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Scientific Report 2007-2009<br />
Theoretical physics<br />
T3. Flavor, CP violation and Matter-Antimatter asymmetry<br />
The past decade has seen tremendous progress in the<br />
study of flavor and CP violation. B-factories have collected<br />
and analyzed an impressive amount of experimental<br />
data, that led to the confirmation of the Cabibbo-<br />
Kobayashi-Maskawa (CKM) mechanism for flavor and<br />
CP violation. While sizable New Physics (NP) contributions<br />
may still hide in b → s penguin decays [1], the<br />
bulk of CP violation in the K and B sectors can be correctly<br />
accounted for within the Standard Model (SM),<br />
with possible new sources of flavor and CP violation being<br />
confined to the level of 20-30% corrections [2]. If NP<br />
is of Minimal Flavor Violation (MFV) type, however, its<br />
contributions can be much larger without spoiling the<br />
consistency with experimental data. Until one year ago,<br />
MFV extensions of the SM seemed phenomenologically<br />
very appealing, although they give only a description<br />
of the NP flavor structure and not a solution to the<br />
origin of flavor. However, the recent Tevatron experiments<br />
presented their first measurement of CP violation<br />
in B s → J/Ψϕ decays, showing a discrepancy from the<br />
SM expectation at the level of three standard deviations.<br />
If this indication is confirmed, it will represent a major<br />
breakthrough in flavor physics and in model building,<br />
leaving behind MFV models and pointing to a more fundamental<br />
origin of flavor mixing. It would also open up<br />
very interesting perspectives for the LHCb experiment,<br />
which may become a primary source of indirect NP signals<br />
and a gold mine for the determination of NP flavor<br />
couplings. In any case, it is of the utmost importance<br />
to be ready to study in detail the possible signals of a<br />
non-MFV NP at the Large Hadron Collider (LHC) experiments.<br />
Concerning the theoretical evaluation of hadronic flavor<br />
and CP violation at low energies, most of the relevant<br />
processes have been computed in all known extensions<br />
of the SM, including the Minimal Supersymmetric<br />
Standard Model (MSSM), extra-dimensional models,<br />
composite Higgs theories, etc. The Particle Theory<br />
Group (PTG) in Rome has given major contributions<br />
in these directions, pioneering the study of NP contributions<br />
to flavor and CP violation beyond the leading<br />
order in QCD. One of the fundamental results achieved<br />
by the PTG is the calculation of ∆F = 2 hadronic matrix<br />
elements in Lattice QCD, with the computation of<br />
Next-to-Leading order (NLO) anomalous dimensions for<br />
the most general ∆F = 2 operator basis and the calculation<br />
of the NLO matching for these operators in the<br />
MSSM.<br />
Working in tight collaboration with experimental<br />
physicists, the UTfit collaboration, of which Guido Martinelli<br />
was one of the founders, has a world-leading role<br />
in performing combined analyses of flavor and CP violation<br />
in the SM and beyond. It has developed efficient<br />
tools to simultaneously constrain the CKM matrix and<br />
the NP contributions to ∆F = 2 processes. These tools,<br />
η<br />
1<br />
0.5<br />
0<br />
-0.5<br />
-1<br />
ε K<br />
β<br />
V ub<br />
V cb<br />
-1 -0.5 0 0.5 1<br />
Figure 1: Constraints on the Wolfenstein parameters ¯ρ and<br />
¯η from the Unitarity Triangle analysis [2].<br />
combined with the model-specific ones for the known<br />
theoretical extensions of the SM, will form the starting<br />
point for the implementation of flavor and CP violation<br />
constraints on the NP Lagrangian. The missing ingredients<br />
(additional processes and/or new models) will be<br />
implemented in this framework. The PTG has also pioneered<br />
the phenomenology of non-leptonic decays, devising<br />
several strategies to estimate the SM uncertainty in a<br />
reliable, mostly data-driven way, as well as new methods<br />
to extract short-distance information from non-leptonic<br />
decays.<br />
The extraction from experiments of useful phenomenological<br />
information on the SM and/or NP fundamental<br />
parameters may require an accurate knowledge of the<br />
relevant hadronic matrix elements of the effective weak<br />
Hamiltonian, which can be evaluated in Lattice QCD.<br />
The PTG in Rome is part of an important large-scale<br />
lattice collaboration, the European Twisted-Mass Collaboration.<br />
Thanks to the use of the ApeNext machines<br />
of INFN the PTG in Rome has a world-leading role in<br />
LQCD simulations and has provided accurate determinations<br />
of many important hadronic quantities, like: 1)<br />
light, strange and charm quark masses; 2) the decay constants<br />
of K-, D- and B-mesons; 3) the vector and scalar<br />
form factors relevant in the semileptonic decays of K-,<br />
D- and B-mesons relevant for the determination of the<br />
entries of the CKM matrix; 4) the bag parameters of the<br />
kaon relevant for the study of CP violation in the SM as<br />
well as in NP scenarios.<br />
The future research activity of the PTG will continue<br />
along this lines, to keep up with the experimental results<br />
and to estimate the uncertainties in any NP model<br />
singled out by direct searches at the LHC.<br />
References<br />
1. M. Bona et al. PMC Phys. A3, 6 (2009)<br />
2. M. Bona et al. J. High Energy Phys. 0803, 049 (2008)<br />
Authors<br />
R. Contino, E. Franco 1 , G. Martinelli, L. Silvestrini 1<br />
γ<br />
∆m d<br />
∆m s<br />
α<br />
∆md<br />
ρ<br />
<strong>Sapienza</strong> Università di Roma 26 Dipartimento di Fisica