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Cecilia Tarantino

Publications and source records attributed to Cecilia Tarantino.

33 records · Page 2Linked to original sources
arXiv2009

Update of the Unitarity Triangle Analysis

We present the update of the Unitarity Triangle (UT) analysis within the Standard Model (SM) and beyond. Within the SM, combining the direct measurements on sides and angles, the UT turns out to be overconstraint in a consistent way, showing that the CKM matrix is the dominant source of flavour mixing and CP-violation and that New Physics (NP) effects can appear at most as small corrections to the CKM picture. Generalizing the UT analysis to investigate NP effects, constraints on b -> s transitions are also included and both CKM and NP parameters are fitted simultaneously. While no evidence of NP effects is found in K-\bar K and B_d-\bar B_d mixing, in the B_s-\bar B_s mixing an hint of NP is found at the 2.9 σlevel. The UT analysis beyond the SM also allows us to derive bounds on the coefficients of the most general ΔF=2 effective Hamiltonian, that can be translated into bounds on the NP scale.

hep-ph↗
arXiv2008

Flavour physics and Lattice QCD: averages of lattice inputs for the Unitarity Triangle Analysis

We review recent results of Lattice QCD calculations relevant for flavour physics. We discuss in particular the hadronic parameters entering the amplitudes of K0-K0bar, D0-D0bar and B0-B0bar mixing, the B- and D-meson decay constants and the form factors controlling B-meson semileptonic decays. On the basis of these lattice results, which are extensively collected in the paper, we also derive our averages of the relevant hadronic parameters.

hep-lat↗
arXiv2007

Light quark masses and pseudoscalar decay constants from Nf=2 twisted mass QCD

We present the results of the lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants, recently performed with Nf=2 dynamical fermions by the ETM Collaboration. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_{ud}^{MSbar}(2 Gev)=3.85 +- 0.12 +- 0.40 MeV, m_s^{MSbar}(2 Gev)=105 +- 3 +- 9 MeV and m_s/m_{ud}=27.3 +- 0.3 +- 1.2. We also obtain f_K=161.7 +- 1.2 +- 3.1 MeV and the ratio f_K/f_pi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K -> mu {bar nu}_mu (gamma))/Gamma(pi -> mu {bar nu}_mu (gamma)) and the average value of |V_{ud}| from nuclear beta decays, we obtain |V_{us}|=0.2192(5)(45), in agreement with the determination from K_{l3} decays and the unitarity constraint.

hep-lat↗
arXiv2007

Lepton Flavour Violating Decays in the Littlest Higgs Model with T-Parity

We present the results of an extensive analysis of lepton flavour violating decays in the Littlest Higgs model with T-parity (LHT). As lepton flavour violation is highly suppressed in the Standard Model by small neutrino masses, the LHT effects turn out to be naturally huge and could be seen in the near future experiments.

hep-ph↗
arXiv2007

Rare Kaon Decays Beyond the Standard Model

The rare kaon decays K_L -> pi^0 nu {bar nu}, K^+ -> pi^+ nu {bar nu}, K_L -> pi^0 e^+ e^- and K_L -> pi^0 mu^+ mu^- are theoretically very clean and, being strongly CKM suppressed, highly sensitive to New Physics (NP). Recent Flavour Physics analyses show that they represent unique probes for revealing NP effects and to provide information on the NP flavour structure. After a brief discussion of the main properties that make rare K decays so promising and of the basic ideas of the most interesting NP models, we review the results of recent phenomenological analyses both within and beyond the framework of Minimal Flavour Violation (MFV), where the sources of flavour violation are the same as in the Standard Model. Within MFV we present the expectations found for rare K decays from a model-independent analysis and in three MFV models: the Littlest Higgs (LH) model, the (extra-dimension) Appelquist-Cheng-Dobrescu model and the Minimal Supersymmetric Standard Model (MSSM) with MFV. Beyond MFV, we discuss the results recently found within the MSSM (without MFV), the LH model with T-parity (LHT) and the 3-3-1 (Z') model. While in MFV models only small (<30%) NP effects are allowed in the branching ratios of K_L -> pi^0 nu {bar nu}, K^+ -> pi^+ nu {bar nu}, K_L -> pi^0 e^+ e^- and K_L -> pi^0 mu^+ mu^-, beyond MFV, in particular in the MSSM and in the LHT model, large (up to an order of magnitude) enhancements w.r.t. the SM turn out to be possible.

hep-ph↗
arXiv2007

Flavour Physics in the Littlest Higgs Model with T-Parity

We present the results of an extensive analysis of flavour physics in both quark and lepton sectors, in the Littlest Higgs model with T-parity (LHT). In the quark sector, we identify some interesting scenarios for new mirror quark masses and V_Hd mixing matrix that satisfy the existing experimental constraints from K and B physics and simultaneously allow large New Physics effects in rare decays and CP-violating observables. In the lepton sector, where flavour violation in the Standard Model is highly suppressed by small neutrino masses, LHT effects turn out to be naturally huge and could be seen in the near future measurements of lepton flavour violating decays.

hep-ph↗
arXiv2007

Quark and Lepton Flavour Physics in the Littlest Higgs Model with T-Parity

The Littlest Higgs model with T-parity (LHT) contains new sources of flavour and CP violation both in the quark and the lepton sector. They originate from the interactions of ordinary fermions with mirror fermions mediated by new gauge bosons: W_H, Z_H and A_H. The most spectacular departures from the Standard Model are found in K_L -> pi^0 nu {bar nu}, K^+ -> pi^+ nu {bar nu}, in the CP-asymmetry S_{psi phi} and in lepton flavour violating decays. In particular, the latter decays offer a clear distinction between the LHT model and the MSSM. We summarize the most interesting results of three extensive analyses of flavour physics in the LHT model.

