#
Stefan Sint

Associate Professor, Pure & Applied Mathematics

## Publications and Further Research Outputs

### Peer-Reviewed Publications

**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-**

**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 N f= 3 QCD: ALPHA Collaboration, European Physical Journal C, 78, (5), 2018**

**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 200Â MeV to 4Â GeV inNf=3QCD, Physical Review D, 95, (1), 2017**

**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-**

**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 Î± sby the ALPHA collaboration, Nuclear and Particle Physics Proceedings, 285-286, 2017, p132-138 **

**Bruno, M. and Brida, M.D. and Fritzsch, P. and Korzec, T. and Ramos, A. and Schaefer, S. and Simma, H. and Sint, S. and Sommer, R., QCD Coupling from a Nonperturbative Determination of the Three-Flavor Î Parameter, Physical Review Letters, 119, (10), 2017**

**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 Î -parameter in 3-flavour QCD and Î± s(mZ) by the ALPHA collaboration, Part F128557, 2016**

**Brida M., Sint S., Vilaseca P., The chirally rotated Schrödinger functional: theoretical expectations and perturbative tests, Journal of High Energy Physics, 2016, (8), 2016, p102-**

**Dalla Brida M, Fritzsch P, Korzec T, Ramos A, Sint S, Sommer R, Determination of the QCD Î Parameter and the Accuracy of Perturbation Theory at High Energies, Physical Review Letters, 117, (18), 2016, p182001-**

**Rubeo, A. and Sint, S., Perturbative O(a2) effects in gradient flow couplings with SF and SF-open boundary conditions, Part F128557, 2016**

**Mattia Dalla Brida, A dynamical study of the chirally rotated Schroedinger funcitonal in lattice QCD, Trinity College Dublin, 2015**

**Alberto Ramos, Stefan Sint, Symanzik Improvement of the gradient flow in lattice gauge theories, European Physical Journal C, 76, 2015, p15-**

**Pol Vilaseca, Perturbative study of the Chirally Rotated Schroedinger Functional in Lattice QCD, Trinity College Dublin, 2014**

**Rubio, P.P., Sint, S., Takeda, S., An O(a) modified lattice set-up of the Schrödinger functional in SU(3) gauge theory, Journal of High Energy Physics, 2011, (7), 2011, part. no. 116 **

**Stefan Sint, The chirally rotated Schrödinger functional with Wilson fermions and automatic O(a) improvement, Nuclear Physics B, 847, 2011, p491 - 531**

**Paula Perez-Rubio, Running of the renormalized strong coupling with four flavours of staggered quarks, Universidad Autonoma de Madrid, 2010**

**Petros Dimopoulos, Jochen Heitger, Filippo Palombi, Carlos Pena, Stefan Sint, Anastassios Vladikas, Flavour symmetry restoration and kaon weak matrix elements in quenched twisted mass QCD, Nuclear Physics B, 2007, 258-285 **

**Petros Dimopoulos, Jochen Heitger, Filippo Palombi, Carlos Pena, Stefan Sint, Anastassios Vladikas, A precise determination of B_K in quenched QCD, Nuclear Physics B, 749, 2006, p69 - 108**

**Marco Guagnelli, Jochen Heitger, Carlos Pena, Stefan Sint, Anastassios Vladikas, Non-perturbative renormalization of left-left four-fermion operators in quenched lattice QCD, Journal of High Energy Physics, 0603, 2006, p088-**

**Filippo Palombi, Carlos Pena, Stefan Sint, A perturbative study of two four-quark operators in finite volume renormalization schemes, Journal of High Energy Physics, 0603, 2006, p089-**

**Carlos Pena, Stefan Sint, Anastassios Vladikas, Twisted mass QCD and lattice approaches to the Delta I=1/2 rule, Journal of High Energy Physics, 0409, 2004, p069-**

**Juri Rolf, Stefan Sint, A precise determination of the charm quark's mass in quenched QCD, Journal of High Energy Physics, 0212, 2002, p007-**

**Roberto Frezzotti, Pietro Antonio Grassi, Stefan Sint, Peter Weisz, Lattice QCD with a chirally twisted mass term, Journal of High Energy Physics, 0108, 2001, p058-**

**Michele Della Morte, Roberto Frezzotti, Jochen Heitger, Stefan Sint, Cutoff effects in twisted mass lattice QCD, Journal of High Energy Physics, 0110, 2001, p041-**

**Roberto Frezzotti, Stefan Sint, Peter Weisz, O(a) improved twisted mass QCD, Journal of High Energy Phyisics, 0107, 2001, p048-**

