Theory Seminars Archive

Thursday, February 8, 2018

Speaker: Jean-François Fortin

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Conformal Field Theory in Embedding Space

Abstract: Conformal field theories (CFTs) are special quantum field theories (QFTs) with extra spacetime symmetries. Amongst other things, they play an important role in determining the phase diagrams of QFTs and in the study of second-order phase transitions in condensed matter physics. The extra spacetime symmetries of CFTs lead to an algebra of operators dictated by the operator product expansion (OPE). Contrary to QFTs where perturbation theory is often the only computational handle available, the existence of OPEs allows a specific understanding of CFTs through consistency conditions of correlation functions, even at strong coupling. In this talk we review conformal field theory and discuss the embedding space point of view. Contrary to position space where the conformal algebra action on fields is complicated, the conformal algebra action in embedding space is homogeneous and thus simpler. The use of embedding space allows an easier computation of the correlation functions and the associated conformal blocks from the OPEs in embedding space. The most general function appearing in the conformal blocks is obtained in terms of infinite sums on the conformal cross ratios. Several interesting properties of this function are found and it is shown that it is invariant under the dihedral group of order 12.

Thursday, February 1, 2018

Speaker: Jesse Thaler

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: On the Topic of Jets

Abstract: When quarks and gluons are produced in high-energy collisions, their fragmentation and hadronization via QCD results in collimated sprays of particles called jets. While quark and gluon partons carry color charge, jets are composed of color-singlet hadrons, so there is no unambiguous definition of "quark" and "gluon" at the hadron level. Remarkably, a similar kind of problem is faced when analyzing the distribution of words in a set of documents, and there is a framework called "topic modeling" to identify emergent themes in a corpus without having to specify those themes a priori. In this talk, I present preliminary studies applying topic modeling to jet physics, and I speculate on a possible application of jet topics to extract the strong coupling constant.

Thursday, January 11, 2018

Speaker: Gabriel Lee

Time: 3:30PM -- 4:30PM

Location: HP4351

Title:  Bound State Formation for Dark Hadrons

Abstract:  Dark matter charged under a hidden nonabelian gauge group generically undergoes a confining phase transition in the early universe. Depending on the matter content in the model, this transition can produce a variety of colour singlet states in the confined phase, and these can undergo a second stage of annihilation. It has previously been claimed that this second-stage cross section is geometric. We examine this claim by calculating the cross section using two different methods.

Thursday, November 23, 2017

Speaker: Ahmed Ismail

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Signatures of New Anomalous Gauge Bosons

Abstract:  Gauge anomalies occur in nearly all Abelian extensions of the Standard Model without additional chiral fermions. The lack of detection of new particles suggests that if a new gauge boson exists, we can integrate out the heavy anomaly-canceling fermions at high scales to obtain a low-energy effective field theory with a non-conserved current. We review the construction of this theory and discuss its phenomenological applications, with a focus on the Wess-Zumino terms describing the effective low energy anomalies. In particular, we show that the requirement of theoretical consistency in dark matter models can lead to enhanced indirect detection signatures.

Thursday, November 9, 2017

Time: 2:00 PM -- 5:00 PM

 Location: HP4351

 Speaker: Jonathan Feng

 Title: FASER

 Speaker: Tracy Slatyer

 Title: Resummation for WIMPs

 Speaker: Michael Peskin

 Title: Extracting High-Precision Higgs Boson Couplings at the 250 GeV IL


Thursday, October 12, 2017

Speaker: Yongcheng Wu

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Searching for CPV effects in h->\tau\tau at the LHC and future e+e- collider

Abstract: TBD

Thursday, October 5, 2017

Speaker: Simon Caron-Huot

Time: 2:30PM -- 4:30PM

Location: HP4351

Title: When does the gluon reggeize?

Abstract: I will review the phenomenon of gluon reggeization, and how it controls the energy dependence of high energy forward scattering in perturbative QCD, from a modern perspective based on the eikonal approximation. I will present several novel applications, including its interplay with infrared logarithms and with the more standard evolution of parton distribution functions at small momentum fraction, and present recent progress toward determining the evolution to three-loops. Based on 1309.6521 and 1604.07417.


Thursday, September 28, 2017

Speaker: Ariel Edery

Time: 3:30PM -- 4:30PM

Location: HP4351

Title:  Where does the scale originate from in going from pure R^gravity to the equivalent Einstein gravity?

Abstract: Higher-derivative gravity theories have the well-known problem of not being unitary. However, there is one exception: pure R^2 gravity (R^2 gravity alone). Not only is it unitary but it has recently been shown by a few groups that this theory is equivalent to Einstein gravity with a non-zero cosmological constant minimally coupled to a massless scalar field. The original theory is scale-invariant but the equivalent Einstein theory is not. A crucial question is ``where does the scale originate from?" We point out that the conformal transformation that is performed in going from R^2 to Einstein gravity naturally selects a background spacetime with non-zero Ricci scalar R. This vacuum state does not preserve the symmetry of the action and the scale symmetry is spontaneously broken. We identify the massless scalar field as the Nambu-Goldstone boson associated with the broken symmetry.

Thursday, September 14, 2017
Speaker: Miki Gintner

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: The direct and indirect limits for the strong BSM SU(2)_L+R vector resonance phenomenology

Abstract: First, a simple effective model for the early LHC signs ofstrongly-interacting new physics including a new SU(2)_L+R vectorresonance triplet will be introduced. Then, the current limits for the model's free parameters based on the latest LHC measurements will be shown. Besides, the low-energy electroweak precision data restrictionsalong with the unitarity limits on the validity of the model will be discussed.

Thursday, July 27, 2017
Speaker: Jérôme Claude

Time: 3:30PM -- 4:30PM

Location: HP4351

Title: Search for a doubly charged Higgs boson through vector boson scattering with the ATLAS detector


Abstract: The hierarchy problem suggests that there must be physics beyond the Standard Model (SM) in the electroweak sector. A deviation from SM-predicted values in the Higgs coupling to vector bosons would allow these new physics in the form of an extension to the Higgs sector. The Georgi-Machacek model introduces scalars in higher isospin multiplets to the SM, including a doubly-charged Higgs, while preserving custodial symmetry. This new scalar is potentially accessible as a resonance through charged vector boson scattering (W+ W+ → W+ W+) in the 30 fb-1 of √s = 13 TeV data collected by the ATLAS detector at the Large Hadron Collider (LHC).

This search focuses on the final state of this resonance which includes a pair of same-sign leptons accompanied by a pair of forward jets and missing transverse momentum (MET). Same-sign leptons in the final state are a rare feature of the standard model, and so the background is dominated by charge misidentification. Techniques to reduce these types of background are presented, and the potential for discovery or exclusion is discussed.