Cecilia Tarantino | Università Roma Tre (original) (raw)

Papers by Cecilia Tarantino

Research paper thumbnail of Flavor physics of leptons and dipole moments

European Physical Journal C, 2008

This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretic... more This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the standard model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

Research paper thumbnail of Flavor physics in the quark sector

Physics Reports-review Section of Physics Letters, 2010

In the past decade, one of the major challenges of particle physics has been to gain an in-depth ... more In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved, apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model.

Research paper thumbnail of Flavor Physics in the Quark Sector

In the past decade, one of the major challenges of particle physics has been to gain an in-depth ... more In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved, apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model.

Research paper thumbnail of B, D and K decays

European Physical Journal C, 2008

The present report documents the results of Working Group 2: B, D and K decays, of the workshop o... more The present report documents the results of Working Group 2: B, D and K decays, of the workshop on Flavour in the Era of the LHC, held at CERN from November 2005 through March 2007.

Research paper thumbnail of Another look at the flavour structure of the Littlest Higgs model with T-parity

Physics Letters B, 2007

We discuss the mixing matrix V Hd that describes the charged and neutral current interactions bet... more 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.

Research paper thumbnail of Rare and CP-violating K and B decays in the Littlest Higgs model with T-parity

Journal of High Energy Physics, 2007

We calculate the most interesting rare and CP-violating K and B decays in the Littlest Higgs mode... more We calculate the most interesting rare and CP-violating K and B decays in the Littlest Higgs model with T-parity. We give a collection of Feynman rules including v 2 /f 2 contributions that are presented here for the first time and could turn out to be useful also for applications outside flavour physics. We adopt a modelindependent parameterization of rare decays in terms of the gauge independent functions X i , Y i , Z i (i = K, d, s), which is in particular useful for the study of the breaking of the universality between K, B d and B s systems through non-MFV interactions. Performing the calculation in the unitary and 't Hooft-Feynman gauge, we find that the final result contains a divergence which signals some sensitivity to the ultraviolet completion of the theory. Including an estimate of this contribution, we calculate the branching ratios for the decays

Research paper thumbnail of The Littlest Higgs Model with T-Parity Facing CP-Violation in B_s - anti-B_s Mixing

The non-minimal flavour violating interactions of mirror quarks and new heavy gauge bosons in the... more The non-minimal flavour violating interactions of mirror quarks and new heavy gauge bosons in the Littlest Higgs model with T-parity (LHT) give rise to naturally large CP-violating effects in the B s system. In view of a large new CP phase in B s −B s mixing hinted by the CDF and DØ data and the recent UTfit analysis, we update our 2006 analysis of particle-antiparticle mixing and rare K and B decays in the LHT model, using the most recent values of a number of input parameters and performing a more careful error analysis. We find that the CP-asymmetry S ψφ can easily reach values ∼ 0.15 − 0.20, compared to the SM value ∼ 0.04, while higher values are rather unlikely though not excluded. Large enhancements are also possible in the branching ratios for K L → π 0 νν, K + → π + νν and K L → π 0 ℓ + ℓ − with much more modest effects in B s,d → µ + µ − . We perform a detailed study of correlations between the latter decays and S ψφ as well as of the correlation between S ψφ and S ψK S . We also point out that the possible tension between ε K and the tree level CKM determination recently hinted by various analyses can easily be resolved in the LHT model.

Research paper thumbnail of Littlest Higgs model with T-parity confronting the new data on D 0 – D ¯ 0 mixing

Physics Letters B, 2007

Motivated by the first experimental evidence of meson oscillations in the D system, we study D 0 ... more Motivated by the first experimental evidence of meson oscillations in the D system, we study D 0 −D 0 mixing in the Littlest Higgs model with T-parity, we investigate its role in constraining the model parameters and its impact on the most interesting flavour observables. We find that the experimental data are potentially strongly constraining but at present limited by large theoretical uncertainties in the longdistance Standard Model contribution to D 0 −D 0 mixing.