**Marco Guagnelli, Roberto Petronzio, Juri Rolf, Stefan Sint, Rainer Sommer, Ulli Wolff, Non-perturbative results for the coefficients b_m and b_A - b_P in O(a) improved lattice QCD, Nulcear Physics B, 595, 2001, p44 - 62**

**Achim Bode, Roberto Frezzotti, Bernd Gehrmann, Martin Hasenbusch, Jochen Heitger, Karl Jansen, Stefan Kurth, Juri Rolf, Hubert Simma, Stefan Sint, Rainer Sommer, Peter Weisz, Hartmut Wittig, Ulli Wolff, First results on the running coupling in QCD with two massless flavors, Physics Letters B, 515, 2001, p49 - 56**

**Stefan sint, Peter Weisz, The running quark mass in the SF scheme and its two-loop anomalous dimension, Nuclear Physics B, 545, 1999, p529 - 542**

**Martin Luescher, Stefan Sint, Rainer Sommer, Hartmut Wittig, Non-perturbative determination of the axial current normalization constant in O(a) improved lattice QCD, Nulcear Physics B, 491, 1997, p344 - 364**

**Stefan Sint, Peter Weisz, Further results on O(a) improved lattice QCD to one-loop order of perturbation theory, Nuclear Physics B, 502, 1997, p251 - 268**

**Martin Luscher, Stefan Sint, Rainer sommer, Peter Weisz, Ulli Wolff, Non-perturbative O(a) improvement of lattice QCD, Nuclear Physics B, 491, 1997, p323 - 343**

**Stefan Sint, Rainer Sommer, The Running Coupling from the QCD Schroedinger functional: a one-loop analysis, Nuclear Physics B, 465, 1996, p71 - 98**

**Martin Luescher, Stefan Sint, Rainer Sommer, Peter Weisz, Chiral Symmetry and O(a) improvement in lattice QCD, Nuclear Physics B, 478, 1996, p365 - 400**

**Karl Jansen, Chuan Liu, Martin Luescher, Hubert Simma, Stefan Sint, Rainer Sommer, Peter Weisz, Non-perturbative Renormalization of lattice QCD at all scales, Physics Letters B, 372, 1996, p275 - 282**

**Stefan Sint, One-loop renormalization of the QCD Schroedinger functional, Nuclear Physics B, 451, 1995, p416 - 444**

### Non-Peer-Reviewed Publications

**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 **

**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**

**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 **

**Alberto Ramos, Stefan Sint, On O(a, 2) effects in gradient flow observables, Proceedings of Science, 32nd International Symposium on Lattice Field Theory (Lattice 2014), Columbia University, New York, USA, June, 23-28, 2014, PoS(LATTICE2014)329, 2014, pp7 **

**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 **

**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 **

**Michele Brambilla, Mattia Dalla Brida, Francesco Di Renzo, Dirk Hesse, Stefan Sint, Numerical Stochastic Perturbation Theory in the Schroedinger Functional, Proceedings of Science (PoS), Lattice 2013, Mainz, Germany, 29 Jul - 03 Aug 2013, 2013, pp7 **

**Stefan Sint, Pol Vilaseca, Lattice artefacts in the Schroedinger Functional coupling for strongly interacting theories, Proceedings of Science (PoS), Lattice 2012, Cairns, Australia, 24-29 Jun 2012, 2012, pp7 **

**Stefan Sint, Pol Vilaseca, Perturbative lattice artefacts in the SF coupling for technicolor-inspired models , Proceedings of Science (PoS), Lattice 2011, Squaw Valley, Lake Tahoe, California, USA, 10-16 Jul 2011, edited by Pavlos Vranas , 2011, pp7 **

**Bjorn Leder, Stefan Sint, Testing universality and automatic O(a) improvement in massless lattice QCD with Wilson quarks, Proceedings of Science, Lattice 2010, Villasimius, Italy, June 14-19, 2010, 265, 2010, pp7 **

**Paula Perez-Rubio, Stefan Sint, The running of the Schroedinger functional coupling from four-flavour lattice QCD with staggered quarks, AIP Conference Proceedings, IX International Conference on Quark Confinement and Hadron Spectrum - QCHS-09, Madrid, Spain, 30.8.-3.9.2010, edited by Felipe J. Llanes-Estrada, Jose R. Pelaez , 1343, (ISBN 978-0-7354-0899), American Institute of Physics, 2010, pp4 **

