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Fulvia De Fazio

Publications and source records attributed to Fulvia De Fazio.

At least 55 records · Page 3Linked to original sources
arXiv2013

The Anatomy of Z' and Z with Flavour Changing Neutral Currents in the Flavour Precision Era

The simplest extension of the SM that generally introduces new sources of flavour and CP violation as well as right-handed currents is the addition of a U(1) gauge symmetry to the SM gauge group. If the corresponding heavy gauge boson Z' mediates FCNC processes in the quark sector at tree-level, these new physics contributions imply a pattern of deviations from SM expectations for FCNC processes depending only on Z' couplings to fermions and on its mass. This implies stringent correlations between Delta F=2 and Delta F=1 observables which govern the landscape of the allowed parameter space for Z'-models. Anticipating the Flavour Precision Era (FPE) ahead of us we illustrate this by searching for allowed oases in this landscape assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze Delta F=2 observables in K^0-bar K^0 and B^0_{s,d}-bar B^0_{s,d} systems and rare K and B decays including both left-handed and right-handed Z'-couplings to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different Z' scenarios. The important role of b->s l^+ l^- and b->s nu bar nu transitions in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in B_{s,d} and K meson systems emerges provided M_Z'<3 TeV. While for M_Z'>5 TeV Z' effects in rare B_{s,d} decays are found typically below 10% and hard to measure even in the FPE, K->pi nu bar nu and K_L-> pi^0 l^+ l^- decays provide an important portal to scales beyond those explored by the LHC. We apply our formalism to NP scenarios with induced flavour changing neutral Z-couplings to quarks. We find that in the case of B_d and K decays, but not B_s decays, such Z-couplings still allow for sizable departures from the SM.

hep-ph↗
arXiv2013

Anomalous AV^*V vertex function in the soft-wall holographic model of QCD

I consider the three-point function of two vector and one axial-vector currents. In the kinematic configuration in which one of the two vector currents corresponds to an on-shell soft photon, such a vertex is described in QCD by two functions, $w_L$ and $w_T$. After reviewing the properties of these functions in QCD, I describe the result obtained using the soft-wall holographic model of QCD with the addition of the Chern-Simons term and I compare it with the QCD outcome. I also discuss a relation, proposed by Son and Yamamoto, that connects $w_L$ and $w_T$ to the two-point functions $Π_{VV}$ and $Π_{AA}$.

hep-ph↗
arXiv2012

The Anatomy of Quark Flavour Observables in 331 Models in the Flavour Precision Era

The coming flavour precision era will allow to uncover various patterns of flavour violation in different New Physics (NP) scenarios that are presently washed out by hadronic and experimental uncertainties. We illustrate this by performing the anatomy of flavour violation in the 331 models, based on the gauge group SU(3)_C X SU(3)_L X U(1)_X that are among the simplest NP scenarios with new sources of flavour and CP violation. The latter originate dominantly through the flavour violating interactions of ordinary quarks and leptons with a new heavy Z' gauge boson. After discussing first these models in some generality, we present a detailed study of Delta F=2 observables and of rare K and B meson decays in the specific beta=1/\sqrt{3} model (to be called overline{331} model) assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. The most prominent roles in our analysis play epsilon_K, Delta M_q (q=d,s), the mixing induced CP asymmetries S_{psi K_S} and S_{psi phi}, rare decays B_{s,d}-> mu^+ mu^- and in particular the CP-asymmetry S_{mu^+ mu^-}^s in B_s ->mu^+ mu^-. We identify a number of correlations between various observables that differ from those known from CMFV models. While, the Delta F=2 observables allow still for four oases in the new parameter space, we demonstrate how the inclusion of Delta F=1 observables can in the future identify the optimal oasis for this model. For 1 TeV <= M_{Z'}<= 3 TeV the overline{331} model is in good agreement with the recent data for B^+->tau^+ nu_tau, it removes the epsilon_K-S_{psi K_S} tension present in the SM and the epsilon_K-Delta M_{s,d} tension present in CMFV models. Simultaneously, while differing from the SM, it is consistent with the present data on BR(B_{s,d}->mu^+ mu^-) and S_{psi phi}. We identify the triple correlation BR(B_s->mu^+ mu^-)-S_{psi phi}-S_{mu^+ mu^-}^s.

