Physics at the Terascale Helmholtz Gemeinschaft

Theorist of the Month

The "Theorist of the Month" is a concept installed in order to improve the exchange between theory and experiment and to strengthen the theory background of experimental Ph.D. students. The Theorist of the Month will spend about one week at DESY and in this time give one basic seminar on his/her research topic, be available for all kinds of theory questions and discussions, and at the end of his/her stay summarise the discussions and questions of the week.

Future "Theorists of the Month"

June 2020: Anna Kulesza

Anna will visit DESY from 15-19 June.

April 2020: David Shih

David will visit DESY from 23-29 April.

Previous "Theorists of the Month"

Theorists of the month in 2019:

September: David Curtin

David visited DESY from 9-13 September. His talk was about "Cosmology and Astrophysics of the Twin Higgs: from the CMB to Mirror Stars"

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, including the search for Mirror Stars in optical and X-ray observations, that are motivated by the hierarchy problem.

July: Martin Hentschinski

Martin was at DESY on 22.-26. July. He talked about "Signs for the onset of gluon saturation in exclusive photo-production of vector mesons at LHC":

We investigate photo-production of vector mesons J/Psi and Upsilon measured both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution (Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading order evolution can only describe production at highest energies, if perturbative corrections are increased to unnaturally large values; rendering this corrections to a perturbative size, the growth with energy is too strong and the description fails. At the same time, the KS gluon, which we explore both with and without non-linear corrections, requires the latter to achieve an accurate description of the energy dependence of data. We interpret this observation as a clear signal for the presence of high gluon densities in the proton, characteristic for the onset of gluon saturation.

April: Jun Gao

Jun Gao will visit DESY from 16.-30.04.2019 and will gave a seminar talk during his visit. He works on several theoretical topics of particle physics focusing on current and future high energy collider experiments, including precision test of the standard model of particle physics, search for new physics beyond the standard model, and applications of quantum chromodynamics (QCD). He received his Ph.D. from institute of theoretical physics, Peking University in 2011. Thereafter he joined department of physics of Southern Methodist University in Dallas, where he was working on theoretical QCD in the CTEQ collaboration. In 2014 he moved to high energy physics division at Argonne National Laboratory in Chicago. Currently, he is a professor in Shanghai Jiao Tong University, where he holds Distinguished Research Fellowship. DESY groups collaborate with Jun Gao in the context of searches for contact interactions using the jet production at the LHC.

February: Simon Plaetzer

Simon will visit DESY from 13.-27.02.2019 and will give two talks during his visit. He works on Monte Carlo Simulations.

January: Ilaria Brivio

Ilaria will visit DESY from 7.-12.01.2019 and will gave a seminar talk during her visit. Ilaria is a leader in the field of Effective Field Theories for the Higgs sector and is the author of the "SMEFTSIM" model.

Theorists of the month in 2018:

November: Michael Spannowsky

Michael will visit DESY from 19.-23.11. and will gave a seminar talk. He will discuss the possibility to measure dark energy at the LHC.

November: Simone Marzani

Simone will visit DESY from 12.11.-16.11. and will gave a seminar talk on QCD@small-x: new developments and their impact on PDF determination.

October: Jonas Lindert

Jonas will visit DESY from 22.10.-26.10. and will gave a seminar talk on extrapolations between electroweak bosons and the evaluation of theory uncertainties in the VBF phase space which has a significant impact on the VBF Higgs to invisible analysis.

June/July: Valerio Bertone

Valerio visited DESY from 25.6.-18.7. and will gave a seminar talk on extraction of collinear unpolarised fragmentation functions.

May: Cen Zhang

He will visit DESY from 22.-25.5. and will give a seminar talk.

Topic: Standard Model effective field theory for top quark physics

Standard Model effective field theory provides an efficient way for characterizing and analyzing physics beyond the Standard Model. I will discuss its application in top-quark physics at the LHC. Topics will include common standards for the interpretation of top-quark measurements, the status and plans for NLO predictions in the form of automatic MC tools, and phenomenology of rare processes such as tt+X, tj+X, tttt and ttbb. I will also present some recent efforts on including EW corrections from top-quark operators to Higgs measurements, where sizable corrections are found and seem to indicate that a more global point of view is needed for the future runs at the LHC.

April: Richard Ruiz

Topic: Left-right symmetric models at the LHC

March: Gennady Lykasov

Gennady Lykasov will visit DESY from 19.-23.3. and will give a seminar talk.

Topic: Unintegrated PDF and its application to describe the structure functions measured at HERA and the hard processes
studied at LHC.

Past "Theorists of the Month"

February: Darren Scott

Topic: Top quark physics (top quark pair production at the LHC at NNLO+NNLL')

January: Xiaohui Liu

Topic: Inclusive jet production at the LHC.