Research paper thumbnail of Minimal Flavour Violation Waiting for Precise Measurements

We emphasize that the recent measurements of the B 0 s −B 0 s mass difference ∆M s by the CDF and... more We emphasize that the recent measurements of the B 0 s −B 0 s mass difference ∆M s by the CDF and DØ collaborations offer an important model independent test of minimal flavour violation (MFV). The improved measurements of the angle γ in the unitarity triangle and of |V ub | from tree level decays, combined with future accurate measurements of ∆M s ,

Research paper thumbnail of Charged lepton flavour violation and (g-2)mu in the Littlest Higgs model with T-Parity: a clear distinction from Supersymmetry

Journal of High Energy Physics, 2007

We calculate the rates for the charged lepton flavour violating decays ℓ i → ℓ j γ, τ → ℓπ, τ → ℓ... more We calculate the rates for the charged lepton flavour violating decays ℓ i → ℓ j γ, τ → ℓπ, τ → ℓη, τ → ℓη ′ , µ − → e − e + e − , the six three body leptonic decays τ − → ℓ − i ℓ + j ℓ − k and the rate for µ−e conversion in nuclei in the Littlest Higgs model with T-Parity (LHT). We also calculate the rates for K L,S → µe, K L,S → π 0 µe and B d,s → ℓ i ℓ j . We find that the relative effects of mirror leptons in these transitions are by many orders of magnitude larger than analogous mirror quark effects in rare K and B decays analyzed recently. In particular, in order to suppress the µ → eγ and µ − → e − e + e − decay rates and the µ − e conversion rate below the experimental upper bounds, the relevant mixing matrix in the mirror lepton sector V Hℓ must be rather hierarchical, unless the spectrum of mirror leptons is quasi-degenerate. We find that the pattern of the LFV branching ratios in the LHT model differs significantly from the one encountered in the MSSM, allowing in a transparent manner to distinguish these two models with the help of LFV processes. We also calculate (g − 2) µ and find the new contributions to a µ below 1 · 10 −10 and consequently negligible. We compare our results with those present in the literature.

Research paper thumbnail of FCNC Processes in the Littlest Higgs Model with T-Parity: an Update

We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT... more We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT). The removal of the logarithmic UV cutoff dependence in our previous results through a new contribution to the Z 0 -penguin diagrams identified by Goto et al. and del Aguila et al., while making the deviations from the SM expectations in the quark sector less spectacular, still allows for sizable new physics effects in K → πνν and K L → π 0 + − decays and in the CP-asymmetry S ψφ with the latter unaffected by the new contribution. We extend our analysis by a study of the fine-tuning required to fit the data on ε K and by the inclusion of the decay K L → µ + µ − . A number of correlations can distinguish this model from the custodially protected Randall-Sundrum model analysed recently. We also reconsider lepton flavour violating decays, including now a discussion of finetuning. While the i → j γ decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like µ → 3e are lowered by almost an order of magnitude. In spite of this, the pattern of lepton flavour violation in the LHT model can still be distinguished from the one in supersymmetric models. arXiv:0906.5454v2 [hep-ph]

Research paper thumbnail of Pseudoscalar meson decay constants fK, fD and fDs, from Nf = 2 twisted mass Lattice QCD

Research paper thumbnail of Lifetime differences and CP violation parameters of neutral B mesons at the next-to-leading order in QCD

Journal of High Energy Physics, 2003

We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-wi... more We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-width matrix Γ entering the neutral B-meson oscillations. From this calculation the width differences ∆Γ and the CP violation parameters (q/p) of B d and B s mesons are estimated, including the complete O(α s ) QCD corrections and the 1/m b contributions. For the width difference ∆Γ s we agree with previous results. By using the lattice determinations of the relevant hadronic matrix elements we obtain the theoretical predictions ∆Γ d /Γ d = (2.42 ± 0.59) × 10 −3 and ∆Γ s /Γ s = (7.4 ± 2.4) × 10 −2 . For the CP violation parameters, we find |(q/p) d | − 1 = (2.96 ± 0.67) × 10 −4 and |(q/p) s | − 1 = −(1.28 ± 0.27) × 10 −5 . These predictions are compatible with the experimental measurements which, however, suffer at present from large uncertainties.

Research paper thumbnail of Continuum determination of light quark masses from quenched lattice QCD

Physics Letters B, 2003

We compute the strange and the average up/down quark masses in the quenched approximation of latt... more 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 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 is m MS s (2 GeV) = (106 ± 2 ± 8) MeV. For the average up/down quark mass we obtain m MS ℓ (2 GeV) = (4.4 ± 0.1 ± 0.4) MeV and the ratio m s /m ℓ = (24.3 ± 0.2 ± 0.6).