hep-ph↗
arXiv2012

New Spectroscopy of Heavy Mesons

I discuss the most recently discovered open charm mesons, both with and without strangeness. By exploiting the heavy quark limit, strong decay widths of such mesons are computed. Comparison between theoretical predictions and experimental measurements are useful to assign the right quantum numbers to such states. As for hidden charm mesons, I consider the case of X(3872). Analysis of its radiative decays to $J/ψγ$ and $ψ(2S) γ$ shows the plausibility of the identification with $χ_{c1}(2P)$.

hep-ph↗
arXiv2012

$B\to K η^{(\prime)} γ$ decays in the standard model and in scenarios with universal extra dimensions

We study the radiative $B \to K η^{(\prime)} γ$ decays, which are important to investigate CP violation, and are also relevant to assess the role of the exclusive modes induced by the $b \to s γ$ transition to saturate the inclusive $B \to X_s γ$ decay rate. Moreover, these channels do not display the same hierarchy as $B \to K η^{(\prime)}$ modes, for which the decay into $η^\prime$ is enhanced with respect to one into $η$. The three-body radiative decays reverse the role: we find that this experimentally observed behavior (although affected by a large uncertainty in the case of the $η^\prime$) is reproduced in the theoretical analysis. We compute a $B^* \to K$ form factor, needed for this study, using light cone QCD sum rules, and discuss a relation expected to hold in the large energy limit for the light meson. Finally, we examine $B\to K ηγ$ in two extensions of the standard model with universal extra dimensions, to investigate the sensitivity of this rare mode to such a kind of new physics effects.

hep-ph↗
arXiv2011

Latest Developments in Heavy Meson Spectroscopy

I discuss developments in heavy meson spectroscopy. In particular, I consider the system of $c{\bar s}$ mesons and the puzzling state X(3872), with focus on the strategies for their classification.

hep-ph↗
arXiv2011

Radiative transitions of heavy quarkonium states

We study radiative decays of heavy $Q{\bar Q}$ states, both for $Q=c$ and $Q=b$, using an effective Lagrangian approach which exploits spin symmetry for such states. We use existing data on radiative quarkonium transitions to predict some unmeasured decay rates. We also discuss how these modes can be useful to understand the structure of X(3872).

hep-ph↗
arXiv2010

Nonleptonic $B_s$ to charmonium decays: analyses in pursuit of determining the weak phase $β_s$

We analyze nonleptonic $B_s$ decays to a charmonium state and a light meson, induced by the $b \to c {\bar c}s$ transition, which are useful to access the $B_s$-${\bar B}_s$ mixing phase $β_s$. We use generalized factorization and $SU(3)_F$ symmetry to relate such modes to correspondent $B$ decay channels. We discuss the feasibility of the measurements in the various channels, stressing the importance of comparing different determinations of $β_s$ in view of the hints of new physics effects (NP) recently emerged in the $B_s$ sector. Finally, adopting a general parametrization of NP contributions to the decay amplitudes, we discuss how to experimentally constrain new physics parameters.

hep-ph↗
arXiv2010

$B_s \to f_0(980)$ decays: Results from light-cone QCD Sum Rules

We describe a light-cone QCD sum rule calculation of the $B_s\to f_0(980)$ transition form factors useful to predict the branching ratios of the rare decays $B_s \to f_0 \ell^+ \ell^-$, $B_s \to f_0 ν\bar ν$ and of $B_s\to J/ψf_0$ decay assuming factorization. We compare this channel to $B_s \to J/ψϕ$ as far as the possibility to determine the $B_s$ mixing phase is concerned.

hep-ph↗
arXiv2010

$B_s\to f_0(980)$ form factors and $B_s$ decays into $f_0(980)$

We compute the $B_s\to f_0(980)$ transition form factors using light-cone QCD sum rules at leading order in the strong coupling constant, and also including an estimate of next-to-leading order corrections. We use the results to predict the branching fractions of the rare decay modes $B_s \to f_0 \ell^+ \ell^-$ and $B_s \to f_0 ν\bar ν$, which turn out to be ${\cal O}(10^{-7})$ ($B_s\to f_0(980)\ell^+\ell^-$, with $\ell=e,μ$), ${\cal O}(10^{-8})$ ($B_s\to f_0(980)τ^+τ^-$) and ${\cal O}(10^{-6})$($B_s\to f_0(980)ν\barν$). We also predict the branching ratio of $B_s\to J/ψf_0(980)$ decay under the factorization assumption, and discuss the role of this channel for the determination of the $B_s$ mixing phase compared to the golden mode $B_s \to J/ψϕ$. As a last application, we consider $D_s \to f_0$ form factors, providing a determination of the branching ratio of $D_s \to f_0 e^+ ν_e$.

