Roberto Frezzotti

Associate Professor of Theoretical High Energy / Elementary Particle Physics

Roberto Frezzotti is a theoretical particle physicist working on Quantum Field Theory, Monte Carlo simulations of lattice QCD and their applications to problems of elementary Particle Physics, with special focus on Flavour and Beyond-Standard Model Physics. He carried his first steps in research within groups and/or collaborations led by prof. Roberto Petronzio and prof.  Martin Luscher. He subsequently collaborated with several European leading scientists, among whom prof. Giancarlo Rossi, Rainer Sommer, Karl Jansen, Chris Michael, Guido Martinelli, Olivier Pene, Vittorio Lubicz, Constantia Alexandrou. He held temporary research positions at DESY (Hamburg), Max-Planck-Institut fuer Physik (Munich), Univ Milano-Bicocca and CERN before joining as a staff member the Physics Department of the Univ. Roma Tor Vergata.

He has been key scientist or PI of several national and/or international research projects and has presented his results in several seminars, among which a few plenary talks in conferences and a number of invited talks in international workshops. His main research results are summarized below.

a) Fermionic regularizations for lattice QCD: he introduced and developed the formulation known as "twisted mass lattice QCD". With a 90 degree angle of "chiral twist" between the Wilson term and the soft quark mass terms in the Lagrangian this
formulation allows to evaluate (by means of simulations whose numerical stability is well controlled by the quark mass) all
physical quantities with sistematically reduced lattice artifacts. He contributed to the foundation of the "European Twisted Mass Collaboration" (, one of the world-level leader groups in the study of QCD in non-perturbative regime and hadron flavour physics and participated in several supercomputing projects at national (Italy,Germany, France) and EU (PRACE calls) level.

b) Simulation algorithms for lattice QCD with two or four dynamical flavours: He developed and optimized the "Polynomial Hybrid Monte Carlo" simulation algorithm. He studied the phase structure of Wilson lattice QCD.

c) Optimization of non-perturbative renormalization methods that are necessary to obtain from experimental data both first principle determinations of some basic Standar Model (SM) parameters, such as quark masses or CKM matrix elements, and constraints on beyond-SM models.

d) By means of numerical simulations of lattice QCD he carried out:
- the computation of hadron masses, the QCD Lambda-parameter, the mass of u, d, s, c and b quarks, the leptonic decay constants of pions, kaons, D- and B-mesons;
- the computation of some low energy constants of the effective chiral Lagrangian for QCD and the study of the pion form factor;
- the computation of several matrix elements of the effective weak Hamiltonian, e.g. the ones that control the K0-antiK0
oscillations within the SM and its extensions.

e) In the last few years he was active in two new research lines. On one hand, within ETMC and the RM123 group, he has contributed to including in lattice computations of particle physics observables the leading isospin breaking effects due to electromagnetic corrections and up-down mass difference. These effects, althogh small (at the percent level), are crucial in certain hadronic observables that are already very precisely computed in order to carry out indirect searches of new physics.

f) On the other hand he has been working together with collaborators in Italy and in Germany at the formulation and the numerical check via lattice simulations of a new non-perturbative mechanism for dynamical and "natural" generation of elementary particle masses. The origin of the masses of elementary fermions and weak gauge bosons and their relation with the electroweak scale represents a key problem that remains open in particle physics, given the impressive phenomenological success of the SM together and lack of evidence for any supersymmetric particle partner. Answering these questions is crucial to determine the scale of new physics (beyond the Standard Model one) and can also have an important impact on  the problems of Dark Matter, CP violation, Baryogenesis, and possible gauge coupling unification.

Author of >130 publications with more than 6250 citations and h-index=41 on Inspire-HEP database

with h-index=36 and more than 5550 citations on the Google Scholar database (see my personal profile)

Selected papers:

1) R.~Frezzotti, P. A. Grassi, S. Sint and P. Weisz  [Alpha], `Lattice QCD with a chirally twisted mass term,''
JHEP \textbf{08} (2001), 058 [arXiv:hep-lat/0101001 [hep-lat]].

2) R. Frezzotti and G. Rossi, ``Chirally improving Wilson fermions. 1. O(a) improvement,''
JHEP \textbf{08} (2004), 007 [arXiv:hep-lat/0306014 [hep-lat]].

3) R. Frezzotti and G. Rossi,``Chirally improving Wilson fermions. II. Four-quark operators,''
JHEP \textbf{10} (2004), 070 [arXiv:hep-lat/0407002 [hep-lat]].

4) P.~Boucaud et al. [ETM], ``Dynamical twisted mass fermions with light quarks,''
Phys. Lett. B \textbf{650} (2007), 304-311 [arXiv:hep-lat/0701012 [hep-lat]].

