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Dr. Stefan Sint

Associate Professor (Pure & Applied Mathematics)
LLOYD INSTITUTE
      
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Dr. Stefan Sint

Associate Professor (Pure & Applied Mathematics)
LLOYD INSTITUTE

 STEFAN.SINT@tcd.ie

 3531896 8559


  Mathematical Physics   Nuclear Physics   Numerical Analysis   Particle Physics   Physics   Quantum Mechanics   Quantum Physics   Theoretical Physics   Thermodynamics
Project Title
 A strongly interacting electroweak symmetry breaking sector
From
1 June 2011
To
31 May 2015
Summary
This research is in elementary particle physics. All our knowledge about the basic constituents of matter and their interactions (except gravity) is summarized in the so-called standard model. The recent discovery of what seems to be the standard Higgs boson (Nobel prize 2013 to Englert and Higgs) provides one of the last missing pieces to the puzzle. Nevertheless, there are many shortcomings of the standard model which await clarification. For instance, there is no explanation of the family structure of matter, the mechanism for CP violation can't explain the observed matter-antimatter asymmetry of the universe, there are no candidates for dark matter and there is no explanation for the strong disparity of particle masses. In order to make progress and discover new physics, it is mandatory to obtain precision standard model results also in cases where the strong nuclear force prevents the use of analytic techniques. A prime example are the values of fundamental standard model parameters such as the strong coupling constant or the quark masses. Pinning their values down to the percent level would have a major phenomenological impact on the determination of many derived observables and could help uncover small contributions by yet unknown physics. A bit more speculative are ideas that the Higgs boson might not be elementary but rather a composite particle of more fundamental ingredients still to be discovered. This research project uses numerical simulations of lattice gauge theories and recursive finite size techniques to study the coupling constant in such models, thereby testing their phenomenological viability. In addition a precision determination of the strong coupling constant is being carried out based on the same techniques.
Funding Agency
Science Foundation Ireland
Programme
Research Frontiers Programme
Project Title
 Unveiling physics beyond the Standard Model of elementary particle physics
From
1 December 2011
To
30 November 2015
Summary
The key objective of this project is to help unveil new physics beyond the known physics described by the Standard Model (SM) of elementary particle physics. The main focus is on strongly coupled theories where methods of lattice gauge theory are best placed to make progress. This includes Quantum Chromo Dynamics (QCD), i.e. the component of the SM describing the strong interactions of quarks and gluons, as well as more hypothetical models potentially underlying the SM Higgs sector. The common denominator for both applications is the identical methodology. Another key objective and major component of this research project thus consists in the further development of the methods with the aim to significantly reduce systematic errors.
Funding Agency
Irish Research Council (IRC, formerly IRCSET)
Programme
EMBARK
Project Type
PhD studentship Mattia Dalla Brida