hep-ph↗
arXiv2009

New Charm Spectroscopy: Insights from Theory

We discuss several new observations of mesons with open charm. In particular, we consider $D_{sJ}(2317)$ and $D_{sJ}(2460)$ and compare their isospin violating decays into $D^{(*)}_s π$ to the radiative decays analysed using light-cone QCD sum rules. The results support the interpretation of these two mesons as ordinary $c{\bar s}$ states. In the case of $D_{sJ}(2860)$ and $D_{sJ}(2710)$ we compute the strong decays in the heavy quark limit. Comparison of the results with recent measurements of the BaBar Collaboration leads to identify $D_{sJ}(2710)$ with the first radial excitation of $D_s^*$, while the identification is still uncertain in the case of $D_{sJ}(2860)$.

hep-ph↗
arXiv2008

Soft-wall model of AdS/QCD: The case of light scalar mesons

We study light scalar mesons in the AdS/QCD soft-wall model with a background dilaton field, to investigate the features of this approach in describing QCD properties in the strong coupling regime. We find that the masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: this discrepancy is related to the description of chiral symmetry breaking in this holographic model.

hep-ph↗
arXiv2008

Light-cone sum rules in soft-collinear effective theory

We derive light-cone sum rules (LCSRs) for exclusive B-meson decays into light energetic hadrons from correlation functions within soft-collinear effective theory (SCET). In these sum rules the short-distance scale refers to ``hard-collinear'' interactions with virtualities of order (Lambda_{QCD}*m_b). Hard scales (related to virtualities of order m_b^2) are integrated out and enter via external coefficient functions in the sum rule. Soft dynamics is encoded in light-cone distribution amplitudes for the B-meson, which describe both the factorizable and non-factorizable contributions to exclusive B-meson decay amplitudes. As an example, we provide a detailed study of the SCET sum rule for the B -> pi transition form factor at large recoil, including radiative corrections from hard-collinear loop diagrams at first order in the strong coupling constant. We find remarkable conceptual and numerical differences with the heavy-quark limit of the conventional LCSR approach in QCD.

hep-ph↗
arXiv2006

Rare B decays in a single Universal Extra Dimension scenario

Exclusive rare $B \to K^{(*)} \ell^+ \ell^-$, $B \to K^{(*)} ν\bar ν$ and $B \to K^* γ$ decays are studied within the Applequist-Cheng-Dobrescu model, an extension of the Standard Model in presence of universal extra dimensions. In the case of a single universal extra dimension compactified on a circle of radius R, we study the dependence of several observables on 1/R, and discuss whether the hadronic uncertainty due to the form factors obscures or not such a dependence. We find that, using present data, it is possible in many cases to put a sensible lower bound to 1/R, the most stringent one coming from $B \to K^* γ$.

hep-ph↗
arXiv2006

Constraining Universal Extra Dimensions through B decays

We analyze the exclusive rare $B \to K^{(*)} \ell^+ \ell^-$, $B \to K^{(*)} ν\bar ν$ and $B \to K^* γ$ decays in the Applequist-Cheng-Dobrescu model, an extension of the Standard Model in presence of universal extra dimensions. In the case of a single universal extra dimension, we study the dependence of several observables on the compactification parameter 1/R, and discuss whether the hadronic uncertainty due to the form factors obscures or not such a dependence. We find that, using present data, it is possible in many cases to put a sensible lower bound to 1/R, the most stringent one coming from $B \to K^* γ$.

hep-ph↗
arXiv2005

The B --> pi form factor from light-cone sum rules in soft-collinear effective theory

Recently, we have derived light-cone sum rules for exclusive B-meson decays into light energetic hadrons from correlation functions within soft-collinear effective theory. In these sum rules the short-distance scale refers to ``hard-collinear'' interactions with virtualities of order Λ_{QCD} m_b. Hard scales (related to virtualities of order m_b^2) are integrated out and enter via external coefficient functions in the sum rule. Soft dynamics is encoded in light-cone distribution amplitudes for the B-meson, which describe both the factorizable and non-factorizable contributions to exclusive B-meson decay amplitudes. Factorization of the correlation function has been verified to one-loop accuracy. Thus, a systematic separation of hard, hard-collinear, and soft dynamics in the heavy-quark limit is possible.

hep-ph↗