hep-ph↗
arXiv2007

B-Hadron Lifetimes, Width Differences and Semileptonic CP-Asymmetries

B-hadron physics plays a fundamental role to test and improve our understanding of flavor dynamics within and beyond the Standard Model. Of particular phenomenological interest are beauty hadron lifetime ratios and, width differences and semileptonic CP-asymmetries in B_d and B_s systems. We discuss their theoretical predictions which, in the last years, have been improved thanks to accurate lattice calculations of operator matrix elements and perturbative computations of Wilson coefficients.

hep-ph↗
arXiv2006

Mixing and CP-Violation in the Littlest Higgs Model with T-Parity

The results of an extensive flavour physics analysis in the Littlest Higgs model with T-parity are presented. In particular, mixing and CP-violation in K^0 and B^0_{d,s} systems have been studied. Several scenarios defined by the values of mirror quark masses and the parameters of the new flavour mixing matrix V_Hd have been considered. A very interesting scenario is identified, where the well-known kaon constraints are satisfied, the sin(2beta) and Delta M_s issues are improved w.r.t the Standard Model and visible effects could be soon found in A_SL^s and S_{psi phi}.

hep-ph↗
arXiv2006

Another Look at the Flavour Structure of the Littlest Higgs Model with T-Parity

We discuss the mixing matrix V_Hd that describes the charged and neutral current interactions between ordinary down-quarks and up- and down-mirror quarks in the Littlest Higgs Model with T-parity (LHT). We point out that this matrix in addition to three mixing angles contains three physical complex phases and not only one as used in the present literature. We explain the reason for the presence of two additional phases, propose a new standard parameterization of V_Hd and briefly comment on the relevance of these new phases for the phenomenology of FCNC processes in the LHT model. In a separate paper we present a detailed numerical analysis, including these new phases, of K and B physics, with particular attention to the most interesting rare decays.

hep-ph↗
arXiv2006

Minimal Flavour Violation Waiting for Precise Measurements of Delta M_s, S_{psi phi}, A^s_SL, |V_ub|, gamma and B^0_{s,d} -> mu+ mu-

We emphasize that the recent measurements of the B^0_s - bar B^0_s mass difference Delta M_s by the CDF and D0 collaborations offer an important model independent test of minimal flavour violation (MFV). The improved measurements of the angle gamma in the unitarity triangle and of |V_ub| from tree level decays, combined with future accurate measurements of Delta M_s, S_{psi K_S}, S_{psi phi}, Br(B_{d,s} -> mu+ mu-), Br(B -> X_{d,s} nu bar nu), Br(K+ -> pi+ nu bar nu) and Br(K_L -> pi^0 nu bar nu) and improved values of the relevant non-perturbative parameters, will allow to test the MFV hypothesis in a model independent manner to a high accuracy. In particular, the difference between the reference unitarity triangle obtained from tree level processes and the universal unitarity triangle (UUT) in MFV models would signal either new flavour violating interactions and/or new local operators that are suppressed in MFV models with low tan(beta), with the former best tested through S_{psi phi} and K_L -> pi^0 nu bar nu. A brief discussion of non-MFV scenarios is also given. In this context we identify in the recent literature a relative sign error between Standard Model and new physics contributions to S_{psi phi}, that has an impact on the correlation between S_{psi phi} and A^s_SL. We point out that the ratios S_{psi phi}/A^s_SL and (Delta M_s)/(Delta Gamma_s) will allow to determine (Delta M_s)/(Delta M_s)^SM. Similar proposals for the determination of (Delta M_d)/(Delta M_d)^SM are also given.

hep-ph↗
arXiv2003

Beauty Hadron Lifetimes and B-Meson CP-Violation Parameters from Lattice QCD

The present status of the theoretical estimates of beauty hadron lifetime ratios and of width differences and CP-violation parameters in $B_d$ and $B_s$ systems is reviewed. In the last two years accurate lattice calculations and next-to-leading order perturbative computations have improved these theoretical predictions, leading to the following updated results: τ(B^+)/τ(B_d)=1.06 +- 0.02, τ(B_s)/τ(B_d)=1.00 +- 0.01, τ(Λ_b)/τ(B_d)=0.88 +- 0.05, ΔΓ_{d}/Γ_{d} = (2.42 +- 0.59)10^{-3}, ΔΓ_{s}/Γ_{s} = (7.4 +- 2.4)10^{-2}, |(q/p)_d|-1=(2.96 +- 0.67) 10^{-4}$ and |(q/p)_s|-1=-(1.28 +- 0.28) 10^{-5}

hep-ph↗
arXiv2003

Coupling of the light vector meson to the vector and to the tensor current

We present results for the coupling of the light vector mesons to the tensor current, relative to the standard vector meson decay constants. From an O(a)-improved lattice study, performed at three values of the lattice spacing in the quenched approximation, our final values (in the continuum limit), in the MS-scheme at 2 GeV, are: (f^T/f)_rho =0.72(2)(+2/-0), (f^T/f)_K* =0.74(2), (f^T/f)_phi =0.76(1).

hep-lat↗
arXiv2002

Continuum Determination of Light Quark Masses from Quenched Lattice QCD

We compute the strange and the average up/down quark masses in the quenched approximation of lattice QCD, by using the O(a)-improved Wilson action and operators and by implementing the non-perturbative renormalization. Our computation is performed at four values of the lattice spacing, from which we could extrapolate to the continuum limit. Our final result for the strange quark mass (in the MSbar scheme) is ms(2 GeV) = (106 +/- 2 +/- 8) MeV. For the average up/down quark mass we have ml(2 GeV) = (4.4 +/- 0.1 +/- 0.4) MeV. The ratio ms/ml = (24.3 +/- 0.2 +/- 0.6).

hep-lat↗