Research paper thumbnail of K-->pilnu semileptonic form factors from two-flavor lattice QCD

Physical Review D, 2009

We present new lattice results of the K → πℓν semileptonic form factors obtained from simulations... more We present new lattice results of the K → πℓν semileptonic form factors obtained from simulations with two flavors of dynamical twisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f+(0) = 0.9560(84), which, combined with the latest experimental data for K ℓ3 decays, leads to |Vus| = 0.2267(5)exp.(20) f + (0) . Using the PDG(2008) determinations of |V ud | and |V ub | our result implies for the unitarity relation |V ud | 2 + |Vus| 2 + |V ub | 2 = 1.0004(15). For the O(p 6 ) term of the chiral expansion of f+(0) we get ∆f ≡ f+(0) − 1 − f2 = −0.0214(84).

Research paper thumbnail of An Improved Standard Model Prediction Of BR(B -> tau nu) And Its Implications For New Physics

Research paper thumbnail of Exploring twisted mass lattice QCD with the Clover term

Physical Review D, 2006

It has been shown that in the twisted mass formulation of Lattice QCD at maximal twist large cuto... more It has been shown that in the twisted mass formulation of Lattice QCD at maximal twist large cutoff effects are generated when the quark mass becomes of O(aΛ 2 QCD ). In general, these effects can be suppressed in two ways: either by choosing the critical quark mass in an "optimal way", or by adding the Clover term to the twisted action. We investigate the second option by performing a quenched lattice QCD simulation with twisted Clover fermions and pion masses as low as 280 MeV. We show that the Clover term is indeed efficient in reducing the large cutoff effects. In particular, the socalled bending phenomenon observed in the determination of the pion decay constant is cured in this way. In addition, by using maximally twisted Clover fermions, we provide a non-perturbative determination of the vector current renormalization constant Z V as well as of the non-perturbatively renormalized light quark masses. Finally, we calculate the connected contribution to the charged-neutral pseudoscalar meson mass splitting, finding that the introduction of the Clover term in the twisted action is also beneficial, in the quenched approximation, in reducing cutoff effects related to the isospin symmetry breaking at finite lattice spacing.

Research paper thumbnail of An improved Standard Model prediction of BR ( B → τ ν ) and its implications for New Physics

Research paper thumbnail of A proposal for B physics on current lattices

Journal of High Energy Physics, 2010

A method to extract B-physics parameters (b-quark mass and f B , $ {f_{{B_s}}} $ decay constants)... more A method to extract B-physics parameters (b-quark mass and f B , $ {f_{{B_s}}} $ decay constants) from currently available lattice data is presented and tested. The approach is based on the idea of constructing appropriate ratios of heavy-light meson masses and decay constants, respectively, possessing a precisely known static limit, and evaluating them at various pairs of heavy quark masses around the charm. Via a smooth interpolation in the heavy quark mass from the easily accessible charm region to the asymptotic point, B-physics parameters are computed with a few percent (statistical + systematic) error using recently produced N f = 2 maximally twisted Wilson fermions data.

Research paper thumbnail of New Physics from Flavour

The UTfit Collaboration has produced several analyses in the context of flavour physics both with... more The UTfit Collaboration has produced several analyses in the context of flavour physics both within and beyond the Standard Model. In this paper we present updated results for the Standard Model analysis of the Unitarity Triangle using the latest experimental and lattice QCD inputs, as well as an update of the Unitarity Triangle analysis in a scenario beyond the Standard Model. Combining all available experimental and theoretical information on ∆F = 2 processes and using a model-independent parameterization, we extract the allowed New Physics contributions in the K 0 , D 0 , B d , and Bs sectors. We observe a departure of the Bs mixing phase from the Standard Model expectation with a significance of about 3σ.

Research paper thumbnail of Flavor physics of leptons and dipole moments

European Physical Journal C, 2008

This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretic... more This chapter of the report of the “Flavor in the era of the LHC” Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the standard model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

Research paper thumbnail of Flavor physics in the quark sector

Physics Reports-review Section of Physics Letters, 2010

In the past decade, one of the major challenges of particle physics has been to gain an in-depth ... more In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved, apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model.