Language Skill Reading Skill Writing Skill Speaking
English Fluent Fluent Fluent
French Fluent Fluent Fluent
German Fluent Fluent Fluent
Italian Medium Medium Medium
Russian Basic Basic Basic
Dalla Brida, Mattia and Hollwieser, Roman and Knechtli, Francesco and Korzec, Tomasz and Ramos, Alberto and Sint, Stefan and Sommer, Rainer, High-precision calculation of the quark-gluon coupling from lattice QCD, Springer Nature, 652, 2026, p328 - 334, Notes: [https://doi.org/10.1038/s41586-026-10339-4], Journal Article, PUBLISHED  URL
Y. Aoki, T. Blum, S. Collins, L. Del Debbio, M. Della Morte, P. Dimopoulos, X. Feng, M. Golterman, Steven Gottlieb, R. Gupta, G. Herdoíza, P. Hernandez, A. Jüttner, T. Kaneko, E. Lunghi, S. Meinel, C. Monahan, A. Nicholson, T. Onogi, P. Petreczky, A. Portelli, A. Ramos, S.R. Sharpe, J.N. Simone, S. Sint, R. Sommer, N. Tantalo, R. Van de Water, A. Vaquero, U. Wenger, H. Wittig, FLAG review 2024, Physical Review D, 113, 2026, p014508 - 014945, Journal Article, PUBLISHED  DOI
Brida, M.D. and Hoelllwieser, R. and Knechtli, F. and Korzec, T. and Sint, S. and Sommer, R., Heavy Wilson quarks and O(a) improvement: nonperturbative results for b g, Journal of High Energy Physics, 2024, (1), 2024, p188 - 214, Journal Article, PUBLISHED  DOI
Aoki, Y. and Blum, T. and Colangelo, G. and Collins, S. and Morte, M.D. and Dimopoulos, P. and DÃŒrr, S. and Feng, X. and Fukaya, H. and Golterman, M. and Gottlieb, S. and Gupta, R. and Hashimoto, S. and Heller, U.M. and Herdoiza, G. and Hernandez, P. and Horsley, R. and JÃŒttner, A. and Kaneko, T. and Lunghi, E. and Meinel, S. and Monahan, C. and Nicholson, A. and Onogi, T. and Pena, C. and Petreczky, P. and Portelli, A. and Ramos, A. and Sharpe, S.R. and Simone, J.N. and Simula, S. and Sint, S. and Sommer, R. and Tantalo, N. and Van de Water, R. and Wenger, U. and Wittig, H., FLAG Review 2021, European Physical Journal C, 82, (10), 2022, Notes: [cited By 18], Journal Article, PUBLISHED  DOI
Dalla Brida, M. and Hoellwieser, R. and Knechtli, F. and Korzec, T. and Nada, A. and Ramos, A. and Sint, S. and Sommer, R., Determination of alpha_s(mZ) by the non-perturbative decoupling method, European Physical Journal C, 82, (12), 2022, Journal Article, PUBLISHED  DOI
Mattia Dalla Brida, Tomasz Korzec, Stefan Sint, Pol Vilaseca, High precision renormalization of the flavour non-singlet Noether currents in lattice QCD with Wilson quarks, Eur. Phys. J. C, 2019, p23-, Journal Article, PUBLISHED  TARA - Full Text  DOI
Dalla Brida, M. and Fritzsch, P. and Korzec, T. and Ramos, A. and Sint, S. and Sommer, R., A non-perturbative exploration of the high energy regime in Nf= 3 QCD: ALPHA Collaboration, European Physical Journal C, 78, (5), 2018, Notes: [cited By 0], Journal Article, PUBLISHED  TARA - Full Text  DOI
Sint, S., Probing QCD perturbation theory at high energies with continuum extrapolated lattice data, EPJ Web of Conferences, XIIth Quark Confinement and the Hadron Spectrum , 137, (08014), 2017, 08014-, Notes: [cited By 0], Conference Paper, PUBLISHED  TARA - Full Text  DOI
Dalla Brida, M. and Fritzsch, P. and Korzec, T. and Ramos, A. and Sint, S. and Sommer, R., Slow running of the gradient flow coupling from 200 MeV to 4 GeV inNf=3QCD, Physical Review D, 95, (1), 2017, Notes: [cited By 9], Journal Article, PUBLISHED  TARA - Full Text  DOI
Bruno, M. and Dalla Brida, M. and Fritzsch, P. and Korzec, T. and Ramos, A. and Schaefer, S. and Simma, H. and Sint, S. and Sommer, R., The determination of αsby the ALPHA collaboration, Nuclear and Particle Physics Proceedings, 285-286, 2017, p132-138 , Notes: [cited By 2], Journal Article, PUBLISHED  DOI
  

