Flavour changing neutral current (FCNC) processes are described by loop diagrams in the Standard Model (SM), while in 331 models, based on the gauge group SU(3)C×SU(3)L×U(1)X, they are dominated by ...tree-level exchanges of a new heavy neutral gauge boson Z′. By exploiting this feature, observables related to FCNC decays of K, Bd and Bs mesons can be considered in several variants of 331 models. The variants are distinguished by the value of a parameter β that plays a key role in this framework. Imposing constraints on the ΔF=2 observables, we select possible ranges for the mass of the Z′ boson in correspondence to the values β=±k/3, with k=1,2. The results are used to determine the impact of 331 models on b→s processes and on the correlations among them, in the light of new experimental data recently released.
The increasing number of flavour anomalies motivates the investigation of new processes where tensions similar to the observed ones may emerge. It is necessary to identify observables sensitive to ...physics beyond the Standard Model. The analysis which follows concerns the inclusive semileptonic decays of polarized beauty baryons, computed through the Heavy Quark Expansion at
O
(1/
m
b
3
) and at the leading order in α
s
. New Physics interactions have been taken into account, extending the Standard Model
b
→
Ulv¯
l
low-energy Hamiltonian, where
U
= {c, u} and ℓ = {
e
, μ, τ}, including the full set of
D
= 6 operators with left-handed neutrinos. Among the possible observables one can consider, the ones depending on the spin of the decaying baryon are very appealing and can be considered for physics programmes of future facilities, such as FCC-ee.
The charm of 331 Buras, Andrzej J.; Colangelo, Pietro; De Fazio, Fulvia ...
The journal of high energy physics,
10/2021, Letnik:
2021, Številka:
10
Journal Article
Recenzirano
Odprti dostop
A
bstract
We perform a detailed analysis of flavour changing neutral current processes in the charm sector in the context of 331 models. As pointed out recently, in the case of
Z′
contributions in ...these models there are no new free parameters beyond those already present in the
B
d,s
and
K
meson systems analyzed in the past. As a result, definite ranges for new Physics (NP) effects in various charm observables could be obtained. While generally NP effects turn out to be small, in a number of observables they are much larger than the tiny effects predicted within the Standard Model. In particular we find that the branching ratio of the mode
D
0
→ μ
+
μ
−
, despite remaining tiny, can be enhanced by 6 orders of magnitude with respect to the SM. We work out correlations between this mode and rare
B
d,s
and
K
decays. We also discuss neutral charm meson oscillations and CP violation in the charm system. In particular, we point out that 331 models provide new weak phases that are a necessary condition to have non-vanishing CP asymmetries. In the case of ∆
A
CP, the difference between the CP asymmetries in
D
0
→ K
+
K
−
and
D
0
→ π
+
π
−
, we find that agreement with experiment can be obtained provided that two conditions are verified: the phases in the ranges predicted in 331 models and large hadronic matrix elements.
Flavour changing neutral current (FCNC) processes are described by loop diagrams in the Standard Model (SM), while in 331 models, based on the gauge group SU(3)sub.C×SU(3)sub.L×U(1)sub.X, they are ...dominated by tree-level exchanges of a new heavy neutral gauge boson Zsup.′. By exploiting this feature, observables related to FCNC decays of K, Bsub.d and Bsub.s mesons can be considered in several variants of 331 models. The variants are distinguished by the value of a parameter β that plays a key role in this framework. Imposing constraints on the ΔF=2 observables, we select possible ranges for the mass of the Zsup.′ boson in correspondence to the values β=±k/square root of 3, with k=1,2. The results are used to determine the impact of 331 models on b→s processes and on the correlations among them, in the light of new experimental data recently released.
Anomalies recently observed in semileptonic b → c ℓ − ν ¯ ℓ and b → s ℓ + ℓ − transitions point to violation of Lepton Flavour Universality. Strategies for new analyses of different modes are ...required, in particular for the modes induced by the b → u transition. We describe the purely leptonic B decay, the B ¯ → π ℓ − ν ¯ ℓ channel and the B semileptonic modes to ρ ( 770 ) and a 1 ( 1260 ) in extensions of the Standard Model involving Lepton Flavour Universality violating b → u operators. In particular, we review the observables in the four-dimensional angular B ¯ → ρ ( π π ) ℓ − ν ¯ ℓ and B ¯ → a 1 ( ρ π ) ℓ − ν ¯ ℓ distributions, suitable to pin down deviations from the Standard Model. We discuss the complementarity among the various modes for New Physics searches.
We study the constraints on low-energy coefficients of the ν SMEFT generalization of the Standard Model effective theory in the simple case of a U ( 1 ) ′ enlargement of the Standard Model gauge ...group. In particular, we analyze the constraints imposed by the requirement that the extended theory remains free of gauge anomalies. We present the cases of explicit realizations, showing the obtained correlations among the coefficients of d = 6 operators. Published by the American Physical Society 2024
The decays Bc+ → Baℓνℓ and Bc+ → Ba∗ ( → Baγ )ℓνℓ, with a = s , d and ℓ = e , μ , are studied in the Standard Model (SM) and in the extension based on the low-energy Hamiltonian comprising the full ...set of dimension-6 semileptonic c → s,d operators with left-handed neutrinos. Tests of μ / e universality are investigated using such modes. The heavy quark spin symmetry is applied to relate the relevant hadronic matrix elements and to exploit lattice QCD results on Bc form factors. Optimized observables are selected, and the pattern of their correlations is studied to identify the effects of the various operators in the extended low-energy Hamiltonian.
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