Research paper thumbnail of Flavor Physics in the Quark Sector

In the past decade, one of the major challenges of particle physics has been to gain an in-depth ... more In the past decade, one of the major challenges of particle physics has been to gain an in-depth understanding of the role of quark flavor. In this time frame, measurements and the theoretical interpretation of their results have advanced tremendously. A much broader understanding of flavor particles has been achieved, apart from their masses and quantum numbers, there now exist detailed measurements of the characteristics of their interactions allowing stringent tests of Standard Model predictions. Among the most interesting phenomena of flavor physics is the violation of the CP symmetry that has been subtle and difficult to explore. In the past, observations of CP violation were confined to neutral K mesons, but since the early 1990s, a large number of CP-violating processes have been studied in detail in neutral B mesons. In parallel, measurements of the couplings of the heavy quarks and the dynamics for their decays in large samples of K, D, and B mesons have been greatly improved in accuracy and the results are being used as probes in the search for deviations from the Standard Model.

Research paper thumbnail of B, D and K decays

European Physical Journal C, 2008

The present report documents the results of Working Group 2: B, D and K decays, of the workshop o... more The present report documents the results of Working Group 2: B, D and K decays, of the workshop on Flavour in the Era of the LHC, held at CERN from November 2005 through March 2007.

Research paper thumbnail of Another look at the flavour structure of the Littlest Higgs model with T-parity

Physics Letters B, 2007

We discuss the mixing matrix V Hd that describes the charged and neutral current interactions bet... more 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.

Research paper thumbnail of Rare and CP-violating K and B decays in the Littlest Higgs model with T-parity

Journal of High Energy Physics, 2007

We calculate the most interesting rare and CP-violating K and B decays in the Littlest Higgs mode... more We calculate the most interesting rare and CP-violating K and B decays in the Littlest Higgs model with T-parity. We give a collection of Feynman rules including v 2 /f 2 contributions that are presented here for the first time and could turn out to be useful also for applications outside flavour physics. We adopt a modelindependent parameterization of rare decays in terms of the gauge independent functions X i , Y i , Z i (i = K, d, s), which is in particular useful for the study of the breaking of the universality between K, B d and B s systems through non-MFV interactions. Performing the calculation in the unitary and 't Hooft-Feynman gauge, we find that the final result contains a divergence which signals some sensitivity to the ultraviolet completion of the theory. Including an estimate of this contribution, we calculate the branching ratios for the decays

Research paper thumbnail of The Littlest Higgs Model with T-Parity Facing CP-Violation in B_s - anti-B_s Mixing

The non-minimal flavour violating interactions of mirror quarks and new heavy gauge bosons in the... more The non-minimal flavour violating interactions of mirror quarks and new heavy gauge bosons in the Littlest Higgs model with T-parity (LHT) give rise to naturally large CP-violating effects in the B s system. In view of a large new CP phase in B s −B s mixing hinted by the CDF and DØ data and the recent UTfit analysis, we update our 2006 analysis of particle-antiparticle mixing and rare K and B decays in the LHT model, using the most recent values of a number of input parameters and performing a more careful error analysis. We find that the CP-asymmetry S ψφ can easily reach values ∼ 0.15 − 0.20, compared to the SM value ∼ 0.04, while higher values are rather unlikely though not excluded. Large enhancements are also possible in the branching ratios for K L → π 0 νν, K + → π + νν and K L → π 0 ℓ + ℓ − with much more modest effects in B s,d → µ + µ − . We perform a detailed study of correlations between the latter decays and S ψφ as well as of the correlation between S ψφ and S ψK S . We also point out that the possible tension between ε K and the tree level CKM determination recently hinted by various analyses can easily be resolved in the LHT model.

Research paper thumbnail of Littlest Higgs model with T-parity confronting the new data on D 0 – D ¯ 0 mixing

Physics Letters B, 2007

Motivated by the first experimental evidence of meson oscillations in the D system, we study D 0 ... more Motivated by the first experimental evidence of meson oscillations in the D system, we study D 0 −D 0 mixing in the Littlest Higgs model with T-parity, we investigate its role in constraining the model parameters and its impact on the most interesting flavour observables. We find that the experimental data are potentially strongly constraining but at present limited by large theoretical uncertainties in the longdistance Standard Model contribution to D 0 −D 0 mixing.