**Paula Perez-Rubio, Stefan Sint, Non-perturbative running of the coupling from four flavour lattice QCD with staggered quarks, Proceedings of Science, Lattice 2010, Villasimius, Italy, June 14-19, 2010, 236, 2010, pp7 **

**Lattice QCD with a chiral twist in, editor(s)Y. Kuramashi , Perspectives in Lattice QCD, Nara, Japan, World Scientific, 2008, pp169 - 208, [Stefan Sint]**

**Paula Perez Rubio, Stefan Sint, Fermionic correlation functions from the staggered Schrodinger functional, 26th International Symposium On Lattice Field Theory (Lattice 2008), Williamsburg, Virginia, U.S.A., July 14 - 19, 2008 , Proceedings of Science, 2008, pp6 **

**Paula Perez Rubio, Stefan Sint, The SF running coupling with four flavours of staggered quarks, 25th International Symposium on Lattice Field Theory (Lattice 2007), Regensburg, Germany, 30 Jul - 4 Aug 2007, Proceedings of Science, 2007, pp6 **

**Stefan Sint, Schroedinger functional boundary conditions for Domain Wall Quarks, Domain Wall Fermions at 10 Years, Brookhaven National Laboratory, New York, USA, 13-15/3/2007, 2007, Thomas Blum, Amarjit Soni**

**Stefan Sint, Schroedinger functional renormalization schemes for Ginsparg-Wilson quarks, 25th International Symposium on Lattice Field Theory (Lattice 2007), Regensburg, Germany, 30 Jul - 4 Aug 2007, Proceedings of Science, 2007, pp6 **

**A. Dobado, F.J. Llanes-Estrada and V. Vento, The IVth International Conference on Quarks and Nuclear Physics, June 5-10, 2006, 2007, Madrid, A. Dobado, F.J. Llanes-Estrada and V. Vento, Springer, (4), Volume 31, The European Physical Journal A- Hadrons and Nuclei**

**Stefan Sint, The Kaon B-parameter in quenched QCD, International Journal of Modern Physics A, International Conference on QCD and Hadronic Physics, Beijing, China, 16-20 June 2005, 21, 2006, pp865 - 868**

**Stefan Sint, The Schroedinger functional with chirally rotated boundary conditions, 23rd International Symposium on Lattice Field Theory "Lattice 2005", Trinity College Dublin, Ireland, 25-30/7/2005, Proceedings of Science, 2006, pp235-**

**Petros Dimopoulos, Gregorio Herdoiza, Filippo Palombi, Carlos Pena, Stefan Sint, Anastassios Vladikas, Non-perturbative scale evolution of four-fermion operators in two-flavour QCD, 24th International Symposium on Lattice Field Theory (Lattice 2006), Tucson, Arizona, USA, 23-28 Jul 2006, Proceedings of Science, 2006, pp6 **

**P. Dimopoulos, J. Heitger, C. Pena, S. Sint, A. Vladikas, Precision computation of B(K) in quenched lattice QCD, Nuclear Physics (Proceedings Supplement), 22nd International Symposium on Lattice Field Theory (Lattice 2004), Batavia, Illinois, USA, 21-26 June 2004, 140, 2005, pp362-364 **

**Filippo Palombi, Carlos Pena, Stefan Sint, NLO anomalous dimension of multiplicatively renormalizable four-fermion operators in Schrodinger functional schemes, Nuclear Physics (Proceedings Supplement), 22nd International Symposium on Lattice Field Theory (Lattice 2004), Batavia, Illinois, USA, 21-26 June 2004, 140, Elsevier, 2005, pp725-727 **

**P. Dimopoulos, J. Heitger, C. Pena, S. Sint, A. Vladikas, B(K) from twisted mass QCD, Nuclear Physics (Proceedings Supplement), 21st International Symposium on Lattice Field Theory (LATTICE 2003), Tsukuba, Ibaraki, Japan, 15-19 Jul 2003, 129, 2004, pp308-310 **

**Carlos Pena, Stefan Sint, Anastassios Vladikas, Towards a determination of g(8) and g(27) from twisted mass lattice QCD, Nuclear Physics (Proceedings Supplement), 21st International Symposium on Lattice Field Theory (LATTICE 2003), Tsukuba, Ibaraki, Japan, 15-19 Jul 2003, 129, 2004, pp263-265 **

**M. Guagnelli, J. Heitger, C. Pena, S. Sint, A. Vladikas, Nonperturbative scale evolution of four fermion operators, Nuclear Physics (Proceedings Supplement), 20th International Symposium on Lattice Field Theory (LATTICE 2002), Boston, Massachusetts, USA, 119, (24-29 June 2002), Elsevier, 2003, pp436-438 **