5) S.~Capitani, P.~Dimopoulos, R.~Frezzotti, M.~Garofalo, B.~Kostrzewa, F.~Pittler, G.~Rossi and C.~Urbach, ``Dynamical Generation of Elementary Fermion Mass: First Lattice Evidence,'' Phys. Rev. Lett. \textbf{123} (2019) no.6, 061802,
doi:10.1103/PhysRevLett.123.061802 [arXiv:1901.09872 [hep-th]].

6) R.~Frezzotti, M.~Garofalo and G.~Rossi,
``Nonsupersymmetric model with unification of electroweak and strong interactions,'' Phys. Rev. D \textbf{93} (2016) no.10, 105030 [arXiv:1602.03684 [hep-ph]].

7) R.~Frezzotti and G.~Rossi,
``Nonperturbative mechanism for elementary particle mass generation,''
Phys. Rev. D \textbf{92} (2015) no.5, 054505 [arXiv:1402.0389 [hep-lat]].

8) P.~Boucaud et al. [ETM],
``Dynamical Twisted Mass Fermions with Light Quarks: Simulation and Analysis Details,''
Comput. Phys. Commun. \textbf{179} (2008), 695-715 [arXiv:0803.0224 [hep-lat]].

9) M.~Della Morte et al. [ALPHA],
``Computation of the strong coupling in QCD with two dynamical flavors,''
Nucl. Phys. B \textbf{713} (2005), 378-406 [arXiv:hep-lat/0411025 [hep-lat]].

10) R.~Frezzotti and G.~Rossi,
`Twisted mass lattice QCD with mass nondegenerate quarks,''
Nucl. Phys. B Proc. Suppl. \textbf{128} (2004), 193-202 [arXiv:hep-lat/0311008 [hep-lat]].

11) R.~Baron et al. [ETM],
``Light Meson Physics from Maximally Twisted Mass Lattice QCD,''
JHEP \textbf{08} (2010), 097 [arXiv:0911.5061 [hep-lat]].

12) B.~Blossier et al. [ETM],
``Pseudoscalar decay constants of kaon and D-mesons from $N_f=2$ twisted mass Lattice QCD,''
JHEP \textbf{07} (2009), 043 [arXiv:0904.0954 [hep-lat]].

13) N.~Carrasco et al. [European Twisted Mass],
``Up, down, strange and charm quark masses with N$_f$ = 2+1+1 twisted mass lattice QCD,''
Nucl. Phys. B \textbf{887} (2014), 19-68
[arXiv:1403.4504 [hep-lat]].

14) N.~Carrasco et al. [ETM],
``B-physics from $N_f$ = 2 tmQCD: the Standard Model and beyond,''
JHEP \textbf{03} (2014), 016 [arXiv:1308.1851 [hep-lat]].

15) d.~Divitiis, G.M. et al. [RM123],
``Leading isospin breaking effects on the lattice,''
Phys. Rev. D \textbf{87} (2013) no.11, 114505 [arXiv:1303.4896 [hep-lat]].

16) R.~Frezzotti and K.~Jansen,
``A Polynomial hybrid Monte Carlo algorithm,''
Phys. Lett. B \textbf{402} (1997), 328-334 [arXiv:hep-lat/9702016 [hep-lat]].

17) C.~Alexandrou et al. [European Twisted Mass],
``Light baryon masses with dynamical twisted mass fermions,''
Phys. Rev. D \textbf{78} (2008), 014509 [arXiv:0803.3190 [hep-lat]].

18) P.~Dimopoulos et al. [ETM],
``Lattice QCD determination of m_b, f_B and f_Bs with twisted mass Wilson fermions,''
JHEP \textbf{01} (2012), 046 [arXiv:1107.1441 [hep-lat]].

19) R.~Frezzotti, G.~Martinelli, M.~Papinutto and G.~Rossi,  ``Reducing cutoff effects in maximally twisted lattice QCD close to the chiral limit,'' JHEP \textbf{04} (2006), 038 [arXiv:hep-lat/0503034 [hep-lat]].

20) G.~de Divitiis et al. [Alpha], ``Universality and the approach to the continuum limit in lattice gauge theory,''
Nucl. Phys. B \textbf{437} (1995), 447-470 [arXiv:hep-lat/9411017 [hep-lat]].

21) V.~Bertone et al. [ETM],
``Kaon Mixing Beyond the SM from N$_{f}$=2 tmQD and model independent constraints from the UTA,''
JHEP \textbf{03} (2013), 089 [arXiv:1207.1287 [hep-lat]].


Teaching in the Physics Department
ID Course Name Semester Length CFU