Research paper thumbnail of Minimal Flavour Violation Waiting for Precise Measurements

We emphasize that the recent measurements of the B 0 s −B 0 s mass difference ∆M s by the CDF and... more We emphasize that the recent measurements of the B 0 s −B 0 s mass difference ∆M s by the CDF and DØ collaborations offer an important model independent test of minimal flavour violation (MFV). The improved measurements of the angle γ in the unitarity triangle and of |V ub | from tree level decays, combined with future accurate measurements of ∆M s ,

Research paper thumbnail of Charged lepton flavour violation and (g-2)mu in the Littlest Higgs model with T-Parity: a clear distinction from Supersymmetry

Journal of High Energy Physics, 2007

We calculate the rates for the charged lepton flavour violating decays ℓ i → ℓ j γ, τ → ℓπ, τ → ℓ... more We calculate the rates for the charged lepton flavour violating decays ℓ i → ℓ j γ, τ → ℓπ, τ → ℓη, τ → ℓη ′ , µ − → e − e + e − , the six three body leptonic decays τ − → ℓ − i ℓ + j ℓ − k and the rate for µ−e conversion in nuclei in the Littlest Higgs model with T-Parity (LHT). We also calculate the rates for K L,S → µe, K L,S → π 0 µe and B d,s → ℓ i ℓ j . We find that the relative effects of mirror leptons in these transitions are by many orders of magnitude larger than analogous mirror quark effects in rare K and B decays analyzed recently. In particular, in order to suppress the µ → eγ and µ − → e − e + e − decay rates and the µ − e conversion rate below the experimental upper bounds, the relevant mixing matrix in the mirror lepton sector V Hℓ must be rather hierarchical, unless the spectrum of mirror leptons is quasi-degenerate. We find that the pattern of the LFV branching ratios in the LHT model differs significantly from the one encountered in the MSSM, allowing in a transparent manner to distinguish these two models with the help of LFV processes. We also calculate (g − 2) µ and find the new contributions to a µ below 1 · 10 −10 and consequently negligible. We compare our results with those present in the literature.

Research paper thumbnail of FCNC Processes in the Littlest Higgs Model with T-Parity: an Update

We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT... more We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT). The removal of the logarithmic UV cutoff dependence in our previous results through a new contribution to the Z 0 -penguin diagrams identified by Goto et al. and del Aguila et al., while making the deviations from the SM expectations in the quark sector less spectacular, still allows for sizable new physics effects in K → πνν and K L → π 0 + − decays and in the CP-asymmetry S ψφ with the latter unaffected by the new contribution. We extend our analysis by a study of the fine-tuning required to fit the data on ε K and by the inclusion of the decay K L → µ + µ − . A number of correlations can distinguish this model from the custodially protected Randall-Sundrum model analysed recently. We also reconsider lepton flavour violating decays, including now a discussion of finetuning. While the i → j γ decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like µ → 3e are lowered by almost an order of magnitude. In spite of this, the pattern of lepton flavour violation in the LHT model can still be distinguished from the one in supersymmetric models. arXiv:0906.5454v2 [hep-ph]

Research paper thumbnail of Pseudoscalar meson decay constants fK, fD and fDs, from Nf = 2 twisted mass Lattice QCD

Research paper thumbnail of Lifetime differences and CP violation parameters of neutral B mesons at the next-to-leading order in QCD

Journal of High Energy Physics, 2003

We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-wi... more We compute the next-to-leading order QCD corrections to the off-diagonal elements of the decay-width matrix Γ entering the neutral B-meson oscillations. From this calculation the width differences ∆Γ and the CP violation parameters (q/p) of B d and B s mesons are estimated, including the complete O(α s ) QCD corrections and the 1/m b contributions. For the width difference ∆Γ s we agree with previous results. By using the lattice determinations of the relevant hadronic matrix elements we obtain the theoretical predictions ∆Γ d /Γ d = (2.42 ± 0.59) × 10 −3 and ∆Γ s /Γ s = (7.4 ± 2.4) × 10 −2 . For the CP violation parameters, we find |(q/p) d | − 1 = (2.96 ± 0.67) × 10 −4 and |(q/p) s | − 1 = −(1.28 ± 0.27) × 10 −5 . These predictions are compatible with the experimental measurements which, however, suffer at present from large uncertainties.