November: Andrea Ferroglia

Topic: Top quark physics.

September: Alessandro Vicini

Topics: Drell-Yan, electroweak corrections, W mass measurement, Higgs physics, PDF uncertainties, Monte Carlo

March: Gennady Lykasov

Topic: Unintegrated PDF and its application to describe the structure functions measured at HERA and the hard processes
studied at LHC.

February: Valerio Bertone

Topic: The xFitter project is an open-source framework devoted to the analysis of high-energy experimental measurements and the assessment of their impact on relevant physical quantities such as Parton Distribution Functions (PDFs) and the strong coupling alpha_s.

The power of the xFitter project stems from its flexibility that in turn is the result of a coordinate effort aimed at developing and joining in one single framework tools for data analysis. The successful employment of xFitter in a large number of analyses testifies its capabilities. On the other hand, due to the contribution of a large number of developers, its complexity is quickly growing. In order to facilitate the maintenance and ensure the functionality, a modular structure able to minimize as much as possible the overlap of different development lines is required.

January: Francesco Hautmann

Topic: Color correlations in top quark and jet production in the multi-TeV region

In the theory of boosted top quark and multi-TeV jet production at the LHC and future colliders one of the most challenging topical questions concerns the role of color correlations induced by soft gluons coupling the initial and final states of the high-energy collision. It has been pointed out that such correlations may spoil perturbative QCD factorization theorems and lead to new color entanglement effects. The question arises of whether such effects may be responsible for significant corrections to transverse momentum spectra and angular correlations measured in the multi-TeV region of interest for the LHC and future high-energy experiments. We illustrate these open issues and propose new approaches to the QCD evolution of parton cascades, designed to be well-suited for the treatment of inclusive variables but also of correlations and the analysis of exclusive components of final states in high-energy collisions.


Theorists of the Month in 2015 and earlier

Fernando Febres Cordero was at DESY from 22-24 April 2015.

THURSDAY 23 April 2015, 16:00, SR1
(coffee & tea served at 15:45pm)

Title: "Processes with Many Jets at the LHC"

Abstract: We study the impact of NLO QCD corrections to processes with many jets at the LHC. We study universal behavior that appears for large enough multiplicity and use it for extrapolating predictions. We show predictions for the 13TeV LHC. As a practical application, we show the BlackHat+Sherpa Ntuple format that allows theorist and experimentalist to access complex fully differential NLO QCD results.


Fernando Febres Cordero was at DESY from 22-24 April 2015.

He discussed the impact of NLO QCD corrections to processes with many jets at the LHC. As a practical application, he showed the BlackHat+Sherpa Ntuple format that allows theorist and experimentalist to access complex fully differential NLO QCD results.

Michael Krämer was staying at DESY from 25 February - 1 March, 2013. His seminar on 28 February was about "Searching for new physics at the Large Hadron Collider: some frustration, but no despair".
   - Slides
   - Poster

Nigel Glover was staying at DESY from 22 - 25 January 2013. His seminar on 24 January was about "Prospects for NNLO measurements using jets at the LHC".
   - Slides
   - Poster

Nikolaos Kidonakis (Kennesaw State University) was staying at DESY from 15 - 21 July 2012. His seminar on 19 July was about Top pair and single top differential cross sections .

John Collins (Penn State) was staying at DESY from 4 - 8 June 2012. His seminar was on a "New definition of Transverse Momentum Dependent parton densities".
   - Poster

Marco Guzzi (Southern Methodist University / CTEQ) was staying at DESY from 23-27 April 2012. In his seminar , he will discussed "Heavy-flavor treatment at NNLO in CTEQ PDF analysis".

Mrinal Dasgupta (University of Manchester) was staying at DESY from 12 - 16 September 2011. His seminar discussed "Theory of QCD jets".
   - Slides
   - Poster

Yuri Dokshitzer (Paris) was staying at DESY from 18 - 22 July 2011. On Thursday, 21 July, he gave a seminar on "Some entertaining aspects of Multiple Parton Interactions physics".
   - Slides

Torbjorn Sjostrand (University of Lund) was staying at DESY from 27 February - 5 March 2011. On Tuesday, March 1, Torbjorn gave a seminar on "Progress on event generation with Pythia 8".

Davison Soper (University of Oregon) was staying at DESY from 8-23 September 2010 and gave a seminar on 20 September 2010: "QCD and Jets".

Fred Olness (SMU) was staying at DESY from 8-12 March 2010. He is one of the key persons of the CTEQ collaboration and in his seminar discussed "W/Z/Higgs Production at LHC and PDF Uncertainties".