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Dalla Brida, M. and Hoellwieser, R. and Knechtli, F. and Korzec, T. and Nada, A. and Ramos, A. and Sint, S. and Sommer, R., Heavy Quarks in a Can and the QCD Coupling, Proceedings of Science, Lattice 2022, Bonn, Germany, August 8-13, 2022, 430, (286), 2023, Conference Paper, PUBLISHED
Dalla Brida, M. and Hoellwieser, R. and Knechtli, F. and Korzec, T. and Nada, A. and Ramos, A. and Sint, S. and Sommer, R., Results for alpha_s from the decoupling strategy, Proceedings of Science, Lattice 2021, online conference, United States, 26-31 July 2021, 396, (492), 2022, Conference Paper, PUBLISHED
Battelli, N. and Sint, S., Finite volume renormalization schemes and the fermionic gradient flow, Proceedings of Science, Lattice 2021, online conference United States, 26-31 July 2021, 396, (437), 2022, Conference Paper, PUBLISHED
Sint, S., alpha_s from the ALPHA collaboration (part I), alphas-2019, ECT*, Trento, Italy, 365, 2019, Notes: [cited By 0], Conference Paper, PUBLISHED
Alekhin, S. and Barreiro, F. and Bethke, S. and Brambilla, N. and Britzger, D. and Brodsky, S.J. and Camarda, S. and d†Enterria, D. and Brida, M.D. and Golterman, M. and Huston, J. and Kluth, S. and KÃŒhn, J.H. and Miravitllas, R. and Pérez-Ramos, R. and Peris, S. and Petreczky, P. and Pires, J. and Põldaru, A. and Rabbertz, K. and Ringer, F. and Sint, S. and Sommer, R. and Somogyi, G. and Takaura, H. and Verbytskyi, A., alpha_s(2019) discussions summary, Workshop on precision measurements of the QCD coupling constant (alphas-2019), ECT* Trento, Italy, 11-15 February 2019., 365, 2019, Conference Paper, PUBLISHED
Anthony D. Kennedy, Stefan Sint, Renormalizability of the Schroedinger functional, Proceedings of Science, The 33rd International Symposium on Lattice Field Theory, Kobe International Conference Center, Kobe, Japan, July 14-18, 2015, 274, 2015, pp7 , Conference Paper, SUBMITTED
Mattia Dalla Brida, Patrick Fritzsch, Tomasz Korzec, Alberto Ramos, Stefan Sint and Rainer Sommer, A status update on the determination of Λ(Nf=3, MSbar) by the ALPHA collaboration, Proceedings of Science, The 33rd International Symposium on Lattice Field Theory, Kobe International Conference Center, Kobe, Japan , July 14-18, 2015, , PoS(LATTICE 2015)248, 2015, pp1 - 7, Conference Paper, SUBMITTED
Mattia Dalla Brida, Patrick Fritzsch, Tomasz Korzec, Alberto Ramos, Stefan Sint and Rainer Sommer, Towards a new determination of the QCD Lambda parameter from running couplings in the three-flavour theory, Proceedings of Science, 32nd International Symposium on Lattice Field Theory (Lattice 2014), Columbia University, New York, USA, June 23-28, 2014, , PoS(LATTICE2014)291, 2014, pp7 , Conference Paper, PUBLISHED
Mattia Dalla Brida, Stefan Sint, A dynamical study of the chirally rotated Schroedinger functional in QCD, Proceedings of Science, 32nd International Symposium on Lattice Field Theory (Lattice 2014), Columbia University, New York, USA, June 23-28, 2014, PoS(LATTICE2014)280, 2014, pp7 , Conference Paper, PUBLISHED
Stefan Sint, Pol Vilaseca, A perturbative study of the chirally rotated Schroedinger functional in QCD, Proceedings of Science, 32nd International Symposium on Lattice Field Theory (Lattice 2014), Columbia University, New York, USA, June 23-28, 2014, PoS(LATTICE2014)279, 2014, pp7 , Conference Paper, PUBLISHED

  


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My research interests are in Elementary Particle Physics and more particularly Quantum Chromo Dynamics (QCD) which constitutes a main pillar of the so-called Standard Model of elementary particle physics. This theory summarizes our current knowledge of the electro-weak and strong interactions and rather economically (with ca. 20 free parameters) describes all experiments carried out to date. Yet, the Standard Model has known limitations and physicists are keen to replace it by a more complete theory. Unfortunately, effects of unknown physics are difficult to detect and require very good quantitative control of the strong interactions, i.e. QCD. The only technique currently able to achieve this uses a lattice regularized version of QCD in combination with large scale numerical simulations. This approach ("lattice QCD") shares many features with real experiments, for instance one needs to control both statistical and systematic errors. Much of my work has been on the development of methods and techniques which have enabled progress in this area. Examples are non-perturbative renormalization and improvemnent techniques which help to accelerate and control the approach to the continuous limit and my results have been adopted by several other collaborations. Another example is a reformulation called "twisted mass QCD", a term I have coined and which was adopted by the European Twisted Mass Collaboration, involving ca. 30 researchers across Europe. I have applied lattice QCD to obtain results for elusive parameters such as the charm quark mass and the strong coupling constant alpha_s(m_Z). The latter is an important input parameter for the proton structure functions or predictions of certain Higgs decay rates. Finally I am interested in more formal developments, such as quantum field theories on manifolds with boundaries, which raises interesting conceptual questions.