**Carlos Pena, Stefan Sint, Anastassios Vladikas, Twisted mass QCD and the Delta I = 1/2 rule., Nuclear Physics (Proceedings Supplement), 20th International Symposium on Lattice Field Theory (LATTICE 2002), Boston, Massachusetts, USA, 24-29 June 2002, 119, Elsevier, 2003, pp368-370 **

**Roberto Frezzotti, Stefan Sint, Some remarks on O(a) improved twisted mass QCD, Nuclear Physics (Proceedings Supplement), 19th International Symposium on Lattice Field Theory (Lattice 2001), Berlin, Germany, 19-24 Aug 2001, 106, Elsevier, 2002, pp814-816 **

**Juri Rolf, Stefan Sint, The Charm quark's mass in quenched QCD, Nuclear Physics (Proceedings Supplement), 19th International Symposium on Lattice Field Theory (Lattice 2001), Berlin, Germany, 19-24 Aug 2001, 106, Elsevier, 2002, pp239-241 **

**M. Guagnelli, J. Heitger, C. Pena, S. Sint, A. Vladikas, K0 - anti-K0 mixing from the Schrodinger functional and twisted mass QCD, Nuclear Physics (Proceedings Supplement), 19th International Symposium on Lattice Field Theory (Lattice 2001), Berlin, Germany, 19-24 Aug 2001, 106, Elsevier, 2002, pp320-322 **

**M. Della Morte, R. Frezzotti, S. Sint, Nonperturbative scaling tests of twisted mass QCD, Nuclear Physics (Proceedings Supplement), 19th International Symposium on Lattice Field Theory (Lattice 2000), Bangalore, India, 17-22 August 2000, 94, Elsevier, 2001, pp617-621 **

**Stefan Sint, Non-perturbative renormalization in lattice field theory, Nuclear Physics (Proceedings Supplements), 18th International Symposium on Lattice Field Theory "Lattice 2000", Bangalore, India, 17-22/8/2000, 94, Elsevier, 2001, pp79 - 94**

**Roberto Frezzotti, Pietro Antonio Grassi, Stefan Sint, Peter Weisz, A local formulation of lattice QCD without unphysical fermion zero modes, Nuclear Physics (Proceedings Supplements), 17th International Symposium on Lattice Field Theory "Lattice 1999", Pisa, Italy, 29/6-3/7/1999, 83, Elsevier, 2000, pp941 - 946**

**Stefan Sint, Renormalization of the iso-singlet scalar density in lattice QCD with Wilson quarks, Nuclear Physics (Proceedings Supplement), 16th International Symposium on Lattice Field Theory (LATTICE 98), Boulder, Colorado, USA, 13-18 July 1998, 73, Elsevier, 1999, pp282-284 **

**A.D. Kennedy, I. Horvath, S. Sint, A New exact method for dynamical fermion computations with nonlocal actions, Nuclear Physics (Proceedings Supplement), 16th International Symposium on Lattice Field Theory (LATTICE 98), Boulder, Colorado, USA, 13-18 July 1998, 73, Elsevier, 1999, pp834-836 **

**Stefan Sint, Peter Weisz, Further one loop results in O(a) improved lattice QCD, Nuclear Physics (Proceedings Supplement), 15th International Symposium on Lattice Field Theory (Lattice '97), Edinburgh, Scotland, 22-26 July 1997, 63, Elsevier, 1998, pp856-858 **

**M. Luescher, S. Sint, R. Sommer, P. Weisz, H. Wittig, U. Wolff, Some new results in O(a) improved lattice QCD, Nuclear Physics (Proceedings Supplement), 14th International Symposium on Lattice Field Theory (Lattice '96), St. Louis, MO, USA, 4-8 June 1996, 53, Elsevier, 1997, pp905-913 **

**Stefan Sint, The Schrodinger functional in QCD, Nuclear Physics (Proceedings Supplement), 12th International Symposium on Lattice Field Theory (Lattice '94), Bielefeld, Germany, 27 Sep - 1 Oct 1994, 42, Elsevier, 1995, pp835-837 **

## Research Expertise

### Description

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.### Projects

**Title****A strongly interacting electroweak symmetry breaking sector**

**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

**Date From**- 1 June 2011

**Date To**- 31 May 2015

**Title****Unveiling physics beyond the Standard Model of elementary particle physics**

**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)

**Date From**- 1 December 2011

**Date To**- 30 November 2015