios
that explain the possible signal of galactic center gamma-ray. A
collider search of such signals requires good invariant-mass and
vertex resolution, as well as a good particle id to veto the
background. I will explain why the LHCb experiment has a great
potential in seeing these dark shower events and compare the estimated
sensitivity to that of the future ATLAS/CMS searches.


Thursday, November 10, 2016

Speaker: Harri Waltari

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Collider signatures of sneutrino dark matter in left-right symmetric supersymmetry

Abstract:

A right-handed sneutrino is a viable dark matter candidate in supersymmetry in addition to the more conventional neutralino option. Right-handed sneutrinos are a natural part of left-right symmetric supersymmetric models, where the gauge sector is extended with right-handed weak interactions. We studied the sneutrino dark matter option in left-right supersymmetry and its signatures at the LHC. We find that we may satisfy the constraints from relic density, low-energy observables and direct SUSY searches. The easiest way to produce the sneutrino would be via the right-handed gauge sector, where the decays of W_R to sleptons lead to multilepton final states. We compare some benchmarks to the case of a neutralino LSP. We may get a detectable signal with high luminosities even with the right-handed W-boson being around 3.5 TeV.

Thursday, November 3, 2016

Speaker: Matthew Reece

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Exploring the Weak Gravity Conjecture

Abstract: 

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 discuss some of the arguments linking the conjecture to cosmology, and present some new evidence that strong versions of the conjecture are likely to be true.

Thursday, October 20, 2016

Speaker: Csaba Csaki

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Twin phenomenology

Abstract: 

I discuss three aspects of phenomenology of twin Higgs models. First I argue that some versions of these models will produce displaced Higgs decays and examine in detail the feasibility of discovering such displaced decays in the tracker of the LHC experiments. Second I will examine flavor bounds on composite twin Higgs models. Finally I investigate how feasible identical twin Higgs models are: the number of relativistic degrees of freedom depends strongly on the decoupling temperature which can be dialed via the structure of the twin neutrino sector.

Thursday, October 6, 2016

Speaker: David  Curtin

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: The Lifetime Frontier

Abstract: Searches for long-lived particles (LLPs) at the LHC are broadly motivated in almost any BSM scenario that addresses one or more of the long-standing puzzles of high energy physics. I will focus on some recent theory developments in Neutral Naturalness to motivate study of exotic Higgs decays to LLPs, the production and annihilation of quirkonia into Emerging-Jet-like final states, and additional cosmological probes. The LLP signature space is as big as the space of prompt searches, and is just starting to be explored. In particular, very long and very short lifetimes have not yet been adequately studied. I outline how such signatures can be looked for at the LHC, and advocate for the construction of a dedicated surface detector called MATHUSLA for the HL-LHC upgrade.

Thursday, September 15, 2016

Speaker: Prateek Agrawal

Time: 3:30PM -- 4:30PM

Location: HP5345

Title: The cosmological constant problem in scalar gravity

Abstract: 

I will discuss a toy theory of gravity where the gravitational force is mediated by a scalar particle. This theory can be understood as the low-energy limit of a spontaneously broken Conformal Field Theory, and serves as an intriguing analog to General Relativity, capturing many qualitative features. In fact, it exhibits a fine-tuning problem closely resembling the cosmological constant problem. A solution to this cosmological constant problem in scalar gravity has been proposed. I will discuss an explicit realization of this solution and its connections with the cosmological constant problem in our universe.

Thursday, April 7, 2016

Speaker: Ian Low

Time: 3:30PM -- 4:30PM

Location: PA 234

Title: "The LHC Awakens: Signs of Hope (and Despair)"

Abstract: 

I will summarize findings from Run 1 and early Run 2 of the LHC, focusing on signs of (non)deviations from the standard model of particle physics.