Research paper thumbnail of Continuum determination of light quark masses from quenched lattice QCD

Physics Letters B, 2003

We compute the strange and the average up/down quark masses in the quenched approximation of latt... more 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 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 is m MS s (2 GeV) = (106 ± 2 ± 8) MeV. For the average up/down quark mass we obtain m MS ℓ (2 GeV) = (4.4 ± 0.1 ± 0.4) MeV and the ratio m s /m ℓ = (24.3 ± 0.2 ± 0.6).

Research paper thumbnail of K-->pilnu semileptonic form factors from two-flavor lattice QCD

Physical Review D, 2009

We present new lattice results of the K → πℓν semileptonic form factors obtained from simulations... more We present new lattice results of the K → πℓν semileptonic form factors obtained from simulations with two flavors of dynamical twisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f+(0) = 0.9560(84), which, combined with the latest experimental data for K ℓ3 decays, leads to |Vus| = 0.2267(5)exp.(20) f + (0) . Using the PDG(2008) determinations of |V ud | and |V ub | our result implies for the unitarity relation |V ud | 2 + |Vus| 2 + |V ub | 2 = 1.0004(15). For the O(p 6 ) term of the chiral expansion of f+(0) we get ∆f ≡ f+(0) − 1 − f2 = −0.0214(84).

Research paper thumbnail of An Improved Standard Model Prediction Of BR(B -> tau nu) And Its Implications For New Physics

Research paper thumbnail of Exploring twisted mass lattice QCD with the Clover term

Physical Review D, 2006

It has been shown that in the twisted mass formulation of Lattice QCD at maximal twist large cuto... more It has been shown that in the twisted mass formulation of Lattice QCD at maximal twist large cutoff effects are generated when the quark mass becomes of O(aΛ 2 QCD ). In general, these effects can be suppressed in two ways: either by choosing the critical quark mass in an "optimal way", or by adding the Clover term to the twisted action. We investigate the second option by performing a quenched lattice QCD simulation with twisted Clover fermions and pion masses as low as 280 MeV. We show that the Clover term is indeed efficient in reducing the large cutoff effects. In particular, the socalled bending phenomenon observed in the determination of the pion decay constant is cured in this way. In addition, by using maximally twisted Clover fermions, we provide a non-perturbative determination of the vector current renormalization constant Z V as well as of the non-perturbatively renormalized light quark masses. Finally, we calculate the connected contribution to the charged-neutral pseudoscalar meson mass splitting, finding that the introduction of the Clover term in the twisted action is also beneficial, in the quenched approximation, in reducing cutoff effects related to the isospin symmetry breaking at finite lattice spacing.

Research paper thumbnail of An improved Standard Model prediction of BR ( B → τ ν ) and its implications for New Physics

Research paper thumbnail of A proposal for B physics on current lattices

Journal of High Energy Physics, 2010

A method to extract B-physics parameters (b-quark mass and f B , $ {f_{{B_s}}} $ decay constants)... more A method to extract B-physics parameters (b-quark mass and f B , $ {f_{{B_s}}} $ decay constants) from currently available lattice data is presented and tested. The approach is based on the idea of constructing appropriate ratios of heavy-light meson masses and decay constants, respectively, possessing a precisely known static limit, and evaluating them at various pairs of heavy quark masses around the charm. Via a smooth interpolation in the heavy quark mass from the easily accessible charm region to the asymptotic point, B-physics parameters are computed with a few percent (statistical + systematic) error using recently produced N f = 2 maximally twisted Wilson fermions data.

Research paper thumbnail of New Physics from Flavour

The UTfit Collaboration has produced several analyses in the context of flavour physics both with... more The UTfit Collaboration has produced several analyses in the context of flavour physics both within and beyond the Standard Model. In this paper we present updated results for the Standard Model analysis of the Unitarity Triangle using the latest experimental and lattice QCD inputs, as well as an update of the Unitarity Triangle analysis in a scenario beyond the Standard Model. Combining all available experimental and theoretical information on ∆F = 2 processes and using a model-independent parameterization, we extract the allowed New Physics contributions in the K 0 , D 0 , B d , and Bs sectors. We observe a departure of the Bs mixing phase from the Standard Model expectation with a significance of about 3σ.